performance/tuning
talontsi26
08-08-2006, 11:16 PM
I just intalled dsm 450 injectors, walbro 255 fuel pump, fuel lab regulator and an safc2 in my stealth rt tt. I turned the corrections down to about -22 for high throttle because this gave a an air/fuel ratio of 11.9 on my wideband, but when my car reaches about 15 psi it starts stumbling really badly. What could be the cause of this stumbling, could it be fuel cut, fouled plugs or are the stock turbos just not able to go above 15 psi? I also had a question about the fpr, I started the car and adjusted the fuel pressure to 43 psi,which is stock fuel pressure, but when I reconnected the vacuum line the pressure drops to 30. Is this normal? I was also wondering if anyone knows how to use the knock feature on the safc2? Thanks ahead for any help!!
Igovert500
08-08-2006, 11:34 PM
Don't have an safc, so I can't help you there. STock turbos are pretty much worthless after 15psi. They only hold 10psi to redline, so when you start upping the boost, basically it is only for a partial part of your powerband. Anything over 15psi, and you are basically just blowing hot air. Some would argue 17psi, but you get the point.
Stumbling...is it like an on and off hesitation...I'd first guess spark plug blowout. What plugs do you have and what are they gapped at? Throw in some copper NGKs and gap them to .32, if you still have the problem, put them down to .28
The fuel pressure should be 38psi under vacuum and 43psi without vacuum. So 30 is definantly low. Dunno what's causing it, but pressure testing the intake for vacuum/boost leaks would be a good idea.
Stumbling...is it like an on and off hesitation...I'd first guess spark plug blowout. What plugs do you have and what are they gapped at? Throw in some copper NGKs and gap them to .32, if you still have the problem, put them down to .28
The fuel pressure should be 38psi under vacuum and 43psi without vacuum. So 30 is definantly low. Dunno what's causing it, but pressure testing the intake for vacuum/boost leaks would be a good idea.
talontsi26
08-10-2006, 03:15 PM
I have nkg iridium spark plugs, but I've had them in for about 1 year now
Igovert500
08-10-2006, 03:59 PM
Fuel cut is usually pretty abrupt. Some say it is semi-violent. I have only hit fuel cut in our Subaru, not my vr4, so I dunno, but if it were ignition related, ie spark blowout, it would be more of an on and off hesitation.
Are you datalogging by any chance?
My guess is spark blowout. Iridiums aren't as good as coppers when it comes to boost. Basically the coppers produce a better spark at the same gap. While iridiums aren't technically supposed to be gapped, many do gap them...CAREFULLY. Jsut because you had them in for a year and they ran fine, probably just means this recent additional boost is probably enough to blowout the spark. Try gapping them down a bit or switching over to coppers.
Are you datalogging by any chance?
My guess is spark blowout. Iridiums aren't as good as coppers when it comes to boost. Basically the coppers produce a better spark at the same gap. While iridiums aren't technically supposed to be gapped, many do gap them...CAREFULLY. Jsut because you had them in for a year and they ran fine, probably just means this recent additional boost is probably enough to blowout the spark. Try gapping them down a bit or switching over to coppers.
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