WHat kind of fuel pressure should I be looking for out of this new Walbro 255 HP? After I put the pump in, the car seemed to go like a bat out of hell. Now, it feels sluggish again and I checked the pressure between 40-45 PSI. Ive got 13 volts at the pump with the car running. My long term fuel trim is at 25%, but for all I know, Ed Wright could have programmed it that way.
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96 WS6 Formula: Ram Air, 383 Stroker, Ported LT4 Heads and Manifold, 1.6 Crane Rollers, 58MM T.B., AS&M Headers, Borla Exhaust, Meziere Elec. H2O Pump, Canton Deep Sump Oil Pan, 100 HP OF TNT N2O!! , T56 Conversion w/ Pro 5.0 shifter, SPEC Stage 3 Clutch, Hotchkiss Subframe Conn., Lakewood Adj. Panhard Bar, Spohn Adj. LCA's, BMR Adj. T.A., Custom 12 bolt w/ 3:73's, Moser Axles, Eaton Posi, Moser Girdle
11.6 @ 123mph (1.6 60' - getting there
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The fuel pressure sounds right to me. Regardless of what size or how many pumps you have, pressure is still regulated at the regulator. You could have 100 psi coming out of the pump but the fuel rail will only see what's coming out of the regulator."No, officer, that bottle is my onboard Halon system" -
SO, the LT1 shouldnt have more than 45 PSI?96 WS6 Formula: Ram Air, 383 Stroker, Ported LT4 Heads and Manifold, 1.6 Crane Rollers, 58MM T.B., AS&M Headers, Borla Exhaust, Meziere Elec. H2O Pump, Canton Deep Sump Oil Pan, 100 HP OF TNT N2O!! , T56 Conversion w/ Pro 5.0 shifter, SPEC Stage 3 Clutch, Hotchkiss Subframe Conn., Lakewood Adj. Panhard Bar, Spohn Adj. LCA's, BMR Adj. T.A., Custom 12 bolt w/ 3:73's, Moser Axles, Eaton Posi, Moser Girdle
11.6 @ 123mph (1.6 60' - getting there )
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Are you checking the pressure under load and higher rpms or just at idle?
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Load and idle is a good question too. My car stays in the 35-42 range regardless of load conditions. Usually around 38-ish at idle, kinda jumps around a little bit, but that could be my gauge too. On the bottle (5176 dry kit) it's more like 80-82
"No, officer, that bottle is my onboard Halon system"Comment
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At idle, engine running, FPR vacuum compensation line removed and plugged - 43.5psi +/-2.5 psi, so anything from 41 - 46psi meets specs (actually, I think the manual quotes 41 - 47psi).
Reconnect the vacuum line. Fuel pressure should drop proportional to intake manifold vacuum. As much as 8psi lower than "no vacuum" measurement on a stock cam. Maybe only 4-5psi lower on a "cammed" setup.
Then take it out and run it to max rpm/max load - the fuel pressure should stay within 1 to 2psi of the "no vacuum" reading.
To clarify why your larger pump should not increase fuel pressure. A pump has a "curve" of flow (gpm, lph) vs. discharge pressure (psi). That curve will generally show a very high flow at low pressures, and a much lower flow at high pressures. How high a pump can go on pressure is a function of the design of the pump. Not all pumps can reach 80-100psi.
The pump will increase flow until it reaches the limits of the backpressure it sees from the fuel system. The main source of "backpressure" is the fuel pressure regulator. The regulator is on the OUTLET of the fuel rails, and controls how much fuel gets returned to the tank. If it needs more pressure, it closes down until the total flow from the pump (fuel used by the injectors + fuel returned to the tank) is reduced and the pump can develop a higher pressure. But, point is, the fuel pressure regulator is controlling flow, so that the pump only needs to develop a few psi more than the required rail pressure. It isn't a matter of the pump putting out 100psi, and the regulator reducing that pressure to 43.5psi at the rails. Even the larger pump will still be putting out less than 50psi or so.Fred
381ci all-forged stroker - 10.8:1 - CNC LT4 heads/intake - CC solid roller - MoTeC engine management - 8 LS1 coils - 58mm TB - 78# injectors - 300-shot dry nitrous - TH400 - Gear Vendor O/D - Strange 12-bolt - 4.11's - AS&M headers - duals - Corbeau seat - AutoMeter gauges - roll bar - Spohn suspension - QA1 shocks - a few other odds 'n ends. 800HP/800lb-ft at the flywheel, on a 300-shot. 11.5 @ 117MPH straight motorComment
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Thanks everyone for the input. I seem to be right in spec on everything. 41-42 PSI at idle. 47 PSI with the vacuum line disconnnected. 46 PSI at WOT. With the vacuum line unplugged, should the pressure drop 2 PSI as I rev it up?
It just seems weird. The car feels sluggish, exactly like it did before I replaced the fuel pump. After I did the pump, it ran FAST. A week later, back to where it was. I dont get it. Everything looks normal on the scanner except my long term fuel trim - at 25%.
This may seem like a weird question......Does anyone know if the ABS wiring for the sensor in the differential has anything to do with the fuel pump wiring? They both plug into the same junction block in the back of the car. Do they share common grounds or anything? Would having the ABS harness unplugged effect voltage or ground at the pump? It just seems like maybe the volume isnt there, but pressure is??
96 WS6 Formula: Ram Air, 383 Stroker, Ported LT4 Heads and Manifold, 1.6 Crane Rollers, 58MM T.B., AS&M Headers, Borla Exhaust, Meziere Elec. H2O Pump, Canton Deep Sump Oil Pan, 100 HP OF TNT N2O!! , T56 Conversion w/ Pro 5.0 shifter, SPEC Stage 3 Clutch, Hotchkiss Subframe Conn., Lakewood Adj. Panhard Bar, Spohn Adj. LCA's, BMR Adj. T.A., Custom 12 bolt w/ 3:73's, Moser Axles, Eaton Posi, Moser Girdle
11.6 @ 123mph (1.6 60' - getting there )
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Long as there isn't some crap in the tank, or the filter is clogged...Comment
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If your long term fuel trims are max'd out at 25%, you have a problem. And, since 25% is the max fuel that the long terms can add, you may still be running lean if it needs to add more than 25%. Or you have a "false lean" and the system is adding fuel you don't need. Either way, you need to identify the problem.
What are the O2 sensor readings at WOT? While the stock narrow-band sensors aren't very accurate at the rich A/F ratios needed for maximum power/torque, they can be a rough indication of what is wrong with the system.Fred
381ci all-forged stroker - 10.8:1 - CNC LT4 heads/intake - CC solid roller - MoTeC engine management - 8 LS1 coils - 58mm TB - 78# injectors - 300-shot dry nitrous - TH400 - Gear Vendor O/D - Strange 12-bolt - 4.11's - AS&M headers - duals - Corbeau seat - AutoMeter gauges - roll bar - Spohn suspension - QA1 shocks - a few other odds 'n ends. 800HP/800lb-ft at the flywheel, on a 300-shot. 11.5 @ 117MPH straight motorComment
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It was hard to read them on the scanner while blasting down the road at WOT, but I think they maxed at about 850 mv. This seems lean to me. Is it possible to have enough pressure, but still not have ebough fuel?96 WS6 Formula: Ram Air, 383 Stroker, Ported LT4 Heads and Manifold, 1.6 Crane Rollers, 58MM T.B., AS&M Headers, Borla Exhaust, Meziere Elec. H2O Pump, Canton Deep Sump Oil Pan, 100 HP OF TNT N2O!! , T56 Conversion w/ Pro 5.0 shifter, SPEC Stage 3 Clutch, Hotchkiss Subframe Conn., Lakewood Adj. Panhard Bar, Spohn Adj. LCA's, BMR Adj. T.A., Custom 12 bolt w/ 3:73's, Moser Axles, Eaton Posi, Moser Girdle
11.6 @ 123mph (1.6 60' - getting there )
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That doesn't necessarily sound real bad.... possibly toward the lean side. Are you sure the injectors are the same size you told Ed Wright you would be using? And you told him you were running them at stock pressure (he should have asked you both those questions)?
There are lots of possible problems.... air getting into the system without being measured by the MAF sensor. Are you sure there are no tears in the inlet bellows, after the MAF? No other possible major vacuum leaks?
Do you have a way to log a WOT pass? I'd be glad to review the data log for you.Fred
381ci all-forged stroker - 10.8:1 - CNC LT4 heads/intake - CC solid roller - MoTeC engine management - 8 LS1 coils - 58mm TB - 78# injectors - 300-shot dry nitrous - TH400 - Gear Vendor O/D - Strange 12-bolt - 4.11's - AS&M headers - duals - Corbeau seat - AutoMeter gauges - roll bar - Spohn suspension - QA1 shocks - a few other odds 'n ends. 800HP/800lb-ft at the flywheel, on a 300-shot. 11.5 @ 117MPH straight motorComment
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This morning I went out and changed the PCM (MadZ28 tuned) and upped the injectors to 30lb Ford red tops. The calibration is matched to the injectors (supposedly). The car runs much worse now. The O2's are at .4 volts at WOT and the PCM is pulling like 10 degrees of timing out. There is no throttle response and its runs like its running out of fuel. The pressures are fine though. Maybe a volume issue?? I feel like I should change the pump again, but dont want to make a 100 dollar mistake.
It seems to idle well, but I will check the false air possibility. Any other ideas?
Oh, more thing......the needle on the gauge "bounces" back and forth about 1 degree or so as the car runs.96 WS6 Formula: Ram Air, 383 Stroker, Ported LT4 Heads and Manifold, 1.6 Crane Rollers, 58MM T.B., AS&M Headers, Borla Exhaust, Meziere Elec. H2O Pump, Canton Deep Sump Oil Pan, 100 HP OF TNT N2O!! , T56 Conversion w/ Pro 5.0 shifter, SPEC Stage 3 Clutch, Hotchkiss Subframe Conn., Lakewood Adj. Panhard Bar, Spohn Adj. LCA's, BMR Adj. T.A., Custom 12 bolt w/ 3:73's, Moser Axles, Eaton Posi, Moser Girdle
11.6 @ 123mph (1.6 60' - getting there )
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Do you have a pressure gauge in the dash? If not:
Some gauges have a hose and it attaches to the schrader tube. You can tape it to the windshield and make a short run then see if you lose pressure. if there is pressure when your foot is in it, then there is volume. The old school way was to flow x gallons in a minute from the pump to meet spec, but it woudl be tricky to try that with high pressure. Essentially, if it is gulping gas and the pressure stays up, you're OK. You're not going to have high pressure at the rails during WOT and no volume. if the voluem increases to the point the pump can't keep up, the pressure will fall.
Case in point, I have an auxiliary pump which I usually leave off. If I floor it with the stock pump only, the pressure will drop dramatically & the car will fall flat on it's face. With the auxilliary pump on, it doesn't lose pressure when I floor it.Comment
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