I'm trying to replace the coil packs on my 1990 Chevy Celebrity Eurosport Wagon with the 3.1L V6. The bottom bolts on each coil pack come out fairly easy but the top bolts all seem like a different size or all rusted out. The 5.5mm socket slips on one of them and the other two it won't grab onto at all. I have tried metric and SAE from a little bigger to a lot smaller and nothing will grip onto these. I have also tried female torx and still no luck. On one I finally got sick of it and ground the head of the bolt off so that I could get the coil pack out of the way and have room to get the bolt out. The joke is on me, now the bolt is frozen in place and even vice grips won't break it lose. I have had it soaking in penetrating fluid for days but it won't free up. To make things worse the coil packs are mounted on the front of the engine so I am working blind and there is almost no room to get anything in the small space where the bolt head is. Any ideas?

Do you know off hand what size the bolts are that hold the module on?

I don't have a good answer for you but a few questions.

Other than the three coil packs, what else was replaced?

Was the battery ever disconnected?

The engine runs fine when started from dead cold. When the engine gets up to temp, does the idle surge and does the engine act like it wants to die?

• paulo57509 Said:

Spark plugs were also replaced.
Battery was not disconnected.
Starting from cold it runs great and continues to run great even at full temp as long as I keep driving and don't shut it off. The problem only seems to happen after it's up to full temp and then shut off.

• Turbo2 Said:

I forgot to ask, why did you replace the coil packs in the first place?

For the "new" issue, I'd confirm that all the plugs are firing when it's acting up. I think they still make those pen-like testers that you touch to the plug wires. If the plug is firing, the pen lights up. I've done this same test with an inductive timing light.

If all the plugs are firing, you can look elsewhere for the problem.

Link

Not usually on this forum since I have a 1966, but I saw your title and had a shiver... lots of memories.
Just a thought about your latest question, be very careful in checking spark on this system. It was called a "waste spark" design because it fires both plugs on that coil each time. If you reduce the needed voltage on one of the cylinders then the other cylinder will look like it is firing just fine, but not the case.
Example: say the coil will only put out 40K, when it needs to put out 60K plus. Then the cylinder that is firing takes 35K because of the need to overcome the compression trying to squish the spark out. Now the "waste" cylinder needs 5K to 7K to overcome the spark plug gap and the plug wire resistance. You now can't supply the needed voltage to cylinder on compression stroke.
So you install a spark checker in the "waste" plug wire and the dead cylinder starts working. It can be very challenging to properly diagnosis this system without a tech 1 and some experience. You could use a meter like a Fluke with true RMS and mapping but you have to check it at the output of the pickup which is can be very difficult. I was "bit" many times back in the day.
Check all your plug wire resistances when it's acting up (hot) and if you have a scanner of any type check that you have a steady pick up (rpm) signal so you know it's not the pick up. My experience (as I remember it) is I replaced about as many pick ups as modules for these type of complaints. The problem is that it's not all the time. But I think from your description of the symptoms one of those will be your culprit.
The pick up is a extra bit of fun to get out if it's been in there for years! No Fun!!!

Sorry for the long post. Good luck.

Sam