1999 Pontiac Grand Am

Engine Performance problem
1999 Pontiac Grand Am 4 cyl Front Wheel Drive Automatic 130, 00 miles

I have an intermittent problem with the engine running rough, missing and hesitating. It happens at all speeds from idle to highway. It comes and gos, sometimes running fine for months before acting up again. I have replaced the coil housing, the ignition wires, the spark plugs, the fuel filter and I have had the fuel injectors cleaned on the car. I've also tried fuel injector cleaner in the gas tank. Nothing seems to have helped as the problem continues to plague me. Any ideas what it could be?
October 21, 2008.


There are a couple of things. First, run by Auto Zone or O'Reilly's and for free they can pull the codes on the car. This is extremely important to know.

Next, have them for free, they can hook a tester up to the car and check your battery, alternator and starter. Pour electrical output can cause all types of problems.

If the above doesn't show anything, take a spray bottle of water, and spray a mist over the plug wires from one end to the other and see if this causes the car to run ruff at any time. Sometimes even though you have replaced the wires you will have sparks jumping. Many times it is best to only use OEM wires to prevent sparks jumping. Make sure you spray down by the boot where it connects to the plug too.

Next is the ignition module: The electronic Ignition Control Module (ICM) monitors the CKP sensor signals and based on these signals, sends a 7X reference signal to the PCM so that correct spark timing and fuel injector control can be maintained during all crank and run conditions. Since the PCM controls spark timing and ignition control during crank and run, there is no bypass mode.

The ICM is not repairable. When a module is diagnosed to be faulty, it is replaced as a separate component

The other strong possibility is the fuel pump. You do have 130,000 on the car. You need to check the fuel pressure. The pump can be intermediate for some time and cause you problems.


Oct 21, 2008.
I will do as you suggest, checking at Autozone for the codes and the electrical system. The ICM was replaced by a local mechanic in an attemtp to solve the problem. It didn't help. Also, several times in the past few days, rough running and hesitation of the engine has caused the " Trac off" warning light to come on and stay on for a while. On the 99 Pontiac there is an electronic traction system. I don't understand why a rough running engine would trigger it. Perhaps this symptom is a clue that would help you to diagnose the problem? Or maybe it's not related at all. Also, I have found that rough running of the engine can be temporarily " fixed" by simply flooring the accelerator. The engine smooths out immediately and runs fine until the next time it misbehaves. It sounds like a fuel pump problem to me, but I'm not a mechanic. Finally, there is no fuel pressure test port on the 99 Pontiac. How do I test the fuel pressure?

Oct 22, 2008.
I took your advice about Autozone. Their computer hookup said: " Misfire, cylinder 1.&Quot; I also had Sears check out the electrical system, battery, alternator and starter. Everything is OK.

Next, I sprayed the wires and boots with the engine running, looking for sparks from hidden breaks in the wires. I saturated the wires and the boots, but it produced no effect on the engine. It kept running smoothly.

What next?

Oct 22, 2008.

A miss fire could be several things. Faulty spark plug or wire, Faulty coil (pack), Faulty oxygen sensor(s), Faulty fuel injector, Burned exhaust valve, Faulty catalytic converter(s), Running out of fuel, Poor compression, Defective computer.

My suggestion. You have replaced many of these things. I would think if it were a oxygen sensor, you should get that code. I don't think it is a faulty catalytic converter or defective computer. You are going to have to be able to clear the code and check each time for this or end up taking it somewhere. Auto Zone or O'Reilly's may let you buy/return under the tool loan program the tester for codes.

First since you have replaced numerous things, do a compression check on all the cylinders. If number one is really low, then you probably have a burnt valve. If all okay or close to the same, then I would do the below next.

Starting simple, you can crack a plug putting it in. I would clear codes, swap #1 plug with another cylinder. Drive it see what you get. If you get number one again, then swap the plug wire, clear the code and try it again. If you get number one, swap fuel injector. If any of these moves to the other cylinder then you have found the problem and you replace that part.

From what I see to test the fuel pressure you would need disconnect the fuel line, hook the pressure tester to the end, have a tester to turn on the fuel pump and then see what the pressure is.

It appears you need some test equipment for some of this. Why don't you do the easy things above and let's see what you come up with from there.

If it were a steady misfire and running rough, you could isolating the misfiring cylinder the old-fashioned method for finding a weak cylinder is to temporarily disconnect each of the spark plug wires, one at a time, while the engine is idling. When there's no change in the idle speed, then you have pinpointed the weak cylinder. Careful though, if the spark jumps to you it isn't going to feel good.

My bet with that many miles is a bad fuel injector or fuel pump. But let's see.

Oct 22, 2008.
Thanks for the suggestions. I will pull the plugs tomorrow, run the compression check and move the wires around. Hopefully I will find something amiss. I think we are moving closer to solving this problem. Thanks again for your help.


Oct 22, 2008.
Hello Ted

Please when you do the checks write down the info you have to let me know the specifics.
Also, when you encounter codes, please provide the number also, like "code P0301 - Misfire cylinder 1." Sometimes the info is only by code number. Sometimes codes are different.

You also might consider picking up some injector "O" rings before you remove them. The few cents will save a leak. Put a dab of Vaseline on them to go in smooth.

Good luck on the checks

Oct 22, 2008.
I ran the compression test as you suggested. Cylinders 1-4 read 197, 196, 200 and 197, respectively. The car ran perfectly on the way to the mechanic, but terrible on the way back. I put the trans in neutral, floored the accelerator and it smoothed right out. The mechanic did find that I had the wrong plugs. The plugs I have are for a 99 Pontiac 6-cyl engine. Mine is a 2.4L, 4-cylinder. I have ordered the right plugs and will install them tomorrow. What now?


Oct 23, 2008.
I forgot to say the code is PO301 Misfire Cylinder 1. Also, I could not switch spark plug wires around because my car has a plastic housing with the four plug boots imbedded in it. The whole thing goes on as a unit and can't be switched around.


Oct 23, 2008.
Hello Ted

The compression looks good. No cylinder is supposed to be less than 100 and the lowest one should not be less than 70% of the highest.....which is 140. So I would think that would rule out the valves.

Having the wrong plug - make sure when you put the correct plugs in the gap should be 1.27mm or 0.050 in.

Since you will have that stuff apart, really look the plug boots....inspect really good. Put a little ignition grease in the boot. When you take the plugs out, really look at the ends that were in the cylinders and see if number 1 looks any different that the others. Compression is the same as 4 and higher than 2.......but still look really good.

Also, they have a technical service bulletin out on misfire, rough idle. When you have it apart really look to make sure the spring is there. I have attached the bulletin.

Bulletin No.:
File In Section:
06 - Engine/Propulsion System
February, 2000
Rough Engine Idle, Misfire, Possible DTC P0300 (Replace Spark Plug Boot Assembly)
1999 Chevrolet Malibu
1999-2000 Chevrolet Cavalier
1999-2000 Oldsmobile Alero
1999-2000 Pontiac Grand Am, Sunfire
with 2.4 L Engine (VIN T - RPO LD9)
Some customers may comment on a rough engine idle and/or misfire. The Check Engine Light (CEL) may or may not be illuminated, and DTC P0300 may or may not be set under rough idle conditions.
Condition may be due to a missing spark plug boot spring.


(1) Spark Plug Boot Spring

Check for presence of the spark plug boot spring (1) by removing each boot and checking for spring presence at the boot to coil tower connection If the spring is missing, replace the spark plug boot assembly

Also there was a important note for the ICM cover bolts. Make sure you follow that. Install the Ignition Coil and Electronic Ignition Control Module assembly to the engine while carefully aligning the spark boots to the spark plug terminals. IMPORTANT: The ICM cover bolts must be installed with isolator washers with the rubber side facing down

You said you took the car to the mechanic...........are you able to do these things yourself or have to take it to someone? If you are using a mechanic, then have him do the fuel pump pressure check. I have attached a pic. It is an inline fuel pressure gauge.

With the ignition switch "ON" and the fuel pump "RUNNING", the fuel pressure indicated by the fuel pressure gage should be:
With EGR 284-325 kPa (41-47 psi).
Without EGR 358-405 kPa (52-58 psi).

Once you change the plugs, see how it does. If it is still there, my earlier suggestion was to swap the number one fuel injector with another. Again, don't forget new O'rings with a little vaseline on them. Then make sure there is no codes, run it and check for codes and let's see how it does. It would be nice if the code jumped to the other cylinder. Then you would know the injector is bad.

Also the TRAC light - not to go too much into this right now but did it come on when you would floor it and then the car smoothed out for a little, or just normal driving......or when it starts to run rough......light comes on?

Here is some info on the TRAC light for your reading enjoyment though for now.

The amber TRAC OFF indicator will illuminate in order to alert the driver of an existing malfunction with the Enhanced Traction System (ETS). In this situation, enhanced traction will not be available. The ABS VI/ETS must be serviced in order to regain enhanced traction ability.

The amber LOW TRAC indicator illuminates in order to alert the driver when the ABS or ETS is active. Whenever the EBCM determines that the vehicle has entered a braking event that requires the ABS or an ETS event is occurring, the amber LOW TRAC indicator will turn ON. The amber LOW TRAC indicator will remain ON for approximately 3 to 4 seconds after the ABS/ETS event is completed.

The ABS VI with the ETS includes the following components:
" The ABS modulator/motor pack assembly
" An Electronic Brake Control Module (EBCM)
" Four wheel speed sensors
" An electronic brake control relay
" An ETS OFF switch
" An amber ABS warning indicator
" Amber TRAC OFF and LO TRAC warning indicators
" The interconnecting wiring

Okay Ted..........let us know............

Oct 23, 2008.
I will check for the boot spring tomorrow when I install the new plugs. The isolator washers for the ICM cover bolts are all in place and in good condition. I took the car to a mechanic because I do not have a compression testing guage. I also asked him to do the fuel pressure test, but without a test port on the fuel rail he said he could not do it. The inline fuel pressure guage shown in the diagram: Is it a standard unit that can be bought off the shelf or is it a homemade rig? My mechanic said he has no idea how to read the fuel pressure on my car, without a test port.

The material you attached on the Trac warning light was not helpful to me. It tells me a lot about Trac lights, but nothing about why the light would go on while my engine is running rough.

Hopefully, the new plugs will help and perhaps I will discover a missing boot spring. But if not, can you think of other possible causes of the symptoms on my car? What about a bad injector? How about a bad coil housing? Are there any sensors in the fuel, electrical or exhaust systems that might cause these symptoms?


Oct 23, 2008.