TEST 6: Other Common Causes Of A Misfire
Over the past few years I've noticed a few other things that can cause a misfire code to set that are not caused by the ignition coil itself having gone bad. Some of these have already been covered in the article:
- The fuel injector connector's locking tab is broken. This is a very, very common problem with all Ford vehicles. So, if you have a broken fuel injector connector locking tab, you've probably have found the cause of the misfire!
- The ignition coil connector's are not making a good solid contact with the male spade terminals of the ignition coil. This is the result of human error and the most likely cause is that someone inserted something into the female terminals (of the ignition coil connector) that was bigger/thicker than the male spade terminals that fit into them. This has caused the female terminals (of the ignition coil's connector) to open up permanently and causing a full-time or intermittent false contact condition.
- An open in the wiring has developed somewhere in the wiring-harness that does not let the Switching signal thru'. This is also normally caused by human error after an engine replacement.
- Anti-freeze or engine oil leaking into the spark plug tube and drowning the spark plug and spark plug boot.
- The ignition coil's connector's locking tab has broken. This locking tab is the one that makes sure the connector does not become un-plugged from the ignition coil. This tab usually breaks when the ignition coil is disconnected, either to replace it or the spark plugs.
Real Life Case Studies From easyautodiagnostics.com Readers
In this section, is input and feedback from all of the folks who have had a similar issue with their vehicle and found a solution. If you're one of them, thank you for sharing your experience with all of us!
If you want to share your repair and/or diagnostic experience, you can use the contact form below.
Real Life Case Study 1
Vehicle: 1998 Ford Crown Victoria 4.6L
Trouble Codes: P0300 after washing engine at car wash.
Complaint: “...Anytime I would drive it and give it gas, the engine would miss big time...”
Test Notes: “...What helped me nail down the problem was doing the cylinder balance test, the P0300 codes says they are all missing but it was only two of tehm. the two cylinders were #7 and #5. I took out the plugs and the cop coils and they were wet with water. Man, i cleaned them and dried them like 3 times and also blew out the water in the plug wells and the dang missing would not go away. I knew the coils were good cause they were sparking according to your test with a spark tester...”
“...On the balance test, i didn't use a vacuum gague like you ask, i didn't have one, just unplugging the injectors was enough to tell the difference...”
Repair: REPLACED ALL SPARK PLUGS AND BOOTS “...After pulling my hair out for a few hours, i decided to just replace the spark plugs and the two coil boots. This cured the problem. Since i got the whole engine wet, i decided to go back to the AutoZone and get the rest of the spark plugs and cop boots. Dude, thanks for showing how to do the balance test, it saved my butt. I have learned my lesson, i will never wash an engine again! I did not replace any of the cop coils... ”
Courtesy of: J. Tims
Real Life Case Study 2
Vehicle: 1997 Ford F150 5.4L
Trouble Codes: P0306.
Complaint: “...Misfire...”
Test Notes: “...I had replaced the ignitioncoil for cylinder 6 two times. Both ignition coils I bought brand new (one from Autozone and the other from Orellys). I though maybe I had bought a defective part the first time anyway, I found your website and did the spark test and no spark. The test that finally helped was checking the switching signal with an LED that I bought at AutoZone...”
“...Prior to finding your tests, I had done a compression test figuring maybe the rings were bad but the compression of #6 was almost the same as the rest. Also checked the fuel injector and tested for the injection signal with a noid light and they were good. I even swapped out the injector with another just in case but it didn't improve a thing...”
Repair: REPAIRED SHORT IN COP COIL WIRE “...I'm no professional mechanic (but i can turn a mean wrench) and wiring problems have always stumped me so I took it to my buddy at his mechanic shop. I told them I was not buying another coil because I already knew that was not the solution. The guys were able to find out that one of the 2 coil wires had a short and that was the reason the cop coil was not working. It was the wire that feeds the activation signal (which you call the switching signal) to the coil. I got it fixed and problem solved. Even though I didn't fix it myself your write up was able to guide me in the right direction. Thank you and with this email I just wanted to pass on my experience to others... ”
Courtesy of: C. T.
If this info saved the day, buy me a beer!
