CaptDistraction

I can't figure this one out. Since I last installed this motor (I've had it out once for rebuild, and once again after the build to adjust a number of things), I've had this weird vibration/hesitation/miss at WOT in higher gears at lower RPM ranges (anything sub 3000 and presumably higher but I'm afraid to stay in it). Car is smooth otherwise, including high RPM operation.

I've checked the following:
-Verify that the motor mounts and trans mount were tight
-Unplugged knock sensors to see if it was timing being pulled (I have monitoring gear, timing did not change with the sensors unplugged) Its possible the banks are flipped due to the harness, but it seemed like it only went on one way for the two sensors
-Switched tune revisions, and try a previous tune from another vendor
-Tested on two throttle bodies

During this time the spark advance is usually between 15-17 degrees, AFR around 12.2. No codes, which is frustrating, coolant temp of 179. Car drives fine all day long outside this issue. No abnormalities on the highway when cruising.

I did find a leak in the inlet tube after the maf and before the throttle body, but I've resolved it and while the engine runs more smoothly at wot, its still breaking up.

The builder believes this could be the clutch having a weird wear issue (and there's merit to the thought as I used a mcleod RXT on a stock flywheel, which wears the overhang 1" or so on the inside of the flywheel disc). However the more I test this, the more I feel like its engine management or something in the motor. It also happens close to wot, but I believe these cars consider over 80% as wot? I am not terribly educated on the subject but wouldn't any sort of misbalance in the clutch or any part of the rotating assembly show itself at more than just wot?

I'm going to clear the memory on the car, reprogram it with the latest tune I have from AED, and do some datalogging. Additionally, I'm going to feed the car some 100 octane (as I just use 91 per the tune and availability) in a blend to see if this is knock-retard.

After logging and sending the logs off, the next step for me should be to take the car to a shop or dealer to have them run it through their diagnostic processes as I have no idea what could cause this.

Anyone have thoughts? The engine build is below:

MMR 1000 shortblock, 11.5:1 compression
Boss 302 heads
Boss 302R exhaust cams (the factory boss 302 cam)
Boss 302 intake
JLT Cold air intake
CJ competition pulse ring (just added on last install)
Accufab throttle body
fresh o2 sensors
stock ford plugs (gap unmodified from box, though I thought the instructions say not to alter those?)
stock coils
AED tuning
stock exhaust manifolds
jegs cat deletes
stock mounts

I'm at my wit's end, just can't figure this out. Any help is appreciated, this is the last thing between me and enjoying my car.

going for broke

Hmmm. I wonder if you have either a weak/bad plug or if you have one that is gapped to far and it's being "blown out"?? The latter is usually only something seen on a boosted application though.. I would start with the simple stuff.. Fuel pressure, spark and air.

CaptDistraction

So the new plugs come out of the box at 0.051" gap. How does that sound? Should I gap them closer or leave them alone and install as-is? I haven't removed the existing plugs yet.

Here's an interesting excerpt from the Boss302S manual:
Spark Plugs
BR3E-12405-DA (Heat Range 1) or M-12405-M50 (Heat range 0)
SP519-Motorcraft
GAP= 0.04 (1.0 mm)
Replace after every 6 hours of usage

CaptDistraction

Its fixed:




All that trouble from one little plug

stangfoeva

Duh! I coulda told you that!

going for broke

Your welcome.. Hehe