Air bubbles in fuel lines

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

bj74redrider

bj74redrider

10 Year 15 Year
Joined
Sep 26, 2009
Threads
19
Messages
131
Location
Vicoria BC
I've been trying to trace a hard starting rough idle problem for months now.
Some background, Valves adjusted, timing bang on, Bosch primer installed, banjo bolt mesh filter cleaned at lift pump, I'm using standyne in the fuel. New fuel filter/ air filter. Water sedimented removed for now.

Yesterday I used some clear hose and worked my way back from the injection pump and fund there is a steady stream of air bubbles. I'd say 30/70 air bubbles to fuel though that ratio varies with different rpm. So I replaced all the hose clamps and hoses and still bubbles. dropped the fuel tank inspected the pickup, it was good, still bubbles. I have inspected all the hard lines and they seem fine, no leaks.

Question is, does anyone have any tricks to finding an air leak in a diesel system. Is there a vacuum test or something else I can try? Snap on has a vary expensive smoke machine that seems like it may help but it is 600 bones.

Thanks
 
Install an electric pusher pump near the tank. It will then push diesel out any small cracks rather then suck air like you lift pump is doing. Look for any damp or dripping diesel spot on the connections, metal lines and hoses. With 30% air bubbles, I am surprised it ran at all. You must of had big clouds of white smoke.
 
I'd check the pickup again, it can be cracked and let air inside the system.... maybe replace all soft lines with clear lines so you can see where the air is coming in the system...
 
Apply air pressure to your fuel tank and check for damp spots around suspect areas using facial tissues.
 
I posted this for a similar thread some time ago. Perhaps some of this will be helpful.

The IP has two "pumps", the first ( on the side of the IP) is the transfer pump that moves fuel from the tank to the IP.

A good check is to remove the fuel line from the transfer line and put clear plastic fuel line from the transfer pump into a container of diesel on the ground under the engine. Bleed the system with the primer pump (I like to keep a short - 10" or so - piece of clear line on the bleeder screw and keep it submerged in a plastic water bottle about half full of clean diesel - that keeps air from coming back into the system and avoids the mess associated with bleeding the system).

Start the engine, let it run for a while and see if there is any air in the supply line.

If there isn't, shut the engine down and keep an eye on the clear line. If bubbles start to move through the line you know that you have a leak in the primer or the line from the injector return line to the banjo fitting on the transfer pump. There is short piece of flex line at the back of the return rail that goes onto a steel line that runs behind the intake manifold down to the transfer pump.

A leak in that 3" line took me 2 days to isolate and 5 minutes to fix!

The clear line to the transfer pump was the answer for me but for all it takes to change that line it is worth it to assume that it might be leaking and replace it.

Of course all of the other suggestions you are getting could also be the problem.

Good luck!
 
buy some cheap petrochemical UV die.. ( a few bucks..) add it to the fuel.. then pressurize the system as stated by all.. then get up under there with your UV flashlight.. We use that die in everything.. oil, hydraulics, fuels, etc super easy to use and find leaks.. and then if you are really looking and you cannot find it.. use spray on foot powder and then it will really hold the dye and keep it form running.. super useful..
 
Thanks guys
I looked at the pickup again and it was fine, checked it with some air and it held psi. Placed clear tube on all soft connections and found the bubbles slowly grow as they make there way to the ip. Drained all of the fuel and plugged one end of the intake line while shooting air into the other I worked my way around the lines with soapy water a few times and found no leaks. Finally borrowed a friends vacuum tester, pumped 25psi into te lines and it held for over 20 mins. Started thinking that the intake and return ends of the pickup are so close together maybe I am sucking bubbles that are being pushed out of the return line, I separated the end and still have some bubbles. I tightened up all my clamps put everthing back together and found that the bubbles where noticeably better miraculously, but still there...some other things to note, when I remove the fuel cap, I get a loud hiss, like the take is pressurizing, shouldn't it be vented to atmospheric pressure?
Next is to check in front of the pump as canCrusher suggested.
Thanks for your ideas guys and gals.
 
Did your problem start after u removed the water sedimenter?
When u pump the primer does it build preasure and allow you to bleed the fuel filter? Pump primer and don't build presure and try to bleed filter and get a mixture of air and fuel?
 
I removed sedimenter after the problem started while troubleshooting. I can pump my primer and build pressure, when I crack the bleed screw I get mostly fuel with very small bubbles.
 
I had the same problem and found a large crack in the return side. Couldn't get much pressure with the pump but could not find any leaks either. Finally found the crack. Sounds like u have a handle on it. The pressure in your tank is the same thing mine does and I never Had a problem with it. Since your tank is holding vaccume, and if the problem is the supply side, it should be after the tank.
 
Was the crack you found a Rubber line? I just ran clear hose from the return and intake into a seperate bottle. The return line shoots out 50/50 bubbles to air and made a foamy bubbly mess in the bottle.
 
the tank shouldnt build any pressure/vacuum if all the breathers are allright, so maybe check the breather hoses from tank and "black box" inside the rear fender...
 
bj74redrider said:
Was the crack you found a Rubber line? I just ran clear hose from the return and intake into a seperate bottle. The return line shoots out 50/50 bubbles to air and made a foamy bubbly mess in the bottle.
Click to expand...

The crack was here in yellow and the rubber hose that attaches to the red arrow was old and worn so I replaced that too.
diesel return line.webp
 
Interesting, I will have a look at that pipe. Do any of the symptoms I describe match a dying lift pump of IP. My thought is if a lift pump is dying I wouldn't have much pressure in the return line, but fuel shoots out of there no problem.
 
I don't think your pump is bad. U might check the rubber hose that connects to that nipple in the pic. The metal line after the rubber hose that goes to the primer pump body can get a pin hole in it too and it's hard to see.
 
Some updates,

I tried running the UV dye through the entire system and did not find any leaks. I used some clear line as intake and return lines off the lift pump, and did notice many tiny bubbles being sucked through at a high rate.

Yesterday I installed a 24V Carter pusher pump near the tank. It has made the truck much worse, the idle is very rough now, with light surging and momentary losses in RPM.

I am now able to get fuel out of my injectors by cracking them, before the pusher pump, I was not able to get any fuel below about 1200 RPM.

Any ideas? I'm lost.
 
Very odd you did not find the leak after all that. Especially the electric pump install.

Confirm the following:
1. Did you put clear line on the fuel inlet of the filter? If yes were there bubbles?
2. Fuel outlet of the filter? Bubbles
3. Is it possible your fuel filter head is leaking the air?
4. I am thinking your fuel filter has a plastic bottom to drain water and contamination. If this plastic piece is cracked it is a hard find when looking for air leaks.


You posted after lots of looking the bubbles were better. Iam thinking you mean less bubbles. Trace your steps back to find out why the bubble factor has change.

Hope you find it.
 
Still looking for help on this issue.

I disconnected the pusher pump because it seemed to exasperate the rough idle. Now when I stop at a light the idle may be 1000rpm or 700rpm, I have a hand throttle and I am constantly adjusting it. The throttle cable is not binding at all. Is my IP governer going?

Confirm the following:
1. Did you put clear line on the fuel inlet of the filter? If yes were there bubbles?
2. Fuel outlet of the filter? Bubbles
3. Is it possible your fuel filter head is leaking the air?
4. I am thinking your fuel filter has a plastic bottom to drain water and contamination. If this plastic piece is cracked it is a hard find when looking for air leaks.
Click to expand...

1. I've put a clear line with a hose clamp on the inlet side of the lift pump, and have steady bubbles. When I pump the primer I get bubbles. no wet spots in that area, confirmed with the UV dye (which is very visible).
2. The return line is almost all bubbles, it looks like soapy water.
3. The fuel filter does not leak and I have recently replaced the inlet line and all the copper/rubber washers thinking the same thing.
4. I don't have the plastic bowl.
 
You must log in or register to reply here.

Share this page

IH8MUD Forum | Toyota, Lexus & Off-Road Community
Community platform by XenForo® © 2010-2026 XenForo Ltd.

© 2000-2026 Tie Rod Media LLC

Back
Top Bottom