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1989 Pontiac Grand Prix:
Engine Misses Slightly When Accelerating

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Alex Steele
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Question:

 

I have an '89 Pontiac Grand Prix with a 3.1 Liter V-6 MPFI Engine, usually I don't have my car worked on unless it won't go, stop, or the noise is so loud you can't hear the radio, but this problem is really starting to bug me.

 

When I am accelerating, the engine misses slightly and later at 45-55 MPH it chugs a couple of times. It chugs a little while in gear at a stop light also.

 

Answer:

 

Let's go down the list of what it might possibly be, and what it probably is. Number one: we can pretty much eliminate a mechanical problem with the engine, assuming the "miss" is coming and going. A hard internal failure would result in a solid miss that won't stop until you fix it. Number two: Multi Port Fuel Injection ( MPFI ). There could be an intermittent cause of a misfire in this system, maybe a fuel injector on its way out, a problem with the computer that electronically controls the injectors, or perhaps a short or bad connection in the wiring between the two. Number three: the ignition system. This is the first place to start looking, and the most common cause of a miss in any engine. To get even more specific we go right to the secondary ignition system, in your case that includes the ignition coils, spark plug wires and spark plugs. Notice I left out a distributor cap. That's because you don't have a distributer. Your engine uses what they call DIS (Direct Ignition System) which utilizes a combination of sensors instead of a distributor.

 

Bottom line: the most likely problem is a breakdown in the plug wires and/or ignition coils. When a plug wire deteriorates, it increases in resistance, meaning it is that much harder for the spark to get from the coil (producing the spark) to the plug (receiving the spark). So if that 60,000 volt spark no longer has a good path to the spark plug, it will either break through the insulation of the bad wire to the nearest path to ground (the engine block) or not get out of the coil at all and start eating it away from the inside out.

 

That's why driving for a long period of time with bad plug wires, before replacing them, may bring you back in the shop a week later with a faulty coil. In other words, if you have been chugging along for quite a while you may have added to the expense of the repair.

www.realworldautomotive.com

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Pontiac | Misfires | Ignition
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Comments:

TechHelp2
07 Aug 2016, 06:50
RE:J, The important thing is to see which system is failing. Is it spark or is it fuel or engine compression. If it runs then compression is ruled out and now you need to see if it is fuel or spark. Check these when it doesn't start.

Another issue that nobody has checked is to see if you have a clogged catalytic converter by checking the back pressure. To check this remove the oxygen sensor before the converter and install a pressure gauge. When the engine starts the pressure should remain near zero to almost one Psi. If it is two or more then you have a clogged exhaust system which usually is the catalytic converter.

Let me know your results.
J
06 Aug 2016, 22:58
Hello I'm back with my 1989 Pontiac Grand Prix 3.1 and am still having stalling issues with it after I took it to a shop and they replaced the ICM, checked the fuel pressure, crankshaft position sensor, camshaft position sensor and all were good. Only other thing maybe the ECM? I am drawing a blank. It starts, runs, dies and won't restart for 3-5 hours. Any help would be great. Thanks.
TechHelp2
08 Jun 2016, 15:02
RE: J, The important part of this is to clean the throttle plate first. Then go and clean or replace the IAC motor if needed.

We can diagnosis the problem further if needed.
J
08 Jun 2016, 13:55
Thank You for the info I will try and clean or replace the iac, also I was thinking it to be a bad throttle position sensor. I will try if not. lmk
TechHelp2
08 Jun 2016, 05:40
RE:J, It sounds like the Idle Air Control (IAC) could be stuck or the throttle plate is caked up with carbon (coking). Take the tubing of the air cleaner off until you reach the IAC and throttle plate and open the throttle (with the engine off) and spray carburetor cleaner in the bore of the throttle plate and wipe off with a rag.

Carbon clogs up the air passage causing the engine to stall and can stop the IAC to stop operating.

You may need to clean the throttle plate and replace the IAC motor.

Have someone scan your computer with a real time scan tool that can read all the data of all the sensors to make sure there is nothing else going on with another sensor.
J
07 Jun 2016, 17:55
I have an 1989 grand prix 3.1 that has starting acting up. It starts and idles for about 5-10 seconds and then dies. Before that whenever you pressed the gas it would stall and die when accelerating or decelerating. Changed filter and a few other things, everything looks good and no trouble codes. think it could be the map sensor?
Admin
30 Oct 2009, 11:59
If the check engine light was on (while running) before the engine shut down, I would first check what trouble codes were stored in the Powertrain Control Module's memory. That may lead you to the problem.

Did you notice if the light was flashing kind of erratically, and the engine was missing and bogging down as the light was flashing?

That's a big-time symptom of a bad control module.

A simple test we use is to lightly tap on the control module while the engine is running. If the light flashes and the engine spits while tapping the module is bad.

In your case you might want to tap on it while cranking to see if it starts, or tap on it with the ignition on (not running), and see if the light flickers (it should be on steady).

After that, you want to see if you've lost both spark and fuel injector pulse and diagnose from there. But you really need the service manual information and some experience at that point.


Charles
30 Oct 2009, 11:07
yes it was on to answer your question in regards to the check engine light
Admin
24 Oct 2009, 10:53
Hi Charles:

Not a lot to go on. No spark can mean a lot of things.

If there is no spark at any plug, or signals to any fuel injectors, I would probably be looking into the crank shaft position sensor first. The Powertrain Control Module (PCM) is a common failure on this model which could cause the same symptoms.

You said there was a "check engine" light on. Well, if the engine won't start it's supposed to stay on. Did you mean it was on while the engine was running, before the no-start problem began?

Don't change parts randomly. Get it to a technician if you're not sure.
Charles Chapman
23 Oct 2009, 21:32
my 1989 grand prix 2.8L turns over but wont start the plugs are not getting any fire. and also my check engine light is on.i put fuel

 

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