Can't properly set ignition timing

[stuartgipson]

Freshly rebuilt 87 4YEC engine with brand new timing chain, sprockets, and brand new camshaft. Verified harmonic balancer mark lines up with 0 degrees BTDC when #1 cylinder is exactly at top. Engine at operating temp, service connector jumpered, ISC valve disconnected, and RPMs at 700. The engine runs ok but I can't dial in the timing quite right to 12 degrees BTDC. The problem I'm having is that when I stab the distributor in the block I run out of travel on the slot for the distributor hold down bolt. I can only get close but not on the money. It's slightly retarted a few degrees even though the distributor is rotated fully counter-clockwise....So, I pull the distributor out and re-index it one gear tooth over then I get the complete opposite problem. Timing is now a few degrees too advanced even though the distributor is turned as far clockwise as it will go. I've double checked to make sure I've only moved over one tooth on the drive gear. Shouldn't I be able to get the timing to be right on with the hold down bolt more or less in the center of the adjustment slot and still have room to adjust either way some? Can't seem to see the problem....Stu

[Burntboot]

Are you are absolutely SURE that you are only moving the distributor shaft by 1 tooth?

The only thing I can think of that could cause that would be if the cam timing is off.

[stuartgipson]

Yeah, 99.9% sure. I do notice the rotor isn't the best fit onto the distributor and can be twisted back and forth a little.

[VanCo]

The rotor shouldn't have movement back and forth. That will cause difficulty timing and potentially the issue you're experiencing.

Where did you get the cam? Is it OEM?

[stuartgipson]

No, the cam is not OEM. I bought it from Rock Auto. It is a Sealed Power CS875. It's supposed to have the same specs as OEM for my 87 4Y engine. I'm going to take a better look at the rotor tomorrow and see why there's some rotational play in it. I'll report back. Thanks

[Burntboot]

Odds are that one is after market, they often dont fit well and allow rotational movement, affecting timing.

Personally I wouldn't waste any time "looking" at it, just stop by a Toy Dealer and get a new rotor.

[stuartgipson]

So I have another distributor and rotor in my parts collection. The rotor fits nice and snug. I put it on the engine and have the same problem. I did notice this time though that when I jumper the diagnostic plug the check engine light starts to flash as expected, but it doesn't seem to change the timing. Shouldn't it retard the timing or disable the timing advance so you can set it to 12 degrees BTDC? I checked and cleaned all the electrical connectors on the distributor and ECM. They all look clean and good condition. I verified that the TPS is set properly with an .028" feeler gauge......Anyways, I just went ahead and disconnected the ISC solenoid by the air cleaner, adjusted idle air screw to get 700 RPM (MT) and set the timing to 20 degrees BTDC with no jumper on the diagnostic connector. The van seems to run just fine like this. Dunno what's going on. A question I have is when jumping the diagnostic connector, do I do it while the vehicle it running or do you I to turn off the vehicle, jumper, then restart? Also I notice sometimes the check engine light gives a steady flash about 1 time per second, and sometimes it'll flash a code 11 depending on when I jumper the diagnostic connector. I believe the code 11 is a stored code from when I had the TPS disconnected. Hmmm. Am I going nuts?

[VanCo]

I jump the connector with it running at idle. Regarding the 11 code, it can be set when the ECU detects an open condition in the TPS circuit, when it isn't expecting it. When this happens the ECU will not go to base timing mode.

The 11 code doesn't get stored really. Not like it would in a modern car. The code will go away if the circuit is good.

If you open the throttle while it is in diagnostic mode it can set the code. This is because you're disrupting the TPS circuit.

If the TPS gap isn't set right (or the TPS is faulty) you'll get an intermittent code. This is because the circuit isn't always completing when the throttle is closed. This will make it really hard to time because the ECU will jump back and forth from base timing to ECU controlled.

[stuartgipson]

That's some good info. That very well could be the problem. I did open the throttle when in diagnostic mode. I'll have another look. Do you think I'm ok for now with the timing at 20 degrees at idle in normal (not diagnostic) mode? Thanks!

[VanCo]

That should be okay. I've done that before when I had a non functioning TPS. If you're concerned the timing is too advanced, remove the power steering access panel and drive around. It's the perfect access port to listen for pinging while driving. If it pings, back the timing off a couple degrees (or get better gas), if it doesn't, just leave it.