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1989 Chevy Celebrity 2.8 MPFI CAR WONT START / TRIES TO CRANK AND SOMETIMES CATCHES BUT FAILS

Engine is 2.8 mpfi and I have been able to get it to start by pumping the gas pedal while cranking and keeping it running by having the gas pedal depressed slightly but as soon as I let off the gas the car will die. It has a new starter, new fuel filter, half a tank of gas, new battery…

Check engine light came on and i did the paperclip trick and it showed code 43 which was knock sensor.

I’m assuming mpfi means multi port fuel injection. hmmm … to me this sounds like the idle adjustment mechanism is on the fritz. On cars of that era, this function was done in a variety of ways, most common is called the IAC == idle air control. Those devices can gum up, and cause this symptom. Do you know what technique your car uses to maintain the correct idle rpm?

Code 43 doesn’t necessarilly indicate a faulty knock sensor. That code indicates that there is a problem with the electronic spark control system. More often than not the ignition control module was the failing part that caused that code for me but it is a difficult code to diagnose whithout some expensive equipment and a diagnostic chart.

It would be worthwhile to carefully inspect the wiring/connections at all the components and the knock sensors can fail but they usually don’t usually cause erratic running when they fail. Check the fuel pump pressure and if it is 45+psi it isn’t the problem. Next pull the distributor cap and inspect the cap and rotor for indications of spark flashing through the rotor to the module and pickup coil which is usually caused by old plug wires. If the cap and rotor look suspect replace them and the wires and also the distributor.

There is an ESC module under the hood on that car as I recall and it is rarely the cause of a probem unless there is apparent damage from heat or impact.

FWIW I seem to recall that years ago the GM code 43 was termed “code from hell” because it was so difficult to diagnose with any certainty without installing ‘known good parts’ to experiment.

Edit;
Excuse me @Defcon3, et al. I posted from recollection and obviously I am off a year or two.

I believe it uses an IAC valve

There isnt a cap and rotor on the car, it uses a distributor-less ignition system with 3 coil packs , do you know if and how often coil packs go bad? I am going to replace the plugs and wires… should i replace the coil packs at the same time?

@ GeorgeSanJose I agree with George that it is likely the IAC. My '87 Cutlass Ciera (same A body) with the 2.8 had the exact same setup. I often had trouble with it getting gunked up. Cleaned it often but finally had to replace it.

Incidentally, You probably don’t have to actually have to pump the accelerator, just press at down a little and hold it there while starting it. This will provide an air bypass for the IAC. Of course it will still stall when you release the accelerator. You can try cleaning it but you may have to replace it.

I remember once I had to drive with two feet for a couple days until I could get to it.

How abruptly did this symptom appear? Just one morning it showed up, and every day for the most part before that it was running fine? And what is the relationship between this symptom and the CEL coming on? Did the CEL come on, then this symptom appeared? Or was the symptom already occurring, then the CEL came on?

the symptom of not starting just started this morning i was driving the vehicle yesterday and for the most part it was starting and running fine. The CEL light comes on periodically when i would be driving but maintaining speed. If i were to speed up or slow down the CEL light will go off eventually. It seems to come on most of the time when im just maintaining speed though.

the CEL light was coming on and going off before the engine not cranking symptom started. but like i said the symptom just appeared at 8am this morning and i was driving the vehicle at midnight last night.

The coil packs were quite troublesome on my '87 Cutlass Cierra. They’re mounted way down low on the ignition module just behind the bottom of the radiator and were subject to a lot of water etc. being thrown up from the road. When a coil pack went bad it could take out the ignition module.

Edit: However, I still think your problem is more likely to be the IAC considering that it runs but won’t idle. The above post was in answer to your question on coil packs on this particular vehicle.

you need a new MAF.

@Defcon3 See my edit on my last post.