Need Help Diagnosing Fuel Delivery Issue

[huskerfan]

Hey everyone, need some help diagnosing a fuel problem i am having with my 1986 M1028

I have wheeled this truck for a few years now, recently it started dying when i would let off the throttle. Changed the fuel filter and fuel pump, but now i cant get it to even fire. I back pressured the fuel tank from the IP, cracked every break in the fuel line from the tank to the fuel pump and had fuel at each break, but not at the inlet to the filter. Finally was able to get fuel to the filter by hooking a shop vac to the inlet line of the fuel filter while having the fuel tank pressurized. Then hooked the fuel inlet to the filter back up (it has a CAT 175-2949 spin on filter and i made sure to fill it with fresh diesel before putting it on) then hooked the IP return line hose back to the fuel shutoff solenoid (had it unhooked as that was where i was pressurizing the fuel tank from) and tried to start it but no luck. It will crank forever but wont fire. Cranked the front drivers injector line and there's fuel there, but i dont think it had much pressure as it wasnt spraying out much at all, just kind of dripping/bubbling out. Do you think my injector pump is shot? Only other thing i could think of was that maybe the sock in the fuel tank is clogged or something?

Thanks in advance for the help! Long time reader, first time poster, love this site!

 

[WWRD99]

If you're having a tough time getting fuel to the filter with it cranking a bunch then you have to start there. Is the fuel pump the right one? 60281 Carter number...others have the same. There's 2 pumps that come up in the parts catalog one works one doesn't. Could be a tank issue like the pickup sock is clogged. Since you popped air in the tank and couldn't get fuel up there it leans towards the tank. Second is glow plugs. These trucks will be extremely difficult to start without them unless it's already warmed up good.

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[huskerfan]

I guess I am not sure if it is the right one, but it is the same one that has always been on it and never had any issues - previous owner installed it

Truck should be warmed up just fine as it sits in my garage and it's easily 80 degrees out there

You think i should drop the tank and check the sock then?

 

[WWRD99]

I guess I am not sure if it is the right one, but it is the same one that has always been on it and never had any issues - previous owner installed it

Truck should be warmed up just fine as it sits in my garage and it's easily 80 degrees out there

You think i should drop the tank and check the sock then?

Oh I thought you changed the pump and fuel filter?

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[CARC686]

My lift pump's failure mode was a massive fuel leak. The truck still ran fine. When I had the symptoms described, the problem was my injector pump.

 

[huskerfan]

Oh I thought you changed the pump and fuel filter?

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I replaced the fuel pump and the filter with the same ones, just brand new

 

[huskerfan]

My lift pump's failure mode was a massive fuel leak. The truck still ran fine. When I had the symptoms described, the problem was my injector pump.

Where was it leaking from?

 

[CARC686]

Straight down onto the ground from the lift pump under the passenger side alternator.

 

[huskerfan]

Straight down onto the ground from the lift pump under the passenger side alternator.

Hmm yeah mine doesn't leak from there

 

[CARC686]

When I had your symptoms, the problem was the injector pump. The lift pump leak didn't stop the truck running. The failing injector pump did stop the truck running.

 

[huskerfan]

When I had your symptoms, the problem was the injector pump. The lift pump leak didn't stop the truck running. The failing injector pump did stop the truck running.

Did you by chance crack injector lines and see fuel getting there but not really spraying out under pressure like it should be? (at least i thought it should be)

 

[CARC686]

No, I just swapped in a new one and the truck ran again.

 

[Barrman]

Have you removed the check valve for the return line on the IP to see if it has a bunch of little black pebbles from a disintegrating IP?

Near the end of this video is what I am referring to:

 

[huskerfan]

Have you removed the check valve for the return line on the IP to see if it has a bunch of little black pebbles from a disintegrating IP?

Near the end of this video is what I am referring to:

Just tried that and there were no black pebbles or anything. Pulled the inlet line from the fuel pump and stuck a hose on it and put the other end in a diesel tank and still only cranked but wouldn’t fire. Gave it a little ether and it tried to fire but no dice. Cracked injector line and it took a bit to clear the air out but then it did the same thing and just was sort of pissing out. Think the IP is shot

 

[WWRD99]

Just tried that and there were no black pebbles or anything. Pulled the inlet line from the fuel pump and stuck a hose on it and put the other end in a diesel tank and still only cranked but wouldn’t fire. Gave it a little ether and it tried to fire but no dice. Cracked injector line and it took a bit to clear the air out but then it did the same thing and just was sort of pissing out. Think the IP is shot

Are you getting fuel to the filter though. You said it wasn't getting fuel through the filter. When you open the bleeder on the filter does fuel come out?

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[huskerfan]

Are you getting fuel to the filter though. You said it wasn't getting fuel through the filter. When you open the bleeder on the filter does fuel come out?

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Yes, I have fuel to the injector lines because when i crack them, fuel spurts out, but not really under pressure.

 

[WWRD99]

Yes, I have fuel to the injector lines because when i crack them, fuel spurts out, but not really under pressure.

That's not what I asked. Are you getting fuel out of the filter bleed screw. Best to hook the bleed screw to a bottle to see how much fuel is coming out.

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[huskerfan]

That's not what I asked. Are you getting fuel out of the filter bleed screw. Best to hook the bleed screw to a bottle to see how much fuel is coming out.

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My apologies - mine does not have a bleed screw since it is the CAT one - just the drain plug on the bottom to drain out water. I should unhook the outlet side of the filter and see how much fuel is coming out

 

[WWRD99]

My apologies - mine does not have a bleed screw since it is the CAT one - just the drain plug on the bottom to drain out water. I should unhook the outlet side of the filter and see how much fuel is coming out

Ohhh ok. Yes...looking for fuel pump volume fuel flow to the ip.

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[huskerfan]

Ohhh ok. Yes...looking for fuel pump volume fuel flow to the ip.

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I will check it tonight, but if it is a new filter, and it ran fine before, it *shouldn't* be an issue, but i get what you mean - need to check to make sure that filter isn't an issue to fully narrow it down to being a bad IP