I have a '90 5.0 TPI with a mysterious stalling problem. Car will start fine but after 5-10 minutes driving, it will begin stalling out at stop signs and lights - whenever the car sits for a few seconds. But for some crazy reason, when the A/C is on the problem goes away! Of course as soon as I turn the A/C off, the stalling comes back.

My mechanic did a tune-up, replaced the IAC, the fuel pump (since he already had to replace the sender) and replaced the fuel injectors with these: http://www.fiveomotorsport.com/Injec...sTPI.asp#caddy
And after all that, it's still stalling.

He then said the pickup on the Distributor was bad so he replaced the distributor with a rebuilt Cardone from Auto Zone. The distributor made sense to me since he said the A/C generates a charge which raises the idle enough to keep the engine from stalling. And now of course...it's still stalling. My mechanic is about out of ideas and he said there is no vacum leaks but he now thinks it could be the service bulletin #91-239-6E Low Speed Drivability (PROM) New Knock Sensor Available (Feb. 28, 1991) and that I need to replace the PROM with #16163139.

Does anyone know of this PROM chip is still available and/or do you think this is the problem? The car is bone stock except for the Flowmaster and the exhaust smells kinda bad when the car starts up but gradually goes away after the car drives for awhile.

Apologies for the long post and any help is greatly appreciated.

 

could the A/c clutch be dragging/not disengauging?

 

Could a dragging or non-disengaged A/C clutch cause the engine to stall with the A/C turned off?

 

This is something that may be worth checking out. When the AC is turned on, the ECM automatically increases the idle a hair to compensate for the extra drag of turning the compressor. You can actually hear it when you turn on the AC, you should hear the RPMs drop for a split second, then it goes back up a hair.

If it isn't doing that, then you may need that PROM, but I've never had to deal with that.

Don't quote me on this, but I believe that there is a switch either on the compressor that tells the ECM the compressor is on, or there is one on an AC line that turns on when high pressure is detected in the system, like when the AC is on, and that tells the ECM the AC is on so it can increase the idle. That may be your problem as well, if the compressor is good, that switch may be bad.

 

Thanks man. My mechanic said that exactly re: the A/C and idle. One thing I should mention is that the car sat in a barn for 2-3 years and I bought it from that guy about 6 months ago. I've heard people say it could be water in the tank or a faulty fuel pump but my mechanic replaced pump and emptied tank when he replaced the sender.

Does anyone know about this PROM #16163139 and where I can get one?

 

You can try the dealer, I dunno if they can still get PROMs for these cars or not. But, I may be going to a junkyard or two today, if so, I will keep my eyes peeled for any TPI Motors and see what I can do about getting a PROM from it.

 

Thanks Kevin - appreciate it. Anyone else have any advice? Getting to the end of my rope with this problem.

 

Just wanted to let ya know, I found no TPI cars today at the yard.