Supercharged Roush Mustang stutters, stalls right after shifting gears and giving it gas

I have a problem with my 2012 Roush Mustang. I recently upgraded everything along the air flow path, injectors and new custom tune, and now it stalls when I shift gears at WOT and it dies or has erratic idle after I shift from gear to neutral while cruising

I’ve blown some smoke up the air intake tube, but could not find any vacuum leaks, maybe vacuum only leaks under engine load, while I am driving, because cat temps run really high when I give it gas, not sure

It was fine before the air flow and injectors upgrade. Here is a list of what I changed:

Throttle body: from stock ford 60mm twin to VMP 67mm twin

Supercharger elbow: from stock roush to VMP high flow elbow (ported)

Intake tube: from roush 90mm to JLT 95mm tube

Injectors: from ford racing 47lb to injector dynamics 1000’s 98lb injectors

Coil packs: from ford stock to granatelli extreme coil packs

Fuel type: from 93 to 98 octane

MAF sensor is clean

Installed 2 oil catch cans: one for the engine manifold and one for the air intake tube

Everything else is stock

New Tune: XP racing tune

Dyno results: 640 rwhp and 530lb/ft rwt

I’ve not seen any posts linking acceleration stuttering to any of the upgrades above. Does anybody have an idea or a lead I can follow to try and get to the root of this issue?

More than likely that JLT CAI is the problem. Put the roush back on and have your tuner update your tune. That CAI is known to have issues. Or find a different tuner who can tune that CAI like Lund.

do you have the MAF installed correctly? Could also be the new tune.

I'd start with reinstalling the tune.

I had that problem on my old 2012 tvs with the JLT CAI. The JLT was tuned by two different tuners who are both very well known (Lund & AED). The surging, stalling, ect, sometimes the car would die as well. Lund was able to get most of the bugs out but it still had it's issues. I went to a Roush CAI and had them both retune the car and not one issue after that from either tuner and the car ran flawlessly.

The MAF is installed correctly, since there's only one way to install it. I will probably run one more test this coming Friday to ensure there is no vacuum leaks before I travel 200 miles and take the car back to the tuner
There's something I stop thinking about: fuel pump. I still have the stock one (12 GT), but fuel pressure has been running 55-56 psi, A/F ranges from 13.5 to 14.5
Could it be the fuel pump not being able to keep up with the demand or that would have been an issue when tuner was tuning it on the dyno?

If everything is installed correctly, it's tune related.


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Subbed. Mine doesnt die, but under gradual acceleration, its rough. Vmp has tried numerous attempts and got it slightly better, but its still annoying.

Got a P0300 code which jives with unmetered air sneaking in
Can this be also the infamous cylinder 8 issue with S197's?
Here are a couple of pics of the gauge I just took with car at idle





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I ran 123mm jlt intake with my VMP tune and no issues. They should be able to figure it out with a log. The p300 is a misfire code and sound like you need a crank relearn done or the oring upgrade on cam position sensor.
Do you have an sct4?

I have the original SCT, but not the 4
I really wanted to keep my JLT CAI, but I have heard they are known for creating tuning issues. I also read that one of the many possible causes of code P0300 is vacuum leaks, which causes hesitation
Why do you ask about SCT4?

Sct4 can do a crank relearn where as the 3 can not.

The other possibility for the hesitation under boost after shifting gears could be carbon build up. I know my Roush has only 12k miles on it, but it has been some serious combustion issues recently that even caused of my O2 sensors to go bad. I'm wondering if that also caused carbon to build up inside the upper engine areas, even though I run pure, non ethanol 98 octane gas. Has anyone ever used the infamous Seafoam product? is it possible to do it safely in the SC car? do you have any pictures of where and how you poured/sprayed it in? I am thinking of doing this tomorrow, before I replace my old spark plugs and change oil/filter. Thoughts?

Just drive easy with the seafoam because when I added to my vmp stang, it didn't like it. Seemed like I was driving on crap gas until I burned through that tank of gas. The idle was ruff and it seemed down on power.

I did not seafom it. Everyone says there is no way my car has carbon deposits to worry about. So now I am at the point where I am going to start investigating the last item on the check list before I take it back to the tuner: O2 sensors
The hesitation under boost right after I shift gears and give it gas could be because it is starving for fuel at that exact point. I have a stand alone AF sensor, but readings are normal there, very close to commanded ratio
Also I noticed car jerks at steady speeds. Signs of bad sensor? In this instance both short and long fuel trims were super positive high, double digits
I have aeroforce gauges that read sensor signals from the OB2 in millivolts
How do I test my o2 sensors to see if they are faulty? What else can I do to either confirm the culprit are the sensors or rule it out altogether?


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Replaced O2 sensors. Nothing happened
Issue is in the tune after all
I am not sure what decision to make:
1. Spend $500 to trailer the car to the inexperienced tuner (on top of the $640 I had already paid to have it custom dyno tuned): Pros: dyno tuned, Cons: tuner will not give me the tune, so I have to spend $300-$500 to go and see him every time I need to adjust something
OR
2. Spend $550 to have John Lund create a new tune and email it to me. Pros: experience, can be done over emailing, $0 cost after the initial fee, Cons: no dyno


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Update:
Tuner does not know what he is doing. This place XP Racing in Oklahoma City has your typical dynotuners who can only tune WOT and nothing else, because it is easy and a quick turnaround
Car drives like crap while cruising below 3k RPM
I just purchased a custom tune from VMP Performance. Waiting to arrive
Hope this will work


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I have the VMP 675 HP upgrade on mine which includes their "canned" tune. Car drives fine 99.9% of the time but when the outside temp is <60, I get occasional stalling (at least 10-15 times in the past 1 1/2 years since the install) for no apparent reason. Usually it is when I first start it up after sitting cold, drive, and come to the first stop light or stop sign on the way to my destination. Sometimes it happens 1x, others it happens 3 or 4 times. It happens when I shift into neutral and coast to a stop AND when I use the transmission to slow down to a stop. Car comes to a complete stop, tach needle fluctuates up and down a little from idle, then drops to zero for a stall. I need to datalog it for them to look at it, but currently only have a work laptop with a lockdown on file transfers via USB ports.

madscotsman said:

I have the VMP 675 HP upgrade on mine which includes their "canned" tune. Car drives fine 99.9% of the time but when the outside temp is <60, I get occasional stalling (at least 10-15 times in the past 1 1/2 years since the install) for no apparent reason. Usually it is when I first start it up after sitting cold, drive, and come to the first stop light or stop sign on the way to my destination. Sometimes it happens 1x, others it happens 3 or 4 times. It happens when I shift into neutral and coast to a stop AND when I use the transmission to slow down to a stop. Car comes to a complete stop, tach needle fluctuates up and down a little from idle, then drops to zero for a stall. I need to datalog it for them to look at it, but currently only have a work laptop with a lockdown on file transfers via USB ports.

Click to expand...

Mine is doing that too. What CAI and TB do you have?


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nuacr0s said:

Mine is doing that too. What CAI and TB do you have?

Click to expand...

I have the JLT 123mm CAI that came with the kit and the stock TB.

I'm not looking forward to dealing with VMP again now based on my recent experience with trying to get an updated tune. Its been almost a month since I requested and paid for a updated tune so I could install their fuel pump booster I purchased. Their site says 7-10 business days for a tune update unless you paid extra $$$ for the rapid turn around (WTF?!?). Called last Friday for a status update and they said my original tune was in their old system and they were trying to locate/extract it. Must be on cassette tape or 8mm reel to reel!!!!!

Cant imagine how long it's gonna take for them to go through and evaluate and update a tune from datalogging if it takes over a month to make some minor adjustments in a tune to the Fuel Pump Voltage tables........