HELP! Mystery Cyl #1 & #5 Misfire...

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:


Plugs and Wires
Cleaned EGR and EGR Passage
Swapped injectors and bought 1 new one
Changed Plenum and Intake gaskets
Changed Coil Packs
Changed Ignition Control Module
Changed the fuel filter
New Mass Air Flow and Air Flow Sensor/Switch
New Throttle Positioning Sensor
A Compression Check – Holds 178 to 180 psi in every cylinder.
Had voltage check on every injector and every sensor on the car by all 4 mechanics.
Checked fuel psi and it is within parameters.
All of the plugs get fire – Cylinder #1 plug is a little wet from fuel and cylinder #5 plug is a little black.
Checked cam lobes and they are good
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.
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

I would pull the injector harness and ohm all wires and also visually inspect them. I would also ohm all the wires for the injector back to the computer.
From my past experience with fords you have a computer harness wiring problem. Also put one end of ohm meter on a body ground and check for bleed through. Also check for bleed between two wires.
A full day at home wire and a good ohm meter and you should find the problem. Also wiggle each injector plug you may have a bad terminal.
Most mechanics won't spend the time as customers don't want to pay the shop labor rate and they slap on new parts.

i had similar problem with another ford but it was a 4cyl car and i changed just about everything the problem was that i put bosch plugs in the car that were 3 dollars a piece, and i needed the motorcraft plugs that were .80 cents a piece. you might try that if you put different plugs than motorcraft plugs. let me know if this helps