'94 Previa LE S/C unusual acceleration problem

[jmrodz0]

I have a '94 Previa LE S/C that I have been refurbishing. The list of repairs made is extensive and includes replacing the head gasket. While everything was apart, I cleaned up the EGR valve, the engine throttle body, PCV, replaced the vacuum lines on the vapor canister, replaced the belts, distributor cap, rotor, wires, plugs, coil, transmission filter, O2 sensors, fuel injector O-rings/insulators, and fuel filter. This set of repairs followed replacing the engine wiring harness two years ago.

Aside from an ongoing vibration at idle while in drive (suspected SADS coupling issue), the van is running better than ever. The only problem I have now is that under full acceleration, the van feels like it is getting choked out and loses power. Gradual acceleration does not exhibit any problems until the van gets to 75MPH when it again starts to shudder and "misfire" (for lack of a better word). There is also a faint smell of gas in the cabin on occasion.

I have had the van at two different dealers and neither has been able to diagnose the problem. I have ordered a Throttle Position Sensor in hopes that a miracle will occur upon replacement, but thought I'd give a shout out for help to see if this sounds like a problem anyone has already encountered. Again, there are no check engine lights and the van runs well other than this full acceleration problem.

Thanks in advance!
Jim

[TheMAN]

check for boost leaks in the charge pipes? what are the condition of the spark plugs? which brand and # are they?

[jmrodz0]

check for boost leaks in the charge pipes? what are the condition of the spark plugs? which brand and # are they?

Thanks for the reply!

The spark plugs were new in October. They are NGK plugs, but I will have to pull one to check the number since I'm not sure if they were Iridium.

I am in the process of replacing the SAD couplings and was going to take off the belt to the supercharger to see if that would isolate the problem. There isn't much information available on testing/servicing the supercharger, so it's a black box to me, but I'll check the charge pipes...as soon as I learn about what charge pipes are. :)

Jim

[jmrodz0]

check for boost leaks in the charge pipes? what are the condition of the spark plugs? which brand and # are they?
The plugs are NGK IR IFR5T. No obvious vacuum leaks. No change in performance after changing the throttle position sensor, but the van still seems to be running rich.

Thanks
Jim

[TheMAN]

those plugs are too hot... they are for the non-S/C engine... it will cause preignition issues.... ignition timing maybe pulled and cause richness
you need to get IFR6T-11, or BKR6EP-11 (factory equivalent)

or get Denso PK20R11 (same as factory), or SK20R11 (iridium type)

[jmrodz0]

those plugs are too hot... they are for the non-S/C engine... it will cause preignition issues.... ignition timing maybe pulled and cause richness
you need to get IFR6T-11, or BKR6EP-11 (factory equivalent)

or get Denso PK20R11 (same as factory), or SK20R11 (iridium type)

Damn those Autozone folks! LOL
The plugs were pretty dirty when I pulled them so that makes a lot of sense. I'll change the plugs to the Denso PK20R11.

Thanks!
Jim

[TheMAN]

you can't really fault them too much... the NGK catalog lists the 94 previa as using IFR5T-11, and autozone usually use catalog data from the parts makers... but you must remember 94 was an odd year for the previa... they came out with the S/C model mid year... so for all intents and purposes, whenever you're buying parts for your van at the parts store, just say it's a 95 and you should have a better chance of getting the right parts

[jmrodz0]

you can't really fault them too much... the NGK catalog lists the 94 previa as using IFR5T-11, and autozone usually use catalog data from the parts makers... but you must remember 94 was an odd year for the previa... they came out with the S/C model mid year... so for all intents and purposes, whenever you're buying parts for your van at the parts store, just say it's a 95 and you should have a better chance of getting the right parts

I installed a new Throttle Position Sensor and the Denso plugs yesterday but haven't done much driving with it yet. The hesitation/shuddering at full throttle is still there, but I'm planning a little jaunt this afternoon which hopefully will get the timing self adjusted. Regardless, the gas smell in the exhaust is now gone and the van is running a bit smoother which is a big step forward.

Thanks for the advice on both the plugs and for future parts ordering!

[jmrodz0]

The plugs resolved some of the issues with general performance, but I've still got a problem with the shuddering at full acceleration. If I ever find the cause I'll post it here in case anyone else runs into the problem.

[jmrodz0]

Update: I've taken a couple of 200+ mile trips since replacing the TPS and the SAD couplings with no significant improvement. On my trip home the other day I got a check engine light! Normally this would be bad news, but I've been waiting for some electronic indication that something wasn't right, so it was a bit of a relief to see it. Turns out it was two codes: P0505 and P0773. I have seen the P0773 before but the P0505 was new. Seems it's related to the Idle Air Control (or the throttle body) which would make some sense given the issue at hand.

I haven't done anything about it yet, but I plan to pull the throttle body and clean the IAC next week.

I did have a couple of epiphanies along the way so I thought I'd share those in hopes it might help someone in the future. The first was that the charcoal canister was connected incorrectly. The vacuum line to the canister was attached to the wrong connecter at the purge solenoid...and the worst part is that I connected it. Thing was, that both hoses were disconnected before I started working on the van, so I just connected the short hose to the canister because it wouldn't have reached to the intake pipe. Then I had my epiphany when I looked under the hood and saw the vacuum diagram....which I had been searching for months to locate.

After finding the diagram, I had my second epiphany when I saw the procedure for resetting the timing was also under the hood. Go figure. Since this is a '94 SC, the Haynes manual had been no use for this problem since it talks about rotating the distributor which is not possible on this vehicle. With great trepidation, I followed the procedure of a short circuit between the TE1 and E1 terminals and the engine smoothed out...a bit.

My next step will be to service the throttle body (which had been cleaned up a bit months ago), but I never took off the IAC, so this time it gets the full monty. It also wasn't clear from the Haynes manual that there are two throttle bodies: one that has the TPS in the engine bay and the other that connects the air intake to the intake manifold. Course, they may not both be called throttle bodies per se, but since the procedure to clean the carbon gunk out of the "throttle body" that affects the EGR system is the one under the driver's seat and the other "throttle body" in the engine is where the TPS connects, I'll just assert there are two until someone corrects me.

No idea on the P0773 code, but the Toyota dealer wasn't too concerned with it.

[TheMAN]

there is only one throttle body and one throttle body only.... and that is under the hood on the S/C
the one under the driver seat is where the N/A one would go... it's just an adapter/coupler that fits a "square peg in a round hole"... this is just a carry over legacy from the N/A engine, despite the fact that the S/C intake manifold uses a different part number... I bet you it's all the same except for some minor differences, thus they saved money by not making a new mould for casting a completely different intake\

be sure to get yourself a JIS P2 screwdriver before taking off the IAC.... you'll save lots of headaches this way.... you can find them easily on ebay and other places online

and the P0773 code seems to be a shift solenoid code... if your trans hasn't been shifting right, then that will explain why

[jmrodz0]

there is only one throttle body and one throttle body only.... and that is under the hood on the S/C
the one under the driver seat is where the N/A one would go... it's just an adapter/coupler that fits a "square peg in a round hole"... this is just a carry over legacy from the N/A engine, despite the fact that the S/C intake manifold uses a different part number... I bet you it's all the same except for some minor differences, thus they saved money by not making a new mould for casting a completely different intake\

be sure to get yourself a JIS P2 screwdriver before taking off the IAC.... you'll save lots of headaches this way.... you can find them easily on ebay and other places online

and the P0773 code seems to be a shift solenoid code... if your trans hasn't been shifting right, then that will explain why

Thanks for the info on the throttle body. After getting check engine codes for the EGR system and cleaning the throttle body with no success, I eventually removed the other thingy and the air line to the EGR valve was completely choked with carbon deposits. A can of brake cleaner later and the engine code hasn't came back...yet.

The transmission has been good. The fluid and filter was changed recently and with the new SAD couplings it has been driving very good. Now that I'm thinking about it, there may be an issue under full acceleration when then transmission (I assume) tries to downshift, but since the acceleration problem exists in Park it may just be coincidental.

Good tip on the screwdriver (no pun intended). Any idea what the thread specs are on the screws? I'll probably to replace them with bolts or hex screws. Too inconvenient a location for a screw.

[TheMAN]

There's no need to replace the screws as long as you have the right screwdriver... they are supposed to be very tight and the JIS cuts are at an angle where cam out is basically impossible... using anything else is asking for over torquing and stripping the threads from the aluminum throttle body

[jmrodz0]

Good point!

[tbkilb01]

I'm looking to clean my EGR, passage, and pipe and wondering what size wrench you used to remove the pipe nut? I read two other postings and each differ on this subject... my van is a 92 previa. the vans in other postings were 95 S/C and another toy van of yesteryear.... :cnfsd:

[jmrodz0]

I'm looking to clean my EGR, passage, and pipe and wondering what size wrench you used to remove the pipe nut? I read two other postings and each differ on this subject... my van is a 92 previa. the vans in other postings were 95 S/C and another toy van of yesteryear.... :cnfsd:

I don't know the technical size in metric, but I used a 15/16" open end wrench and it fit like a glove. I can also attest that a crescent won't work.

You might also want to consider getting a 12mm/14mm offset wrench if you don't already have one. I found one at NAPA and it has many applications for this van.

UPDATE: I just looked at the photo you supplied and it said 15/16" too. LOL

[tbkilb01]

hey thanks, and sorry, I attached wrong picture...DOH..:doh:
and I thought it was a 15/16 its just the other picture ( of S/C) uses 1" crowfoot
but I will go with 15/16 and check into the off sets.... :thmbup:

[TheMAN]

15/16" should be a little more than 23mm, but not quite 24mm (that's close to 1")

[jmrodz0]

I heard a hissing noise coming from the engine compartment and it appears to be coming from a little thingamajig attached to the throttle body. I haven't been able to find a part number for it, nor do I have any idea exactly what it does. It has a little vacuum actuated plunger on the bottom that acts as a stop for the throttle, so I'm guessing it regulates the throttle somehow and in turn affects the supercharger operation (I think).
2161

Anyway, if anybody has any idea exactly what this part does and how to get a replacement (short of buying a new throttle body) please let me know.

Thanks
Jim

[TheMAN]

EGR valve?

[jmrodz0]

EGR valve?

That's certainly what it looks like, but the EGR is in under seat engine compartment.

It may be a moot point though, since there is a problem with the vacuum line. I've replaced it twice (not with OEM hose) and finally got so disgusted I just plugged it off.

[jmrodz0]

I replaced the bad vacuum line with a hard plastic type hose from Autozone. I had to heat the ends a bit to get a nice tight fit, but the vacuum leak is now gone. I also had a broken PCV grommet and replaced that too. Note to self: anytime you remove the PCV valve, replace the grommet so you don't have to remove the valve cover to extract the broken pieces!

I bought an OBD scan tool and the Haynes ODB-II Techbook and with the vacuum leak, the Short Term Fuel Trim was way off >13, but after replacing the vacuum line it was oscillating around zero +-2. After reading through the book (which I wouldn't buy again), it seems like I've done all the applicable things and replaced all the likely suspects, but one thing I read that I hadn't considered is exhaust back pressure.

Since the problem of shuddering/backfire only occurs at high revs (>2500) I'm wondering if this might be the cause. Has anyone else run into a similar problem or is this just something they added to fill up the manual?

[timsrv]

I'm not saying it's back pressure, but that could explain things. About the only thing that can create a back pressure issue is a plugged up cat converter........and yes, this can create massive performance issues. The few times I've seen this it was also accompanied by a melted EGR modulator (too much heat due to back-pressure). It's possible yours might be starting to plug. The only way I know to test is to run it with a temporary test pipe or take a very loud and obnoxious test drive with an open header :lol:. I've been following this thread, but sadly I don't have much to contribute as I've never owned or worked on a supercharged Previa. Good luck. Tim

[jmrodz0]

I'm not saying it's back pressure, but that could explain things. About the only thing that can create a back pressure issue is a plugged up cat converter........and yes, this can create massive performance issues. The few times I've seen this it was also accompanied by a melted EGR modulator (too much heat due to back-pressure). It's possible yours might be starting to plug. The only way I know to test is to run it with a temporary test pipe or take a very loud and obnoxious test drive with an open header :lol:. I've been following this thread, but sadly I don't have much to contribute as I've never owned or worked on a supercharged Previa. Good luck. Tim

The Hayne's manual says the test for back pressure is:

Test the vacuum pressure (at the intake manifold) at idle and if the pressure slowly drops toward zero, then there is a restriction.

It goes on to describe the test for an exhaust restriction as:

Record the idle pressure, then rev to 2000 RPM which should reach about 16 in-Hg and then quickly release the throttle. The pressure should lower at the same rate that it increased. If the vacuum pressure is 5 in-Hg or more higher then there is an exhaust restriction.

Course, once having found there is a restriction the only real test is to remove the exhaust manifold. :LOL2:

I'm wondering if simply removing the pre-cat O2 sensor would provide enough of an air leak to test it for blockage to avoid taking off the header?

I'm on vacation in SC and the area is generally agricultural, but I'm loathe to pull off the exhaust header if I can avoid it....cuz the SC police just love to ticket the vacationing New Englanders.

[timsrv]

No reason to pull the header, just pull the cat. Quite often a visual inspection is good enough to verify. Just shine a bright light in one end, and look through the other end. You should see light through the mesh inside. If it's pitch black, or if there's junk in there (like balls of soot), then you found your problem. If that's the case, you can gut it out by ramming a rod through it and break out the guts. After that you can bolt it back up and use it as a test pipe. Test drives with open exhaust are always a fun way to verify, but usually are not necessary. I've never done the visual inspection with a Pevia cat before, but think it should work. The only problem I can think of is all the pipe that's included as part of it. This might make it harder to inspect. If the pipe makes it visually difficult, you could always use an inspection camera (assuming you have access to one). Tim

[jmrodz0]

No reason to pull the header, just pull the cat. Quite often a visual inspection is good enough to verify. Just shine a bright light in one end, and look through the other end. You should see light through the mesh inside. If it's pitch black, or if there's junk in there (like balls of soot), then you found your problem. If that's the case, you can gut it out by ramming a rod through it and break out the guts. After that you can bolt it back up and use it as a test pipe. Test drives with open exhaust are always a fun way to verify, but usually are not necessary. I've never done the visual inspection with a Pevia cat before, but think it should work. The only problem I can think of is all the pipe that's included as part of it. This might make it harder to inspect. If the pipe makes it visually difficult, you could always use an inspection camera (assuming you have access to one). Tim

Gee Tim, you make it sound so easy. :LOL2:

From the looks of it, the exhaust system is original to the van and since I'm on vacation I don't have a spare vehicle to fetch replacement hardware for the case where the bolts are [invariably] frozen. So, I'm probably in for a penny, in for a pound once I start to disassemble. I do have an inspection camera, but no rebar (or other suitable destruction tool). Regardless, it's a slippery slope under the circumstances. I'm gonna test it with the O2 sensor removed. If the hesitation problem goes away, at least I'll know that backpressure is the problem, and if it doesn't make any difference then I'm back to square one anyway.

[TheMAN]

if the engine ever ran rich before, it would've melted the cat, after quite some time

gutting the cat will result in a check engine light due to OBD2 monitoring for cat efficiency... the light should have came on by now if the cat was bad, but then again, we're dealing with early OBD2, it might not be so smart....

[jmrodz0]

if the engine ever ran rich before, it would've melted the cat, after quite some time

gutting the cat will result in a check engine light due to OBD2 monitoring for cat efficiency... the light should have came on by now if the cat was bad, but then again, we're dealing with early OBD2, it might not be so smart....

Update: I took off the pre-cat O2 sensor and it seemed to make an appreciable difference! There was still some backfire at higher revs but I couldn't say whether that is a function of my hack, or if removing the O2 sensor didn't release enough pressure, or if the problem persists. These vans seem to have a lot of variables with the air/fuel system, so it wouldn't surprise me if the lack of the O2 sensor was a new culprit. I didn't put a vacuum gauge on it, so I don't know the exact difference the increased air flow made with respect to vacuum pressure. I also did not take it on an extensive test drive. Regardless, there was enough improvement for me to justify replacing the cat.

The engine had been running rich for some time with various engine codes indicating bad O2 sensors. Thing is, I don't really know when this stuttering/hesitation problem started and I've made so many repairs lately that it's hard to remember the order of things but I had replaced the O2 sensors...twice!

Course, hindsight is always 20/20, but as I reflect on it, excess backpressure in the exhaust may have increased the heat retention in the engine which may have been a component of the head gasket failure. Likewise, it may have had something to do with the vacuum system problems that manifested themselves in many places: EGR, Throttle body, EVAP, all of which were repaired at one time or another.

All the maintenance stuff that was done may have compensated for the problem with the backpressure which may actually be the root cause...and the supercharger adds some additional complexity to the air flow dynamic and is completely foreign to me.

[jmrodz0]

Update: I finally got the new cat, but it was the wrong part....but of course, I had already removed the old one before realizing it. Regardless, while I had the old cat off, I took a peek inside and could see light shining through. Then I used my handy dandy scope camera and verified that it was in good shape.

Since back pressure isn't an issue, I'm starting to think that I must have F'd something up when I replaced the head gasket. Course, the van is running excellent at low speed (<60MPH), so whatever I did wrong won't be obvious.

That said, while I had the head off, I lapped the valves and replaced the valve seals. What I didn't do is reshim the valves (though I was very careful to put back everything in the same place from whence they came).

Is reshimming the valves a critical component of a head gasket change? Does anyone have any instructions on how to go about the process and whether this may be the problem?

Thanks

[timsrv]

Probably not the valve shims. I doubt you could have removed enough material with a hand lapping to create an issue, but not a bad idea to check it out during a major service like that. Due to wear on the camshaft lobes, shims, and valve stems, valves can get a bit loose. A slightly loose valve (due to normal wear) is no big deal. Wear on the valve head & valve seat can however make the valves tighter. If you only hand lapped to verify a good seal, then you're probably okay. If however you worked it hard and removed a lot of material, this might have created an issue (but not too likely). Tight valves can be a problem because the valve relies on it's contact with the seat to cool (especially true with exhaust valves). For this reason, tight valves typically run hot & valves that run hot have a tendency to burn or warp. I doubt you have this issue because burned or warped valves do not seal and there would be an obvious miss (especially at idle). Since intake valves are cooled by air/fuel mix coming through them they usually don't burn or warp (this is also the reason intake valves are typically adjusted tighter than exhaust valves). Severe intake valve leaks are usually accompanied by backfire noises up through the intake. Severe exhaust valve leaks are usually accompanied by backfire noises out through the exhaust. Severe valve leaks (of either kind) can also be detected by a compression test and/or by listening to the cranking of the engine with the ignition disabled. If you have a compression problem in a cylinder that is not improved when oil is introduced, then that indicates a bad valve.

If the manual you are using is anything other than a genuine Toyota factory service manual, then I'd highly recommend you get the Toyota one. There is a highly detailed area that explains setting valve clearance. The FSM is very thorough (perhaps to a fault) in some areas. Here are links to a couple of threads where I attempt to explain setting valve lash. http://www.toyotavantech.com/forum/showthread.php?1111-Previa-S-C-vs-Non-S-C-Cams-Interchangable, http://www.toyotavantech.com/forum/showthread.php?552-Replacing-a-Previa-head-gasket. The 1st thread is short. On the 2nd one this is discussed near the bottom of the 1st page. I'm guessing this is not your issue, but after the head has been off it's always a good idea to check & adjust as required. Tim

[jmrodz0]

Thanks Tim!

I did lap the valves by hand, but the van does backfire at higher RPMs (>2500). I also had sent out the head to get resurfaced. The cylinders all had pretty good compression (~120PSI) prior to the head gasket change and I had read your posts which were the impetus for testing for valve leaks and subsequently lapping the valves.

I don't have the Factory Service Manual, nor do I have the special Valve Clearance Adjustment tool. I did find a Youtube video of this procedure. Regardless, I appreciate the info and it's good to know that the likelihood that I screwed things up significantly is minimal! I've ordered a micrometer that should arrive tomorrow.

During the process of reinstalling the old catalytic converter (after receiving the wrong part), I replaced the gaskets on both ends. I went for a long drive yesterday and the van was running noticeably better. I'm not sure if the gaskets tightened things up with respect to air flow or whether it was just coincidence, but as long as I didn't abuse the throttle, the van performed very well through the driving range up to around 70MPH. It eventually started to sputter around 72-75MPH, but it was a very pleasurable ride!

[timsrv]

If the machinist ground the valves, I would be concerned about adjustment. A light hand lapping only would not likely have much affect on valve lash (adjustment). Replacing gaskets on the cat would not have an effect on performance. Might however affect sound, which can change your perception of performance. Tim

[jmrodz0]

If the machinist ground the valves, I would be concerned about adjustment. A light hand lapping only would not likely have much affect on valve lash (adjustment). Replacing gaskets on the cat would not have an effect on performance. Might however affect sound, which can change your perception of performance. Tim

Thanks Tim! Sound like I couldn't have screwed things up too badly by lapping the valves so that's great news!

I haven't adjusted the valves yet. I'm heading back to MA in 5 days so I don't want to get too creative at the moment. The van is running well at low RPM so as long as it gets me home, I'll revisit when I get back to the frozen tundra.

[jmrodz0]

Since I will be checking the valve clearance, I'm thinking that I will verify the camshaft installation at the same time. When I originally installed the camshafts, I had set the engine to TDC and tied the timing chain to the sprocket, but I didn't pay any attention to the actual timing mark on the crankshaft pulley.

After reading through Tim's excellent write up on rebuilding the 4yec engine, I notice that he set TDC with a gauge on the piston and then redefined a new crank pulley mark to align with the "0". My question is whether this same procedure applies to the 2ZFZE engine as well?

My plan now is to set the crank pulley mark to "0", then check the camshaft orientation and reinstall them if the timing marks on the cams are not properly aligned. However, if the crankshaft mark does not take precedence over the cam position and sprocket, then I would align the cam timing marks and redefine the crankshaft pulley mark to correspond.

[timsrv]

Are you saying that you never checked the ignition timing after doing a head gasket? Ignition timing is important and needs to be set any time the distributor is disturbed (as required while doing a head gasket). I wouldn't worry too much about the accuracy of the timing mark on the crankshaft pulley. Besides, with the head installed, there's no easy way to check it anyhow. If you're concerned it's off, you could always get another one from a salvage yard and compare (the odds of two being off the exact amount are almost nil). FYI, these are almost always accurate.

The pulley timing mark being off that far (in my overhaul thread) was an exception to the norm (unusual). When checking the ignition timing on Previa, you'll need to jump the pins in the box under the driver's seat to put it into the diagnostic mode (refer to that section of the service manual). With a timing light, check the orientation of that pulley notch with the marks on the timing cover. Adjust the timing only while in the diagnostic mode, then pull the jumper and check with the light again to verify the electronic advance is working (timing should be different with the jumper removed). Good luck. Tim

[jmrodz0]

Are you saying that you never checked the ignition timing after doing a head gasket? Ignition timing is important and needs to be set any time the distributor is disturbed (as required while doing a head gasket). I wouldn't worry too much about the accuracy of the timing mark on the crankshaft pulley. Besides, with the head installed, there's no easy way to check it anyhow. If you're concerned it's off, you could always get another one from a salvage yard and compare (the odds of two being off the exact amount are almost nil). FYI, these are almost always accurate.

The pulley being off the far (in my overhaul thread) was an exception to the norm (unusual). When checking the timing on Previa, you'll need to jump the pins in the box under the driver's seat to put it into the diagnostic mode (refer to that section of the service manual). Adjust the timing only while in that mode, then pull the jumper and check again to verify the electronic advance is working (timing should be different with the jumper removed). Good luck. Tim

Thanks for the information Tim. That's what I was hoping to hear.

FWIW, I had marked the distributor orientation during the head gasket repair and when completed I took the van to the local dealer to set the timing. However, after they probed around for 45 minutes, they informed me that the timing on this model year cannot be manually adjusted! I have tried resetting the electronic timing with a jumper across the TE1/E1 terminals under the driver's seat, but as far as I can tell, there is no other way to adjust the timing.

[timsrv]

I'll admit I know nothing about SC models, but I find it a bit hard to swallow there would be no ignition timing adjustment. On NA models the distributor set bolts are in slots. To adjust ignition timing you loosen these bolts, then rotate the distributor to adjust. Once correct ignition timing is established, you tighten the distributor bolts to lock into place. After tightening the bolts, I will usually double check with a timing light (to make sure tightening didn't move things). If you have the 94 factory service manual that should shed some light. I'd look it up for you, but my newest manual is 93, and there were no SC models until 94. Tim

[jmrodz0]

I'll admit I know nothing about SC models, but I find it a bit hard to swallow there would be no ignition timing adjustment. On NA models the distributor set bolts are in slots. To adjust ignition timing you loosen these bolts, then rotate the distributor to adjust. Once correct ignition timing is established, you tighten the distributor bolts to lock into place. After tightening the bolts, I will usually double check with a timing light (to make sure tightening didn't move things). If you have the 94 factory service manual that should shed some light. I'd look it up for you, but my newest manual is 93, and there were no SC models until 94. Tim

Thanks Tim. This '94 LE/SC model does not have slotted holes in the distributor, just round ones....and I was just as incredulous as you when I was told of this. Course, I'm a bit of a dope for not realizing this when I had the distributor out, but since I had marked the distributor location before removing it, I didn't even think about future adjustments.

[timsrv]

Do you have the 94 factory service manual? If so, look it up. If not, you should focus on getting one, then look it up. Tim

[jmrodz0]

Do you have the 94 factory service manual? If so, look it up. If not, you should focus on getting one, then look it up. Tim

I don't have the Factory Service manual, but I'll check out ebay and see what they've got.

[pdgizwiz]

I don't have an SC, but I have the '94 supplemental manual. It shows a distributor with holes instead of slots as you describe.
The SC has a crank position sensor that the NA engines don't. I expect that the computer handles ignition timing using that signal.
Heck, most cars these days don't have distributors at all. Timing lights have become as old-fashioned as point files.

[jmrodz0]

I don't have an SC, but I have the '94 supplemental manual. It shows a distributor with holes instead of slots as you describe.
The SC has a crank position sensor that the NA engines don't. I expect that the computer handles ignition timing using that signal.
Heck, most cars these days don't have distributors at all. Timing lights have become as old-fashioned as point files.

I've ordered the Factory Repair manual...and fully expect the procedure to set the timing will include the sacrifice of a live chicken. :)

[timsrv]

I don't have an SC, but I have the '94 supplemental manual. It shows a distributor with holes instead of slots as you describe.
The SC has a crank position sensor that the NA engines don't. I expect that the computer handles ignition timing using that signal.
Heck, most cars these days don't have distributors at all. Timing lights have become as old-fashioned as point files.

Makes sense. Why would you run off a phone modem when you have wifi? When you think about it, given the level of technology, it's almost surprising that they still had distributors at all in 94. Of course my brain is still oriented to 1985.........gosh, I'm getting old :doh:

[jmrodz0]

I've ordered the Factory Repair manual...and fully expect the procedure to set the timing will include the sacrifice of a live chicken. :)

I'm finally back in MA with my Official Previa Repair Manual!

The manual asserts that the timing can be adjusted by loosening the distributor and turning. Unfortunately, the distributor on this van doesn't have that option. I guess it could be that this has a nonstandard type distributor without the slots, but the van drove pretty well from SC to MA albeit with the same shudder/lack of power at 2500RPM. Upon my return, I gave the engine compartment(s) a visual check and everything seemed to be in place (ie PCV, vacuum hoses, no leaks, and of course no ck eng lights). So, I'm back to square one with this issue.

I'm fairly confident of all the repairs made to date, and the van runs very well under most conditions. The big variable in all this is the supercharger which is not documented in the repair manual. I have ordered the Supplemental Repair Manual which covers the 2TZFZE engine....I hope.

Understanding the cause of this problem has become a quixotic quest! I did get a referral to a Toyota specialist in Quincy MA, but they were too busy on other projects, so if anyone knows of a Toyota specialist in MA please pass it along.

[timsrv]

The supercharged units have a crank position sensor. With that, the ECU adjusts timing. No need for you to do anything.

[timsrv]

BTW, I would have offered this information earlier, but just recently discovered this while working on another Toyota from this era. There was absolutely nothing in the service manual to suggest this was the case. I figured it out when I found holes on the distributor mounts (instead of slots). That got me looking around and sure enough, there was a crank position sensor. Tim

[jmrodz0]

Last week I located the Air Control Valve that is mounted on the radiator. This valve somehow regulates the air flow/pressure to the supercharger. The Supplemental Repair Manual has some information about the operation but not much. Anyway, after locating the valve, I disconnected the attached vacuum hoses and the electrical connection and started the van. It ran like crap and eventually stalled. I reinstalled the ACV and it returned to normal operation however I got a P0800 and a P0401 code. I did not clear the codes and took the van for a few errands and when I got back I checked the codes again. This time the 401 code was still there, but the 800 code was gone and a P0006 code showed up.

There is no explanation of either the P0800 or P0006 codes in the Repair Manual, but the P0401 is an ERG insufficient flow problem. This morning, I drove 50 miles and again checked the codes. The only code that showed up was the 401 EGR insufficient flow. The more significant epiphany was that I was able to rev the engine over 2500 RPM without any problems!

This was a revelation and a frustration since I hadn't done anything [of significance] that would change the behavior. I had tested the EGR months ago with a vacuum gauge and it seemed to be operating properly, that is, the engine stalled when I put vacuum to it. I had cleaned the EGR and the pipe also.

This can't be a self correcting problem, so I'll revisit the EGR system. The manual claims it may be the VSV or the Camshaft Position Sensor and since the van is running great otherwise, I'm discounting a fundamental problem with valve timing, compression, MAF sensor, and ECM.

[jmrodz0]

The supercharged units have a crank position sensor. With that, the ECU adjusts timing. No need for you to do anything.

Tim,

I found the problem...and feel very stupid.

The issue was with the connector on the crankshaft position sensor! It appeared to be connected, but popped right off when I wiggled it. After cleaning it out with some electric spray and seating it properly, the van is now running perfectly through the entire rpm range.

Thanks for all the help!

Jim

[timsrv]

Thanks, but admittedly I got there by fumbling around (I learned something too). pdgizwiz actually had the timing/sensor thing nailed early on. That's awesome you got it figured out. On the one I was working on (a NA 95 Corolla) a crank position sensor was the last thing I expected to find. I swapped distributors, igniters, and the ECU (ECU is a real PITA on the Corolla) before fumbling my way to the crank position sensor. What gave it away was pdgizwiz's comments about the lack of slots in the distributor.

I was using a factory service manual, but it was a 94 (shouldn't have mattered I thought). Absolutely nothing in there about a CPS. No big deal now that it's over. Stuff like this just makes us better mechanics. :doh: Tim

[tbkilb01]

I don't have an SC, but I have the '94 supplemental manual. It shows a distributor with holes instead of slots as you describe.
The SC has a crank position sensor that the NA engines don't. I expect that the computer handles ignition timing using that signal.
Heck, most cars these days don't have distributors at all. Timing lights have become as old-fashioned as point files.

I had forgotten about those points.. I was steady filing on them back then, under the distro cap!