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Fuel pressure drop #2837771
10/26/20 08:24 PM
10/26/20 08:24 PM
Joined: Sep 2020
Posts: 13
Tampa FL
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BillR1212 Offline OP
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BillR1212  Offline OP
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Joined: Sep 2020
Posts: 13
Tampa FL
Hi Team,

I've owned my Cuda for 5 years now, but I'm new to boost. Admittedly, I'm not the most savvy person when it comes to diagnosing issues, and since I moved to a new city for my job I lost my support group and now have a parking garage where I can't tinker on her. With that said, it's pricey to have a shop test and tune this thing all the time at 125 dollars an hour to figure it out. I'd like to get some ideas to check prior to dropping her off. Engine is a 440 - 505 stroker. should make around 425-450 NA with the compression drop.

I wrote about my new engine in a prior thread, and that it's procharged. Really happy with it, but I'm noticing some inconsistencies with my fuel pressure. Sometimes it runs strong, other times it will build to about 3 PSI and the fuel pressure will drop from 60 to 20. I immediately let out. I've tried keeping the tank full, but does not seem to matter. sometimes it will work and pull other times it won't. no rhyme or reason to it that I can figure out. It's hard to watch air fuel and fuel pressure while boosting down the highway. I'd like to get this figured out so I can get to the track and test her out.

Fuel tank is fairly new, 2 years old and an in tank kit I got from Holley. I'm running a Holley 510-12-167 in tank pump rated for 1200HP 525lph.. My engine should be well under that especially at 3-6psi which is when I see the drop.I managed a few logs and the sniper was calling for 400 LPH of fuel when the pressure dropped on my gauge. Pump should be able to handle that. I have a Aeromotive boost pressure regulator, and a 100 micron fuel filter that I just put in today. I was hoping that my old filter was the restriction. I thought that did the trick, but about 30 miles into my drive the PSI was dropping again under low boost. (inspection of the old filter did not have any clues, looked clean) Holley sniper is feeding the engine. I'm open to any other suggestions. There was an option for a Aeromotive fuel filter for about 80 dollars more, but the speed shop didn't think I demanded that kind of flow based on my build. Voltage is 13.4 on the sniper, so I"m assuming the rest of the car is strong too. battery is trunk located so my assumption is the pump is tied directly to it. I did the original fuel pump, but had it changed out with the Procharger so not positive, but I'd imagine it's better than how I had it. Any thoughts are appreciated.

I will note that it's an absolute gas hog. 7-8 MPG. Maybe I need more flow to feed my inefficient engine than say an LS making the same HP? idk, just guessing. Air fuel seems decent from what I can see while driving. I'll also note that I'm running -8 feed and return lines.

Thank you

Re: Fuel pressure drop [Re: BillR1212] #2838972
10/29/20 07:14 PM
10/29/20 07:14 PM
Joined: Oct 2004
Posts: 3,051
back in Georgia
dthemi Offline
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dthemi  Offline
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Joined: Oct 2004
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Try pulling the boost reference line off the regulator and plug it. Since it's doing it at 3 psi that shouldn't be enough to throw the tune off much. See if it still drops with the reference line plugged, and the reg at 1 atmosphere. I've seen regs do weird stuff, when they transition from vacuum to boost.

Re: Fuel pressure drop [Re: BillR1212] #2839033
10/29/20 08:52 PM
10/29/20 08:52 PM
Joined: May 2019
Posts: 172
Lake Villa Il
INTMD8 Offline
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INTMD8  Offline
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Lake Villa Il
A few things. Are you running a sniper tank or another baffled tank?

If it's not baffled it will starve the pump (which by the way would never support 1200hp). Probably at absolute best 750hp with forced induction.

Should test that it does in fact have proper voltage (and an excellent ground).

If it's a sniper module, the one I bought had a very small orifice on the outlet port which I drilled oversize. (not to mention it's a hard 90deg turn).


Another common mistake I see is running the feed -through- the regulator rather than the feed directly to rails and regulator on return side.

What are you using for an efi system and injectors? If you have a lot of injector overhead you can start out with a lower base pressure(say 43 instead of 60). That will increase injector duty cycle for a given power level but get you more out of the pump.

Re: Fuel pressure drop [Re: BillR1212] #2839050
10/29/20 09:26 PM
10/29/20 09:26 PM
Joined: Jan 2003
Posts: 27,792
Oregon
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AndyF Offline
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AndyF  Offline
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How are you measuring the fuel pressure? What does the inlet side of the fuel pump look like? Can you do a flow test thru a restriction (ball valve or small orifice)? Are you data logging the events?

Re: Fuel pressure drop [Re: INTMD8] #2839305
10/30/20 12:54 PM
10/30/20 12:54 PM
Joined: Sep 2020
Posts: 13
Tampa FL
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BillR1212 Offline OP
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BillR1212  Offline OP
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Joined: Sep 2020
Posts: 13
Tampa FL
Thanks for the replies guys. I ended up dropping the car off Wednesday so I don't risk damage to it. Odd thing is, is that I fired it up for the 60 mile drive to the speed shop I use, and for about 30 miles it ran perfectly. 9-10PSI pulls with no issues. Then after 30 miles it was back to it's old tricks of dropping pressure.



A few things. Are you running a sniper tank or another baffled tank?

I am using a sniper tank, I bought the master fuel kit a few years back. I did however upgrade the pump to the in tank one listed with a rated flow of 525L per hour. Per your suggestion my thought is the pump is not enough. I suppose I can't go by what Holley tech says. Thats what they recommended. I believe the shop is switching to a dual Aeromotive in tank design.

If it's not baffled it will starve the pump (which by the way would never support 1200hp). Probably at absolute best 750hp with forced induction.

Should test that it does in fact have proper voltage (and an excellent ground).

- Voltage could be the issue. My optima battery seemed hammered. I think it spent a lot of time idling at the shop and not charging since you need some RPMs for the alternator to kick on. I thought 600 miles of driving would get her topped off, but once my fans kick on the voltage drops to 12.4 from 13.5 . With that said, pump was being erratic even when no accessories were pulling, and working fine at times when the fans were on.

If it's a sniper module, the one I bought had a very small orifice on the outlet port which I drilled oversize. (not to mention it's a hard 90deg turn).

I'll have to take a look, I don't think I have 90 degree fittings on the inlet side of the sniper, good idea to oversize the port!!


Another common mistake I see is running the feed -through- the regulator rather than the feed directly to rails and regulator on return side.

I obviously have a lot to learn on boosted engines and set up. I had the Procharger installed at a different shop than I use now. I believe they have regulator on the supply side, which dead heads to sniper, and a return off the regulator back to tank. Now that I look at the Holley manual for the sniper online I can see that this is wrong. Good call out, lesson learned.


What are you using for an efi system and injectors? If you have a lot of injector overhead you can start out with a lower base pressure(say 43 instead of 60). That will increase injector duty cycle for a given power level but get you more out of the pump.

Using Sniper - which wants 60PSI I believe


i'm using an auto-meter electric fuel gauge. I believe that was asked.

Thanks for the feedback. I'll confirm the regulator, and maybe in a few weeks I can try again when she returns.


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