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AleroB888
06-18-2008, 01:02 PM
Having a problem with fuel pressure gradually dropping to zero after the engine warms up. When the temperature in the intake manifold rises to about 105 to 110 degrees, the whine from the fuel pump gets higher pitched and louder, pressure drops to zero gradually over about 20 seconds.

Pump voltage at the canister harness stays at 12 or higher. I am reading less than 1 ohm resistance across the pump wiring at the harness. I need to know if that's normal (it's a Walbro pump).

I am using the rising rate regulator from the Magnuson kit. Is it possible for a regulator to have a problem that shows up after warm-up? The gas tank is full.

TIA

silvergtjrad
06-18-2008, 03:18 PM
I would imagine you are having a problem with your regulator. The 1ohm resistance on the pump winding is fine, and the fact that you mention it is whining more as it warms up makes me think the regulator too.

When the engine warms up the idle rpms drop, and the amount of vaccum in the manifold changes. Hook up a vaccum gauge and watch the values on that versus your fuel pressure.

AleroB888
06-23-2008, 01:59 AM
I would imagine you are having a problem with your regulator. The 1ohm resistance on the pump winding is fine, and the fact that you mention it is whining more as it warms up makes me think the regulator too. ..............

Yeah, everybody including me thought it was going to be the regulator, but no such luck. I took the compound regulator off (it mounts on the stock one), and replaced that assembly with a new stock-type regulator. Same result.

I replaced the Walbro modded pump canister with an "Airtex" OEM type from Autozone, and that fixed it. This unit came with a new wiring harness as well. I did not do the recommended wiring upgrade on the Walbro. It could be that hot return line fuel going into the canister was causing connectors to flex causing high resistance. No way to monitor the actual voltage at the pump itself though.

I am getting about 35 psi fuel pressure at idle now, and mid-forties at WOT. If anybody is using the M62 kit, let me know what your pressures are.

AaronGTR
06-23-2008, 10:14 PM
That's pretty low. My stock fuel pressures where 48psi at idle and 55psi WOT. With the pressure riser from the magnacharger kit it would get up to around 62psi. I use a caspers AFPR now with the idle pressure set to 46psi.

AleroB888
06-25-2008, 11:31 PM
I am getting about 35 psi fuel pressure at idle now, and mid-forties at WOT..



That's pretty low. My stock fuel pressures where 48psi at idle and 55psi WOT. With the pressure riser from the magnacharger kit it would get up to around 62psi. I use a caspers AFPR now with the idle pressure set to 46psi.

The Haynes manual said 35 was not too far off for a 1999. Then I put the gauge on my 2003 Alero and it ran about 10 psi higher.

So I checked FPR part numbers for '99 vs '03 and sure enough they were different. Went to Autozone and got an '03 3400 regulator, and now have 48 psi for key-on, engine off mode. I took the car around the block for a quick test and scan, now psi is between 45 and 60.

Th LTFT's, as you might expect, went way negative by 10 to 15 %. Now of course I will have to reset my IFR, and retune.

What I don't know is if GM used a higher rated fuel pump in the later models, or if they kept the same one. Anybody know this?

plastic_indian
06-27-2008, 10:00 PM
99 m/y pressure specification is 41-47 psi, fuel pump GM #25317984.
00-05 m/y pressure specification is 52-59 KOEO, pump GM #88957239

Regulator for m/y 99 GM #17120665, subsequent m/ys 17113622

Don't know how much of the discrepancy in pressure specs is attributable to regulator change vs. pump change, but stands to reason the 'newer' pump was necessary to feed the increased pressure spec.