[font size="1" color="#FF0000"]LAST EDITED ON 15-Mar-01 AT 04:32 PM (EST)[/font][p]OK, first, this is what I'm working on: 1989 F250, 5.0L, M5OD.
Next, this is what I replaced: Plugs, wires, cap, rotor, and fuel filter.
Now, here is my problem, I seem to have developed a miss after the above items were replaced. The miss is most noticable at part throttle, low RPM usage (IE: crusing at 35MPH in 4th).
This is what I have tried to diagnose this problem, I have seperated the 7 an 8 plug wires, I've triple checked all plug wires (firing order and routing), and I have made sure the cap and rotor were installed right.
My, question is, what in the world do I check next? I've been pulling my hair out for almost 2 weeks trying to find the problem. If anyone has anymore suggestions for me, I'm all ears.
TIA

Roger Lane
Test Analyst
Sr. Automated Test Engineer
IBP, Inc.

 

Did you install spiral core wires? Several years ago I attempted to use spiral core magnetic supression ignition wires on a 89 F150 with 5.0/302. The same symptoms you describe occured. I tried 2 sets of the Splitfire wires thinking the 1st set was defective. Tried carefully routing and separating them. Nothing seemed to prevent the misfire which occurs at low rpm, part to mid throttle operation. Most noticeable in higher gears. One other time I tried to use a Jacobs Ultra Team ignition system which cost over $400! Same problem occured since it came with spiral core wires. I switched back to stock wires and the misfire went away. I did return the Jacobs system however, for the price it did not meet thier claims, no noticeable power or mileage increases. I don't know why this misfire occurs, perhaps it is cross fire in the cap, since at the mentioned driving condition I believe the advance would be near maximum. Or maybe electromagnetic interference affecting the engine control signals. Anyone with any ideas?
Mark
mjb1962(No Email Addresses In Posts!)

 

check the plug gap again and carefully check the ceramic on the plugs you may have a cracked plug. that wont give a misfire at idle but it will misfire under load like you have spoken about.

 

What brand plugs did you use? I have had problems with certain brand plugs in Ford engines. I would suggest Motorcraft plugs. I used Champion plugs in a Ford engine one time and had a nasty miss. I also had it happen once using platinum plugs. Just a thought. Good luck.

Jakegypsum // Ford fleet, soup to nuts.

 

Hi Roger


I am no expert at mechanics. I have always done just the basics on my rigs such as plugs wires distributor cap rotors and so on. The one thing I never did when I did these things was to gap my plugs. Well I finally learned a lesson on that. I have 90 F150 with a 302 AOD and I just changed my plugs, and after hearing every one say to use motorcraft only so I did I slapped them all in started that thing up and it sounded like it was missing I had no Idea what was wrong. I ended up at the Ford dealer in time to embarrass my self. They said did you gap them no never thought about it after all on the last five rigs I had I never did but I bought my plugs for them at a local auto part store. They said oh well we dropped them more than likely and sure enough they pulled one and it was bent pretty bad. So I just had them pull them all and gap them for me and lost a hundred bucks for it.

I am not implying that you have done this but just thought that I would pass it your way.