1997 Chevrolet Silverado



June, 24, 2008 AT 10:32 AM

Engine Performance problem
1997 Chevy Silverado V8 Four Wheel Drive Automatic 350000 miles

I have a Silverado C1500 with a 5.7L 350 Vortec engine. The engine will idle fine, but rough and will run so rough going down the road that it will literally shake the entire truck. Power has dropped and passing someone on the highway is nearly impossible.

I've changed plugs, wires, distributer cap, rotor, coil and fuel filter. I've even pulled both upstream O2 sensors to see if I possibly had a plugged Converter or Muffler, but this did not seem to help.

I know this truck has a lot of miles, but has always run well, and I've run out of ideas. The OBD scan shows " Manufacturer Ignition Control or Misfire" or something similar.

Any ideas?


Running Rough


Idles Rough/changed Ects


4 Answers



June, 24, 2008 AT 5:45 PM

If you have the actual error code it would be helpful, but with 350,000? Miles, it can be valve springs or other internal engine parts, start with a compression test, wet and dry! Post results here.



June, 26, 2008 AT 8:25 AM

I only did a dry compression test. I can do a wet test if needed, I just didn't have anything handy to get oil into the cylinders.

I pulled out all plugs, stuck a screwdriver in the air intake to hold it open, and pulled the coil wire, then cranked the engine about 5 times and took my readings.

All were between 170-180psi, except cylinder 4 which was 162. I think these readings are acceptable considering the mileage on this truck.

Oddly the plugs from cylinders 5 and 6 were already very black (only in for two weeks) 6 was probably non-functional, as it was just a big glob of tar like substance on it. The engine does not use a lot of oil, and does not smoke.

I cleaned the plugs, checked the gap at.06 and replaced the plugs.

Now the truck won't start at all.

It does not seem to have any spark at all. Perhaps I have finally found my problem or maybe caused a new one. I double checked all the wires, and made sure I hadn't bumped anything while working and didn't see anything. With a screwdriver in the end of a wire, I got no spark at all when turning the motor over.

Is it possible I harmed the coil?

Is there a way to test the coil and/or ignition module with a standard multimeter?



June, 26, 2008 AT 1:42 PM



June, 27, 2008 AT 8:43 AM


That is a very helpful and thorough, step by step procedure.

I kinda got thrown off on step 5, since the coil connector is not labeled, I assumed the 'pink' wire was 'C' and was chasing my tail until I looked at a wiring schematic. Then I assumed the 'black/wht' wire was 'C' since it was connected to the control module.

Assuming that is correct, I then proceeded down to until I got to step 12, where I did not show the 1-4 VAC, I only showed about.4 VAC on my meter.

I was not sure which connector was the 'VCM C3' connector, or which terminal was the ignition control (IC) circuit as described in steps 15-17, but I did disconnect all plugs from the module, then re-connect.

At this point, I am assuming it is the VCM since I do not seem to be getting hardly any AC control voltage to the Ignition Control Module.

If you have any other ideas, I would appreciate it.

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