View Full Version : new plugs/wires= shaking and misfires

07-29-2007, 07:28 PM
Hello I have a 99 SS with 110k miles on it. I bought it at 90k miles and that was a year and a half ago. The previous owner took care of the car and everything about the car was in good working condition, till about two months ago.
The first thing that happened was that the service engine light came on. It was not a constant thing and it came on sometimes and sometimes it didnít. The next thing that i noticed was poor fuel consumption. When I got the oil changed on it last weekend I asked the guy what codes were messed up and they all dealt with O2 sensors. I figured that this may have been due to bad spark and I decided to take a look at the spark plugs to see if they needed to be replaced because i had not previously checked those out. I took the spark plugs out and they were really worn. I put in Bosch platinum +2s(which have two filaments as opposed to one) and replaced the wires with autolite professional 97009s (which look identical to the ones i took out). I went around and checked all of the wires to make sure they were tightly secured onto the plugs. I finished up the process and started the car up. at low idle the engine started to shake. It was not off the 900-1000 it usually idles at, yet the motor still shook. I was not sure if this was just some residue of some sort that need to be forced out by a little ride around the block. So i drove it around the block and it started to misfire... i was getting slightly disappointed and worried i had not secured the wires properly so i went home and got out of the car and it smelled of sulfur. (I wouldnt think the cats would be clogged after changing the plugs?) I checked the wires and all were secure. I filled up the tank and added a little injector cleaner even though the injectors were cleaned less than 10k ago.

Any suggestions?

07-29-2007, 08:14 PM
did it skip before the plug swap????sounds like a cracked plug,
it happens, esp. #8-the hard one to get at.
have it scaned again to check for a misfire code

07-29-2007, 08:21 PM
Sounds like a nice little drivability problem. First off, and I donít mean to criticize you, but in my opinion, Bosch spark plugs are junk. Iv seen many vehicles with these plugs come in and they either ground out in the head, foul out or the ceramic in them cracks or some dumb ass problem. I would highly recommend staying with AC delco platinumís or iridium if you can swing the extra cash. As for wires.. I would again use the AC delcos or the MSD wires. If you go aftermarket, make sure they donít drape across the exhaust and get burned and ground out and stuff and check to make sure they are electrically/magnetically shielded. As for the misfiring and shaking engine, check the codes again. If the codes are on the front sensors, that will affect performance/timing and may lead to the problem which you are currently experiencing. The computer may be trying to pull timing too far out. You could also have bad knock sensors, when you start your car, it will pull timing out as far as it can until it detects detonation. After it detects detonation it will pull the timing back and retard it. If the knock sensors are broken or not working correctly, the computer may not detect detonation and will not pull the timing back because it has not detected detonation yet, even though your engine is shaking around like a mother. Your car could also be trying to relearn the idle. If thatís the case, just start it, let it run for a bit, shut it off. Repeat several times and drive it a few miles. If you do that make sure the engine isnít detonating early, because it can destroy your engine. Thatís all I can really think of off the top of my head for now..

07-29-2007, 08:29 PM
+1 bosch plugs are junk. I work at a Chrysler Jeep dealer and have worked at several GM dealers and we require removal of these plugs before any drivability diagnostics are performed as these plugs are usually the cause of the problem. I would reccomend using an iridium type plug since that is what is used from the factory and be careful not to crack them when installing them. Try using a wrench on the end of the socket
instead of your ratchet for #7 and #8 Hope this helps.

07-29-2007, 09:45 PM
Check your oxygen sensors. Replace them if they are covered with carbon build-up. Also check to make sure all the plug wires are secured.

If that doesn't fix it you should just change spark plugs to NGK TR-55 or step up to a platinum or iridium plug if you want to swing the extra cash.

I had a misfire for a while and replaced spark plugs, wires and oxygen sensors. It turned out to be a coil pack that went bad.

Good luck.

07-29-2007, 09:51 PM
Take all your plugs out and check them for cracks. Happened to me before.

07-31-2007, 03:24 AM
My dad and I have run Bosch plugs in everything we own and have never had a problem with them. I usually stick to the single electrode platinum plugs. I have never had one crack, but I did have one brake while taking it out of my 89 Fireird once. Luckily it was just the ceramic part and I could still get a socket on the rest of the plug to get it out.

07-31-2007, 06:08 AM
Moving to General Maintenance & Repairs.....

07-31-2007, 10:16 AM
The only thing worse than Bosch plugs are Bosch wire sets. I now inspect and test all wires for resistance before installation. Doing so has found potential problems.

Damaged plug, wire or coil pack...Also get those front O2's out of there.