Ok, here's the deal, i'm still troubleshooting an idle problem. it idles like crap. so far i have changed the plugs, changed the timing chain, inspected all of the air ducts and pcv system for leaks, all is well. I noticed today that while i was trying to set timing the mark was jumping around a lot. and with the est bypass unplugged I can time it but if I tap the throttle it retards like 8 degrees then bounces back and if I rev it above three grand then it suddenly snaps to like 26 deg advance and stays there, then when i snap it shut it just goes back to 10. I was under the impression that with that connector unplugged it should not be able to control timing period.

I also looked at the drive gear on the dist. it looks all fine, will check cam gear when engine cools off. minilal shaft play on dist.

sorry about the length, just been hunting this problem for a year or so off and on

 

I may have read your post wrong, but for clarification, you have terminals A and B grounded out right?

(take a paperclip make a U shape and connect terminal A and B in the little connector that would be by your right knee if you were in the drivers seat)

The computer will not allow for the change if you do not do that.

 

unhook the wire (brown and white stripe) by the pass side firewall. Big black plug.

Hook the timing cable to the first plug on the passanger side.
Loosen distrib and set to 12*. Bet it runs like a champ. And remember to hook the brown/white cable back up.

 

this is an mpfi v6.
the brown wire with the black tracer IS the EST (electronic spark timing) bypass. It is unhooked while trying to time the car.

I think this is something a little more advanced than just setting base timing.

 

Sounds to me that the hold down bolt may not be tightened all the way OR you're unhooking the wrong plug.

 

be sure you have the est bypass unplugged and not the tach unplugged....I did that once

 

hopefully, your solution is beter than what I had to do.

 

I'm sure it is the right plug.
I have the small cap with remote coil, so I don't have to go near the dist
I'm pretty familiar with these systems, I'm just hoping someone can give me something i haven't thought of yet.

Also in-cap module just tested fine.

with that plug unhooked the computer has no control over spark timing so my scatter problem has to be something non computer related.

drive gear on cam is also fine.

 

well idle probs originate...

1 timing.
2 PCV probs
3 leaking vac hoses
4 leaking intake gaskets
5 poor plugs
6 egr stuck
7 bad wires
8 bad coil
9 bad cap(build up of carbon)
10 distrib out of phase
11 IAC malfuntioning

list goes on...

If you have base timing set at 12*, and the electronics are good as far as you can tell, test the wires.

You may have to cut up an old cap to test the internal postion of the rotor during idle.

To check the phase of the distrib, cut a hole to where you can clearly see the #1 point on the cap. Hook up timing light and see how far the rotor is off dead center on the point during idle.
If it is out, advanced, or retarded you will have to remove the cap, and lossen the 2 screws to change the pick-up head position on the distrib. until the rotor and the point are lined up correctly.

EDIT: A long and tedious task, but if nothing else works, it's pretty much your last option.

 

Hate to be the one to tell you but it sounds to me like your motor is toast- You are most likely getting severe endplay on your crankshaft.

 

well, checked rotor alignment, that's fine, my dist doesn't seem to be adjustable. wires are new, and it was the same with another set.

Also I'm very curious how excessive endplay can translate into over 20 degrees of non random spark scatter.

 

Here is how the ignition module should operate with the EST disconnected:

At idle speeds the timing will be the base setting. The timing should be steady with very little varience.

Slowly increase the engine speed while observing the timing. The timing should remain steady until 1600-2000 RPM. At this point the timing should suddenly advance ( can't remember how much, 16-20 deg seems to be correct).

As the engine speed continues to increase the timing should stay steady at the advanced amount.

With a decrease in engine speed the timing should return to the base setting below 1600-2000 RPM.

Try the slow increase in engine speed, if the timing retards as you previously mentioned sounds like it is time for a new distributor.

I take it that the timing chain has already been replaced?

RBob.

 

ok, so it's supposed to do the advance thing?
That's good, I was wracking my brain trying to figure that one out.
as far as the quick retard, what part of the dist would be bad, my unit seems to be in pretty good condition.

 

In order of possibility: ignition module, reluctor, pickup coil. Also check that the reluctor is still firmly attached to the shaft. There are known to come loose.

It is also nice to shim the shaft between the gear/housing for .015" of end play.

RBob.

 

Yep, that's normal.

 

I'm talking about your base idle timing walking around- you stated that is jumps back to 8* then to 10*. Excessive crank endplay will cause this too (or bad timming chain)- a sign that the motors life is limited if the crank is moving that much. Its a common problem for the 2.8 and 3.1 blocks

 

I am at a loss here. Gave it thought and can't visualize the circumstances that would cause a timing problem.

RBob.

 

Crank walks the chain back and forth- tanting and relaxing it- causes timing mark to wander.

I have personally witnessed this on several 2.8 motors- one I have seen with just over a 1/2" endplay.

Edit: These motors have always been label 2.crap in the automotive circles I am affiliated with.

 

OK, just didn't add the 1/2" of end play into the visual. Figuring .005-.010" endplay is typical, a 1/2" means that the thrust bearing isn't there any more. . . Yikes.

I can see that causing problems. Could probably check for this by pushing/pulling on the damper.

Hmm, "label 2.crap" as in a #2? LOL.

RBob.