I have been having problems with my tranny vibrating when it is shifted into overdrive. I was told that it could be because my engine is missfiring. How can I check my motor for a missfire?

 

First, make sure your hands are soaking wet.... Then start the car and let it idle..... one by one pull a sparkplug wire off the plug.... if it seems to run worse then put it back on and continue to the next one... keep doing this until you hear no change after pulling the wire off. When you come upon the cylinder that made no change int he cars running you have found the cylinder that has a problem. Could be a spark plug wire or a plug or a broken valvespring....

Oh, and about the soaking wet hands.... I was j/k about that You'll get a new hairdo if you try it They have special sparkplug wire pliers that are insulated at the local parts store.....

 

inductive light will save you some time over pulling each wire. run compression test as well, change plugs while you have them out, scan for codes.

 

n/m..ede beat me to it.

 

How do I go about running a compression check?

 

screw it in place of the spark plug and fire her up

 

A vacuum guage always helps me. If it stutters from a high vacuum right down to 0 you got a dead cylinder.

As far as a compression test, i would do it with all the plugs removed from the engine. Remember to disconnect the coil wire.
Each cylinder should be within 10% of each other. After, add some oil from an oil can to each cylinder & repeat the test. If it goes up, you have may have a ring problem.

 

Umm, you could open the hood and look. If you can see the ground, it's probably missing....


But seriously (or at least a little more so) you can perform a power balance test with a tachometer. Don't rely on the one on your dash, since it isn't graduated precisely enough to register any significant difference.

1. Start the engine and allow it to reach full operating temperature.

2. Stop the engine.

3. Bypass the EST circuit to prevent the ECM from trying to correct for any changes in operation while you temporarily disable each cylinder.

4. Insert a jumper in the ALDL connector between terminals 'A' and 'B', then turn the ignition to RUN without starting the engine.

5. Wait at least twenty seconds for the IAC stepper motor to extend fully, then disconnect the IAC electrical connector.

6. Turn off the ignition and remove the ALDL jumper wire. This will force the engine to run only on throttle body bypass air and will again prevent the ECM from adjusting the idle speed or timing to compensate for your disabling of cylinders.

7. Connect your tachometer.

8. Restart the engine and allow it to idle. If there is any difficulty in getting it to maintain idle, you may have to temporarily increase the minimum air position of the throttle plates by turning the adjustment screw - just count the number of turns since you'll have to reset it later. Try to set it at a nice round number, like 600 RPM or so.

9. One cylinder at a time, disconnect a spark plug wire, noting the RPM drop on the tachometer as you do. You may find that insulated spark plug wire pliers are very desirable for this test, since not many people like repeated jolts of 20,000 volts through their forearms. At least I don't any more...

10. Make a note of the changes caused by disabling the cylinder, reconnect the spark plug wire, then move to the next cylinder.

When all cylinders are checked, you should have an equal RPM drop caused by disabling each cylinder. If disabling one or more cylinders resulted in a smaller RPM drop or no change, it wasn't making an equal amount of power to begin with and is weak. This cylinder(s) is the place to start checking for weak spark, poor compression, sticky or burned valves, etc. .

Incidentally, if the symptoms are only occurring in O.D., you may have a torque converter clutch or transmission problem, and not a misfire.

 

When pulling plugs for this test, can you do it at the distributer, rather than the plugs? It would seem a lot easier than trying to get at the #7 or #8 spark plugs with the engine running. Is this asking for trouble?

 

Dustin,

You could pull the plug wires from the cap, but on the newer style (1985-up) caps the spark from the abandoned terminal tends to find the nearest ground, which may be another plug wire or fuel-related item. Niether of these will give accurate results, and may cause some problems.

 

grafx,

Is there a particular engine RPM that this occurs, or just any time you're in O.D.? Does is make any difference if the converter is in lockup?