Fuel pressure issue - Lateral-g Forums

mikels · #1 10-17-2013, 08:23 AM

Most likely due to pump overtemp during low load (high bypass) operation. Classic problem with fuel pump sized to deliver required fuel @ max power being asked to operate in low load conditions where most fuel is bypassed and returned to tank.

Best solution: Vapor Works or equivalent where pump is only operating at enough load to deliver required fuel (no bypass). This mimics what OEM's are doing for very same reason (along with reduced parasitic loss for increased FE). Carl's system works awesome!

Next best: Staged pumps where only operate on one pump under low flow conditions with secondary pump coming online during increased load conditions. BTW, Vapor Works can also be used with staged pumps for those with greatly varied fuel delivery requirements from idle to max power.

I've fought this very issue so many times and it is extremely fustrating to be stuck on side of road due to such a seemingly simple issue.

This is another reason OEM's mount fuel pumps in tank - for cooling effect (as well as noise supression). But even that is not enough for most aftermarket high flow pumps operating at the now nominal 400 kPa (~60 psig) fuel pressure under high bypass conditions for extended periods of time.

Easy check can be after low speed cruising around in your car (conditions where you noticed fuel pressure fall off), can you even touch your external regulator without buring several layers of skin off your fingers?

hifi875 · #2 10-17-2013, 12:56 PM

I have the tanks inc. setup in my 69 Camaro running the holley terminator system and have put over 4000 miles on it(power tour and other trips+autocrossing) with no issues. Mine only has to run at 43psi though. seems weird to have trash in a brand new tank.

rickpaw · #3 10-18-2013, 04:38 AM

I've searched on here and there were some instances where a few were left stranded due to fuel pump over heat on long trips (ie power tours). The overheated pumps were Aeromotive pumps. Makes me wonder whether the Aeromotive pump I have in there now is too big for my application, and overheated.

rickpaw · #4 10-18-2013, 04:43 AM

Quote:

Originally Posted by mikels

Easy check can be after low speed cruising around in your car (conditions where you noticed fuel pressure fall off), can you even touch your external regulator without buring several layers of skin off your fingers?

The filter/regulator was warm, so was the fuel tank, but not hot to the touch.

**CarlC** · #5 10-18-2013, 03:03 PM

The Aeromotive Stealth 340 is capable of supporting approximately 900 FWHP naturally aspirated @ 60psi. That's a lot of pump for most applications running at battery voltage.

For most N/A applications running 550hp and below (includes a good safety factor) and running a traditional pumping arrangement the Walbro 255lph (GSS340) is a good economical choice that has much less power demand than the Aeromotive 340.

All pumps however are subject to damage when run dry.

The pressure scenarios you mention are typical of a pump that is on it's last legs. When cool they will run for a short time, then pressure will begin to decrease. The "short time" gets shorter and shorter until complete failure arrives. If you have a fuel pressure gauge it's very apparent. I went through multiple GSS340's before I gave up on the traditional systems.

If you're going to stick with either of these pumps I suggest keeping the tank at least 1/2-full. This allows the pump to be partially submerged at all times and allows for a larger mass of fuel to absorb heat.

rickpaw · #6 10-19-2013, 07:54 AM

Thanks Carl for chiming in. In all occasions when the pressure dropped, the tank was at /2 mark, in fact it happened after we filled the tank. I'm very certain that the pump was submerged in fuel the whole time. The pumps are new. First one had 600 miles. The 2nd one has 400 miles.

I'm going to switch the pump over to a mid 90s Chevy pick up pump. That way I can get replacement at local part store. In MS, I walked into the local part store and asked for a walbro or an aeromotive pump, and they had no idea what I was talking about.

Che70velle · #7 10-19-2013, 11:44 AM

Quote:

Originally Posted by rickpaw

Thanks Carl for chiming in. In all occasions when the pressure dropped, the tank was at /2 mark, in fact it happened after we filled the tank. I'm very certain that the pump was submerged in fuel the whole time. The pumps are new. First one had 600 miles. The 2nd one has 400 miles.

I'm going to switch the pump over to a mid 90s Chevy pick up pump. That way I can get replacement at local part store. In MS, I walked into the local part store and asked for a walbro or an aeromotive pump, and they had no idea what I was talking about.

As a suggestion, check your required fuel pressure. If your thinking about going to a mid 90's TBI pump, I'm not sure that would work, as they are 15-18 lb. pumps. The LS engines require almost 60lbs to work properly. I think the later year 96-98 chevy truck "vortec" had more fuel pressure than the TBI engines did, but how much more I'm not sure.

I'm not a fuel system expert by any means, but have you checked your tank venting? Seems like a long shot, but could this be a venting issue, causing a pump to overheat? Sometimes the biggest problems have the simplest fixes.

rickpaw · #8 10-19-2013, 05:57 PM

Quote:

Originally Posted by Che70velle

As a suggestion, check your required fuel pressure. If your thinking about going to a mid 90's TBI pump, I'm not sure that would work, as they are 15-18 lb. pumps. The LS engines require almost 60lbs to work properly. I think the later year 96-98 chevy truck "vortec" had more fuel pressure than the TBI engines did, but how much more I'm not sure.

You're right about the fuel pump from the truck. Actually it's from 97 vortec truck (AC Delso EP381). The same one being used by Rick's tanks, besides the Walbro 255 for stock LS engines.

We checked tank venting as well. It has Finch's dual vent set up. When we removed the fuel assembly, there was not any indications that the tank is not venting (ie no whooshing sound).

rickpaw · #9 10-23-2013, 05:15 AM

Well, I dropped an ACDelco EP381 in the tank. Hope it holds up in long drives. At least I can get a replacement pump at local parts store if that one fail on road trips. One thing I noticed was that the fuel pressure held steady at 58 psi after I shut the engine off (40 psi after 12 hr period), whereas the fuel pressure would immediately dropped to 0 with the old pumps (Aeromotive 340).