Misfiring

pontiac

#1

I had a code read that #5 cylinder was misfiring. I believe that it is not firing at all because the engine is running rough at idle speeds. I have replace the #5 spark plug, checked for arcing at night time, compaired the spark from other wires, tested the coil pack, listened to hear if the injectors were all clicking, and scratched my head. I hoping that is is nothing major, but it looks not good to me? Any suggestions? Thanks!


#2

The first steps when it comes to an engine performance problem is to connect a vacuum gauge and check the compression. If the compression is down one can throw parts at it all day long without improving things one bit.

This not only applies to aged or high mileage engines but also fairly new late models that may have only 10k miles on the car since new.

Once it’s known for a fact the engine is mechanically sound then one can breathe easier and concentrate on the small stuff.
You should have compression readings that are in the 175 PSI or higher range; all depending on mileage, the car’s history, etc. If the compression on No. 5 is 110 or whatever then you’ve got serious issues with the motor.

A vacuum gauge is a very handy and inexpensive tool that can reveal a lot and is a good starting point for an engine diagnosis. If something is abnormal as shown on the dial then one cna proceed to a compression test to verify the problem.


#3

What did you check on the coil pack? and how. Did you check the spark output? You could still have a bad injector or a bad coil pack. Did you look at all the plugs? Any fouling? Compression is an issue but fuel, air, and spark is the first place to go.


#4

From tower to tower, ohms, around 6. I had it done at autozone, and he said that it was to be between 6. & 11. He also checked the back and it was in normal limits too. I used the old spark plug to test spark, with the fuel pump fuse out. I compaired it with another feed, they both looked the same. I did not look at all the plugs. #5 sparkplug was fine as far as I can tell. Not fouled, oily or any major defects. Figured that if the computer said that # 5 was the issue then I was sticking with # 5. Is there a way to test to see if the injector is bad even if I can hear it clicking? I will have to try to get a compression tester too. The car has 97,000 miles on it. Thanks for you help!


#5

I had a plugged up fuel injector in my car not long ago.


#6

Ok, so I have replaced the wires and stuck a new coil pack on with no succsess. It is looking grim! Any other suggestions?


#7

Test the compression. Throw 1 new fuel injector at it.


#8

Fuel injectors are a fairly common problem on these cars. They are also a little expensive to throw at the car, though, around $100, if I remember correctly. Try switching it to a different cylinder and see if the misfire follows it to that cylinder. If it does, replace the fuel injector.


#9

OK! So I did a compression check and 20lb. maybe compaired to the 130lbs. on #3 cylinder. What could be wrong? rings, valves, gasket? d. all of the above?