air getting into fuel lines

[tstone]

I had the exact problem with my M35 about 3 years ago. I replaced my lifter pump with a used one that was in good working order; my problem was resolved.

As long as my rpm's were in the driving range the engine ran ok, as soon as I would slow down or stop at an intersection the vehicle would die. When I bled the fuel system (low presure side, in the intersection) the vehicle would run for a few miles and die again. Replaced the pump and had no more problems. Hope this works for you.

Tom

 

[hawkeyepoole]

Unfortunately, my real job as a highly paid, top secret spy for the federal government on Internet forums, will keep me busy until next weekend. I'm looking at a few possibilities, including the primary filter sucking air despite proper torque and a new filter gasket. Also the in-tank pump possibly having issues. I am running Waste Motor Oil which is thicker than diesel, even when thinned some with diesel.

If anyone else has suggestions, please LMK. I'll post what I find next weekend.

 

[onegmjack]

I only run Diesel,to many threads on unexpected no runs,no starts,pistons and rods getting out of the block and other problems.

 

[hawkeyepoole]

Well, BlueDeuce and I worked on the truck on Sunday afternoon down at the hangar. We discovered something interesting. While experimenting to see where air might be entering the fuel system, I replaced the short piece of rubber hose on the driver's side underneath the IP and steering box, with a piece of clear hose from Home Despot. With the truck running we were watching for bubbles and after a couple of minutes noticed that the line had collapsed on itself indicating that the lift pump was no longer 'pushing' fuel through the system.

As an experiment we separated those lines and started the pump. At first it was a nice big steady flow, but after a minute or two the flow slowed down and after five minutes had only pumped about two gallons into a bucket. We now suspect that a poorly operating in-tank pump is causing some failure elsewhere allowing air into the fuel system.

BlueDeuce is checking with someone else for ideas, but my next one is to get a 30 year newer in-tank pump to replace the old one.

Suggestions? Comments? We did not ever see any air bubbles coming from the primary filter, BTW.

 

[Blueduce]

Hawkeye,

My sources say it's the lift pump in the tank failing. Thus starving the injector pump. Then the high pressure side is sicking air from somewhere? Running the straight WMO may be part of the problem as well. Suggestions would be to replace in tank lift pump, replace all fuel filters and gaskets and instead of running straight WMO Run at around a 60% diesel WMO mix. Let me know if you need a hand. Send Machinist75 a PM he just replaced his lift pump with a new pump from an APC or something like that. He says it works great at almost half the cost.

 

[onegmjack]

I don't knock anyone that runs waste oil or other fuel.Just reading thread after thread about no starts engine running fine then blowing up.I'm just wander if WMO WVO is hard on these trucks at their age.Mine may blow the next time I start or drive it,but it have ran trouble free on Diesel since I got it in 2009.I know everyone will say they are Multi-Fuel engine,but was they made to run only on waste fuel?

 

[hoop]

The Truck will run without the lift pump, if the primary filter will pass enough fuel for the IP.
Yes, Your lift pump may be bad....but that is not where your air is coming from.
Do your same test on the tank side of the Primary filter and see what you come up with.

 

[Kohburn]

The Truck will run without the lift pump, if the primary filter will pass enough fuel for the IP.
Yes, Your lift pump may be bad....but that is not where your air is coming from.
Do your same test on the tank side of the Primary filter and see what you come up with.

I would do this if only to see if the primary filter is causing too much restriction

 

[hoop]

I would do this if only to see if the primary filter is causing too much restriction

Ditto.

 

[hawkeyepoole]

Just so everyone knows, I don't run straight filtered used motor oil. First of all much of my free fuel is very heavy weight oil from radial aircraft engines. I thin it with Jet A (like kerosene) so that it's pretty thin. It's not as thin as diesel, but it is much thinner than straight aircraft oil. Same when I'm running used passenger car oil. It's thinned with Jet A or diesel as well.

There is some seal somewhere that is allowing air into the system when the lift pump isn't pressurizing the entire fuel system properly. I'm afraid it's in the IP itself, and if it is, it's likely beyond my budget to fix for the foreseeable future.

I'm hoping that fresh filters (which I'm pretty certain are not part of the problem as I filter the used motor oil to 1 micron with Duda Diesel bag filters) and a new style and 30 year newer lift pump will fix my issues for now.

I ran 2500 miles last year on waste motor oil and Jet A mix with no issues. BTW. Anybody who blew a piston out of the block didn't do it because of the fuel. 4K rpm will send a piston flying with any fuel.... My truck runs noticeably better on WMO than on straight diesel oil. More power, starts quick, no smoke.
Besides.... I spent $50 on fuel for 2500 miles of driving!

 

[hoop]

"We did not ever see any air bubbles coming from the primary filter, BTW. "
Did you have any air in the system after the test?

 

[hawkeyepoole]

A little. We're thinking there's a weak seal somewhere possibly inside the IP and when it has to pull hard to get fuel from the tank 3 feet below, plus the higher viscosity of the fuel is likely causing the unknown seal to leak.

I bought a completely new set of filters and a new pump last night. Friday I plan to put them on the truck and see what happens.

 

[hoop]

" pull hard to get fuel from the tank 3 feet below"
3 feet below where?
At the most the IP is 18 inches above the bottom of the fuel tank.
Good Luck.
I am Out.

 

[G-Force]

Your primary fuel filter is creating a restriction. This is causing the gear pump, which by the way is the fuel pump, to pull the suction line down into a vacuum....which you witnessed when the clear line collapsed. Take the primary filter out and run it with the clear line and see if it does it again (collapse the clear line) I bet you it doesn't

 

[hawkeyepoole]

I replaced the in-tank fuel pump with a new one made by Parker Airborne that I bought from Beltfed34 on eBay. That thing slings fuel like I could water my lawn with it!

However. I still have the same problem. The primary filter is not likely a restriction, although it was 11pm when I finished with the pump last night and haven't changed it. If it's less than 100deg tomorrow afternoon, I'll go change all three fuel filters just for something fun to do.

The only modification I've done to anything related to the engine is turn up the fuel about one full turn for better power. Still only put out about 7psi of boost.

Is it possible for the main Injector Pump to pull air into the system?

Here's a picture of me (left) BlueDeuce (right) and the Vietnam Veteran's Museum of Mineral Wells (middle) at Meacham Field today for the 87th anniversary of Meacham Field.

 

[silverstate55]

I recently changed out all my filters as well as cleaned out all the crud that had collected in the bottom of the canisters. I don't know how this truck was making fuel pressure at all, as the conical base that the primary filter was supposed to be sitting on was actually placed at the top of the filter (like a Vietnamese field hat), restricting filtered fuel flow. And of course the secondaries were both missing their base plates for the filters to sit on, so they were just flopping around inside the cansiters...I had to use fender washers drilled out the right diameter to just slip over the threaded rods, in order to keep the filters seated against the top plate. I'm just glad that the springs were still on the threaded rods, I have lots of washers & O-rings.

Have you verified that everything is actually installed properly in the primary filter? If so, I'd try replacing it with an aftermarket spin-on unit and see if that helps any.

 

[jimmcld]

I've had a few gas burners do something similar. It was sediment in the tank. When the in-tank pump is running it picks up the sediment and traps it against the in-tank filter to the point that the in-tank pump can no longer pump. The motor quits and sits for a few minutes and the sediments fall back down off the in-tank filter and then the pump will pump again. If this were the case, the air is a separate issue only coming to light when the IP has to try to pump the fuel from a clogged line.

 

[hawkeyepoole]

I have replaced all three filters since initial restoration. I am certain they are properly installed. I am planning to replace all three next weekend, just because...

I filter my WMO to 1 micron with three Duda Diesel filters. I use a 10 micron inside a 5 micron inside a 1 micron.

I have also drained the tank completely and flushed out everything in there. It was relatively clean considering 33 years of use.

Since my vehicle belongs to a 501(c)3 non-profit museum, I'm going to see if I can reach the local National Guard depot, where they have a major repair facility and see if they'll be willing to help at all.

At this point I'm very afraid its something in the Injector Pump causing the issue. We don't have much bux for a major repair.

I travel for work and I'll be back in town this Friday. I'll see what we can figure out between now and then.

BTW the local National Guard outfit is in Saginaw Texas and if anyone knows anyone there who might be helpful, please let me know. I don't know a soul there.

 

[jimmcld]

If I understand you correctly, the short piece of hose that you sucked flat is the hose from the primary filter to the fuel pump. If that is correct, then you have some sort of restriction between the fuel pump and the fuel tank. The only components between the fuel in the tank and the fuel pump are the lift pump, the primary filter, and the connecting lines. It sounds like you have the problem narrowed down. I would check to see what kind of flow your getting out of the primary filter next. It could be that your primary filter just can't flow enough of the heavier oil. If that's the case, it may then be sucking air from the flame heater.

As far as Saginaw is concerned, I don't know if they have anyone left who has worked on these old motors. The old Master Sargeant retired about a year ago and most of the remaining guys are just young kids.

Give me a call if I can help:

Jim
940-368-7560

 

[G-Force]

Hawkeyepoole,
Do this, remove the primary fuel filter element and do the clear hose test again. If the hose does not collapse again then your restriction is your filter. your fuel is too thick to run through your filter or your filter is clogged. Most likely the fuel is too thick.