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M35a2 intermittent power loss at speed

Elijah95

Elijah95

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Hey y'all, searching out some help from the more experienced than me;

Been having this intermittent issue with my truck since the moment I purchased it, sometimes the rig runs excellent, plenty of power, and will pull like a freight train on the hills in my area while other times it's down on power.

I've yet to get my hands on a fuel pressure gauge, but here's what I've done so far:
•Replaced both spin on filters with baldwins (less than 500 miles)
•Replaced fuel line running under radiator from primary to secondary fuel filters (it was kinked)
•Turned up the fuel 2 flats
•Turned fuel down 4 flats, bypassed FDC, verified fuel lines were in decent shape running from pump and surrounding areas (to and from filters etc)

Previous owner:
•dropped tank couple years back, cleaned it out & installed Parker pump
•replaced fuel injector return lines
•replaced frame fuel line with newer push lock style hoses

Truck runs great sometimes, excellent power off idle to governed speed, and may run good 5 miles, to 40 miles, but if driven long enough suddenly anything over 18-1900 rpm truck seems to fall flat on its face starving for fuel, sputtering slightly sounding like the exhaust note is breaking up. Can barely make 45 mph on flat ground wide open when running bad, can normally hit 55-60 no problem. Will surge slightly when backing off the pedal.

Any tips, suggestions or info would be appreciated!


1974 AM General M109A3 w/Deuce Bed, White LDT, Whistler C, and soft top
 
rustystud

rustystud

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You say you replace both fuel filters correct ? But did you replace the water/fuel filter on the right side under the alternator ?
This sounds like a "classic" filter problem is why I ask. Injectors don't magically get better then worse then better, nor does the injection pump. If their going bad they let you know ! If you did replace all three filters then you could have something in the fuel lines or the in-tank fuel pump could have something in it's filter screen. Or the in-tank fuel pump hose could be failing and shedding it's lining and little goobs of gooy rubber is floating around your system. This hose does need to be replaced about every ten years according to "Gates" . If you do end up replacing this hose just remember it "must" be diesel fuel "immersion" rated ! Meaning it must be able to be fully immersed in fuel it's whole life. Normal fuel hose only has a inner lining that is fuel rated not the outside of the hose. This hose is pricey but you only need about 15 inches ( I have a "Parker" pump in one tank and a "Olympic" pump in the other so I have a little longer hose in mine) . I would buy at least three feet though and save the rest for "just in case" emergencies ! I believe "Duda Diesel" sells it. I bought mine here in the Seattle area at a "Gates" supplier.
 
Elijah95

Elijah95

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rustystud said:
You say you replace both fuel filters correct ? But did you replace the water/fuel filter on the right side under the alternator ?
This sounds like a "classic" filter problem is why I ask. Injectors don't magically get better then worse then better, nor does the injection pump. If their going bad they let you know ! If you did replace all three filters then you could have something in the fuel lines or the in-tank fuel pump could have something in it's filter screen. Or the in-tank fuel pump hose could be failing and shedding it's lining and little goobs of gooy rubber is floating around your system. This hose does need to be replaced about every ten years according to "Gates" . If you do end up replacing this hose just remember it "must" be diesel fuel "immersion" rated ! Meaning it must be able to be fully immersed in fuel it's whole life. Normal fuel hose only has a inner lining that is fuel rated not the outside of the hose. This hose is pricey but you only need about 15 inches ( I have a "Parker" pump in one tank and a "Olympic" pump in the other so I have a little longer hose in mine) . I would buy at least three feet though and save the rest for "just in case" emergencies ! I believe "Duda Diesel" sells it. I bought mine here in the Seattle area at a "Gates" supplier.
Click to expand...
The primary filter housing is in foul shape, and doesn't have a filter in it, so I temporarily bypassed it for testing purposes. Looks like I'm going to have to tear into my tank
 
WillWagner

WillWagner

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Get a gauge first and see what the low pressure is doing when the engine acts up
 
orren

orren

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As I understand it once you are up to speed the high pressure pump in the IP is sufficient to
keep pressure OK without help from the intank pump.

I would first check the fittings and fuel line from the final filter to the HH for leaks or collapsing.
 
rustystud

rustystud

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orren said:
As I understand it once you are up to speed the high pressure pump in the IP is sufficient to
keep pressure OK without help from the intank pump.

I would first check the fittings and fuel line from the final filter to the HH for leaks or collapsing.
Click to expand...
That's true, but if the hose or screen is bad or full of crud you will not get any fuel. As far as fuel lines "collapsing" that is pretty hard when they are under pressure, and any fuel leak at 35 PSI (minimum pressure) would be obvious.
 
Elijah95

Elijah95

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How about a rust filled fuel tank? Went fishing with a magnet for several hours and recovered almost an entire red solo cup of rust from the tank, this was 15 minutes inIMG_1397.JPG
 
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