Bought a 99 Expedition 6 weeks ago with 68k miles on it. I got a transmission flush and oil and air filter change done. About 400 miles later, it suddenly had a really bad misfire that only lasted for one 10 mile trip. After that it was fine for a week or 2. Now the problem is back.

Idling, there's a little sputter about every 5-10 seconds. If I pump the throttle momentarily, it bogs the engine. Driving it, I have to be careful not to give it too much throttle. It will only accelerate if I'm real careful about not giving it too much gas. Occasionally, it seems about 95% better.

1. After replacing a really nasty air filter, could it need a computer reset?

2. Does it sound like fuel starvation? I could try a filter or fuel system cleaner.

3. Could it be the IAC valve?

Thanks.

 

Try cleaning the MAF sensor first. Just spray some contac cleaner on it and post back if that doesn't work.

tom

 

I've heard a lot about MAF sensors, but never seen one. If I remove the air filter, will I see it? Thanks!!!!

 

i think if you follow the intake and look for a box with screws on it about mid way and has a plug/clip deal on it, its in there... im not totally sure tho so dont go by my word.

 

If the expy has the same air intake as the F150 it is right behind the clamp that you remove to get the air filter out.

It is sticking in there and you will see a post with two fine wires with a resistor in there.

Some people even say to reset the PCM by removing the batter cable after cleaning. I don't really do that as the PCM will adjust soon enough to the changes from the MAF.

However in cases like what you are describing it might not hurt to let the PCM relearn.

tom

 

Which battery cable, pos or neg?

 

I usually remove both negative first just the habit i have to keep from creating a short when working on the positive side.

I have heard some say to turn the lights on too and leave it for 30 minutes.

I would leave the battery disconnected for atleast 15 minutes.

That will reset the PCM. It may also not shifit exactly right for the first trip you take. That is the PCM relearning and it will or should get the fuel trims right again and settle down after the first couple of times it has reached closed loop.

A search here for MAF sensor should result in several posts the possibly describe the procedure for cleaning and resetting the PCM better than my description.

However accomplishing either of these tasks is not rocket science. Just something ya gotta try. Once ya got the MAF found you have it made.


tom

 

Thanks guys. I'll try tomorrow

 

I cleaned the MAF, added a 20-gallon treatment of Chevron Techron fuel system cleaner, cleaned up a corroded pos. battery terminal, and reset the computer. None of that fixed it, though I know it would take time to see the effect from the fuel system cleaner.

I'm going to try to get the fuel filter changed and see if that helps.

I can't find the IAC valve. It's certainly not where it was on my 97 4.6 p/u.

 

I replaced the fuel filter today, and it's no better. Any other ideas, or do I need to find a mechanic? Thanks.

 

it is prolly the #4 coil pack. because there is a heater hose above it that leaks on the coil and causes it to fail.

if it was a true missfire the CEL would flash as it was missing.

i would guess that you have a combination of problems since it sounds like the truck was not well cared for since the air filter was really bad.

i would clean the MAF again, check the hose above #4 coil, replace the fuel filter, run some sea foam through the intake. then reset the PCM (neg cable only!!)

i still think it is the MAF because of your post about not being able to accelerate. there are only two things that cause you problem. a dirty/faulty MAF or colgged cats.

i doubt it is the IAC because it really only affects the idle not acceleration.

good luck

 

hcmq is probably right , I have seen a lot of the 5.4's with misfires
caused by the coolant hose leaking onto the c.o.p.
( coil on plug ) some werent enough to through the MIL light on

enother thought is if they just did an oil change and washed the engine down if they spill a little oil the coil or plug could have
fouled.
use caution on your choice of spark plug replacement if you ever change them , i have seen a lot of problems with people using autolite spark plugs, ford plugs are a little more money but definately worth the money. also some coils and plugs may look fine but i have also seen a lot of cracked plugs, the porsolin may look fine but if you see a little black line down the white porsolin
it could be cracked

 

Thanks everyone. It really seems to idle about 99% fine. Whatever the problem is, seems to affect most, if not all of the cylinders at once. I can use about 1/4 throttle in first and 2nd gear, but very little throttle in higher gears before essentially having zero acceleration. In park or neutral, the engine still bogs with too much throttle.

 

I would suspect the EGR

tom

 

I don't think it is the EGR for two reasons #1 it is a 5.4 not a 4.6 and they are less prone to the known EGR problems that the 4.6's have and #2 he has not complained of detonation/ping which is more common with the EGR problems.

He is experiencing power loss during acceleration which is classic MAF and/or clogged cats.