1992 Bonne SE power loss

[thomd53]

Vehicle Mileage 187,000
GM Goodwrench engine ~1,500 miles
GM SRTA ~15,000 miles

When returning from vacation, this past weekend, I noticed the vehicle had a sudden loss of power. First the sequence of events -

We'd been driving 75 mph for 150 miles.

Stopped at a Sam's to refuel

Drove car about 10 miles, crossed a state line and began driving 80 mph (speed limit was raised 5 mph between states).

The car was holding 80 for about 5-10 miles when suddenly it started to have a 'mild drivetrain shudder'.

I pulled off (at the first exit) and put the car in park and left the engine run.

The engine was idling like it was running on 4-5 cylinders; however, there were not 'mechanical' noises' and no 'spark popping' as in a bad plug wire.

I said .... 'to heck with it...if it breaks, GM will be paying for it'.

So i finished driving it home (another 300+ miles) and the symptoms did not go away. I did notice that if i forced it to accelerate, it would drop out of lock-up and the shudder went COMPLETELY away. Also, when the car came to a stop, it idled as described above.

Gas mileage was horrible (probably 17-18), so another refuel was necessary (yes, Sam's again). This mandated a stop/restart of the engine.

The car continued to run horribly the remaining 40 miles until we got home (where I turned it off).

The next day, I started the car (to make sure it was still a problem) to take it to a dealer (remember.....warranty!) and it ran flawlessly (as it has all week!)

I tried dumping the codes, but none were stored.

I pulled a transmission service this weekend, expecting 'extra' parts in the pan, but it looked like i'd expect for a transmission being driven for a year (no parts, normal sediment).

I'd take it in and have it checked, but if the car doesn't have any codes and doesn't exhibit the symptoms, i really don't expect a mechanic to find anything.

As a note, the car is probably OVER maintained....so when the engine was replaced (1500 miles ago) numerous new parts (including plugs) were used.

All the plug wires were properly seated; however, because it appears to be spark related, I've ordered a new (acdelco) ignition module and coil pack (the one's on the car are original). I'll be replacing those, this next weekend.

Any thoughts on what to look for would be appreciated.

5/10 - Installed new ignition module/coil pack, problem still persists. Did notice what sounds like a vacuum leak (probably as a result of reusing vacuum hoses during engine replacement). Will be taken back to shop that did the engine swap.

[markwb]

That's an interesting problem, it does sound like it's ignition related. Keep us posted, thanks.

[thomd53]

Well, well....

The shop that did the work, worked on it for most of a day....and told me what it wasn't, they suggested taking it in to a dealer to diagnose the main computer....appeared that it has plenty of spark, probably not sparking at the correct time (cam/crank sensors were just replaced during engine replacement).

There is only other shop that i'd trust with the car, so off it went (before I took it to a dealer). I went in great detail explaining the problem and a couple of hours later, they called.....the car was ready!

Turned out to be a cracked plug on the back bank. They replaced all 3 (on the back) to make sure there wasn't anything wrong with them (e.g. engine was bumped during installation) even though it had all new delco plugs installed with the engine. He showed me the plug, it was broke beneath the metal base.....and it was evident that it wasn't firing (inside of plug was entirely black...soot).

So, once again, the bonne is on the road!

[markwb]

Originally Posted by thomd53

So, once again, the bonne is on the road!

Glad to hear it's resolved, good deal.