Fuel Pressure Regulator Question...
Thread Starter
Melting Slicks
Joined: Oct 2002
Posts: 3,193
Likes: 1
From: Cincinnati Oh
Fuel Pressure Regulator Question...
I have a Holly AFPR installed and I've recently come up with a nasty miss (or more appropriately, a complete but intermittent loss of power up top).
After swapping out the entire ignition system (plugs, wires, module & coil), I started to re-check the fuel system and I noticed the following:
When I rev up the engine, I see the AFPR drop fuel pressure (instead of increasing FP with vacuum). It will go from 30psi or so at idle on the AFPR to 25psi or less when I rev it up. THis of course makes it go lean and gives me a complete loss of power and the engine will stumble back down to a lower RPM - or the FP will pick back up to 32psi or so while I'm revving it.
When I unplug the AFPR (and cap the vacuum line to the plenum), the fuel pressure is 40psi and pretty much stays there when I rev the engine - but it may in fact drop a couple of psi if I stomp on the peddle...
This is pretty much a quintesential fuel pump issue, right? THe pump (walbro 255) and the regulator (holley) are less than 2 yrs old.
Which one is it?
[Modified by Ramanstud, 9:28 PM 7/5/2004]
After swapping out the entire ignition system (plugs, wires, module & coil), I started to re-check the fuel system and I noticed the following:
When I rev up the engine, I see the AFPR drop fuel pressure (instead of increasing FP with vacuum). It will go from 30psi or so at idle on the AFPR to 25psi or less when I rev it up. THis of course makes it go lean and gives me a complete loss of power and the engine will stumble back down to a lower RPM - or the FP will pick back up to 32psi or so while I'm revving it.
When I unplug the AFPR (and cap the vacuum line to the plenum), the fuel pressure is 40psi and pretty much stays there when I rev the engine - but it may in fact drop a couple of psi if I stomp on the peddle...
This is pretty much a quintesential fuel pump issue, right? THe pump (walbro 255) and the regulator (holley) are less than 2 yrs old.
Which one is it?
[Modified by Ramanstud, 9:28 PM 7/5/2004]
Thread Starter
Melting Slicks
Joined: Oct 2002
Posts: 3,193
Likes: 1
From: Cincinnati Oh
Re: Fuel Pressure Regulator Question... (Ramanstud)
Alright... I just replaced the fuel pump and no dice.
I've heard that a loose ground somewhere can (for some reason) mimic the stumble at ~2500rpm that I've had.
I can't believe it's the friggin regulator since it now wants to hold pressure with the new pump (yet still will stumble and sometimes stall out). Feels like it makes power right up until it hits a wall though.
Suggestions?
I've heard that a loose ground somewhere can (for some reason) mimic the stumble at ~2500rpm that I've had.
I can't believe it's the friggin regulator since it now wants to hold pressure with the new pump (yet still will stumble and sometimes stall out). Feels like it makes power right up until it hits a wall though.
Suggestions?
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Re: Fuel Pressure Regulator Question... (Ramanstud)
First off 40psi with no vacuum line is way low for a stock '89 L98. I believe it's just running out of fuel delivery capability at WOT with such low pressure.
Bump fuel pressure to 45psi and see how it performs. Lay the FP gauge on the windshield under a wiper blade and do a WOT blast to see if it holds pressure under those conditions.
If pressure still drops off substantially replace the fuel filter.
What other mods do you have on the motor?
Bump fuel pressure to 45psi and see how it performs. Lay the FP gauge on the windshield under a wiper blade and do a WOT blast to see if it holds pressure under those conditions.
If pressure still drops off substantially replace the fuel filter.
What other mods do you have on the motor?
Thread Starter
Melting Slicks
Joined: Oct 2002
Posts: 3,193
Likes: 1
From: Cincinnati Oh
Re: Fuel Pressure Regulator Question... (65Z01)
I already swapped out the filter yesterday and put a new strainer on with the pump. It's a 383ci Superram with heads & cam....
Thread Starter
Melting Slicks
Joined: Oct 2002
Posts: 3,193
Likes: 1
From: Cincinnati Oh
Re: Fuel Pressure Regulator Question... (65Z01)
Well, problem solved. For anyone in the future with a similar problem (especially one who tinkers with everything in the engine compartment):
check all the ground connections. A nut worked lose and cause an intermittent break in the ground connection for (I assume) either the ECM or the ignition system.
check all the ground connections. A nut worked lose and cause an intermittent break in the ground connection for (I assume) either the ECM or the ignition system.
Burning Brakes
Joined: Jul 2003
Posts: 922
Likes: 1
From: Brisbane Queensland, Australia
Re: Fuel Pressure Regulator Question... (Ramanstud)
Your pressure should be about 42psi.
From what I hear, fuel pumps are pretty hardy items.
Just an abstrct thought-have you checked ALL vacuum lines for holes?
From what I hear, fuel pumps are pretty hardy items.
Just an abstrct thought-have you checked ALL vacuum lines for holes?
Racer
Joined: Sep 2003
Posts: 368
Likes: 0
From: Chicago IL
I just found that my Crane cams fuel pressure regulator is bad. I was experiencing a loss of power up top at first, and then all over the board. I tied off the return line and got a sustained 45 psi. Then I opened the return line back to the tank and - 0 psi. That was all after (of course) I replaced the fuel pump.
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