Slight problem with tuning

[biglady112]

Well after my dyno runs last week, the car has been studdering on pump gas. The motor will studder and make a funny noise like its holding back or cutting something out. Ive tried anywhere from 16PSI to 22PSI. And i've richened it up and leaned it out on top end but there is no difference. It does it usually at full throttle from a roll. Some times it does it if i go at it from a first gear roll some times it doesnt. It is even more prominent when its cold. When i did my dyno runs on pump gas i wasnt having this problem. But the fuel pressure was turned way up from where it is now. its at 24psi at idle. was at about 44psi at idle. am i experiencing fuel cut, leaning out issues, or rich issues.
680cc's, cozmo fuel pump, buschur stage 3 block/head and 60-1
those are the mods
steve

[ryanman]

Did you intentionally set the fuel pressure to 24 psi?





If not I'd say you have a problem with either pump or regulator and therfor not getting enough fuel and running lean.

[biglady112]

Buschur had it set in between 41-44 psi at idle. that was that way for all my runs on pump gas before i put in the leaded gas. after about 12 dyno runs is when i started to turn the pressure down. right now it at about 24psi at idle. i have the sx fpr so its boost dependent. the car was running pig rich when i picked it up form buschur ie- 5:1 on the air to fuel. or at least i think so. it was off the charts. black smoke would come from the exhuast worse than any other car ive ever seen. any way. not sure if i need to turn it back for pump gas. right now boost is at about 18psi. gonna run some 44k through the fuel system in the next week. gonna try two cans to see if it will fix something. any other thoughs?
steve

[fusionsport]

if the car was tuned at 44 psi fuel pressure and you lowered it I would think thats a huge part of the problem. 24psi seems really low to me.
What sort of "tuning" device do you have and where was it dynoed?

[biglady112]

VPC/GCC. i dynoed at MAC. on the leaded gas i couldnt make more than 265 hp corrected without lowering the fuel pressure. it was running off the charts rich as i said above, but when i finished it was at about 11:1. couldnt get and more lean because i couldnt make over 25psi(stock cams, intake/exhaust manifolds, ignition). but it was running great turned the boost down for pump gas and she started sputterng. maybe i should get my calculations and settings for race gas( write them down) and turn fuel pressure back up. have a logger, but it knocks like crazy on pump gas no matter what, even after it was tuned on the dyno, i think it may just be phantom knock and the fact that pump gas pings really bad. I think im leaning out with this situation but the car still blows black smoke when i boost(raw fuel). I guess i'll tinker with the fuel pressure unless anyone else has had similar problems. car runs hard but when i get on it from a role it does this. it almost feels like boost cut but with this much boost and fuel im confused. BUT, at these same settings on quality gas no problems at all. not even a hiccup at 25psi. i dunno?
steve

[v413nc3]

You really shouldn't run lower than 35-36psi on pump gas for fuel pressure. In all honesty you need more to tune your car than what you have, but that is a different story entirely.

[fusionsport]

1) running your fuel pressures that low leads to improper spray patterns, "puddling" and other injector issues

2)if you cant get lean enough it is better to reduce injector on time or size rather than reduce fuel pressure- higher pressure=better spray pattern= better combustion which is much better for boosted cars-

if you need help tuning dont be afraid to ask, just be careful about who you do ask, since there are some people around who shouldnt be tuning a lawn mower, let alone a dsm

[biglady112]

well i richened it up in the middle rpm range and fixed the problem. i turned the fuel pressure back up and it runs ok. buschur rold me running a little rich wont hurt. like i said before, on the dyno i couldnt make to high a boost. but ill fix all my breathing problems soon. some tuning help would be nice, i think i have the VPC/GCC figured out. on pump gas the car doesnt run too good. but i think she'll be under control when i go to bandimere in two weeks. but just need to get a street map figured out

[biglady112]

actually double checked and fuel pressure was at 28PSI ay idle.

[KeltonDSMer]

I thought HKS only made chips for the VPC for stock and 550cc injectors.

[v413nc3]

28 @ idle @ 15in/hg vac should be about 41psi base fuel pressure.

[biglady112]

we never thought to watch the fuel gauge when we were running, we were to busy watching everything else. but yea that sounds right for fuel pressure. my vacumm is normally around 15-17 in/hg. But the chip is a buschur chip. not sure on the HKS chip and wha they have, but it came with a 550 when i bought it and buschur worked their magic.

[KeltonDSMer]

That's awesome those guys were able to do that. They have been using the VPC since Tym broke into the 10s.