Help on Fuel System Issue

[adamsanders]

So some of you may recognize me from a recent thread about a new IP. To summarize, I recently bought and installed a new Mini Moose. The injectors on the truck may be original, they have grey paint, are labeled stanadyne, and have a "D" on them. Anyways, I have a problem where the truck runs really rough in spurts. It misses hard, starts knocking and rattling like crazy but then will usually level out and start idling ok again. This only happens after I actually drive the truck. I can't replicate it by just idling. I had settled on bad injectors but just for kicks I decided to check the Schrader valve while the truck was running. To my surprise NOTHING came out. No air either. I kept holding the valve open and eventually (10-20 seconds) the truck started stumbling bad and died. Took a second to get it fired back. The lift pump is within a month or two old and puts out fuel while cranking. The truck fires right up cold every time. What could this mean?

Here's videos of that sequence I described and the rough stumbling I have been experiencing. The second video is the missing/knocking after I have held that valve down for a while.

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[Thewespaul]

Sound like either a clogged fuel filter or a lift pump that needs returning

 

[adamsanders]

So you are thinking a fuel starvation issue? Would this have similar symptoms as an air intrusion? The knocking and carrying on in the second video is what has me questioning the fuel starvation but I am new to diesels.

 

[Dieselcrawler]

the knocking and carrying on is due to air. if no fuel is coming out the schrader, and you hold it in, you are introducing air into they system.

i have had many faulty lift pumps new. one of them i eventually figured out was not really reaching the cam. after some cuts and welds, i rebent the arm and it has worked great since.

 

[Dieselcrawler]

also the injection pump can pull fuel, but not really enough. i drove on mine for two days before i found out the lift pump was dead.

and btw it sounds like your pump is advanced a little high, unless the cold advance was still being powered in your first video.

 

[adamsanders]

also the injection pump can pull fuel, but not really enough. i drove on mine for two days before i found out the lift pump was dead.

and btw it sounds like your pump is advanced a little high, unless the cold advance was still being powered in your first video.

Ok the truck will also do this though while driving. (Not holding the valve open) Would an air leak prior to the lift pump cause it to not pump as much fuel as it should? I assume yes. So would the lift pump itself be leaking air or lines prior to the lift pump. I have over half a tank in the one I'm pulling from as well.

And the timing was a source of debate in the last thread. That's with the static marks lined up and cold advance unplugged.

 

[Dieselcrawler]

ok it still sounds advanced. if i have time i will post a video of mine and you can compare rattle.

as for the fuel, for a quick test. get 4 feet of rubber fuel line. unhook the inlet side of lift pump and install this line. run it into a can of diesel. then redo the test. if you still dont have fuel spraying out, either your filter is clogged so bad or the lift pump is not working. this eliminates the fuel lines, tanks and selector valve.

 

[adamsanders]

Ok I will try that. I changed the filter when I changed the pump so I would be surprised if it is already clogged. For the sake of being prepared, if I have fuel spraying out, where do I look next? The air leak problem is making the the truck non-drivable its so bad.

 

[adamsanders]

ok it still sounds advanced. if i have time i will post a video of mine and you can compare rattle.

as for the fuel, for a quick test. get 4 feet of rubber fuel line. unhook the inlet side of lift pump and install this line. run it into a can of diesel. then redo the test. if you still dont have fuel spraying out, either your filter is clogged so bad or the lift pump is not working. this eliminates the fuel lines, tanks and selector valve.

Will you or anybody else confirm that this is not right!!? It may be hard to see but I put clear like from the hard line to the lift pump and I would say there's a 50/50 mix of fuel and air going to the lift pump.

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[IDIoit]

youre sucking air in before the lift pump. common issue is the fuel switch valve.
do your fuel tanks read right?

 

[adamsanders]

Yes, I believe so. I've only ever used the back one though because the PO said the front tank had sat for years and had never been drained. I just drained it and cleaned up and got back on the truck a few days ago. Haven't tried it yet though. So I am right in thinking that line should have been pretty much solid fuel?

 

[madpogue]

^^^^ Yes, but without the "pretty much". Try running a line right from a jerry-can of diesel, see if that makes it go away. If so, then just start working your way back. Disconnect the supply at the selector, and run it from a jerry-can. If you get air, there's an air leak between there and the engine. If that's good, run a line from the front or rear supply inlet to the selector from a jerry-can. If there's air, the selector is faulty. If it's good, go as far back as the tank. If there's air, the line from that tank to the selector is the suspect. If good, then the pickup inside the tank is likely picking up air.

 

[adamsanders]

Ok awesome. I will do this and report back this weekend.

 

[adamsanders]

Bypassed the FSV straight to the front tank, no more air. Seemed to run fine as well. Thanks again

 

[adamsanders]

youre sucking air in before the lift pump. common issue is the fuel switch valve.
do your fuel tanks read right?

I do have a question though, I have searched and found good info so far but I wanted to clear up something. Because I go rid of my FSV, I my guage obviously didn't work. I wanted to jump it and make it read front tank only. I took and jumper and jumped the DB/Y wire to the Y/W wire. Before my gauge was pegged full and after doing this it reads empty all the time (it's not). After I turned the ignition off, it drifts to about a half tank but goes back to empty as soon as I turn the key on. I understand this is probably a short to ground. How could I find this?