Idle misfire/ boosted car tuning help

SlowSix01

Active Member
Having some trouble with the idle on my car. It is misfiring and the fuel trims are all wonky. 3.8 v6, IMRC deleted (ported lower intake), EGR deleted, Windstar (different upper intake), TMA single turbo kit. Deatsch Werks 340 lph fuel pump. 39# injectors.
05+ GT slot MAF with a diablo MAFia in a 3" tube. Cold side piping is all 3 inch from the turbo to the intake.

Car has new ntk O2 sensors on both sides, new motorcraft coil pack, new autolite wires, new tr6 plugs gapped at .028. 39# cobra blue injectors. 340 lph pump. New frps, new crank sensor.
The car misses at idle up to about 2000 rpm. Runs great under boost.
My tuner and I both can't figure out the issue.
Checked injector harness with a noid light, fine. Checked plugs, look okay. Checked wires, they were okay.
Car seems to have good compression, oil looks good, coolant looks good.
Timing is around 40 degrees at idle. Tuner backed it off to 20 and it missed worse.
Bumped it to 50 and it stayed about the same.

The miss is always cylinder 2 or 3. Runs great wot, AFR then is typically about 11.3ish.
Previous plugs I pulled looked fine.
MAF counts on the tune look good.

Fuel trims on the car at idle are as such
passenger side - bank 1 - bounces around .80, which is lean.
Driver's side, bank 2 - bounces around 1.20, which is rich.
The miss is on the passenger side. No real difference forcing the car open loop.

Tried swapping injectors 2/3 with two different 39# injectors that we knew to be good. No difference. Don't think I'm maxing the injectors as they hold 11.3 to 11.4 all the way to the limiter in boost. When we tuned it they were fine on the dyno.
Strangely enough, pulling the fuel injector harness plugs off the 2/3 injectors didn't make the car go crazy, but pulling the harness off of the #1 cylinder injector made the car want to die.

Car was previously smoke tested for vacuum leaks, all good.

Thought maybe the o2s were plugged into the wrong side of the harness, but I don't think they could even physically reach the other side.

Tuner messed with various things in the tune for awhile, adding more fuel, less fuel, open loop, idle integration? tables, timing, and probably more.

We have a couple hypothesis
1. bad head gasket - Now, he couldn't find the end to his compression tester, but, pulled a plug and cranked it and cylinder 2 sounded like it had pretty good compression. I changed the oil recently and it looked normal, and the current oil is clean and the coolant doesn't look weird either. I plan on compression testing the car and seeing what I get.

2. May be related to my imrc delete. I originally tried filling the holes between the runners were the rod ran through them, with JB weld, but this failed under boost and left me with big vacuum leaks.
I ended up punching out the bearings, tapping the holes where they were, and threading a pipe thread cap into the rear of the intake, blocking off outside air.
I left the holes in between the runners open. Not sure if this may cause an issue or not.
pictured are the holes.



3. still could be something stupid tune wise, but idk what. or maybe even related to maf setup or something.

Thoughts anyone ?
I can provide data logs if anyone wants them, just let me know what PIDS you want to see.
 

6 Shooter

Well-Known Member
Several things. First, would pull the lower intake and plug/weld closed all of the IMRC holes. You do not want any air cross over which I suspect is happening and causing bank 1 and bank 2 A/F ratios to be very far off. Next, would switch to NGK BR7EF copper plugs gapped at .028". $2 each. They have a higher heat range than the TR6 plugs. If you motor digested JB weld, would do a compression test to verify no damage from the JBWeld material which got digested in the motor. That stuff would be pretty hard and may damage the rings.

From past experience, the V-6 Mustang computers are pretty sensitive to the brand of O2s used in the front. Suggest you get a pair of Motocraft front O2s (green ends) and use those which may be the cause of huge differences in A/F ratios from bank 1 to bank 2. Check with the Rock Auto website for reasonably priced Motorcraft front O2s. You should first data log the front O2 voltages to see if one of your O2s has gotten lazy or is half dead. Check the O2 wires from the sensors to the harness to look for burned/melted wires or wire looms. If you have been burning oil in the motor, that issue will kill O2 sensors.

Tune wise, the system switches for the rear O2s, the EGR, and the IMRCs should be turned off. Adaptive learning should also be turned off while tuning is occurring. My adaptive learning has been turned off for almost 10 years. Rear O2s have also been turned off for years, except for when the egr is plugged back in for an emissions test (one day). Have the tuner first tune the idle in open loop till the A/F ratios are about 14.2:1 at idle. Then, switch back to closed loop for fine tuning adjustments.

Trace plug wire 2 and 3 from the coil pack to the spark plug to make sure they are not switched. Turbo headers get pretty hot and can burn plug wire boots in a hurry. So, pull plug wires 2 and 3 and examine the plug boots carefully for cracks, melting, or burning. Be sure to rotate them 360 degrees under a bright light to make sure they have not failed. Also, pull plugs 2 and 3 and examine the ceramics to make sure they have not fractured and been digested in the motor. Also check plug wires 2 and 3 near the old EGR tube and at the rear of the head to make sure that the wires have not gotten cracked, melted or chaffed somehow which would cause misfires.
 

SlowSix01

Active Member
Several things. First, would pull the lower intake and plug/weld closed all of the IMRC holes. You do not want any air cross over which I suspect is happening and causing bank 1 and bank 2 A/F ratios to be very far off. Next, would switch to NGK BR7EF copper plugs gapped at .028". $2 each. They have a higher heat range than the TR6 plugs. If you motor digested JB weld, would do a compression test to verify no damage from the JBWeld material which got digested in the motor. That stuff would be pretty hard and may damage the rings.
Thinking the lower may be part of the issue. Don't know how easily you could get something in there to weld the holes shut. I would imagine it would be a bit difficult. Don't think the plugs are an issue. I had autolites in it before and the car seemed to like the tr6's more.
I plan on doing a compression test, but more so to look for a head gasket issue. I highly doubt the motor ingested any JB weld, as the car had little runtime on it before I removed the jb weld from the intake. And I've put 2500-3000 miles on the car since it was tuned.


From past experience, the V-6 Mustang computers are pretty sensitive to the brand of O2s used in the front. Suggest you get a pair of Motocraft front O2s (green ends) and use those which may be the cause of huge differences in A/F ratios from bank 1 to bank 2. Check with the Rock Auto website for reasonably priced Motorcraft front O2s. You should first data log the front O2 voltages to see if one of your O2s has gotten lazy or is half dead. Check the O2 wires from the sensors to the harness to look for burned/melted wires or wire looms. If you have been burning oil in the motor, that issue will kill O2 sensors.
Motorcraft o2s are made by NTK. The ntk sensors are the same. We checked o2 voltage and they were both fine, the wires themselves aren't melted or anything either.

Tune wise, the system switches for the rear O2s, the EGR, and the IMRCs should be turned off. Adaptive learning should also be turned off while tuning is occurring. My adaptive learning has been turned off for almost 10 years. Rear O2s have also been turned off for years, except for when the egr is plugged back in for an emissions test (one day). Have the tuner first tune the idle in open loop till the A/F ratios are about 14.2:1 at idle. Then, switch back to closed loop for fine tuning adjustments.

The rear o2s, EGR, and IMRC are all turned off. Tuner tuned the idle in open loop but the car still misses in open loop as well, so we can't quite dial down the AFR there either. He tried fattening the AFR up and leaning it out in open loop as well, with no real difference.

Trace plug wire 2 and 3 from the coil pack to the spark plug to make sure they are not switched. Turbo headers get pretty hot and can burn plug wire boots in a hurry. So, pull plug wires 2 and 3 and examine the plug boots carefully for cracks, melting, or burning. Be sure to rotate them 360 degrees under a bright light to make sure they have not failed. Also, pull plugs 2 and 3 and examine the ceramics to make sure they have not fractured and been digested in the motor. Also check plug wires 2 and 3 near the old EGR tube and at the rear of the head to make sure that the wires have not gotten cracked, melted or chaffed somehow which would cause misfires.
Checked the plugs and the wires. They're all fine. Plug wires are new from last summer, plugs have like 100 miles on them and aren't cracked or anything.

My responses are in red. I've addressed some of these things already.
 
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