07 GT500 sputtering with light throttle

Jeffk

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Got to love trying to diagnose issues for people without seeing the car and experiencing what it is they're trying to explain.

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07 GT500
52000 miles
Kooks Long Tubes w/catted X
Pro-Dyno tuned
VMP 2.5 pulley w/ 90mm idler
K&N CAI (yeah, he's aware that it's a choking point)

Apparently this was happening before the headers, pulley and tune.
He says that when he's accelerating car is fine, it's once you reach your speed and start to let off, the car bucks. He said it's not severe but it is noticeable.

I suggested a new fuel filter and some fuel treatment in the tank. Apparently his wife buys gas for the car wherever. I told him that's probably the culprit right there.


any other suggestions? Everything else on the car is stock.
 

19COBRA93

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I buy gas anywhere/everywhere, and I've never experienced anything like that. The only real way to find the problem is to datalog it. I would normally guess a tune issue, but if the tune didn't fix it, then it should be diag'd properly.
 

Jeffk

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He wanted me to call the tuner and ask him but since it was there periodically before the tune... plus I haven't driven or ridden in the car to experience the issue so that I can accurately explain it to anyone. LOL.

I don't know Sam, we have some shady, shitty gas stations here in the south.
 

AlbertD

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If it were my car I would either put the stock pulley back on or exchange that K&N CAI for one with a larger MAF housing (A JLT 110mm at a minimum). I would imagine since that K&N CAI doesn't require a tune that it probably has a similar if not the same MAF diameter as the stock intake... which is a big no no for a pulley setup imo.

As you said changing out the fuel filter as well as a set of new plugs won't hurt either.
 

Jeffk

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If it were my car I would either put the stock pulley back on or exchange that K&N CAI for one with a larger MAF housing (A JLT 110mm at a minimum). I would imagine since that K&N CAI doesn't require a tune that it probably has a similar if not the same MAF diameter as the stock intake... which is a big no no for a pulley setup.

As you said changing out the fuel filter as well as a set of new plugs won't hurt either.

When we took it to Pro-Dyno for the dyno tune Dan shook his head at the K&N before he started working on it but once he got into tuning it he said that it was actually working well and making good power. He said that eventually the owner would want to upgrade to a JLT though.

He said that he's going to change the fuel filter tonight and top off the tank at a higher volume gas station. I think that being it's so humid down here condensation builds up in the underground tanks if it's not cycled regularly? Maybe I'm retarded.
 

AlbertD

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When we took it to Pro-Dyno for the dyno tune Dan shook his head at the K&N before he started working on it but once he got into tuning it he said that it was actually working well and making good power. He said that eventually the owner would want to upgrade to a JLT though.

He said that he's going to change the fuel filter tonight and top off the tank at a higher volume gas station. I think that being it's so humid down here condensation builds up in the underground tanks if it's not cycled regularly? Maybe I'm retarded.

That certainly is possible. I had a horrible experience when I was living in South Texas... rained for a week straight, humid as hell, all while the GT sat outside with less than a 1/4 tank of gas. The gas ended up going bad and it fouled all my plugs. I had to pull the pump and siphon everything out and refill with fresh gas.

But... the symptoms I had where in all type of driving conditions, idle, accel, cruise, decel. For his car to only sputter on decel makes me thing it is tune related. As 19COBRA93 mentioned, if the fuel isn't the issue then some datalogs and tuner communication would be the next step.
 

Jeffk

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That certainly is possible. I had a horrible experience when I was living in South Texas... rained for a week straight, humid as hell, all while the GT sat outside with less than a 1/4 tank of gas. The gas ended up going bad and it fouled all my plugs. I had to pull the pump and siphon everything out and refill with fresh gas.

But... the symptoms I had where in all type of driving conditions, idle, accel, cruise, decel. For his car to only sputter on decel makes me thing it is tune related. As 19COBRA93 mentioned, if the fuel isn't the issue then some datalogs and tuner communication would be the next step.

I've some how become this guy's "tuner mediator"

I'm going to call Pro-Dyno later, I know they're going crazy getting ready for Mustang Week. I'm sure he'll want the car back down there so that he can see/feel what's going on.

Guy came back to see me and tried to explain it again.

"it's a spitting/spuddering once you get up to cruising speed and let off a little and it also happened to me at about 45mph. Last for a few seconds and then goes away. Sort of feels like running out of gas"

I wonder if there's ever been any issues with the gas pedal contacts on these cars. where there would be a "bad spot".

If it hadn't been present before the tune I'd be convinced it was tune related. I'm not saying it isn't though.
 

GallopingFord

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My best guess is plugs. I'm having some sputtering problems with mine that it just doesn't like to take off, etc. When was the last time he changed the plugs?

When I go to put the TVS on, I'm changing out injectors/plugs and coils (since some of them are mismatched). I hopefully isolate it.
 

Jeffk

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My best guess is plugs. I'm having some sputtering problems with mine that it just doesn't like to take off, etc. When was the last time he changed the plugs?

When I go to put the TVS on, I'm changing out injectors/plugs and coils (since some of them are mismatched). I hopefully isolate it.

As far as he knows the plugs have never been changed.

I told him to get the plugs and I'd install them when I was doing the headers but he didn't.
 

Gabe

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It's the K&N

A friend with an '08 GT500 had a K&N on his car and had similar issues.
Called K&N and they sent him a different tube, it still did it.

Switched to a BBK CAI, no more issues.


Just messaged him about this '07 ... "The air blast from the cooling fan screws up the MAF on some cold air kits. The BBK cold air kit I had worked perfect."
 
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Jeffk

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Hmm. That's interesting Gabe. I already got him a price on the JLT so maybe he will order one. I think there's a shield around the filter that should stop that but maybe not.
 

Gabe

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If he's really still running the stock plugs, he should really think about getting some NGK TR6's installed ... great plugs ... and only $1.79 each at AutoZone
 

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