Fuel pump question on my 2 1/2

[jfnemt1ff1]

I have a question I was going over the m35today and found out that the electric fuel pump in tank is not working good fuses and power to and ground so I think it has a bad pump. The truck seemed to run ok a little slow it is a non turbo.Does the fuel pump make that much of a diffrence. Also when I bypassed my FDC I had a lotttttttt of black smoke, The pump still had the safty cap on the adjuster,so I put it back stock now I am woundering if the fuel pump could cause that problem. Before I bypassed the FDC it run without no smoke.Man I need a turbo.
John

 

[jwaller]

the intake pump will not make that big of a differance. I have a spare D turbo that was just rebuilt and the oil supply and return lines. pmme for prices. I have to look but I think I also have the intake tube and clamps. might also have the exhaust elbow.

 

[cranetruck]

I Also when I bypassed my FDC I had a lotttttttt of black smoke, The pump still had the safty cap on the adjuster,so I put it back stock now I am woundering if the fuel pump could cause that problem. Before I bypassed the FDC it run without no smoke.Man I need a turbo.
John

Bypassing the FDC will give you more fuel, too much for the N/A multi and the black smoke will result. A turbo will solve your problem. Of course you can always turn down the fuel by turning the adjusting nut on the FDC counter clockwise ? (need to check on the direction to be sure...). The adjustment screw is still serving its purpose, with the FDC bypassed or not.

Make sure your air intake filter is clean.

 

[acetomatoco]

RE: Re: Fuel pump question on my 2 1/2

If you ever develop even the smallest leak in any of your supply or return lines, your truck will not run without the intank pump. Its purpose is to supply good clean fuel to the IP. It keeps the fuel in the tank all nice and clean and mixed so fungus will not grow as fast, as it is circulating it thru the three filters all the time the truck is running...it could be as simple as the ground for the tank to frame is not good..

 

[m-35tom]

RE: Re: Fuel pump question on my 2 1/2

fuel circulates in the tank and system with or without the tank pump, it is primarily for bleeding and priming. the booster pump in the IP is all many trucks have

 

[cranetruck]

RE: Re: Fuel pump question on my 2 1/2

If you are running loaded, there is a definite loss of power when the in-tank pump dies, been there done that sort of thing.
Hmm..wonder what the return flow is without the in-tank pump, it's about 2 qts/minute when it's running and the engine is at idle....

The extra fuel flow also help cool the injectors.

 

[jimk]

RE: Re: Fuel pump question on my 2 1/2

Yup, turn IP fuel screw's nut counter clock (looking towards back of vehicle) to reduce fuel del. My LD was a super smoker with FDC working. I put a D turbo and had to back of 8 flats(1-1/3 turn). Still got more power, so prob should have had it backed off even more before the turbo install. I plan to bypass the FDC very soon, maybe tomorrow(got to fetch a dumper in Schenectady). Will make a post afterward as to how many more flats it gets backed off for same output without FDC. JimK

 

[m-35tom]

RE: Re: Fuel pump question on my 2 1/2

extra fuel cooling injectors?? fuel does not flow through the injectors only to them.............
the first thing i do with any 'new' truck is replace all the fuel lines. the old ones will be brittle and subject to breaking and causing fire. i use truck air brake line, it is fuel proof and will handle the pressure of the supply system.
bypassing the fdc AND putting a turbo on without being a qualified diesel mechanic is a real good way to blow head gaskets, melt pistons etc. the engine will be really overfueled. the fuel rate must be readjusted so that the boost is only 9 psi max. but then it is your engine

 

[jimk]

Apparently the army dumped my deuce when a head gasket blew, using the FDC and without a turbo. As for being qualified, I'm just a wannabe. Brittney and Chad at 'Jiffy Lube' tell me what's best.
_______________
JimK
driving the worlds slowest m-35, 'Curly'

 

[cranetruck]

Re: RE: Re: Fuel pump question on my 2 1/2

extra fuel cooling injectors?? fuel does not flow through the injectors only to them.............

Obviously, the extra fuel does not flow through the entire injector, however a substantial amount of heat is transferred via the extra fuel returned to the tank, even if it's only from the upper portion of the injector, it helps cool the entire injector.
Perhaps somone can explain where this heat comes from if not from the injector. The returned fuel is anywhere from 120 to 150 °F when it gets to the tank.

I agree that much care must be exrecised when bypassing the FDC (wonder how many diesel mechanics even know what it is).
Where does the 9 psi number come from and under what conditions is it measured? What procedure does the military follow when bypassing the FDC? Don't think I have ever seen a deuce from the military with boost and EGT gauges. A lot of them have bypassed FDC's.

 

[jimk]

RE: Re: RE: Re: Fuel pump question on my 2 1/2

If you are running loaded, there is a definite loss of power when the in-tank pump dies, been there done that sort of thing.

My tank pump silent. I figure it's bad (have not checked it). Anyways, I don't seem to have power loss, some extreem duty too. Was your power loss using WVO? Bio? JimK

p.s. Help! Chad got fired and Brittney is on vacation.

p.s.s the heat is from high IP fuel compression pressure

 

[m-35tom]

RE: Re: RE: Re: Fuel pump question on my 2 1/2

the heat in the returned fuel is just from the engine as the fuel flows through the injector pump and filters. the 'return' line on the injectors is just to deal with the VERY tiny amount of fuel that has to be vented somewhere due to injector operation. the tech manual for the injection system covers adjusting the fuel rate etc. the 9 psi at the intake test port is at full throttle, full load at 2300 rpm. i think the droop pressure is 5 psi at 1500 rpm.

 

[jimk]

RE: Re: RE: Re: Fuel pump question on my 2 1/2

It is like the heat in any hydraulic system, where the slightest hi-press leakage makes the[just heated] oil even hotter.An example - a worn vane pump...the cause of heat - friction.JimK

 

[cranetruck]

RE: Re: RE: Re: Fuel pump question on my 2 1/2

Thanks for that explanation Tom.
Jim, the power loss was with regular diesel.