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William, ASE Certified Technician
Category: Car
Satisfied Customers: 62
Experience:  15 Years in the field, ASE Master Technician
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99 olds alero 2.4L has misfire on no. 3 cylinder coming up

Resolved Question:

99 olds alero 2.4L has misfire on no. 3 cylinder coming up on scanner as a p0300 random misfire code. I have changed the spark plugs and the boots. I tested resistance between the secondaries for the coil and it was within spec.. I have also checked compression on all cylinders
and they were well above the minimum spec of 100psi and within 5-7 psi of each other. I have tried moving the plug and boot around to different cylinders with no sucess. I have double checked myself to make sure the plugs and boots are in good condition. Also making sure the ign. secondaries are lined up with the plugs. do you have any other ideas that I am overlooking.
Submitted: 7 years ago.
Category: Car
Expert:  William replied 7 years ago.
Hello and welcome to! My name is XXXXX XXXXX I am here to assist you.

Other than the check engine light, are there any other symptoms, such as a rough idle, misfire etc.? Was P0300 the only code in memory?
Customer: replied 7 years ago.
yes the p0300 code was the only code and it does idle rough gets worse when I put it in gear.
Expert:  William replied 7 years ago.
Ok Tom,

The first thing I want you to do is remove the top cover as though you were going to remove the spark plugs again. Do not remove them though. Remove the coil tower (white plastic, 4 screws) from the cover and remove everything out of it you can until it is just the bare part. Using your multi-meter measure resistance between the coil towers, 2 at a time until you have exhausted all combinations. All should read infinite resistance(open circuit). If any 2 have a reading in ohms, replace the coil tower assy. NAPA auto parts sells them for sure as well as many others. It is a readily available part. This is the most common cause of your concern. If you run all tests and everything tests ok, we will go on to the next set of tests.
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Customer: replied 7 years ago.
are you tslking about the secondary terminals on the white plastic or on the coil itself?
Expert:  William replied 7 years ago.
The secondary terminals... but the coils must be removed first. This is a pattern failure on this engine which is why I am steering you here first. The ignition spark cross-fires through pores in the plastic, eventually carbon tracking which can be diagnosed with continuity testing. With coils removed, all 4 tower ends should have no continuity with each other.

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