1988 Pontiac 6000 Engine Shaking

ShadowRiderMech · Posted at Wed Nov 04, 2009 8:41 am

Shakes or Wobbles problem
1988 Pontiac 6000 4 cyl Front Wheel Drive Automatic 105000 miles

I own a 1988 Pontiac 6000 base model with the 2.5L, 4 cyl. engine. The car ran great up until the engine died while driving. I found the ECM fuse blown, replaced fuse after reading out the power wire from the fuse to the ECM, no shorts. Engine started but was runing rough(shaking). Jumped the ALDL pins A&B and code 12 (diagnostic Mode) repeating was the only code. Read out the alterator and the output was fluxuation between 16 and 22 volts. Replaced the alternator, output is now 14.4 volts steady. Engine still running rough(shaking). Verified spark at all 4 cylinders. Pulled the ECM and it had a faint burnt smell, replaced ECM (swapped PROM from old to new ECM), no change, still running rough(shaking). Jumped the ALDL pins A&B and code 12 (diagnostic Mode) repeating was the only code again. Was told by a GM Tech. that the ECM has to reprogram itself and to drive the care some. The car is practically non-drivable. When I put it in gear, the engine bogs down to the point of almost stalling and with the pedal to the floor it take 30 seconds to get up to 20 mph and 20 mph is about all I can get it to. Not sure where to go from here.

Jacobandnickolas · Posted at Wed Nov 04, 2009 8:13 pm

This is a tough one. Code 12 means all clear it flashes that then it pulls up a trouble code if thats all you have then the computer thinks nothings is wrong.

My concern moves me to the old alternator. With the power it was putting out, it could have burned up many things. I want you to check something. I realize that you have spark and fuel, but do you have enough fuel pressure and is the spark at the right time? Have you checked fuel pump pressure? Also, have you checked timing? The crankshaft sensor may have been damaged.

Let me know what you find.

Joe

ShadowRiderMech · Posted at Thu Nov 05, 2009 6:19 pm

Hi Joe, while checking the timing I noticed the engine would stop shaking for a few seconds then start shaking again. I clipped the timing light to each plug wire and found the #3 cylinder firing intermitantly. It would fire for 3 or 4 seconds then stop firing for 10-15 seconds. I would venture a guess, that when I pulled the plug wire the first time it happened to be while it was firing so the engine idle changed. I changed the plug and plug wire with no change. Coil read good. Took the ignition module to the parts store and it passed the first test, then failed the next two. Replaced the module and it seems to be running fine now. You were on the right track with what else did the alternator burn up.
Thanks for the help

Jerry

Jacobandnickolas · Posted at Thu Nov 05, 2009 6:42 pm

I'm glad you found that. That would have been a tough one to find, but you did it. An alternator is able to create way more power than is needed. You saw what yours was producing. I have actually seen regulators go bad and cause fires, smoke radios, wiper motors... A long time ago, I had a 86 Dodge Charger. Not the best car on the road, but it got me where I needed to go. One night, I noticed that my headlights were extreamly bright, (looked like an airplane) the wipers were going extremely fast, the stereo stopped playing, smelled electrical wiring, and had a small fire under the dash. As a result, I had to replace headlights, 1 taillight bult, stereo, the blower motor, and repair wiring under the dash. THe wiper motor made it, but sounded funny when it was used.

It was all caused by a bad voltage regulator. I'll shut up now. (LOL)

THanks for using 2carpros.com and let us know if you have questions in the future.

Joe