Posted this on the Expedition page, but there is alot of smarts on this page I didn't want to miss...............

2001 Expedition- 5.4- 4x4 -74k miles.

Truck stumbles at random RPM , no pattern. When a code is generated it is the infamous and non-discript "Random Mis-Fire". Fuel pressure tested at rail shows 32 at idle, when placed in gear to simulate load and run up to 1500rpm, the fuel pressure goes from 32 to 40 then drops back to 32. Happen to have access to another 2001 exp, basic same configuration and the pressure runs at 35 on idle, and runs to 40 and stays there when under a load. My information calls for a pressure between 35 and 55, so I am under the norm to begin with and then it does not maintain under load. Fuel pump and strainer have been replaced, fuel filter replaced, no leaks found by smell, visual, or otherwise. Regulator "appears" to be o.k.

Since this is random I do not suspect any one injector, coil pack, etc...And then there is the question of the fuel pressure. Any suggestions or past experience with similar???

Also, code can be cleared and then not show up for some time but the vehicle still has pressure issues, performance issues, and the stumble, just like a mis-fire.

Please don't tell me I need a new ECM...but I'm afraid that may be coming.

And...what about the fuel return side and vapor valve operation?

Thanks, please help.

 

Do you only get the 1 code or are there more?
Have you tried checking the fuel pressure while you're driving it?
Usually you can tape the gauge to the bottom of the windshield so you can see it while you drive. Better yet would be to have someone else drive while you watch it. If it doesn't drop more than what you've said so far I doubt that is your problem.
The best thing would probably be to have your dealer monitor the power balance on the road with their WDS scan tool/scope.
That should show which cylinder or cylinders are misfiring.

 

Thanks for the response Racerguy, I knew if i waited long enough you'd pick this one up. Haven't tried pressure testing while driving just foot on brake while in gear at 1500. Will try this evening. The code (didn't get number) is the same each time. Scan on three different occasions, independant shop, yet they have WDS unit we could test during driving.

Thanks and will update...any other thoughts?

 

I am having the same problem. I have a 2000 f150 4X4 with a 4.6 liter. I recently got codes showing multiple misfires and a misfire on cylinder 1. Changed the ignition coil on cylinder 1 and problem went away. A few days after this I experienced some performance problems. It seems to be misfiring. The truck starts jerking at about 1100 to 1400 RPM's and runs much better over 1500 RPM's and under 1100 RPM's, but seems to be misfiring throuhgout. The engine has approx 70,000 miles on it. Do I just need a tune up or is there more to this? Don't want to go out and change all ignition coils if I don't have to.

 

There is alot you can do in eliminating things, such as fuel filter, MAF cleaning, throttle body/valve cleaning, etc...that doesn't cost much more than your own grief. But if you have access to fuel pressure tester, that's easy and a good test. Until you get a solid code that is persistant and/or repeatable it's difficult. When you changed the COP did you check out the plug? May not be a bad idea to check one fo the easier to reach plugs for wear and whatnot. Plugs are not to bad on the wallet or to change, but the COP's get expensive especially if they aren't throwing codes at you. I have always had a code thrown with a bad COP. 4 trucks, same generation, multiple bad COP's thru life. They advertise these plugs going to 100k, but 70k isn't a bad time to check/replace. I've gone to 100k on one without issue and changed another set at 75k to resolve performance/mileage problems.

 

Bump....

Lookin for more ideas!!!! Thanks,

 

Have you tried unplugging the EGR valve and driving it? I would try that and see if it makes any difference. If the EGR is open when it shouldn't be you can have a random miss too. The EGR valve itself could be bad too if just plugging the hose to it doesn't make any difference. A bad Crankshaft Position Sensor can also give you the same problem.
I found out today too that Ford has recently changed up the COPs again. I'm not sure what is new and improved on them but they might be better.

 

Hey Racerguy,
could you let us know about the cop change. We sure have be going through them. Thanks

 

I dont know anything about it other than that the new part number is 3W7Z 12029 AA.
I was also told today that a COP off a CNG powered Crown Victoria is stronger and last longer than a normal one. Again I dont know any more details but that came from a reliable source.
If you go with either of those make sure you keep us posted on any problems with them and I'll try to do the same.

 

I originally changed the plugs in the expedition because the check engine light kept coming on. The code said that there was a misfire in #4 cylinder.. so my dad and I changed all the plugs and did a complete tune up... new fuel filter, PCV valve, Oil change with new filter, and we cleaned and reoiled the K&N. It ran fine for as long as it took for the computer to relearn the settings then it began running like **** again!!!

So, I'm in the same boat as you..

I figure it's a bad COP.. is there anyway to check them?? or do you just replace them if you think they are bad???

 

scottolan....

My experience has been if a COP is bad it will throw a code. Not always right off the bat, but it does shortly. Not being sarcastic, but the best way to test them is run them thru a diagnostic capable scan tool which will somtimes find a failure before the "Check Engine" light comes on.

 

Thanks for all the help. I changed the plug where the coil was and that did the trick. I ended up changing the other plugs too. Truck is running great now. I was able to get to 7 of the 8 plugs without much trouble. I think I can get to the 8'th but I burned my hand. Gonna wait for the engine to cool down. Thanks again for all the input.

 

Let me guess, the difficult one where you get burned is...number four right by the heater hoses!!!! Or not, but that one is a pain and if the engine isn't cooled down it makes for some decent pain.

 

We had Autozone hook it up to an OBDII scanner and pulled the code of a misfire in the #4 cylinder.. it didn't say anything about the COP.. but now that it is running bad again (even after new plugs) and the check engine light has come on AGAIN.. I will have the codes pulled again and if it's reading the same thing I can only assume that it is the COP malfunctioning.

 

Actually it was farthest back on the other side. The engine was cool when I changed the plugs by the heater hoses. The fuel rail is hard to work around on the left side so I think I hit the line that runs from the exhaust to the egr valve. Oh well no biggie, truck is running good and thats what I was trying for.