misfire on cylinder 3

[4.0blues]

I had misfire problems plaguing me for 20k miles. Went through 2 sets of premium wire sets and two brands of plugs. Replaced coil pack too. Finally ran across Ford mechanic that said ONLY OEM Motorcraft wires and plugs for the 4.0. Not one single misfire for several thousand miles now. Just a thought.

 

[Duane867]

That is possible.
I run cheapie plugs in my 2.3 because there are freaking 8 of them and every so often I get a miss fire as well. I know thats the problem but Jesus man $60 plus bucks for plugs ya know !

 

[fordfan86]

without ripping the head off im at a loss as for how to check to see if i have a burnt exhaust valve andy, and you guys might be on to something with the plug i run the platinum's or iridium's in it, im not sure which is in it right now but for 5 bucks i think i will give it a shot.

 

[adsm08]

That is possible.
I run cheapie plugs in my 2.3 because there are freaking 8 of them and every so often I get a miss fire as well. I know thats the problem but Jesus man $60 plus bucks for plugs ya know !

What the heck are you buying that you spend $7.50 for a spark plug?

I can buy the Motorcraft ones for about $2 a piece.


Fordfan, do a compression check. A burnt valve will cause a loss of compression that will show on that check. If you have a loss of compression on that cylinder you will need to tear down and inspect anyway.

 

[Duane867]

Havent priced them at the dealer, but they are not standard Ford Motocraft Company plugs.
They said only iridium. Autrolite XP Iridiums are $6.50 each here at autozone ( they are the cheapest but Like I said I havent checked the dealer yet ). Thats $55 something after tax for the cheap irridiums.

$6.99 each for Bosch iridiums before tax: $55.92
$7.99 each for NKG Ix iridium before tax: $63.92
$13.49 each for NGK laser iridium before tax: $107.92
Dealer ?

The Factory plugs every one has for them ( IE FOMOCO ) ar enot irridiums. They are "fine wire".
Same thing with a FOMOCO spin on it or what ?

 

[woodros460]

Same Problem

I got a 96 4.0 here with the exact same problem. I did all you did AND compression tested it. 150lbs on number 3 with no fuel getting burned. I believe the problem is in the ECM of which thinks the cylinder is lean and flooding it with fuel. Another ECM will be installed this week.

 

[adsm08]

I got a 96 4.0 here with the exact same problem. I did all you did AND compression tested it. 150lbs on number 3 with no fuel getting burned. I believe the problem is in the ECM of which thinks the cylinder is lean and flooding it with fuel. Another ECM will be installed this week.

PCM can't tell if an individual cylinder is lean.

 

[adsm08]

Havent priced them at the dealer, but they are not standard Ford Motocraft Company plugs.
They said only iridium. Autrolite XP Iridiums are $6.50 each here at autozone ( they are the cheapest but Like I said I havent checked the dealer yet ). Thats $55 something after tax for the cheap irridiums.

$6.99 each for Bosch iridiums before tax: $55.92
$7.99 each for NKG Ix iridium before tax: $63.92
$13.49 each for NGK laser iridium before tax: $107.92
Dealer ?

The Factory plugs every one has for them ( IE FOMOCO ) ar enot irridiums. They are "fine wire".
Same thing with a FOMOCO spin on it or what ?

For doesn't use iridium plugs because plats are cheaper and just as good.

 

[Duane867]

FOMOCO it is then by God.




The PCM cant tell if an individual cylinder is lean. true enough, but it does get the CID ( cylinder identification signal ) passed on to it from both the SPOUT and the cranks shaft position sensor. It converts it through the PCM to base timing and RMP information then redistributes that signal to the ICM which controls the coil packs. So, if the PCM, crank shaft position sensor, or the SPOUT connector were damaged via either straight up bad parts, or frayed or burnt wiring it could theoretically cause a consistent miss fire on the same cylinder repeatedly via fubar PIP and or CID.

Barring an intake leak on the number 3 runner, a burnt exhaust valve, worn cam lobe, or leaking gasket I think I would lean towards the PCM, the CPS, or the SPOUT.
That's my 2 cents any ways.

 

[fordfan86]

well gentlemen while i appreciate all the help that you all have given me, we have a winner. low cylinder compression due to worn rings. so now i have some options either rebuild, swap engines, or run it till it blows, THEN do either of the other two mentioned above. suggestions? im leaning towards rebuild when i get he money cause then i can upgrade and get performance stuff

 

[Duane867]

Did a leak down test ?

 

[fordfan86]

im not sure what you mean by leak down test, but heres what we did.

check compression by rolling it over a couple of times it was low compared to the rest.
then put a little fuel oil in the spark plug hole and checked compression again on that cylinder and it was much higher and it held so my mech friend told me that that meant that the rings were starting to go.

 

[adsm08]

A leak down test is where you spin the cylinder to it's compression stroke blow air in it, and then see how long it holds it (in broad strokes). It looks for valves that are not sealing.

But yes, your friend is right. Higher readings on a wet test compared to a dry test means rings.

Try some Lucas in the oil when you change it next. I know it's a band-aid fix, but if the rings are still good enough it works.

 

[adsm08]

The PCM cant tell if an individual cylinder is lean. true enough, but it does get the CID ( cylinder identification signal ) passed on to it from both the SPOUT and the cranks shaft position sensor. It converts it through the PCM to base timing and RMP information then redistributes that signal to the ICM which controls the coil packs. So, if the PCM, crank shaft position sensor, or the SPOUT connector were damaged via either straight up bad parts, or frayed or burnt wiring it could theoretically cause a consistent miss fire on the same cylinder repeatedly via fubar PIP and or CID.

Barring an intake leak on the number 3 runner, a burnt exhaust valve, worn cam lobe, or leaking gasket I think I would lean towards the PCM, the CPS, or the SPOUT.
That's my 2 cents any ways.

While your incredibly complex theory is correct, on paper, it also bypasses the basics of modern misfire diag.

Swap coils (if a COP) or wire (if a waste-spark system) and see if the miss moves. If it does, bad coil. If not, swap plugs. If it moves, bad plug. It not, check for fuel on the plug. If no, check pulse, if yes, check compression.

 

[Duane867]

Yeah I been doing that a lot lately LOL !
Leaning towards the electrical side of trouble shooting and going over board.
I think it due to my work. I have been trouble shooting so many controller boards and CPU software for the new LED 3D's post production I have been carrying that over into my every day life LOL!
Damn Koreans ! Got me acting like a frucking robot.