Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Engine Misfiring! Help! Mechanic Expertise Needed

1999 ford e-450, v10, gasoline

While in park with the gas pedal to the floor, the engine revs high

then drops followed by misfires then continues in that cycle until the

gas pedal is released. Truck seems to idle fine, seems to rev high

until the gas pedal is pushed past the half way point

going to change the spark plugs tomorrow unless told other wise! Thanks

It might be hitting the rev limiter. If so, it’s normal.

Does it behave like this while you’re driving it, in gear and on the street?

it doesnt have rpm gauge so i dont know but when on the road its not running really, lack of power and has trouble climbing hills, also the other day i was on the highway and it messed up i was driving around 100km/h and all of a sudden it starting dropping speed while my foot was still on the gas then i tried to accelerate and it wouldnt so i had to pull over and drive it home slowly

You might want to check the fuel pressure. A weak fuel pump can cause that problem.


things i have changed/repaired:

Fuel Pump
Fuel Filter
10 Fuel Injectors
MAF Sensor
DPFE Sensor
Air Filter
Rebuilt Transmission

Its Running Me $$ and i want to just get it fixed but seems like something is always wrong

Clogged converter(s)? This could easily be verified with a vacuum gauge.

If you’ve replaced all this and still have a problem with misfire, the next thing is engine mechanical. Timing chains?


how do i check a timing chain? or should i have a mechanic check, and should i do the spark plugs

Why did you start a whole new thread? (

And is it a '99 or a '00 ?

Put a fuel pressure gauge on it to check out the fuel pressure - new pump & filter or not. Check it with some load on the engine.

Put a vacuum gauge on it and check for exhaust restrictions.

If the plugs are due or close to due, then just change them.

i started a new thread because i messed up, i checked for fuel pressure already as soon as the pump and filter were changed it the pressure was perfect, i believe the mechanic said 44 psi, and i also brought it to the mechanics and he said there were no exhaust restrictions or vacuum leaks at all! this has been a pain and nobody can put there finger on the problem, so im going to change the plugs today and hopefully that will solve the acceleration issue

I doubt that changing the spark plugs will solve this trouble but if you are due for a change anyways it would be good to do in that case.

I suggest you monitor the throttle position sensor and MAF sensor signals to see what is going on with them while the trouble is occuring. It may also help to watch the O2 sensor signal to see what it shows.

So how did this mechanic check for exhaust restrictions? I’ve seen some whose test was nothing more than sticking their hand behind the tailpipe and making a WAG about how much exhaust flow there was.

Are you doing all the repairs and parts replacements yourself?

If yes, I’d suggest taking it to a Ford dealer and get a good diagnosis. You seem to be chasing your tail on this one replacing a lot of parts without hitting the real problem. Sometimes it is cheaper to let a pro do the work.

If you replace the plugs you might also need to replace the coils on top of the plugs if it has a COP setup. The coils go bad, and the rubber boots and springs that conduct the current from the coil down to the plugs also go bad.

i am getting diagnoses from mechanics but they havnt hit the real problem, also wouldnt the coils send an error code? i had 1 error code before ignition coil j and i replaced that coil! ill probably just take it to ford since there is no luck so far

On my '04 T’bird with cop’s the missing has to get very bad before it throws a code. When it bucks and sputters and can barely make it up a hill I’ll finally get a code and check engine light.

Most often it is the “boots” that have gone bad, and the actual coils are OK. New boots are starting to be available, Advance Auto stocks them now for my T’bird. Since the coils are expensive you might try replacing all 10 plugs and all 10 “boots” and see if it improves.

alright thanks alot, ebay has some cheap coils i can grab 10 for like $150 rather then pay $50 for one here

There’s a lot of pure Chinese junk being peddled on eBay so keep that caveat in mind when buying something at a cut-rate price.

I’m still curious as to how they tested the exhaust for restrictions.

found it, everyone was over looking the problem, it was a clogged fuel filter, my mechanic said it may clog 3 to 4 more times but changed it and boom perfect now

Something is not adding up. You stated the filter was changed previously along with the pump.
You state the filter has now been changed again and that solved the problem along with the mechanic stating the filter may clog 3 or 4 more times.

So this brings up questions about debris in the tank, were you shown a sample of this alleged badly contaminated fuel, why the tank was not inspected when the pump was replaced, why the mechanic is apparently content to allow it to clog repeatedly, and also the tank strainer issue.

it was changed before, twice actually but there was a lot of blockage in it, this is the 3rd change, and i changed it this time, it was heavier and when i shook it black stuff came out of it, completely plugged, my tank was cleaned before and was taken home by the mechanic to clean, im not sure what would cause this to clog again, there is also a hose connected to the tank that he took something out of, it was like a metal thing with holes and he removed it and now there is a completely open hose just sitting there i can see the gas fumes coming out of it! is that bad? and what causes low fuel pressure because i still think its not gettin the full amount