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Discussion Starter · #1 ·
Hey everyone, we have a 1978 Cabover Pete with an 855 Cummins and I was on my way to the elevator this morning and it started running like crap and has no power. My first thought was the fuel filter was plugged. So I called my brother and he brought a new one and we put that on and didn't change anything. So then I thought maybe the little fuel heater canister got plugged on the back of the engine blocked so I by-passed that and hooked the hoses straight together so it sucks straight from the pump to the fuel tank. Again, didn't change anything. Anyone have any ideas what could be the problem? I'm thinking it possibly is the injector pump has gone completely bad. Another thing, we just got the truck last fall and we used it for harvest and hauled a little grain last winter and it has never seemed to have great power like our 87 Freightliner with an 855. The throttle response on our Freight is great while the Pete has always had a slow throttle response ever since we bought it.

Any help would be greatly appreciated. Thanks!

Axialfow1688
 

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Does it seem to not slow down when let up on the throttle also? If that is the case it may be low on fuel or sucking air. The system compresses the air and holds pressure for a bit causing slow throttle response in both directions. cummins PT fuel system is only one I know of that does this.
 

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Yes, it sounds like your fuel system is sucking air. I'd go over every inch of your fuel lines to find where air is getting in or a restriction. I've even had a cracked standpipe inside the tank.
 

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When you say it runs like crap, exactly what is it doing? An 855 will not build power or RPM under load if it is short on fuel. If it is doing something else, you may have another issue.
So many variations of how fuel lines were plumbed among older trucks, some sucked off the bottom of tanks, others from the top. Many only sucked off one tank, some off of both. With it being an older truck, my first place I would go is to the actual lines between the tank and pump, including both sides of the filter. If they are the wire braid style and look old and deteriorated, replace them. It is possible for them to develop pinholes and will suck air in but wont leak fuel out. Filter bases can crack, especially where the lines attach. This heater you mention, could be an issue with it. Any of those places is where the air can get into the system. If it sucks from bottom of tank, pull the line off and check flow. Sometimes valves or fittings can get plugged up with crud on older systems. Very well maybe why the truck was available when you bought it, previous owner may not have been able to find the problem.

The two hardest ones I've found, as mentioned cracked stand pipe in tank, and a cracked brass tee under the cab. Can be a *****, good luck.
 

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"Runs like crap" is not very specific, what do you mean by that? Is it misfiring? The fuel pump itself will not cause the truck to misfire, each injector is it's own injection pump on this engine. If it misfiring you have an issue with an injector, valves, piston, stuck jake piston or valve, things like that. If it's not misfiring but just gutless or not responding or running slow or something then it's a good chance the problem might be in your pump, it effects all cylinders at once. Not sure if air will cause misfiring in a PT fuel system.
 

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Discussion Starter · #7 ·
You guys are right. I should have been more specific in my original post. I can't say it runs like crap. It will run fine for a little it but gutless and will only run for a minute or two. Then she will die and I let it sit for a couple minutes and fires right up and does the same exact thing.

Albertabuck, it does have the old braided fuel lines and they are in pretty bad shape.

So I'm gonna take the sucker pipe out of the tank and check for cracks or anyplace it could be sucking air. Then I'll probably just put new fuel hoses from the tank to the filter and go from there.

Thanks for the help guys and I will let you guys know what happens.
 

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A couple weeks ago we had a Big Cam III just die as we were trucking along, it actually started last fall when we were hauling cattle back from Saskatchewan. It died climbing out of the river valley near Jenner, I figured he just blew a shift but he claimed the engine shut down. It started right up, we went to the top of the hill, checked fuel level, it was just over quarter tank and it ran fine until it started acting up last month. What was happening is after a few hours of running it would just die like you shut the key off, you had to let the engine stop turning then restart it and off you go until it happened again. It only happened under full power but got worse quite fast. If you really babied it it would run fine but the moment you put the throttle to the floor it quit. I brought it in, went through the fuel system, everything seemed fine so I changed out the fuel shutoff solenoid on top of the pump, it hasn't quit since and we've made two trips to Regina with it and a number of trips to the ranch. You might have a similar problem. To double check it you could screw the manual override in and see what happens.
 

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Something floating in the tank? Old braided fuel lines collapsed?
Just take a little tank of fuel and tie into the systemand run it again.
 

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Discussion Starter · #10 ·
Hey guys, sorry I haven't been able to post on here for a while. We did get the truck running good again and it actually has more power than before. So here is what I found out on what wasn't the problem. The fuel sucker pipe going into the tank was good. The suction line going from the filter to the tank was good. We put another new filter on. The only thing the we did that I could see being a problem was that when we took compressed air and blew through the return hose, a bunch of gunk came out and that was it. We also to compressed air the sucker line and that was fine. So the good news is it has more power than before and it stays running.

Thanks for all the help!

Axialflow1688
 

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On my N14 I had the connection going to the fuel shutoff solenoid get corroded and it would starve the engine for fuel. Crimped on a new end and it was fine until the solenoid weakened.
 

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I thought plugging the return on an old 855 caused extra pressure in the rail and extra HP. I had a professor tell me about the old days when the truckers ran the return through the cab so they could block it off and get extra power on the hills. I would wonder if you fixed something else and didn't know it. Either way, glad you fixed it.
 

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one so often missed thing for this issue is when changing the ff105 fuel filter, there is a square cut o-ring that goes on the threaded stem of the filter, if it is missing,falls off, gets two of them installed, etc it will cause all kinds of issues. the design of these filters is such that the o-ring creates the seal for the differential of hi to low side pressure, and without the difference/o-ring, the gear pump is unable to maintain flow, kind of like sucking on a straw with a hole in the side, also if the system draws from the top of the tank and uses a dip tube take special attention to the internal joint of the fitting, it is usually silver soldered and can and do get hairline cracks after years of use. i agree that the return line crap blowing out is not likely the issue with this older classic, but somewhere along the way it has been fixed. i have seen where a service was done and the wrong filter installed by the hired hand and the unit ran but no power or response etc,. the filter that was used had the same thread stem, but no hi/lo differential or o-ring..
 
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