About 5 weeks ago I did a lot of routine maintenance to the car. I changed all the fluids oil, antifreeze, trans fluid M6, cleaned out the throttle body, cleaned out the pcv valve, and rear gear oil. The car has 82000 miles and I figured I might as well do the spark plugs. I installed some Bosch Platinum 2’s not knowing any thing about the plugs being crap for our cars. I took the car to work the next morning and I noticed a vibration in the gear shift that wasn’t there before as soon as I started the engine. The engine seemed to run rough. The vibration seemed to get worse the faster the engine would rev, and the engine seems to cut out at 2200 on up and doing 80 down the interstate. Thinking that the plug wires may not be on the coils and plugs right, I went back and rechecked each wire and made sure they clicked on each plug and coil on change. Thinking I may have cracked a plug and the plugs are no good to begin with I bought and installed some Autolites and put them in and still no change. So I threw away the Autolites and got the AC Delco Iridiums, but the problem is still there. I bought a new set of plug wires and replaced the wires thinking I may have damaged the old ones. I went through every inch and checked all the connections and everything checks. I have not gotten a SES light through all of this and have nothing to go on other than the fact that this all started after my plug change.

The engine seems to have a slight miss at idle and gets worse as you rev the engine. The gear shift, the steering wheel, and the seat all vibrate while the car sits in the driveway. The clutch can be in or out does not matter. It’s worse under load going down the road. The vibration seem to be tied to the engine running rough as you can hear popping through the exhaust the whole time you’re driving. During a hard acceleration it is really bad almost to the point that it makes the car uncomfortable to drive. At cruise speed the engine runs rough and my gas mileage is affected. It seems to be an ignition-related problem but I’m not sure. After three sets of sparkplugs and a set of plug wires I think I have eliminated them as a cause. There is no arcing of the ignition that I can see. The SES light works and is not coming on or blinking. I just don’t get that the car can run so rough and not set a check engine light. Is it possible I may have damaged a coil or cracked the case during the plug wire change? Some of the wires were hard the get off. The car is completely stock. Before I start systematically replacing each coil is there anything that you guys can suggest to check that I may have missed?
Sorry to make this so long just wanted to cover everything.

Thanks,
Matt

 

Bad gas?

 

Not trying to be an *** but, did you gap the plugs correctly? If you did, then I would get a hold of a timing light, and find out witch cylinder is missing. Just hook it up to each plug wire, and shoot the light on the underside of the hood. If its good, the light will have a steady beat to it. If its missing, then the light will blink erratically. I am thinking it could be a bad coil.

 

Try to unplug one coil pack at a time to see if you can find the one that is missing listen for the motor to bog if it bogs then that one is good if it stays the same i would look into it or you can get a good sparkplug put it in the sparplug wire to see if the coil is fireing maybe that will tell you witch one is fouling it sure sound slike a misfire

 

I was thinking bad gas as well, but after 4 tanks and three different brands I don't think it would be the gas. I also change the fuel filter as well. Seawolf18, you're ok, everything helps no matter how insignificant it may be. The plugs came pregapped at 40. The GM guy behind the counter said that was a specific gap for that plug and not to gap them to 60 for our cars. Do you think I may need to gap them to 55 or 60? Timing light is an excellent idea. I have one and will try it when I get home from work tomorrow. I'll post the results when finished. I'll also try unplugging each coil to see if that works. Maybe the combination of both will tell me which one it is.
I always thought that if the engine was misfiring that it would set a SES light. Do you think I may have an erratic misfire that is not long enough to set the light?
Thanks.

 

i know our motors are diff but i had just put the plugs in with out gapping them stock came .060 and it was running like crap so i pulled them and gapped at .045 no difference it turned out to be 2 broken plugs and partially burnt wire i also couldnt see it arching at night stick your had down there and if you get zapped you know smoethings up

 

Now I'm are getting somewere. I tried the timing light and the driver's side bank is firing just fine on all four cylinders. On the passenger side there is a slight pause in the timing light strobe on all four cylinders. I checked the connection for that bank at the top of the engine and the connection is good. Do you think that this could be an oxygen sensor (before the cat) that is on the verge of going out or is it something else? Any ideas as to why all four on that side would be misfiring?
Thanks