Repeated P0102 + SES (1997 3.8)

[Akula]

Hello again everyone,

My '97 Firebird 3.8 is giving me some trouble.

The last few journeys it acted up: felt a judder (like a rev drop/loss of power) for about a second or so, then the car jumped back up to normal rpms (was in 4th gear at the time, maybe 40mph).
It immediately threw the SES light.

Got back home, checked the code - P0102. Figuring it may have been a blip, I cleared the code.
Next time I drove it, the code came back with SES light quickfast but no perceptible jerking or rev loss. Idling the car, it sits around 1200rpm on the gauge and smells super rich, plus it hunts a bit. I know these cars can smell rich normally but this was a little extra, in case that is related.
Code is again P0102. Fair play I thought, so I cleaned the MAF sensor. But same issue. That code keeps coming back with the SES light, within a minute of clearing the code.

MAF sensor is clean as a whistle, nice and shiny. The sensor does register in the OBD scanner I have when I view live data (sits around 1.84g/s).

Where should I look next?

 

[melsg5]

Read through the solutions, you may need to replace it if no wiring or other issues found.

P0102 Mass Airflow (MAF) Circuit High

How to quickly diagnose, repair, and info on symptoms and causes of a P0102 MAF mass airflow code which indicates a low condition in the MAF circuit.

www.obd-codes.com

 

[Akula]

Read through the solutions, you may need to replace it if no wiring or other issues found.

P0102 Mass Airflow (MAF) Circuit High

How to quickly diagnose, repair, and info on symptoms and causes of a P0102 MAF mass airflow code which indicates a low condition in the MAF circuit.

www.obd-codes.com

Thanks Mel, I'll have a read through. Looks simple enough (for once!)

 

[Akula]

And I'm back - I know this essentially thread resurrection here.

The car is still giving me trouble. I did go through the checklist you sent Mel, the MAF sensor looked perfectly fine but I gave it a good spritz with some electrical contact cleaner and it made no difference.

Using a meter, I then checked the terminals with key on, ignition off:

12V power is being supplied
Signal terminal registered as expected (I can't remember the reading but it was good)
Earth is fine, 0V.

So the wiring seems to be OK to me?

Next I checked live data on my scanner: the MAF sensor was at a constant 1.84g/s reading with the engine running, no matter what I did. A little bit of throttle, while at idle, even during a good rev, the reading did not change on my scanner.

At this point, before making any changes, two codes were evident:
- P0304 Cylinder 4 Misfire (Stored code)
- P0102 MAF Circuit Low (Active code)

I cleared these codes. Figuring that the sensor might be duff, I replaced it with a new one.

No change with the rough running, though I now do get a varied air flow reading from the MAF sensor in accordance with engine RPM as I would expect, and while idling the car the P0102 did not come back on. Because of the rough running and misfiring under load, I can't drive it far at all to test whether it will come back again, but I believe that sensor could have been a problem on top of a separate problem (a coincidental failure).

All 3 coil packs were changed about 2 years ago with genuine AC Delco parts, so it's unlikely they are at fault (though I won't rule out the possibility). I will try swapping the packs round to see if the misfire follows the coil.

I've also recently had all 6 spark plugs replaced and the car ran fantastically for a while, but the issue has resurfaced.

Could I be looking at a faulty or corroded ICM here? I'm going to remove the coils and clean/lightly sand the towers, then grease them, but what would I need to do with the ICM?

______________________________

 

[cammerjeff]

I would also check and clean the engine ground(s) also what is your battery voltage? If the battery is weak (under 12.5 V ) weird things can happen on modern (ish) cars. The battery in my old 97 3.8 convertible was down to 11.8 v and it caused misfire codes and rough running. Also how old are the plug wires?

 

[Akula]

A little more investigating today - removed the PCV and cleaned it out, it still rattles, though the was some moisture on it when it came out (condensation perhaps from sitting). It did not have an O-ring on it, and the PCV cover gasket was history. Ill get some RTV and sort that.

Can you tell me where the grounds are located in the engine bay? I've located a couple, but I want to be sure I get them all. If you could point me to a diagram in the service manual, that would be super handy.

The battery is definitely good, it reads 14.4V running and 12.5V off.

I also removed and thoroughly cleaned the ICM and aluminium heat sink, reapplied some new thermal paste compound on both, cleaned the coil terminals, and refitted the coils.
I marked the coil responsible for Cylinder 4 and changed the position of it around when reassembling, thinking the misfire would follow the coil... but the misfire code didn't not come back as an active code during a test drive - just a pending code, which is historic isn't it?

The plugs were changed a few weeks ago, the plug wires (Standard Automotive brand I think) came with the car when I bought it 4+ years ago. I could replace those I guess? Looking inside the coil-side of them all, they were clean and silvery, no rust in there.

The consistent crappy running came on very suddenly, during a drive a few weeks back, though I did have a couple of instances of sudden bogging which came and went quickly (a matter of 1 or 2 seconds-worth) in the weeks beforehand.

I can drive at low speeds, when I give it some gas it bogs hard.
Observing the rev counter, the idle is sits at ~1400.

 

[Akula]

Ok another update - for reference, car is a bone stock 1997 Firebird 3800 Series II.

The car is now undriveable. Stalled out on me on a hill a week ago, and it had to be nursed back a couple of days later when I could finally get it to start.

It has a bad misfire, flashing CEL at idle, and runs like a dog. I've replaced the ICM with a brand new one I had in the garage, and there is no change.

As for codes, so far I've had P0304 and P0306, separately. Never at the same time, which is why I figured the ICM was the culprit, because I've moved the coils around and the issue did not follow.

It's also had a new MAF sensor, no difference.

I just can't seem to get this thing going again, and it's frankly edging towards being sold. I need the thing running if I'm going to be keeping it here.

I can't see any gunky oil in the coolant. Oil smells a little of gas, but is darker gold (kinda halfway between new and used). I can't find any vacuum leaks but to be honest im having trouble tracing all the airlines.

Am I looking at injectors? LIM gaskets?

 

[melsg5]

Any reason why you are not taking it to shop to have them check it?

______________________________

 

[Akula]

I just spent over a grand having the rear main seal, clutch and engine + trans mounts swapped out. It's gonna be a couple of months before I'll be flush enough for another visit to a repair garage.

 

[melsg5]

Not sure if 97 had individual plug wires, but if so, did you test the wire resistance?

 

[Akula]

Not sure if 97 had individual plug wires, but if so, did you test the wire resistance?

The previous owner swapped out the plug wires with a Standard Automotive set. I'll try to check that next, good shout.

 

[Akula]

Just a brief update - I finally got time to swap out the spark plug leads today. That was an unexpectedly difficult task, at least for me and my skills. I always get nervous going underneath the car, but I was safe, used the proper jackpoints and proper stands. So first I wanted to say thank you all for the advice in here.

While down there, I found the spark plug leads for cylinders 4 and 6 (passenger side mid and rear plugs) to be dangling loose in the engine bay. Not attached the plugs themselves at all. Luckily the heat shields on the leads were still present.

Wow. How this happened, I don't know. It had engine-out work done at a local shop in March/April time, but it ran great after for a while. I'm guessing they just weren't properly seated and a firm bump in the road dislodged them.

So. I'm currently waiting for the battery to be recharged on trickle, it was low, but once that's back in I'm hopefully that this whole saga will conclude. I will update one more time if this is the case.

Thank you all again.

______________________________

 

[Akula]

Just a brief update - I finally got time to swap out the spark plug leads today. That was an unexpectedly difficult task, at least for me and my skills. I always get nervous going underneath the car, but I was safe, used the proper jackpoints and proper stands. So first I wanted to say thank you all for the advice in here.

While down there, I found the spark plug leads for cylinders 4 and 6 (passenger side mid and rear plugs) to be dangling loose in the engine bay. Not attached the plugs themselves at all. Luckily the heat shields on the leads were still present.

Wow. How this happened, I don't know. It had engine-out work done at a local shop in March/April time, but it ran great after for a while. I'm guessing they just weren't properly seated and a firm bump in the road dislodged them.

So. I'm currently waiting for the battery to be recharged on trickle, it was low, but once that's back in I'm hopefully that this whole saga will conclude. I will update one more time if this is the case.

Thank you all again.

Just to finish this thread off, perhaps unsurprisingly, this has resolved the problem. Car fired straight up, like nothing had ever happened.

Test drive produced no issues, no CEL and no misfire. I'm not shooting the confetti cannons until it's proven itself a couple of times on longer drives, but at least it runs and drives nicely for now.

Thank you all for your help!


For those searching in the future, the following steps were taken to reach this resolution:

- Cleaned MAF, refitted
- Replaced MAF
- Removed and cleaned ICM, refitted
- Replaced ICM
- Examined earthing points
- Replaced battery negative cable + inner fender earth cable (attached to negative terminal also)
- Tested voltage on starter motor
- Fully recharged battery
- Swapped ignition coils (to attempt to replicate misfire code on alt. cylinder)
- Checked spark plugs for damage
- Replaced spark plugs x6
- Checked spark plug wires* fault found
- Replaced spark plug wires

 

[Akula]

Just to finish this thread off, perhaps unsurprisingly, this has resolved the problem. Car fired straight up, like nothing had ever happened.

Test drive produced no issues, no CEL and no misfire. I'm not shooting the confetti cannons until it's proven itself a couple of times on longer drives, but at least it runs and drives nicely for now.

Thank you all for your help!


For those searching in the future, the following steps were taken to reach this resolution:

- Cleaned MAF, refitted
- Replaced MAF
- Removed and cleaned ICM, refitted
- Replaced ICM
- Examined earthing points
- Replaced battery negative cable + inner fender earth cable (attached to negative terminal also)
- Tested voltage on starter motor
- Fully recharged battery
- Swapped ignition coils (to attempt to replicate misfire code on alt. cylinder)
- Checked spark plugs for damage
- Replaced spark plugs x6
- Checked spark plug wires* fault found
- Replaced spark plug wires

Well I jumped the gun. Today it damned nearly stranded me in the next test drive. Noticed some hesitation on a run, decided to turn back and lost almost all power - massive misfires (though strangely no CEL this time, at all).

Given the length of time this has been going on, I think it's time I admit that this is beyond my ability to resolve.

It was fun while it lasted!

 

[melsg5]

Well I jumped the gun. Today it damned nearly stranded me in the next test drive. Noticed some hesitation on a run, decided to turn back and lost almost all power - massive misfires (though strangely no CEL this time, at all).

Given the length of time this has been going on, I think it's time I admit that this is beyond my ability to resolve.

It was fun while it lasted!

How's your battery?

 

[Akula]

Hmm.. I recharged it the other day on a trickle charger. It started the car today, admittedly on the second attempt.

In truth, the car has been sitting for a number of months each time it's been out of commission. Could that be the case? Dead cell maybe?

Since it runs fine at idle but seems to lose it when hot, could it be the crank or cam sensor?

I'm really reluctant to throw any more money at it, and here in the UK a battery won't be cheap. How can I properly test the battery and those sensors?

______________________________

 

[melsg5]

Hmm.. I recharged it the other day on a trickle charger. It started the car today, admittedly on the second attempt.

In truth, the car has been sitting for a number of months each time it's been out of commission. Could that be the case? Dead cell maybe?

Since it runs fine at idle but seems to lose it when hot, could it be the crank or cam sensor?

I'm really reluctant to throw any more money at it, and here in the UK a battery won't be cheap. How can I properly test the battery and those sensors?

Over here every auto parts store does a battery test.
You can do some basic tests of voltage with engine on and off.

 

[Akula]

Thanks for sticking around Mel, I appreciate the continued help. I'll give those a try.

 

[Akula]

A bit of a resurrection here, but I thought I'd post an update.

It was an ignition coil, and I have a possibly dying battery. I replaced the coils with AC Delco in 2020 when I bought the car, but one has apparently failed already.

Swapped out all three.

Battery will be sorted soon. Annoying, but got there in the end. Thank you to everyone who helped me out.

 

[cammerjeff]

Hopefully a new battery will solve the final issue. People do not realize what odd issues a weak battery can cause in a modern car (Read as OBD II equipped or newer) and I mean under no load 12.5 Volts. The other big item that can cause odd problems is bad engine and chassis grounds. I have seen some really odd issues cured by cleaning the ground wire connections or replacing the battery.