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What fuel pressure to start at?
I put an adjustable regulator on my 86. I have an Autometer gauge(Sport Comp)on the cowl. When setting pressure(at idle with vacuum unhooked), what is a good setting to start with? My motor is stock except for normal bolt-ons. Right now it is at 44 with vacuum unhooked, then as soon as I hook the vacuum up it imediately goes to about 36-37. It seems like it might be rich. Plugs have bronze color to them. Any ideas? Thanks
John ------------------ John Welch 86 GT, 3.73's, H-pipe, No smog pump, pulleys, K&N, and still going. |
stock is 37-40psi..drop it back and bump it 1/2lb at a time if you need to. Make sure you crack the throttle after each adjustment to see where it settles at.
Hope That helps! ------------------ My Ride Check Out My Site 91GT, Holley SysteMAX II Kit-Heads 2.02" x 1.60",Full MAC exhaust 1-5/8" Long tubes, 2-1/2" O.R H-Pipe, 2 1/2" cat back, 12" K&N Filter, RNH PERFORMANCE Ram Air, Ron Davis Radiator, Full Suspension,3:73's, Welds, Best on new motor-12.60 @ 108, no traction 1.98 |
Rick-91GT,
Is that 37-40 with the vacuum unhooked, I assume that a pressure setting on these cars is usually done with the vacuum unhooked? Also what is a good indicator of whether or not I need more or less psi? Plugs, pop out the exhaust, etc? Man thanks alot!!! John ------------------ John Welch 86 GT, 3.73's, H-pipe, No smog pump, pulleys, K&N, and still going. |
Quote:
------------------ My Ride Check Out My Site 91GT, Holley SysteMAX II Kit-Heads 2.02" x 1.60",Full MAC exhaust 1-5/8" Long tubes, 2-1/2" O.R H-Pipe, 2 1/2" cat back, 12" K&N Filter, RNH PERFORMANCE Ram Air, Ron Davis Radiator, Full Suspension,3:73's, Welds, Best on new motor-12.60 @ 108, no traction 1.98 |
what rick said..make sure you have no vaccum leaks or the psi wont drop as much when you put the vacuum line back on..this could cause the car top run good up top but run rich at an idle
------------------ 1987 black notch(ex 4 banger) DSS 306 w/ main support...Elderbrock 6028 heads..gt-40 intake..24# injectors...70 mm tb..77 pro-m...accel 300+..mac full legnth..tremec w/ pro5oh...full MAC exhaust,off road h-pipe,long tubes, catback...ron davis radiator..subframes, control arms...CFDF II..o yea holley FPR sucks..dont buy one.. AIM=onesillynotch |
Could you explain this rich at idle thing? I think I may have this problem. I have been tuning this fuel pressure for weeks now. My car seems to pull good through the gears but seems to kinda surge or fall off spuriously during decel or when cruising and letting of the gas at lower RPM's. My TPS, IAB, TB and etc. are clean and set correctly. Timing is approx. 14 deg. FP is set at 39(off vacuum) then goes to 31(on vacuum) Thanks
------------------ John Welch 86 GT, 3.73's, H-pipe w/ 2-chamber Flows, No smog pump or A/C, crank pulley, K&N in stock box, adj. FPR, bypassed EGR(coolant) Best Run 14.34 @100.0 MPH (on G-Tech) |
The regulator works like this: at idle your vacuum is at its max. When you hit the throttle, vacuum goes down, and fuel pressure goes up- this supplies more fuel at higher RPM's. If your car is running rich at idle it means your pressure is either too high, or you vacuum is low and the difference between vacuum and no vacuum is minimal. Basically its like running your car with the vacuum line off and the pressure will be as high at 1000RPM's as it will be at 5000rpms's, but you obviously don't need the same amount of fuel at 1000rpm's as you do at 5000rpm's. I hope this helps explain it for you. It used to confuse me too, so don't feel bad.
So if you think your car is running good everywhere in the powerband except down low, this is why it was suggested you may have a vacuum leak resulting in higher pressure at idle. ------------------ 95 GT convt' 5 speed, 3.73's,FMS HD clutch, Pro 5.0 shifter, ASP alum. underdrive pulleys, Bassani offroad X pipe, 2 chmbr flowmasters, K&N w/o silencer, edelbrock performer intake, FRPP 65mm T-body, FRPP shorty headers, FRPP aluminum driveshaft.Hooker 4pt chrome car bar, Xenon/Wings West ground effects, custom interior Best ET: 13.83 Best MPH: 98.55mph with Best 60': 1.91 on Nitto DR's Homepage: <A HREF="http://www.angelfire.com/pa2/killercanary" TARGET=_blank>http://www.angelfire |
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