HELP! Mystery Cyl #1 & #5 Misfire.

ARJENMOR

MEMBER
MERCURY COUGAR

I apologize for not being in a position to donate, at this time. The Cougar has me in the red and repairs will likely be on a borrowed basis. If this Cat gets fixed, I will be more than happy to donate, as it is my work car! Thanks in advance for any help!

I have a 1995 Mercury Cougar XR-7, with a 4.6 Liter V-8, that has 157,000 miles on it. It has been regularly maintained. It is running awful and showing codes for Cylinder #1 misfire and Cylinder #5 misfire.

It has been to 2 Ford dealerships and been examined by 2 other experienced certified mechanics. It has left several people pulling at their hair, trying to figure it out.

1 Ford dealership mechanic couldn’t find an exact problem and suggested I replace the engine – I’m not ready to accept that answer.

The other Ford dealership mechanic said that it had a bad intake valve, so I had a scope ran in the cylinder and found no bad valves.

1 Certified mechanic said he ran every test he possibly could and could find nothing wrong with it and said that theoretically, the engine is in perfect order and should have no problem, that he could find and that he couldn’t help.

The other certified mechanic ran all the probes and even used a Sun machine on all the electrical leads and it came back in normal parameters and that he couldn’t determine the cause of the problem.

Here is a list of things that have been done to rule out problems:

1. Plugs and Wires
2. Cleaned EGR and EGR Passage
3. Swapped injectors and bought 1 new one
4. Changed Plenum and Intake gaskets
5. Changed Coil Packs
6. Changed Ignition Control Module
7. Changed the fuel filter
8. New Mass Air Flow and Air Flow Sensor/Switch
9. New Throttle Positioning Sensor
10. A Compression Check – Holds 178 to 180 psi in every cylinder.
11. Had voltage check on every injector and every sensor on the car by all 4 mechanics.
12. Checked fuel psi and it is within parameters.
13. All of the plugs get fire – Cylinder #1 plug is a little wet from fuel and cylinder #5 plug is a little black.
14. Checked cam lobes and they are good
15. The car ran fine – I shut it off at 11:00pm and the next morning I started it up and instantly had a cylinder #1 and #5 misfire.
16. While the engine is running, you can unplug either injector for Cylinder #1 or #5 and it still has the same miss.

Can a computer be causing the problem? Any ideas of where to go or what to do next? Any insight would be sincerely appreciated.

Thanks - Arron

2 Replies

BACKYARDMECHANIC

MECHANIC
337 POSTS

It seems like you have made a good go of it and have performed all the test I would have done. The wet plug indicates to me that the plug isn't firing. You are correct to believe it's not a valve or you need a new engine or you would of had bad compression on the cylinders in question. It also leads me to belive it is not a fuel problem but a ignition problem. I suspect you have a weak spark for the affected cylinders and since you have changed the coil packs, ignition module, plugs and wires the next step is to check the voltage to the primary side of the coils. Compare it to the cylinders that are operating properly, and see if there is a difference. If there is then the problem is either in the wiring to the coils or a defective coil driver inside the PCM. ( What I think you suspect) However before you change anything I suggest checking one more item and that would be the crank senor. Remember the senor is telling the PCM when to fire the plugs and controling the timing. Test it and see if its good if not you are back looking at the PCM or the wiring the the primary side of the coils. Good luck hope this helps.