Fuel pressure dropping when warm

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Fuel pressure dropping when warm

Unread postby jubi351 » Sat Mar 23, 2019 10:25 am

Felt pretty good about where I am at tuning my car with the old draw through setup so it was time to update. I recently converted to blow through using a '05 slot with my mafia and 60lb siemens inj. Got everything running well but started noticing that my fuel error was increasing the longer I idled and when doing my sweep(in the driveway) all points were off the same amount. I noticed at this time that my Autometer fuel pressure gauge was reading 31 w/vac when it was about 35 when I started. I have a genuine Walbro 450lph with 8an supply, aluminum rails, fuelab regulator and using the stock feed as return with 6an at tank.

I shut the car off and let it sit an hour and try again and my fuel pressure is back so now I conduct some tests. I grounded the fuel pump through the self test port and let it run, engine off, for 15 minutes and pressure stayed @ 40. Measured the fuel line temps and where about 82º. Now I start the car and let it idle and within 10 minutes pressure is starting to drop, fuel error is increasing and fuel temp rises over 20º. I then shutoff car, let it cool, run pressure up to 55 and conduct test again. Again pressure starts to fall but not nearly as much. My conclusion after this test was that maybe the spring in the regulator is relaxing due to the heat of the fuel and letting more fuel return to the tank, resulting in lower pressure. Sound feasible?

I have heard many people having problems running big pumps, heating up the fuel so if this is my issue it seems there are two ways to solve. 1. run a voltage controller or 2. smaller pump. The last time the car was tuned it made 552rwhp with 42lb inj and a GSS340 on stock fuel lines and the injectors went static and fuel pressure was dropping at 5200. With the new fuel system on the street when my wife was driving at WOT 3rd gear fuel pressure was solid. I'm reading that to make 650 fwhp I need 65 gph which can done with a 255HP pump if I run at 40psi base fuel pressure and my 60's should support it. Since that dyno pull I have pully'd up to reduce boost so should be low 500's now. What are your thoughts?
jubi351
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Vehicle Information: 1992 LX Coupe, 302, stock cam, TW heads, Systemax intake, V2SQ, A2A intercooler, 60lb inj, '05 slot, Mafia on 4, T5, A9L/GUFX/A9L2, Quarterhorse w/ TunerPro RT.

Re: Fuel pressure dropping when warm

Unread postby decipha » Sat Mar 23, 2019 5:15 pm

get yourself a better regulator or just command a richer mix
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Re: Fuel pressure dropping when warm

Unread postby jubi351 » Sat Mar 23, 2019 7:01 pm

Is there a brand you recommend? I was under the impression that Fuelab was a quality piece.
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Posts: 14
Joined: Mon Oct 27, 2014 8:38 am
Name: Jarrod
Vehicle Information: 1992 LX Coupe, 302, stock cam, TW heads, Systemax intake, V2SQ, A2A intercooler, 60lb inj, '05 slot, Mafia on 4, T5, A9L/GUFX/A9L2, Quarterhorse w/ TunerPro RT.

Re: Fuel pressure dropping when warm

Unread postby decipha » Sat Mar 23, 2019 7:18 pm

for your specific problem no there's nothing that i know of specifically but I always recommend the kirban stock style regulators for stock rails and the aeromotive dwr2000 regulator for in line regulators

if your only dropping a few psi though it shouldn't be a problem. How much does it drop and affect WOT ?
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Vehicle Information: Supercoupin' x10
90 (4x 5spds) - Dante, Ruby, Daja, Ava
91 4r70w - Skarlett
92 (2x) 5spd & auto - Bianqa, Andrea
93 auto - Danika
94 5spd Rionda
95 auto Aisha
Vehicle 2 Information: Others:
00 Lincoln LS - Luanda
98 Camaro SS - Bounquisha
02 Harley F-150 - Sasasha
03 Marauder - DyShyKy
00 Explorer 5L - Bernyce
07 GMC 2500HD 6L - Veranafer

Re: Fuel pressure dropping when warm

Unread postby jubi351 » Sat Mar 23, 2019 7:55 pm

Haven't even driven it on the road, just driveway tuning to get MAF curve happy to start driving. I wonder if once driving and having that forced cooling will help alleviate my issues? I can't say that I remember this happening before when my wife was driving and I was tuning. I will see what it does once on the road. What do you think about deadheading? That would definitely keep hot fuel from recirculating. Seems to be getting more common.
jubi351
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Posts: 14
Joined: Mon Oct 27, 2014 8:38 am
Name: Jarrod
Vehicle Information: 1992 LX Coupe, 302, stock cam, TW heads, Systemax intake, V2SQ, A2A intercooler, 60lb inj, '05 slot, Mafia on 4, T5, A9L/GUFX/A9L2, Quarterhorse w/ TunerPro RT.

Re: Fuel pressure dropping when warm

Unread postby decipha » Sat Mar 23, 2019 8:44 pm

I've always dead headed every fuel system I've ever done and I couldn't even begin to tell you how many. I've never once had a problem with it and I personally don't see the point in people running another line all the way from the front to the back just to return fuel seems idiotic to me.
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91 4r70w - Skarlett
92 (2x) 5spd & auto - Bianqa, Andrea
93 auto - Danika
94 5spd Rionda
95 auto Aisha
Vehicle 2 Information: Others:
00 Lincoln LS - Luanda
98 Camaro SS - Bounquisha
02 Harley F-150 - Sasasha
03 Marauder - DyShyKy
00 Explorer 5L - Bernyce
07 GMC 2500HD 6L - Veranafer

Re: Fuel pressure dropping when warm

Unread postby jubi351 » Mon Apr 15, 2019 5:53 am

Just wanted to clarify, you stated Aeromotive DWR2000. To my knowledge DWR is DeatschWerks. So far I redid the fuel system deadheaded and still experienced fuel pressure loss so bought a new fuel pump and still experiencing same issue. Regulator is only thing left to replace.
jubi351
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Posts: 14
Joined: Mon Oct 27, 2014 8:38 am
Name: Jarrod
Vehicle Information: 1992 LX Coupe, 302, stock cam, TW heads, Systemax intake, V2SQ, A2A intercooler, 60lb inj, '05 slot, Mafia on 4, T5, A9L/GUFX/A9L2, Quarterhorse w/ TunerPro RT.

Re: Fuel pressure dropping when warm

Unread postby AmericanLocomotive » Tue Apr 16, 2019 4:37 am

decipha wrote:I've always dead headed every fuel system I've ever done and I couldn't even begin to tell you how many. I've never once had a problem with it and I personally don't see the point in people running another line all the way from the front to the back just to return fuel seems idiotic to me.

How would the regulator work without a way to return fuel?
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Re: Fuel pressure dropping when warm

Unread postby decipha » Tue Apr 16, 2019 6:25 am

it wouldnt
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Posts: 17001
Joined: Mon Jul 15, 2013 5:29 pm
Location: New Orleans, LA
Name: Michael Ponthieux
Vehicle Information: Supercoupin' x10
90 (4x 5spds) - Dante, Ruby, Daja, Ava
91 4r70w - Skarlett
92 (2x) 5spd & auto - Bianqa, Andrea
93 auto - Danika
94 5spd Rionda
95 auto Aisha
Vehicle 2 Information: Others:
00 Lincoln LS - Luanda
98 Camaro SS - Bounquisha
02 Harley F-150 - Sasasha
03 Marauder - DyShyKy
00 Explorer 5L - Bernyce
07 GMC 2500HD 6L - Veranafer


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