recently bought 98 f150 xlt 3 door 5speed 4x4 4.6l 230k miles for $1k was throwing misfire codes on 1,8,4,3 cylinders. usually throws two cylinders at a time and never the same cylinders consecutively

parts replaced

coils...msd blaster
belden wire
motorcraft plugs...when i did these it ran perfect for a tank of fuel...18mpg no stumble
two cans seafoam through the tank
tank was dropped and drained
fuel filter
one can seafoam intake cleaner
3" exhaust from the Y pipe back
MAF cleaned

previous owner said to have tested and cleaned injectors but im not positive it was done...

i dont think its mechanical because it wanders through the cylinders and when i changed the plugs it ran spot on. it gets worse the warmer the truck gets also.

injectors?
clogged small cats?
sensor?

thanks for any help

 

Check to see if there is moisture in the spark plug wells and if so try blowing out the spark plugs wells.
Pull off the spark plug wires, blow out the plug wells and wire ends really well with compressed air. Put it all back together and see what you've got.

 

no moisture...i just changed the plugs and blew out the ports...greased the boots when i put it back together and have not had a drop of precipitation here since...if it created enough condensation in the wells for an issue then ford has a bigger problem id think

why is this such a common problem with no answer? every thread ive read of similar circumstance never comes to a conclusion...and im not paying someone in a shop to chase could bes around this engine....

maybe ill just junk the FI and and electronics and run it with a carb.

 

that would be hard to do. I suspect either a big vacuum leak, or injectors. you have 2 big coils and spark plug wires? Id be looking for a vacuum leak

 

yeah....im starting to wonder though if it would be as hard as finding this ghost...these over thought systems are a nightmare. engines should have been left at fuel, air, spark...haha

do injectors have any consistency in increasing in failure as they get warmer or the engine has been running?

anyone have any injector recommendations? brands? OEM seem pretty steep even in relative terms.

 

presently you have what codes ??

injectors are rarely the problem.

coils and sensors are normally the problem.

 

Just curious if you had the fuel pressure tested?


^^ I agree^^ considering that you say that your dropping 2 cylinders at a time...wonder if there is a connection issue on the harness coming out of the ECM.

or its something with the emmisions...considering that it doesn't happen until it warmed up

 

Ditto on the fuel pressure.


If your scanner will show fuel trims, that would give an indication if you are having lean misfires. Could be caused by low fuel pump pressure or vacuum leaks.

 

So, I think I have the same issue. Mine is a 00 5.4 F150. When cold it revs high, quite normal. Once it gets to a point of heat the system then lowers rpms and slowly keeps lowering until it gets to about 350-450 rpms. At this point, the engine starts to act like it is choking out. If I keep 1k in rpms until the motor is well warmed it works normally.

This started about Oct 25th. I took a trip with the travel trailer and ended up with cylinder 5 misfiring. I replaced the coil, nothing else. Just getting around to researching things now and came across this post.

This all said, I had a visitor under the hood just a couple days before the 25th. The little rat might have chewed a wire or hose, but I have not seen a frayed wire. As far as a hole in a hose, I'm not equipped to find that.

Thoughts?

 

i have not checked fuel pressure.....and my code readings have only come from stopping at the parts store...thanks for all the advice.
i know the guy i bought it from dropped the tank and flushed it...not sure if the pump was changed. said he had the injectors checked but also not sure if that really happened.

the weird thing is when i put the new plugs in it ran perfect for that whole first tank of fuel. and then it just went back to crap.

i need to find diagrams so i know what sensors are what and where all the connections are as i kinda think its electrical myself. can i check fuel pressure myself?

as far as emissions go, no codes have been popped in that regard, but the big cat after the Y is not in the system anymore, we dont have tests here so i dont plan on putting it back in either. can i adjust for that with a tune or something?

 

the vacuum system on this truck seems to be a labyrinth.... any idea of where to start and or a good diagram?

 

Follow the PCV line around to the back side of the intake manifold, between the intake manifold and the firewall. Where the elbow connects to the back of the manifold, prolly have to use the braile method the elbow can turn mushy and become pouris (sp?) causing a vacuum leak.

 

thanks I will start there!

 

update: question....when i shut the truck off with the hood open I can hear a buzzing noise for up to at least a minute in duration. It is coming from that black pill bottle with two vacuum lines coming out of it and one electrical connector. I think thats called the egr valve or controller? It sits on the driver side of the plastic intake cover....i popped the cap off and there was a small circular foam filter that was solid with fine dust...washed and dried...still buzzes...could this be a problem?

thanks!

 

The solenoid is the EVR.
It is not allowing the EGR to vent it's vacuum but leaks slowly. That is what you hear bleeding down.
Take this EVR off and spray clean it inside until it runs out clean.
It is a 3 port device.
This solenoid malfunction will cause rough running by not bleeding vacuum from the EGR when releases by the computer.
The only time the EGR is supplied vacuum is in OD at light throttle and over 45 mph.
Any other time it should be closed or will cause drivability issues.
Good luck.