Fuel Cavitation & Boiling Issue
Fuel Cavitation & Boiling Issue So I am having a problem with my inline fuel pump cavitating and boiling the fuel causing vapor lock. I am also going through about 1 MSD pump every 5,000 miles or so. The pumps are not dying, but the check valve keeps going bad causing me to have to prime the system (turn the key) a few times before fire up. My fuel pump is mounted in close proximity to my fuel tank, but is mounted on the frame rail. There is nowhere I can mount the pump to increase the air flow in my application. I know the cheap vane pumps are notoriously inefficient and waste most of their amperage through heat. I also know ideally I should have the pump inside the fuel tank but don’t want to spend $700 on a tank. I am looking into a fuel pump controller to solve the issue, but are there other ways to solve this problem that cost less? This is on a '67 Bronco with a stock 5.3 so fuel demand is not high.
Last edited by madmaro00; Aug 5, 2014 at 05:00 PM.
"My fuel pump is mounted in close proximity to my fuel tank, but is mounted on the fuel rail."
Huh??
Tank vented?
Unless the tank is on the hood, it's much lower than the pump. Most any remote pump should be at or below the bottom of the tank. Not the other way around.
Huh??
Tank vented?
Unless the tank is on the hood, it's much lower than the pump. Most any remote pump should be at or below the bottom of the tank. Not the other way around.
Launching!
Joined: May 2012
Posts: 205
Likes: 2
From: Mobile, Alabama
You should google vetteworks - their F body pump kit. Looks like your tank is flat on the top and is deep enough for a late model fuel pump module. I am guessing you meant your regulator is on the rail? You can use the module with the regulator on the pump or on the rail. I used a used module, (not F body but very similar), and put a new 6.0 pump in it. ~$50.00 all in, but I didn't use a kit, I made my own mount for the pump in my stock tank. I ran nylon fuel lines, so I basically have a stock GM fuel system. I left in my stock level sender, or you can use the one on the module.
TECH Resident
Joined: Feb 2014
Posts: 954
Likes: 9
From: Encinitas CA
I run a Bosch pump from an OEM Mercedes application outside of the tank. I removed the check valve with no issues. Engine starts on first crank. I wait until I hear the prime function stop.
This is some derivative of the 044 series Bosch pump. In the OEM application, they were setup to run two in series (not parallel) in case one craps out. I only use one and it works great. I do have a large canister filter between the pump and tank. In the past, I had particles block the pump, so I've been running a non-restrictive filter without issue.
I wonder if you could try removing the check valve? I had thought it was only useful in maintaining system pressure between starts. Given that the GM PCM primes the pump for a few seconds, I don't think this is an issue.
Next, it might be worth locating one of these Bosch pumps? They are readily available at a junkyard. Mine came from a 1992 500E, which is a 5 liter V-8, but any of the 90s V-8 mercedes should have similar. I only suggest junkyard as they are rather expensive new. And they are ultra-reliable.
Curious, how do you know it is cavitating? Seems to me this would:
1. change the tone of the pump (you can hear it working harder)
2. first symptoms would come under WOT (where it would stumble).
Is there a chance there is a restriction between pump and tank causing the pump to work harder?
Doug
This is some derivative of the 044 series Bosch pump. In the OEM application, they were setup to run two in series (not parallel) in case one craps out. I only use one and it works great. I do have a large canister filter between the pump and tank. In the past, I had particles block the pump, so I've been running a non-restrictive filter without issue.
I wonder if you could try removing the check valve? I had thought it was only useful in maintaining system pressure between starts. Given that the GM PCM primes the pump for a few seconds, I don't think this is an issue.
Next, it might be worth locating one of these Bosch pumps? They are readily available at a junkyard. Mine came from a 1992 500E, which is a 5 liter V-8, but any of the 90s V-8 mercedes should have similar. I only suggest junkyard as they are rather expensive new. And they are ultra-reliable.
Curious, how do you know it is cavitating? Seems to me this would:
1. change the tone of the pump (you can hear it working harder)
2. first symptoms would come under WOT (where it would stumble).
Is there a chance there is a restriction between pump and tank causing the pump to work harder?
Doug
Cavitation & boiling the fuel are two different things. Cavitation can be caused by trying to push more fuel than is required, or not having large enough fuel lines.
Boiling is a product of heat.
Either problem can be dealt with, or at least minimized, by using a return type regulator mounted on the fuel rail. Also increasing the size of the fuel lines would help reduce cavitation.
Good luck.
Boiling is a product of heat.
Either problem can be dealt with, or at least minimized, by using a return type regulator mounted on the fuel rail. Also increasing the size of the fuel lines would help reduce cavitation.
Good luck.
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Verdad Gallardo Thanks for all the input guys. I’ve had this setup for about 6 years now and besides the check valve issue I have only had the boiling problem a few times. Problem is that I am afraid to take it on long drives in the summer heat because that is when it will do it. I know it is boiling because I got burned by the fuel when removing the line off the front of the pump trying to diagnose the problem on the side of the road. The pump was incredibly hot to the touch & when the line was removed it spatted a bunch of air out, followed by some crazy hot fuel. It was not one of my brighter moments, but admittedly I don’t do my best thinking in 110° heat on the side of a freeway with a broken down vehicle. I’ve never had the problem unless it is over 100°. I have no problems with fabricating but how do you intelligently clean up a used gas tank for welding? The tank is only a couple years old so the metal shouldn’t be degraded.
I am running the stock fuel rails on my 5.3 so it is a return style with the regulator on the fuel rail.
I am running the stock fuel rails on my 5.3 so it is a return style with the regulator on the fuel rail.
Can you better describe what and how you fuel pump, lines, etc and post pictures of the setup that you have.
You stated that you have the pump mounted on the rail, but the question was asked twice before. Is the pump at or below the bottom of you tank ?
if not... you are going to keep having issues.
You stated that you have the pump mounted on the rail, but the question was asked twice before. Is the pump at or below the bottom of you tank ?
if not... you are going to keep having issues.
The pump is mounted on the frame rail about even with the output of the tank but about 16" away. I cannot mount it any lower or it will get destroyed when rock crawling. It sounds like I need to just stop being cheap and lazy and put in an in-tank style pump. Is a fuel pump controller likely to stop the pump overheating / fuel boiling issue?
12 Second Club
Joined: Jan 2014
Posts: 565
Likes: 0
From: 217
You could put a fuel cell in it mounted between the rear seat area and tailgate. The sump would extend just below floor. You would get syphoning effect after pump primes due to pump being lower than the fuel cell. This will help that pump stay cool and give you more ground clearance. External pump do NOT like to pull fuel only push.
The two most common instalation mistakes on using Inline pumps are 1) not mounting the pump below the tank and 2) mounting the pump to far away from the tank. As stated, inline pumps are designed to pump and do a bad job of sucking, which might be causing the overheating of your pump or adding to the issue.
Being 16" is not to bad, but in combination with a higher pump mount location is combination for problems.
You really need to get some air flow to cool that pump. Heat is a common cause of failure with inline pumps.
I would really recommend going intank. Tanksinc is a good cheap solution and you will not have to do any welding. A good clean out of the tank will do. I am using the Tanksinc PA4 setup in my Nova and have had no problems.
BC
Being 16" is not to bad, but in combination with a higher pump mount location is combination for problems.
You really need to get some air flow to cool that pump. Heat is a common cause of failure with inline pumps.
I would really recommend going intank. Tanksinc is a good cheap solution and you will not have to do any welding. A good clean out of the tank will do. I am using the Tanksinc PA4 setup in my Nova and have had no problems.
BC
The fuel pump getting hot can be caused by it having to work too hard. Being mounted level with the top of the tank is too high. This could also be contributing to the cavitation issue, it would get worse the lower your fuel gets.
The heating issue can also be caused by insufficient electrical system. Check the voltage at the pump. It should be within a few tenths of a volt as your battery. The lower the voltage the higher the amperage goes to perform the same. Higher amperage results in higher heat. This will result in pump failure.
Check the voltage and the wiring. Make sure you have the proper gauge wire. Being to large is almost as bad as being too small.
The heating issue can also be caused by insufficient electrical system. Check the voltage at the pump. It should be within a few tenths of a volt as your battery. The lower the voltage the higher the amperage goes to perform the same. Higher amperage results in higher heat. This will result in pump failure.
Check the voltage and the wiring. Make sure you have the proper gauge wire. Being to large is almost as bad as being too small.
The fuel pump getting hot can be caused by it having to work too hard. Being mounted level with the top of the tank is too high. This could also be contributing to the cavitation issue, it would get worse the lower your fuel gets.
The heating issue can also be caused by insufficient electrical system. Check the voltage at the pump. It should be within a few tenths of a volt as your battery. The lower the voltage the higher the amperage goes to perform the same. Higher amperage results in higher heat. This will result in pump failure.
Check the voltage and the wiring. Make sure you have the proper gauge wire. Being to large is almost as bad as being too small.
The heating issue can also be caused by insufficient electrical system. Check the voltage at the pump. It should be within a few tenths of a volt as your battery. The lower the voltage the higher the amperage goes to perform the same. Higher amperage results in higher heat. This will result in pump failure.
Check the voltage and the wiring. Make sure you have the proper gauge wire. Being to large is almost as bad as being too small.
I've checked the voltage and current draw in the past and it is fine (I'm an electrical engineer). I am using the same inline pump but mounted in immediate proximity and below the tank on my '67 Camaro and it hasn't given me any issues. Sounds like you guys have hit it on the head with my **** poor placement due to lack of options. I will check out Tanksinc for some systems and go from there. Thanks for all the advice guys.