It seems that I'm having to put the ol' Fiero back into time one too many times to be normal. About 100-200 miles after I put the 2.8 in time, it seems it slips back out (12-13*), backfires and runs like poopy. So, I'm wondering if the chain is stretching out and wanting to break. Engine has about 146k miles on it and I know it is in need of a rebuild as it leaks oil and I have varying compression. Was considering on trading my '87 SE in for an '88 GT I found....

------------------
-jason
'87SE
'90GTZ

Sounds to me like your distributor is slightly rotating over time. Are you snugging the bolt up real tight?
If the timing chain was skipping a tooth every now and then, your motor would go from running good to bad immediately. Is the timing increasing slowly over that 100-200 miles, or is it all of a sudden moving up to 13*?

If it's all of a sudden, I'd say it's skipping teeth,
If it comes on slowly, your distributor is moving.

Mark your distributor relative to the block or plenum, make sure it's tight, then see if it has moved after 100-200 miles.

good luck
Dave

wow - that is scary
I would hope its just the dist. not being tight, and slowly moving out of time
if the car goes back to normal when you re-time it, I dont think it would be the timing chain. if it was the timing chain, you cam would be out of time with the crank pretty bad by now. I'm assuming you've done this 3 or more times - making for a total of at least 10*. so, like ditch said - mark the dist postion, and look for movement. and it wont be much - 2-3* is not alot by eye, so make sure its a fine mark & easily viewable.
another thought - if this onyl happend once - maybe the dist wasnt all the way in, then somewhere along the way, it set all the way down. this will give it a slight twist also.

quote Originally posted by ditch: Sounds to me like your distributor is slightly rotating over time. Are you snugging the bolt up real tight? If the timing chain was skipping a tooth every now and then, your motor would go from running good to bad immediately. Is the timing increasing slowly over that 100-200 miles, or is it all of a sudden moving up to 13*? If it's all of a sudden, I'd say it's skipping teeth, If it comes on slowly, your distributor is moving. Mark your distributor relative to the block or plenum, make sure it's tight, then see if it has moved after 100-200 miles. good luck Dave

The timing shift is immediate. Came up to a stop sign and all of a sudden it runs like dookie. I doubt the distro is shifting as I tighten it up once I reset the timing. Sure, I used a universal joint, but I still put plenty of torque onto the hold-down bolt, so I'm thinking it is the chain. If I had $2900, I'd buy that '88 GT. Sure wish I had enough money and a garage to do a motor conversion....

------------------
-jason
'87SE
'90GTZ

quote Originally posted by Dropzone: The timing shift is immediate. Came up to a stop sign and all of a sudden it runs like dookie. I doubt the distro is shifting as I tighten it up once I reset the timing. Sure, I used a universal joint, but I still put plenty of torque onto the hold-down bolt, so I'm thinking it is the chain. If I had $2900, I'd buy that '88 GT. Sure wish I had enough money and a garage to do a motor conversion....

that sucks, if it really is skipping teeth as it apperas, sooner or later you won't be able to fix it with a distributor adjustment, the cam and crank will be way off .

never changed the timing gears on a V6, but the parts are pretty cheap and I bet you could do it with the motor in the car...might have to remove passenger side cradle bolts and let motor sag down a bit to make work easier

Dave

quote Originally posted by ditch: that sucks, if it really is skipping teeth as it apperas, sooner or later you won't be able to fix it with a distributor adjustment, the cam and crank will be way off . never changed the timing gears on a V6, but the parts are pretty cheap and I bet you could do it with the motor in the car...might have to remove passenger side cradle bolts and let motor sag down a bit to make work easier Dave

I'm going to try & reset timing and mark its location. If it is the timing chain, I think I'll rebuild the motor as my high and low psi from cylinders are about 20-30.

------------------
-jason
'87SE
'90GTZ

Signs of a worn timing chain include the timing mark jumping around erraticaly when setting the timing using a light. Jumping one tooth will pretty much make the engine almost undriveable. Two teeth will keep it from running at all. When you set the timing is the distributor moving further and further around? Make a mark on the distributor shaft where it enters the block, and on the block at the same location. Next time it "slips" check the alignment marks and see if they've moved.

A more likely possibility if the distributor is indeed not rotating when the timing "slips" is that the roll pin that holds the distributor gear to the shaft has sheared and the gear itself is rotating. If this is the case get it fixed asap because there's a risk of losing oil pressure if the gear becomes disengaged with the camshaft.

JazzMan

Thanks, Jazzman. I'll give that a try. When you say the timing mark bounces around when trying to set timing, how many degrees are we talking about? More than a degree? I believe that is kinda what it does. I'll check it today when I check timing.

As far as the distro goes, it is only about a year or a year and a half old. Got a rebuilt unit from Advance Auto. Oh, another side note, when the car was running like dookie, the tach would jump around erratically. Didn't do that before the timing went screwy. I'll reset timing and see if that corrects the tach. Doubt it is the filter, but who knows. Thanks all!

------------------
-jason
'87SE
'90GTZ

More than a degree in either direction with the idle steady might indicate chain wear. If the tach is jumping around while the engine is running poorly, that's a common symptom of a module problem, or a bad tach filter.

JazzMan