Need help troubleshooting an engine issue: (vibration/miss at WOT, low rpm) - Ford Mustang Forum
 
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post #1 of 11 (permalink) Old 01-02-2013 Thread Starter
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Need help troubleshooting an engine issue: (vibration/miss at WOT, low rpm)

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
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
CJ competition pulse ring
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.


2011 Mustang GT: Brembo, 401A, Hids, 3.73's. Flowmaster Hushpower AB, Roush Springs, CS/Boss bumpers

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post #2 of 11 (permalink) Old 01-02-2013
glock22357
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My WAG would be a bad coil-pack.

Good luck, I hope you find the gremlin and banish it quickly, I bet you're frustrated all to hell and back.

post #3 of 11 (permalink) Old 01-02-2013
luckypony
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Ah the joys of a modded car. Good luck.
 
post #4 of 11 (permalink) Old 01-03-2013 Thread Starter
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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

2011 Mustang GT: Brembo, 401A, Hids, 3.73's. Flowmaster Hushpower AB, Roush Springs, CS/Boss bumpers

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post #5 of 11 (permalink) Old 01-03-2013
Grimace427
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I took a few notes and will take some time coming up with a few ideas. The first that popped to mind was the cat delete pipes. I threw a set on(they were BBK, I know the quality difference) and immediately felt a vibration exactly as you described, mainly low rpm, under load. After a few weeks I reinstalled the stock cats and the vibration disappeared. Fast forward a few months and I installed a set of longtubes and still no vibration.

I can understand you probably have thousands of miles on them without a single problem only to have an issue pop up this time around. The stock cats are aligned with thick studs but as far as I know the cat delete pipes rely on bolts to fasten them to the rest of the exhaust. Having had the engine in and out of the car a few times leaves several opportunities for the pipes to become misaligned and cause a vibration.

Just for shits and giggles throw the stock cats on and drive for a few minutes and report back if there is a difference. I will have a few more ideas later on. I really really hope you are not having an issue with the MMR engine. We both know their reputation over on S197forum, I hope that has nothing to do with your issue.


Clutch issues would be a PITA to diagnose due to the effort to gain access. I would think a balance issue with the dual plates would present itself just by revving it. Have you launched it yet with that setup? Put some heat into the clutch? Any chatter or rattles at low speed and very low load?
post #6 of 11 (permalink) Old 01-03-2013 Thread Starter
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This definitely feels like a stumble and loss of power. I replaced the bolts the deletes came with some better grade hardware. However if I can't figure anything else out I'll try that.

also, here's the driver's bank of plugs:


2011 Mustang GT: Brembo, 401A, Hids, 3.73's. Flowmaster Hushpower AB, Roush Springs, CS/Boss bumpers

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post #7 of 11 (permalink) Old 01-03-2013 Thread Starter
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well well, lets hope it was this:

2011 Mustang GT: Brembo, 401A, Hids, 3.73's. Flowmaster Hushpower AB, Roush Springs, CS/Boss bumpers

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post #8 of 11 (permalink) Old 01-03-2013
Grimace427
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If that isn't it(and I hope it is), next step would be to check injector and intake seals. I went from the wrong angle, if the problem is a hesitation/sputter/loss of power I'd follow the intake side of things. When installing the injector seals hit with a copious amount of silicone spray. Intake seals should be dry.
post #9 of 11 (permalink) Old 01-03-2013 Thread Starter
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That was it. Time to try out the gopro 240fps mode in the plugs' impending demise.

2011 Mustang GT: Brembo, 401A, Hids, 3.73's. Flowmaster Hushpower AB, Roush Springs, CS/Boss bumpers

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Quote:
Originally Posted by chris_red_v8 View Post
That was it. Time to try out the gopro 240fps mode in the plugs' impending demise.

Sweet! I have been envious of your car for a while now. One of your photos at Chuckwalla was my desktop photo for a while.









No that's not creepy.
post #11 of 11 (permalink) Old 01-04-2013 Thread Starter
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Quote:
Originally Posted by Grimace427 View Post
Sweet! I have been envious of your car for a while now. One of your photos at Chuckwalla was my desktop photo for a while.


No that's not creepy.
I hope to take it back there soon and see the difference in driving.

2011 Mustang GT: Brembo, 401A, Hids, 3.73's. Flowmaster Hushpower AB, Roush Springs, CS/Boss bumpers

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Driver/Captain: audistyleracing . com
Photographer: rolex24pics . com
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