Ok, my 1996 Buick Regal is acting up. I got a CEL, which was a P0306 (Cylinder #6 misfire), took the car to my shop, and they diagnosed as a faulty Ignition Control Module. Fast Forward, a day later, the car now has a hard start problem and throwing the same code, plus a P0102 Mass Airflow Sensor.
So my questions are:
- Could a faulty ICM cause a single cylinder misfire, did they just replaced a random part? I would think a bad ICM would a multiple misfire considering on this car each coil controls 2 cylinders.
- Are the two codes related? ie fix one, and the other would go away? or are they separate issues?
- What could be wrong with my car?
This mechanic has been in my family for years, however, I’m not very pleased that a day later, my car seems to have more problems than before. Am I being too harsh?
How hard is #6 plug to get to? Can you pull it and see what it looks like? (Have a new one handy to replace it with.)
You will no doubt get answers here, but you might get more if you posted this over on the ‘Repair and Maintenance’ forum, @96regalguy. Good luck getting this sorted out. I’m not a mechanic, but there are some great people (who are also mechanics) who post here.
@MarkM - I moved the discussion so @96regalguy doesn’t have to lift a finger.
Take it back to the shop. Maybe they inadvertently knocked the MAS plug loose or something else minor.
what did they replace? a misfire usually means a bad coil. did they change ICM and reuse old coils? or do you have a new ICM and new coils? icm is about $125 and coils are $40 each.
I agree that the coils would be suspect. Also, the car being 19 years old, have the spark plug wires ever been changed? In answer to your second question the two codes would not likely be related.
If there were a coil driver problem in the ign module, it would miss on 3 as well as 6. Have replaced lots of MAFs on this vintage, have also replaced a lot of pigtails. Try cleaning the MAF with electrical cleaner and see if that helps.
Thanks everybody for all your help. and Thank you cdaquila for moving this to the proper forum. Sorry it’s been a crazy week for me. Anyways, I managed to get a friend of a friend to help me sort this problem out. However, I’m not extremely mechanical, so please forgive if I
can get some of these terms wrong.
He did a “wet and dry compression test” on all cylinders. The #6 was reading at about 70% of the spec for this engine. the wet compression was reading at the same level as the dry one. All other cylinders he said was reading within the specs. He told me it was most likely bad engine valves on #6, and I had to go to a shop for major engine repairs. So I took the car to a dealer and shop he recommended (ASE Certified, A+ on BBB, Plus very good reviews on Yelp/Angies List). He also cleaned my MAF sensor which caused that code to go away and has not reoccured.
The dealer told me it was bad piston rings, and about $4500 for a new(used/rebuilt) engine.
The shop told me it was bad engine valves and it would be about $1000 to rebuild that part of the engine, and he recommended, 3 new coils, and spark plugs and wires, which he said he would do for the cost of those parts.
I did not tell both the dealer and the shop what my friend said, because I was trying to get a honest opinion from them both.
However, I’m now confused who is right, do I need a new engine? is it bad piston rings or bad engine valves? Who do I trust? I’m willing to put in ~$1100-1200 if the shop is correct, but a new engine for $4500, that is not worth it to me. So opinions, please.
First off, I would not go with the dealer. They tend to grossly overkill on repairs. The shop would be the better choice. You might consider just changing the coils, wires and plugs for now since you are no longer getting a check engine light and I assume the engine is performing OK and see how it plays out. It all depends on the condition of the rest of the car. After all, it is 19 years old.
If wet and dry readings are the same, its a valve, not rings. That is old school and every mechanic knows this.
However, if this engine has high miles on it, replacing the valve could cause the rings to become unseated. I don’t know why but I have seen this so many times. It may be time to just let go.
Yes, drive it and see how it goes. I can imagine a dirty MAF sensor could affect a weak cylinder (#6) first.
Dry and wet test the same, you either have bad valves, a bad head gasket or a cracked head. You have to pull the head to diagnose any of these (unless you have a borescope to look at the valves with) so the head gasket would get replaced to put it back together.
If the rings were bad, the wet compression test would read higher. The dealer has to know this so they are either completely incompetent or dishonest or their mechanics are so bad they are afraid to let them open up an engine.
Just curious - How many miles on this engine?
Just to Clarify, I still get a p0306 Cylinder #6 misfire code from the engine computer, after cleaning the MAF sensor, the p0102 code went away. The car has 85000 miles on it. Is it for certain that the piston rings will become unseated after new valves are put on? What would have caused the valves to go bad? Old age? Everything else seems “sound” on the car. Even the shop said the engine seems to be in excellent shape besides this issue.
I just recently purchased this car, and spent too much time and money to give up on this car just yet.
OK I didn’t realize you were still getting a P0306 code. 85,000 miles is really low for these engines whether it is a 3.1 or a 3.8. I would go with the valve job considering the car is in good shape. You’ll also get the benefit of new intake manifold gaskets which also are replaced when doing a valve job. Intake manifold gaskets were troublesome on the 3.1s. There are improved versions of these gaskets out now. Whether it’s a burnt valve or a blown head gasket these are addressed when pulling the head(s).
Edit: I’ve never seen replacing a burnt valve causing rings to become unseated. The only thing I can think of is some debris loosened during disassembly got caught between the piston and the cylinder wall.
MY 2 CENTS, that was my mistake I should’ve been more clear in that post and state I was still receiving a code.
I know most people would have walked away from the car after receiving bad news like bad engine valves. I spent $$$ on purchasing the car, than money fixing the tie rods (I knew it had bad tie rods), and four brand new tires. After spending all that time and money, I’m not willing to let it go yet. Plus the friend who did the compression, said the GM 3800 Series 2 engines are super reliable.
Here’s what I know about the car. The PO had some maintenance records for it. However, I don’t know really the full history, so I don’t know how well or poorly it was maintained. The car looks super clean. The interior looks almost brand new and the engine bay you could eat off of. The PO had the dealer replaced the transmission about a year ago. Before they past, the PO was a elderly couple who bought the car new and it was garage kept all of it’s life.
On another note, once the car is fixed, should I use high mileage oil in it? I’m strong believer in Synthetic (it’s all I use in my new car), but I heard Synthetic might not be a wise choice in a car this old and with 85k miles on it.
I suspect the dealer mechanics that diagnosed bad rings . . . in spite of no rise with the wet compression test . . . are inexperienced young guys, that just arrived from the local trade school
A seasoned mechanic would know if wet and dry compression test results are the same, it can’t be the rings
The dealer wants to brag and say their mechanics all graduated from brand x trade school, which is in some cases . . . unfortunately . . . just a feeder program for dealership
Sounds like it’s easily worth the fix. And by all means use synthetic oil. I’ve bought many used cars with over 100k miles and used synthetic oil in all of them with never a problem.
I agree it’s worth pulling the head for a valve job