Fiero Formula. I replaced the distributor o-ring. Timing set to 10 deg BTDC and it idles fine. As soon as A-B jumper is removed, car stalls.
I can get the car to idle but I have to keep pressing the throttle. The car backfires and runs rough. If I put the A-B jumper back in, the car
idles fine. Any ideas?
Thanks,

One possibility is that the outer ring of your harmonic balancer has spun, and therefore your timing is way off.

quote Originally posted by Patrick: One possibility is that the outer ring of your harmonic balancer has spun, and therefore your timing is way off.

If the timing is way off, wouldn't it also not run properly when I have the OBD connector pins a and b shorted?

It runs fine until I pull the jumper.

The only things that were done since it was running were to remove the distributor, install a new o-ring and replace
the distributor.

I set the 'rough timing" by putting cylinder one at TDC. It also runs ok, like that, when A-B are shorted but not
when A - B jumper is removed.

quote Originally posted by pdemondo: If the timing is way off, wouldn't it also not run properly when I have the OBD connector pins a and b shorted?

Not necessarily. When the jumper is not in place, the ECM is advancing the ignition timing by a considerable margin. With the jumper in place, it's possible the engine runs smoother because the ignition isn't as far advanced.

Keep in mind, if the outer ring of the harmonic balancer has spun (which isn't uncommon with a 25 year old balancer), the ignition timing will be incorrect (after using a timing light) as the timing marks will be in the wrong location relative to the crankshaft.

It happens to the best of us... including me. More information HERE.

[This message has been edited by Patrick (edited 12-27-2014).]

I solved the problem. It was the distributor.
I pulled out the distributor and found some wiggle in it.

The engine would run sometimes and then backfire and stall other times.


Thank you Patrick for your help.
I hope this will help anyone else with a similar problem.
If you have ignition problems make sure to check out the distributor.

quote Originally posted by pdemondo: I solved the problem. It was the distributor. I pulled out the distributor and found some wiggle in it.

Where was the "wiggle".... inside the distributor, or was the distributor itself not seated down all the way?

quote Originally posted by Patrick: Where was the "wiggle".... inside the distributor, or was the distributor itself not seated down all the way?

No matter how hard I tightened the distributor bolt down it had some up and down play on the shaft.
I removed the distributor several times and tried to reseat it but I could not get rid of the shaft play.
I put a new distributor in and it seats down nice and tight.

quote Originally posted by pdemondo: No matter how hard I tightened the distributor bolt down it had some up and down play on the shaft. I removed the distributor several times and tried to reseat it but I could not get rid of the shaft play.

Up and down end play of the shaft cannot be eliminated by tightening the mounting bolt down (as you discovered).

The way to properly reduce shaft end play is to install shims between the gear and the body of the distributor.

I'm curious how much up and down play your distributor shaft had. There needs to be some end play. Ordinarily a little extra doesn't result in a non-running engine.