Modified Mountaineer running rough / misfiring | Ford Explorer Forums - Serious Explorations

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Modified Mountaineer running rough / misfiring


February 10, 2005
Reaction score
City, State
Rochester Hills, Michigan
Year, Model & Trim Level
2000 Mountaineer
Well I need some input/ideas from some other people as I'm starting to run out of them... My father in law is a trans tech at Ford and with his computer and help I should be able to do anything... I just need ideas of places to start...

Background -- 2001 Mountaineer 5.0. Explorer Express Eaton M90 ~8lbs . Blue Ford 39lb injectors. Torque Monster Headers, Walbro 255lph in tank pump. Tuning by Alternative Auto.

Engine seems to be running rough. I have had this issue for a couple of years and have either just driven through it or not had the motivation to fix it. Last year only put a couple hundred miles on it because of the issues. Last fall I pulled the motor with intentions of putting it into a Ranger, however that plan got sidetracked and it went back in the mountaineer for this summer. When it went back in I put a brand new alternator on it. Found a ground wire on the main harness that wasn't securely fastened to the block last year. It got all new spark plugs (as i do this once a year). New (Livewires) spark plug wires, heat shields around the plugs and "screamin demon" coil packs.

In the past it would throw a code for the cam position sensor. I replaced the entire synchronizer once, replaced the sensor twice. Had my father in law check the power balance and everything seems to be in check. Ran a jumper wire on that circuit from the sensor directly to the ECM and after all that... it will still continuously throw a code for the cam pos sensor.

Ran a compression check and all cylinders are within 5psi of eachother, all over 140. Pulled valve covers and inspected, everything visually ok. Inspected the entire wiring harness checking continuity between all connectors and ecm connector and it all checked out.

Just got it all back together last night and again it is running rough... very primative diagnosis leads me to believe the #4 cylinder (closest to firewall on passanger side) is not running as hot as the rest of the cylinders... whether that be from fuel or spark, i do not know (motor was warmed up and water squirted onto each tube from the header. #4 cylinders header was significantly cooler than the rest) No CEL as of now, only drove it a few miles.

I've been chasing the problem for a few years and never seem to get it dealt with. Any input, places to look, things to test would be GREATLY appreciated. I will have the assistance of my father in law this weekend so any head starts or ... anything would be awesome.

It could be something among what you have already gone over, or something else like the EGR system, or fuel pressure etc. I was hunting a miss which became a stumble last Fall. I did all of the typical plus wires etc stuff. I found a bad coil(Accel 3000 miles old), a loose ballast resistor at the other coil, check yours.

I have checked my fuel pressure several times over the two years I have had my miss, but in February I finally got a 32psi reading, barely enough for the pre-99 models. I likely have a fuel pressure loss, from either a leaking line at the pump, or a pump about to die. My stumble is erratic, usually more when hot.

Check your fuel pressure often enough to be sure that isn't it. You must have close to 60psi on the 1999+ models. 55psi would be too low, a leak at the pump is common(I had that on my 99 truck). Yours should be steady at any rpm or throttle, say 60psi or more.

After hunting for a long time like that, I suspect the wiring more than other things. Keep trying to confirm that what has been checked, is still good. Swap parts again, like coils and plug wires, plugs.

Also, I do not recommend Livewires, those are a gimmick(plus the insulation is the weakest link of wires, those are the regular plain stuff, not premium quality). Get the best wires, by Magnecore, the next time you have to buy plug wires.

Thanks Don. I'll keep rechecking and test the fuel pressure next. The assumed dead cylinder injector is directly below the fuel pressure regulator on the stock fuel rail. It's nearly impossible to get to the test port on the fuel rail with the way the lower intake mount is on the explorer express kit. I have eliminated the egr system completely along with writing it out if the tunes.

Could the routing of the plug wires cause interference? Number 3 and 4 cylinder plug wires are run around the back of the supercharger. Closer to the firewall, wiring harness and ECM than ever before...

I hope that you can get to the pressure port(Schroeder valve). On the 99+ Fords, that thing on the fuel rail is not a regulator, so it doesn't have any real affect.

The regulator is in the tank with the fuel pump, so there are two short lengths of rubber hose there.

A short from spark plug wires is a worry, but hopefully it would be more obvious, affecting two cylinders or being a bigger miss. Try swapping the wires by moving both the plug and coil ends around. They should be long enough to swap like that for a short test.

Mine is still stock essentially, with different plug wires. I did add some split loom in short pieces between the wires next to the coil bracket and a couple of other parts. I will rearrange things again when I do a blower, but then I'll be looking at wire looms and maybe custom length wires if it could help. I plan to have the blower over the left valve cover, and keep the coils near the center/front.

It made no effect for mine, and my wires look okay, plus I did swap about four of them when I ended up finding the one bad coil. I had a hard miss on cylinders 1 and 3(from the same coil).