sputtering at higher boost

[dale187]

just bought a 99 gsx wednesday drove 250 miles to pick it up. everything was fine when i got there EVERYTHING. was on the way home and went to get on it and as soon as it would hit higher boost it would start bogging and sputtering pretty bad. it has a 16g and aftermarket bov, and adj fpr. i tried setting my base fuel pressure at 43. and then at idle it drops to 33 and im pretty sure its supposed to be between 37-39. so i might have a minor vacuum leak.. enough to bog that hard? anyways the car looks like it has been sitting a while in that case i havent got the chance to change plugs and wires etc. anything else it could possibly be? it has a exhaust leak at the down pipe after the turbo so im sure thats not a problem. if anyone could help me be appreciated.. thanks

 

[pj91gsx]

what kind of fpr do you have on it? When you set the fuel pressure you are supposed to take the vacuum line off then adjust it then put the vacuum line back on. the fuel pressure needs to be 43 psi for 2g.

 

[dale187]

have no idea what kind it is, like i said just bought the car and been extremely busy havent had too much time to tinker with it

 

[pj91gsx]

If its not a good one like aeromotive or fuelab. Then it maybe ebay stuff. The ebay fpr are no good. If the fuel pressure regulator is not you problem it would be a boost leak, but it sounds like you probably hitting fuel cut when you are at high boost because you fuel pressure isn't right.

 

[romeen]

Welcome to the site.

The fuel pressure will drop 1psi for every 2inHg of vacuum. Your idle fuel pressure of 33psi suggests a vacuum of 20inHg which is completely normal. Your good on the fuel pressure.

You may be getting misfire under load. Check plugs and wires. Make sure plugs are gapped to .028"

Also make yourself a boost leak tester as described in the tech section and learn to use it. It should become part of your regular maintenance and will keep your car running strong.

 

[tbonitz301]

I believe that with the vacuum line on it should be around 37psi,but you are supposed to set base fuel pressure with the vacuum line off. I would do a boost leak test. What plugs are you running, and what are they gapped at?

 

[dale187]

like i said i havent changed the plugs. someone was telling me i should be running the vvpr 7s. so im getting those soon. and yea i set the base fuel pressure with the vacuum line off. is 43 right for the base fuel pressure?

 

[fatherbubble]

Hmmm sound like stock injectors. At 16lbs of boost you hit 108% an then your fuel pump goes into over drive. an after that happens your injectors start messing up an you get your problem you have now.

 

[tbonitz301]

43 is correct for base fuel pressure. The plugs you want are NGK BPR6ES gapped to .028. Unless you are running more than 17psi then you would want BPR7ES's gapped to.028. I consider .028 a starting point to gap them out. Personally i had to close my gap to .020 to avoid the sputter, but im running 24psi on a 16g.

 

[romeen]

like i said i havent changed the plugs. someone was telling me i should be running the vvpr 7s. so im getting those soon. and yea i set the base fuel pressure with the vacuum line off. is 43 right for the base fuel pressure?

The plugs most commonly recommended are the NGK's. Most guys recommend BPR6ES's for boost pressures under 17-18psi or the BPR7ES's for higher boost pressures.

Yes, you remove the vacuum line to the FPR and plug the end of it when setting base fuel pressure. Technically it should be 43.5psi for a 2G, 43 is close enough. When you reconnect the vacuum line the fuel pressure will drop. The amount of drop depends on the vacuum level as I described above.

 

[BlackdOutGST]

Had EXACT same problem with my 95 GST right after I bought it. Bad Boost Controller. Switched controllers with a buddy who had a Greddy controller and instantly fixed problem. I hooked up the boost lines factory and also fixed the problem until I could get a better controller. Try just taking the boost controller out of the picture for a sec and see if that works, its fast and simple to try first.

 

[tbonitz301]

Hmmm sound like stock injectors. At 16lbs of boost you hit 108% an then your fuel pump goes into over drive. an after that happens your injectors start messing up an you get your problem you have now.

Not neccesarily. I ran my 16g at 16psi before i got my supporting mods, and it was fine. I did have my fuel pump rewired. I dont believe his high IDC's are contributing to his problemI know of people running in excess of 120%injector duty cycle with no problems. I'm not saying that its a good idea

 

[tbonitz301]

Had EXACT same problem with my 95 GST right after I bought it. Bad Boost Controller. Switched controllers with a buddy who had a Greddy controller and instantly fixed problem. I hooked up the boost lines factory and also fixed the problem until I could get a better controller. Try just taking the boost controller out of the picture for a sec and see if that works, its fast and simple to try first.

Of course running wastegate pressure(lower boost)will hide some misfires, and some boost leaks.

 

[pj91gsx]

I believe that with the vacuum line on it should be around 37psi,but you are supposed to set base fuel pressure with the vacuum line off. I would do a boost leak test. What plugs are you running, and what are they gapped at?

When you set the fuel pressure do I take the vacuum line off and set the fuel pressure to the base pressure then put the vacuum line on or do I need to make the fuel pressure read what the base fuel pressure is at idle?

 

[tbonitz301]

When you set the fuel pressure do I take the vacuum line off and set the fuel pressure to the base pressure then put the vacuum line on

Yes, romeen's post is more descriptive if you wanna take a look

 

[pj91gsx]

well I set mine wrong good thing I didnt put too many miles on it.

 

[tbonitz301]

True that

 

[dale187]

the boost controler that is on there does look ran down. i thought that could be an option ill have to try redoing it...yea i set the base fuel pressure at 43 is it ok to drop to 30-33 at idle?

 

[shaggy4267]

I just had the same issue with mine. Replaced plugs and gapped to .28 Worked wonders!

 

[dale187]

No one here local sells the BPR6s can i use the 7s even though i'm not running at the boost levels it requires?

 

[pj91gsx]

My friends car wouldn't start with 7s and we threw in 6s in his car cranked right up. Extrempsi.com has ngk plugs.

 

[dale187]

Ok cool. Is there anything else major i should worry about as to why it's sputtering that bad other than the little things you guys have describeD?

 

[tbonitz301]

Nope. You should be good to go. 90% of the time the sputtering can be fixed for about 20 bucks wether it be plugs or a boost leak. Napa usaully stocks the BPR6ES's if you have one close by. Good luck, and let us know what fixed your problem

 

[dale187]

Ok thanks a lot and ill be sure to let you guys know. Also 1 more question. The intercooler was never upgraded still the stock side mount. Could that be another thing adding to this problem ?

 

[tbonitz301]

I run 24psi on a stock sidemount with surprisingly low intake temps, never more than 90* which is awesome. Lower than most people with front mounts. By no means am i saying that you should run that much boost through the sidemount. I'm getting away with it somehowI'm fairly certain that you are going to find some boost leaks, and your plugs probably need changed. Don't worry this is a very minor thing as far as getting the car to run right.If you need any help feel free to pm me.