The misfire of all misfires

TylerBowman

TBowman
To start, the car is a 2000 v6 with about 147k on it. I boosted it about 2 years ago and has run extremely well for the most part. I'm having the worst misfire problem (or what I'm assuming is a misfire). When the car was dyno'd, (tuned open loop) they told me it went a little bit lean at 2k rpm and said it wasn't really anything to worry about. Never really had a problem with that until the past year. You could feel when you were at 2k rpm but it would rev over it no problem. That rpm has fluctuated +-500 rpm. Basically regardless of the lean situation, it always ran amazing under wot and even more amazing at the track. Around Christmas, it would kinda stumble really bad at 2k but would go over it if you gave it significantly more throttle. But now, after sitting for a month or two due to the snow, it misses/stumbles/hesitates regardless of how much throttle you give it.

Over the last couple months I've replaced the following:
plugs
wires
coil pack
iac valve
tps
crank pos sensor
fuel filter
and just last weekend, did a compression test which ruled out a broken valve/hole in a piston.

Has anyone else ever had this issue? or have any idea where to look next?
Only things in my head could possibly be a faulty injector? The car isn't throwing any codes either.
It's starting to warm up outside and I just want to drive this thing!

Any help is greatly appreciated!
Some pics of the car-


 

6 Shooter

Well-Known Member
Would start by retracing each plug wire from each spark plug to the coil pack.
top row 4, 6, 5
bottom row 3,2,1
Yes, it is hard to trace each wire. The passenger side is the worst because of wire routing behind the block.

And, what plug are you using?? What plug gap?

Make sure your wire harness to the coil pack is securely plugged in.
 

TylerBowman

TBowman
Thanks for the advise.

Plug wires are on the correct cylinder, I messed that up before lol. I'm using ngk tr6's gaped at .030. Just put a new set of plugs in when I did the compression test this past weekend. As for the coil pack wiring, I'll double check that as soon as I get out to work on it.

Another weird thing to note is that cyl 6 spark plug looked like it was soaked in fuel. Could that be a leaky injector?
 

TylerBowman

TBowman
I had an injector plug that was loose. It runs a little better bit still isn't perfect. And the cool pack is only a couple months old. Don't really want to buy another if that's not the problem.
 

6 Shooter

Well-Known Member
I burned up a fuel pump in the past due to a weak electrical connection at the pump. Not saying you have a burned up or damaged injector, but it is an electrical component and a loose or partially connected harness to that one injector may have damaged it.
 

douglass

Active Member
When all this is happening is the check engine light on or flashing? Do you have a wideband sensor installed? If so what a/f are you getting under normal throttle and WOT? Same question around 2,000 rpms. Do you have any data logging programs? The number #6 plug being fouled with fuel does raise some suspicion.
 

pirate bman

Active Member
Try the coil packs they wear out in the older mustangs I work for a ford dealer ship and my tec told me they were an issue
Same thing today possible or te wires either or. But since I had a tune up done like you all above said that could mean a variety of things to look into
 

cynwigley

New Member
Try the mass airflow sensor too!! Can't hurt to replace parts just in case it will be less to troubleshoot later!!
 

Markstang

Polishing my banhammer
i disagree pirate bman. Replacing parts is a waste of money when you can trouble shoot for close to free.
 

fasterthanyou

Active Member
What are your short term fuel trims when it happens? Basically datalog everything and post up the file in excel. I'm serious, one of the few guys that tune our own cars can look at it and try to help out.
 

fasterthanyou

Active Member
Also a compression test is very different than a cylinder leak down test. Might want to do that to all the cylinders. You can Use YouTube to learn how to do that if you don't already know how.
 
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