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I having been having nothing but issues with my custom fuel system onmy LS powered Volvo 740 since the start for about 1 year now. I used to have LP pump feeding a swirl pot feeding a Bosch 044 fuel pump andhad issues with cavitation after longer drives even after switching the inlet to a -8, buying a new pump, changing the swirl pot feed locations. The pump would destroy itself and send super fine metal grit down thesystem clogging up my fuel injectors (getting passed a 40 micronfilter) after about 40 miles of driving. And I did this about 4 times each time trying to change something. No luck. (but I did put a 10 micronfilter pre injectors that would clog up instead). The pumps have never completely failed but start to affect the motor. So I got mad and ripped all that out and went with a Walbro 255 mounted rightbelow the fuel cell (simple right?) which I thought would be perfect just had to watching getting to low on fuel. I also found out that the anti slosh foam clogged up the first fuel filter (maybe that was the issue with the first setup all along) so I took that all out as well. The pump sounded fine at idle and went for the first drive. It immediately started to sound awful and I assumed that due to not having any anti slosh foam that the pump must have pulled in some air. I had about 5 gallons of gas in the tank at the time. I installed some plastic baffling and reinserted some foam around the pickup filled it full of gas and no luck. Same problem even with a full tank and with the car not even moving. I also observed bubbles coming out of the return line but I have no idea where they are coming from. The fuel system doesn’t leak anywhere. Here is the setup:
Fuel filter: Aeromotive 40 micron https://www.summitracing.com/parts/aei-12353/overview/ Regulator: Aeromotive, set at 58 psi, using the vacuum. ECU has been tuned forthis https://www.summitracing.com/parts/aei-13136?seid=srese1&cm_mmc=pla-google-_-shopping-_-srese1-_-aeromotive&gclid=EAIaIQobChMIoPak1b361gIVw7XACh11o wbTEAQYASABEgKblPD_BwE
100 micron before pump to protect the pump and 10 micron after the pump to protect the injectors. The filter pictured with the pump looks a little bit small, does it flow enough to support the pump? Also, just because it doesn't leak fuel doesn't mean it isn't pulling in air because fuel something like 600 times denser than air. I know nothing about that car, so I can't be sure from the pictures. The lines from the sump of the tank do come off of the rear and the fuel pump is behind the tank?
Whilst it may or may not be the problem, any pre-filter needs to be big. I never understand why people fit tiny little filters in front of high flowing setups.
100 micron before pump to protect the pump and 10 micron after the pump to protect the injectors. The filter pictured with the pump looks a little bit small, does it flow enough to support the pump? Also, just because it doesn't leak fuel doesn't mean it isn't pulling in air because fuel something like 600 times denser than air. I know nothing about that car, so I can't be sure from the pictures. The lines from the sump of the tank do come off of the rear and the fuel pump is behind the tank?
I will try to figure out a larger fuel filter. Packaging is the hardest part to work though since I'm trying to keep the fuel line from going up. Maybe that doesn't matter as much?
I did check all my lines and everything was tight. I think I'm going to redo the copper crush washers on the fuel pump.
The lines from the tank go forward so the fuel pump is in front of the tank mounted to the K-member.
Whilst it may or may not be the problem, any pre-filter needs to be big. I never understand why people fit tiny little filters in front of high flowing setups.
What product would you recommend? Tight packaging was my reasoning. I have an expensive (not that that means it's good) Aeromotive 40 micron fuel filter after the pump and it is not much larger than the one coming off the tank now. The filter element is probably only 1/2 in diameter and and 1 in long. I'm not saying you are wrong but that filter is also brand new and not clogged yet. Now maybe after 500 miles it might get clogged but I wouldn't think it is causing my issue right now.
Maybe its a no no to run a 40 micron pre filter?
I could take it out of the equation for testing reasons, or do you think that is to risky on the fuel pump?
A filter can be brand new and totally clean but still be restrictive because it's too small. The micron size can be right but still be restricted due to low capacity. This might be your problem.
If your pump is below the tank it won't matter much if the line goes up and back down because once it's primed the fuel travels down further pulling it over the hump like when a toilet flushes.
40 before could be your problem in the since that the same size 100 micron filter could flow more through the 250% larger holes. They normally call just for 100, but most of the socks are 100 to 60 micron. You will want to have your filter flow more than your pump so that you run it without cleaning it each weekend.
If the low part of your sump goes forward on the tank you will risk accelerating the fuel away from the pickup any time the tank gets low. Keep the tank above half full while you sort the rest of the system and once it is solid run it low and you'll know what is causing the issue if it comes back.
What product would you recommend? Tight packaging was my reasoning. I have an expensive (not that that means it's good) Aeromotive 40 micron fuel filter after the pump and it is not much larger than the one coming off the tank now. The filter element is probably only 1/2 in diameter and and 1 in long. I'm not saying you are wrong but that filter is also brand new and not clogged yet. Now maybe after 500 miles it might get clogged but I wouldn't think it is causing my issue right now.
Maybe its a no no to run a 40 micron pre filter?
I could take it out of the equation for testing reasons, or do you think that is to risky on the fuel pump?
It's a no no to run a filter with inadequate area for the flow levels required.
Holley, Earls, Aeromotive etc all make larger CSA filters than the little one you have.
When it's gravity only and not pumped....fit the biggest damn filter you can, there are no downsides ( other than finding room of course ). Never go small.
I use the Holley/Earls 260gph filters pre- each pump.
Ok, I got a new Holley fuel filter on order. I'm not 100% sure where I'm going to mount it. I'm thinking on the flat portion of the K member right about the sway bar mount. But that would put it at about 1/2 up the tank. Or I might fabricate a bracket to mount it right about the fuel pump. Either way I should know by Saterday if it will work.
I installed the new fuel filter right above the fuel pump. About 3/4 of the filter is still below the lowest point on the tank so I was happy with it. Got it together, took it for a test drive and the pump was perfectly quiet. Did a WOT pass got it up to about 5k and it leans out. Was much better than it was before but still no good. Under normal acceleration it was fine. Had 2/3 of a fuel in the tank. So I figured must be a baffling issues as the fitting must have ran dry from fuel moving back.
So I get it back to the garage and take my baffling out of the tank and all I see while the pump is running is a very constant flow of air bubbles. I even idled the car for 5 min and the fuel pump inlet was completely submerged the whole time. The bubbles were also not being sucked back into the fuel inlet. I checked all the lines and they were tight. I would think that if I did slosh the fuel around and run air through the system that it would puke it out and get on with normal operation.
How does the pump actually sound ? Does it sound healthy, or does it sound like its cavitating ?
Before the new fuel filter, pump sounded awful and was cavitating. Now the pump is quiet. I even turned the car off during the test drive and cycled the pump to make sure I didn't hear any cavitation.
My thoughts/questions now are:
1. Maybe I'm vaporizing fuel?
2. Maybe I have a bad AN line on the vacuum side?
3. Air is leaking in somewhere further down the pressurized area (fuel filter, regulator), Which I don't think would happen since you are making pressure.
4. Maybe the pump isn't keeping up with motor demands (wouldn't explain bubbles)
I got hp tuners out and left the fuel pump on whilethe engin was off and investigated. I thought the fuel regulator was making some weird noises (maybe it’s normal but could never hear it with the motor) so I bypassed it and no air bubbles. So I took it out, replaced all the fitting o-rings, re did the tape on the gauge npt, and took it apart and cleaned it (wasn’t that dirty and still looked good). Put it back in and same problem..... hmmm.
If the pump is quiet and a nice steady tone, that's usually a good sign that pump is ok and supply to the pump is ok
As for bubbles....it isnt too often the return line needs inspected so hard to comment there as it's maybe been 10 years or so since I've even looked at a return. But lots of fuel is moving, so I guess it's maybe not too unreasonable to see some bubbles.....although during those tests on mine it isnt something I recall.
but as you say, the system is under pressure....any leaks will not introduce bubbles....they will expel fuel all over the place !
With the pump quiet, are there running or pressure problems ?
You indicate earlier "it leans out"...explain ?
The car runs bad and shows a lean AFR ? The car runs fine and sows a lean AFR ?
The car is traction etc throughout this ?
During this lean spell....are injector pulse widths changing, either getting higher than lower than just prior to it happening ?
During this lean spell, what is fuel pressure doing ?
If the pump is quiet and a nice steady tone, that's usually a good sign that pump is ok and supply to the pump is ok
As for bubbles....it isnt too often the return line needs inspected so hard to comment there as it's maybe been 10 years or so since I've even looked at a return. But lots of fuel is moving, so I guess it's maybe not too unreasonable to see some bubbles.....although during those tests on mine it isnt something I recall.
but as you say, the system is under pressure....any leaks will not introduce bubbles....they will expel fuel all over the place !
With the pump quiet, are there running or pressure problems ?
You indicate earlier "it leans out"...explain ?
The car runs bad and shows a lean AFR ? The car runs fine and sows a lean AFR ?
The car is traction etc throughout this ?
During this lean spell....are injector pulse widths changing, either getting higher than lower than just prior to it happening ?
During this lean spell, what is fuel pressure doing ?
I went for a longer drive and the fuel pump started to act up (sounds like it's cavitating/horrible noises), but only for a second or two for every minute of driving. The lean out was the engine completely cutting out at 5k @ WOT and the wide band going from 12 to maxed out lean on the gauge. Under normal driving the car seems perfectly fine minus the LTFT are lean and my bank 1 to bank 2 is way off. So it's compensating and the wide band is giving me 14.7.
The injector pulse widths should be fine as it's been 80% tuned with the other fuel setup with no issues. I don't know about fuel pressure but I'm assuming its dropping off. That is my next step to monitor in the car as I don't have the capability right now. Obviously that is a very important data point.
I did talk to an Aeromotive tech today and he said the following:
1. Take out the post regulator fuel filter it's causing a block
2. Bubbles in the return line is ok, but return that right next to the fuel pump inlet is bad
So I am going to change the 40 micron filter for a new 10 micron Aeromotive cartrige style. Drill a new bulkhead fitting into the fuel tank on the opposite end of the tank up high. Remove the 10 micron filter that I have post regulator.
Anyone want to buy a bunch of slightly used fuel system parts? I'm amassing a big parts bin....
You have to release I'm on the 50th iteration of this thing. I orginally had 2, a 100 and the current 40. I had issues then with my fuel pump disengrating getting though the 40 and clogging up my fuel injectors which have a tiny little 10 micron on them. So I added a 10 before the rails and left the 40 since I didnt think it was hurting anything.
Originally Posted by stevieturbo
Dump either the 40 or the 10, ideally the 40.
I'm getting rid of the 10 after the regulator and turning the 40 into a 10.
Originally Posted by stevieturbo
Dump that check valve, not needed.
Already done as I took that out to rule out durring my weekend testing. I had researched that a check valve helps on hot days for hot startups.
Originally Posted by stevieturbo
Post a picture of how you have the regulator plumbed..
I know I have it plumbed correct but I can get a photo on Thursday. It's a Aeromotive 13129, return out the bottom. Feed and rail out the sides.
Originally Posted by stevieturbo
What do you intend to drill the hole in the tank for another fitting for ?.
The current return and feed are about 3 in apart in the same plane. The Aeromotive guy said that they are way to close together and it's causing turbulant flow right at the feed line. He said if bubbles are being made they could be getting sucked back in which I can see. So I am going to plug the current return line and put another bulkhead fitting on the other side. I was just using what the tank had when I bought it.
Originally Posted by stevieturbo
And as for answers to earlier questions...no assumptions, data is needed.
I agree, but I can't get data to you with gauges I dont have yet. I understand the importance of data.
Lots of OEM's and others return fuel into the bucket the pump actually lifts from, so I'd have a hard time believing a return close to the pump is an actual problem. Possible...but I just dont see it.
I'd maybe try running a long hose back into the fuel filler for example before making permanent holes in the tank.
10-18-2017, 10:39 AM
Fuel Pump Issues 
