Engine Mis-firing?


Old 04-12-07, 04:09 AM
Thread Starter
Join Date: Mar 2003
Location: Pickering, Ontario, Canada
Posts: 8
Engine Mis-firing?

Hi there,
I have a 1995 Pontiac Grand Am GT with a 3.1 LTR. V6 - automatic transmission with 135,000 KMS (90,000 miles). Lately I have noticed that when the weather is damp, the car is starting up a little rough in the morning and then while I am driving(cruising) there seems to be a little "jerking" in the engine. Occasionally, when I hit the gas there is hesitation and a bit more jerking and then she goes. If I push the gas a bit harder it seems to go fine. I also feel the "jerking" while stopped although it is not as noticable as when I am driving at highway speeds. I haven't really noticed any of these problems when it is dry. I am wondering if it is an electrical problem or a fuel problem? I don't think that the transmission is slipping, although I could be wrong. Any advice?
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Old 04-12-07, 04:42 AM
Join Date: Oct 2006
Location: Wilmington
Posts: 4,219
Had a tune up lately?? Try running some fuel system cleaner thru the gas tank. It helps clean the fuel system, injectors, and valves of varnish and carbon.
Old 04-12-07, 04:49 AM
Thread Starter
Join Date: Mar 2003
Location: Pickering, Ontario, Canada
Posts: 8
I was going to do that this weekend as it's due for an oil change as well. As for the tune up I was going to do that as well. I'll let you know if it helps.
Old 04-12-07, 06:05 AM
Join Date: Mar 2007
Posts: 202
Smile Engine misfires

Personally, I don't like "mechanic in a can". Plus I think gas already has fuel additives in it. If you are only having problems when it is wet or damp, you might wanna check your spark-plug wires. The best thing to start is just do a complete tuneup, that usually fixes most problems. Plugs, wires, filters, check cap and rotor, might as well check belts and hoses, too. Wait till it gets dark outside and look at your spark plug wires while engine is running. Rev it up and down and look to see if any arcs are appearing. Plus, if you do have a rotor with cap you can do a cheap cylinder balance test. You will need some vacuum hose that has carbon in its material cause they conduct electricity. Cut the vacuum hose into equal lengths according to how many cylinders you have and pull the spark plug wires off the cap 1 at a time and install those vacuum hoses in between the wire and cap. Usually 1-2 inche pieces of hose are ok. The engine will run like this. Start the engine and use a 12 volt test lite and touch it to each vacuum hose to ground it out and listen or use a tach. The engine rpm should decrease with each cylinder you short out and if you have any dead cylinders switch the plug and/or wire with one that works to confirm whether it is a plug or wire. If you have more than 1 cyclinder not firing than remember how an engine works. Example: Lets say 2 cylinders right next to each other are dead and the plug and wire is ok, then suspect a broken gasket, whether it be head, intake or exhaust between those 2 cylinders. Next, suppose 4 cylinders are dead, 2 on one side on the inside and 2 on the other side on the outside. You look at the intake manifold and notice they all feed from the same carberator of throttle body bore, then suspect a bad injector or carb or gasket or adjustment. I once bought a cheap set of wires and my engine misfired bad. I looked at it at nite and all 8 wires were arcing at the boots to the exhaust manifold. A wet distributor cap can cause misfiring, too, but usually after going through a water puddle. Plus, spark plugs that are oil or gas fouled can cause misfire. Anything that interfears with the combustion, so check the wires and plugs first and cap and rotor.

Last edited by NewHomeowner396; 04-12-07 at 06:08 AM. Reason: mispelled

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