Running Out of Fuel?

[GSXDNA]

I have a 99gsx, totally stock with the exception of a 1G BOV and a 3" turbo-back exhaust with no cat. When I go WOT, boost will peg 15-16psi briefly, then settle to a constant 12psi until it falls off to 9psi by redline. When boost goes much past 13psi, the engine will have this series of split second hesitations. It almost seems like either the engine is either running out of fuel, or so much fuel is being dumped in that it's causing the engine to choke up.

As long as I modulate the throttle around where the boost would normally hit 15psi, the hesitation dissappears. What do you guys think? Too much fuel, or is the fuel pump maxed out?

Thanks.

 

[snowborder714]

Do a boost leak test.

 

[crimsondragon]

I think a boost leak test should be in order.

 

[GSXDNA]

Do a boost leak test.

A boost leak test? The car is building boost just fine. A quick spike to 15psi, settling at 12psi, then dropping off to 9psi by redline is perfectly normal for a stock GSX. My question is, when the car does build more than 12-13psi, the motor hesistates/stutters, as if it is either running out of fuel or being given too much fuel. Which scenario is most likely?

 

[GRAVEDIGGER]

When is the last time you changed your spark plugs and wires? Sometimes this will cause your car to misfire at the higher boost levels, while running fine at lower boost. If you haven't changed them in a while it may be worth a try first to see if that helps.

 

[jm1080]

A boost leak test? The car is building boost just fine. A quick spike to 15psi, settling at 12psi, then dropping off to 9psi by redline is perfectly normal for a stock GSX. My question is, when the car does build more than 12-13psi, the motor hesistates/stutters, as if it is either running out of fuel or being given too much fuel. Which scenario is most likely?

change spark plugs. Same thing happened to me, in high boost it would hesitate, but I had platinums. When I switched them out to the required NGKs no more hesitation.

 

[GSXDNA]

When is the last time you changed your spark plugs and wires? Sometimes this will cause your car to misfire at the higher boost levels, while running fine at lower boost. If you haven't changed them in a while it may be worth a try first to see if that helps.

Awesome...that's the kind of answer I was looking for! I just purchased the car a few months ago with 75k on it, so it's likely been a while since the spark plugs/wires have been replaced.

I was thinking about going with a colder spark plug. Any recommendations?

 

[GRAVEDIGGER]

Yeah, go ahead and go with the colder NGK's. The BPR6ES is what is the normal heat range, but if you want to go colder you will want to run the NGK BPR7ES plugs. That is what I run and I think most others go with those also.

 

[TSi_with_psi]

I have experienced the exact problem that you were describing and it was the spark plugs. I had platnium plugs that were gapped incorrectly. once i put NGK BPR6ES plugs in and gapped them correctly the problem went away.

 

[GSXDNA]

I have experienced the exact problem that you were describing and it was the spark plugs. I had platnium plugs that were gapped incorrectly. once i put NGK BPR6ES plugs in and gapped them correctly the problem went away.

Great, thanks for all the info guys. What should they be gapped to?

 

[GRAVEDIGGER]

.028" That should be how they come. Nine times out of ten they will be right on.

 

[snowborder714]

I was thinking about going with a colder spark plug. Any recommendations?

I would stick with the BPR6ES since you're running a stock setup. The 7ES's (one range colder) are for when you're pushing 18+psi.

Yes, the spark plugs come pre-gapped as gravedigger said above, but please double check this or close the gap and regap them. Better to know they are dead on than assume they come gapped correctly.

And just because you're building boost fine doesn't mean you don't have any leaks. Some may be so small you wouldn't really notice. I would still perform a boost leak test at the turbo and throttle body just to make sure. It can't hurt anything.

 

[GSXDNA]

I would stick with the BPR6ES since you're running a stock setup. The 7ES's (one range colder) are for when you're pushing 18+psi.

Yes, the spark plugs come pre-gapped as gravedigger said above, but please double check this or close the gap and regap them. Better to know they are dead on than assume they come gapped correctly.

And just because you're building boost fine doesn't mean you don't have any leaks. Some may be so small you wouldn't really notice. I would still perform a boost leak test at the turbo and throttle body just to make sure. It can't hurt anything.

I've actually already done a boost leak test when I first bought the car a few months ago. I found out that the stock 2G BOV was leaking like crazy, so I bought a 1G BOV.

And I'm not sure I agree with your statemtent "just because you're building boost fine doesn't mean you don't have any leaks." If the boost is where it should be, then there likely are no leaks. And my boost is right where it should be for my setup, so I don't really see the point in trying to find a tiny leak (that likely doesn't even exist) to raise my boost .1psi. But, thank you for the suggestion.