walnut864

My 20 year old son being impatient bought an 01 GT with issues. Of course he cant figure it out and brings it to me and now Im stuck. Any help is appreciated.

Here is what im battling. Misfire under load.
car seems to idle just fine. I hooked up a scanner and pulled all sorts of codes and went ahead and replaced those parts. MAF sensor, Temperature sensor.

On the cylinder contribution test. Cylinder 5 showed numbers 157 in the count. not negative 157. Usually I see negative numbers for misfires. I have never seen this on a scanner before
I go to coil 5 and someone decided to run a wire to the ignition coil harness and they skinned the wires, wrapped the wire for the aftermarket tachometer and taped it up.

The 2 wires on the connector where they were bear were touching. which made me think it may have shorted a coil driver in the pcm

i removed the coil. the plug was finger loose. I put the plug back into the coil and started it and the plug had fire,
i inspected the plug threads and they were fine. installed a new plug.
installed a good coil i keep around to diagnose misfires on 4.6 engines.
i checked fuel pressure and it was within spec.
i checked the injector with the test kit. tested good. swapped injector 5 for injector 8. contribution test was still showing 157 on cylinder 5 instead of 0 or negative numbers for misfire.

i performed a compression check and all 8 cylinders well withing spec.
leak down test passed

wiring harness appears unharmed.

kid he bought it from "claims" he once had a pro charger on it and had the pcm tuned.
i see no evidence a pro charger was ever installed. normal lying teen i think.

all other codes were lean codes on bank 2, oxygen sensor codes. it has some sort of short exhaust. too loud for my taste.
the rest of the codes were body codes of stuff that are legitimately in need of attention. door switch etc.

at this moment im at a total loss. also found a leak at the pcv hose. repaired that too.

any ideas which way to go now?
still misfiring under load.

Derf00

My Short take, On a car that age, you will be hard pressed to tell if a supercharger was on the car after it was removed since the harnesses and other parts are well aged. If the car was indeed tuned for it and that tune is still on the car, it will wreak havoc on drivability with a stock Motor. Take it to the dealer and have the PCM reflashed to stock.

It's also possible that a wire harness got nicked or is loose if an SC was removed from it.

As far as your son....
Ah the impetuousness and impatientness of kids. Do what I did when my oldest kid (22 at the time) pulled the "can't wait gotta have it now" card and tried to dump the problem on me (blown cylinder head gasket).

Nope, sorry, you didn't want to wait. I don't have time right now to look at it and fix your snap decision. Do what any adult has to do when they make a mistake or don't think things through, fix it yourself or pay someone to do it that can take the time NOW to fix it. If you want my help, its on my schedule. I'll let you know what that looks like when I get around to it. I made him wait a couple of weeks. After he stopped bugging me, I then decided I had time. When he got snippy or became a little s**t about me "taking too long", I'd stop and remind him, he can always take it somewhere else and pay for it if I'm taking too long fix his mistake. When that wasn't enough I stopped working on it for a week. That finally got my point across. Took me three weeks of working on the car at my pace (when I wanted as much or little as I wanted) to get it fixed. Normally it would've been a weekend job but I wanted to teach him a lesson.

I also replaced timing components, rod bearings, got the heads redone locally, and replaced the oil pump while I was in there. Ran like a top, problem free for two years.... until it was totaled …

That was the the first and only time they tried that crap with me (I have three). The younger two saw that and didn't dare try it with me. They were more collaborative with their problems and not demanding.

walnut864

Thanks for the reply.
I have a buddy that tunes cars and said he would drop buy and reflash it to factory.

Yeah I've had to make him wait on me to do anything. When I did help, I made him do lost of the work.

He came by today and I had to tell him too bad I'm installing a new HVAC HVAC on the house.

I had advised him to drop it off at a mechanic friend of mines shop. He complained about the wait.
I told him that's what adults have to do.
Fix it yourself or wait for the mechanic. His livelihood isnt based on your lack patience.

walnut864

*Update*

I can't find a soul in town to diagnose a 4.6 mustang.
After everything I had already tried. If hes gonna throw money at it. Mt best guess was the ECU.
Seeing how it the seller said it was tuned. Also seeing the #5 ignition coil wires grounding out on each other.

So we got the ECU today.
grabbed my friends Snap on scanner.
Installed the ECU, accessed PATS. paired the keys and started it up.

There is no longer a solid number on the cylinder contribution test. 157 was the number and it wasn't a negative number and it didn't fluctuate. Well all cylinders were balanced after new ECU.

I held it between 5 and 6k rpm with no issues.
The problem only happens while driving.

He had already ordered a MAF sensor since it was reading bad and that didnt change anything either.

Checked all the grounds on the engine and body.
no issuesnissues there.

I'm at a total loss

Derf00

Glad to hear you made some progress and you're parenting style is similar, haha. Surprised you can't find a shop to diagnose it. It's the same a s 4.6L F150 of the same years more-or-less.

So misfires resolved but loss of power still there. The snap on tool should have the ability to view live data. What do the Short/Long Term Fuel trims (STFT/LTFT) look like Air/Fuel Ratio (A/FR) look like while driving?

The only other thing would be the O2 sensor readings. With a super charger on it, the exhaust may be modded and the front O2 sensors disconnected.

walnut864

I still need to learn to read and interpret fuel trim.

As for custom exhaust. You are correct. No cats, 2 front o2 sensors disconnected. It has the 2 rear ones right before the mufflers.

Not am exhaust guy but a friend of mine said the rear o2 were in the wrong place and it needs an o2 sensor delete.

Otherwise, I'm still in the same place.

It's now having some idle issues once in awhile. Just a stumble.

6 grand rpm in park sounds perfect.
Put it in drive and 3 grand its bucking like a bronco.

I haven't had time for it lately. Maybe some time this week I can take another look.

Derf00

It sounds like a tune issue....fuel trims are easy to read. Long term on both sides should be +/- 5... 7 MAX. Short term should be +/- 10 when you blip the gas. If the O2 sensors are in the wrong spot, start ther, then
look at fuel trims.

https://www.mechanic.com.au/news/und...rm-fuel-trims1

walnut864

I'll check it out tomorrow of nothing else comes up.
Do you think it could be a tune issue even with replacing the ECU?

That's the one part I told him if I was gonna toss money at a problem it would be that.
ONLY because previous owner spliced both wires to coil 5 and when he taped them up the bare wires were making contact.
The new ECU got rid of the weird reading the cylinder Contribution test was showing. Which was a solid 157 on #5 that didnt fluctuate with throttle. It wasn't a nega negative number either. Just 157.

Derf00

Oh right, forgot about the ECU swap. That rules out the tune. Are you on stock injectors (19 lbs) or are they a higher rating? Again, fuel trims will help you better see what is going on. A higher than expected/normal flow rated fuel injector will have the fuel trims deep into the negative as the ECU keeps trimming the fuel back.

Still, fix the O2 sensor placement and see where you land with that.