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Discussion Starter #1
I've got the prime bolt loose on the top of the filter and I'm pumping the manual pump to prime. As I pump I hear a clicking in the injector pump. I assume it is the pressure relief valve for the return line. Now ,as I pump and this clicking happens, I cannot get enough pressure in the filter to have diesel fuel come out the bleed bolt. A little comes out but not enough to say that it is okay to close it. What say you. Is it air in the supply line or a bad bypass valve spring? Truck has 100,000 on it and I'm sure it has original lines (I'm replacing them now) and original pressure relief valve.

Maybe I'll pinch off he return line behind the filter and see if that causes an increase of fuel from the bleed bolt on the filter top.
 

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Discussion Starter #3
Bill:
I'm learning the hard way the value of a fuel pressure gauge. I couldn't pinch the line today, I've got the lines off at the tank and filter and am replacing from tank to engine. I ain't walking again - I hope. I printed the page you linked me to and I think I have most of the stuff here. I was glad to see the tubes going into the tank were fine and were clear if you blew into them and I could syphon fuel out the supply line at the tank.

Oh, could a bad relief valve cause a 'no start' or die situation? All the links I look at indicate a kind of gradual decline in power and idle.

Because the relief valve ,the way it is ,does not hold back enough fuel to overflow the filter do you think I should stretch the spring? At least till I get it going.
Ken
 

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A bad overflow valve causes low rpm miss/instability, white smoke, hard starting and low power. It has to be very low, like zero pressure for hard starts or dying.

I don't recommend stretching the spring unless you have a FP gauge. It's a guessing game without one.
High pressure can cause problems too but you sometimes have to do what have to to get going.
 

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Discussion Starter #5
Bill:
Thanks for the warning about a fuel gauge. I picked up the new fuel line today and got together a few things around here to put in a pressure gauge. Tomorrow should be dry and warmer, truck outside right where the Ford towed it, hmmmmm.
The article you linked me to was great. I can go two ways with this gauge. Off the bleed bolt on the filter or banjo on the pump. I've got the stuff to go either way. For now though I'll do a quickie on the bleed bolt just to see where we are on pressure - that's if it starts. Called dealership here for relief valve $238cdn, diesel repair shop using Bosh number $125. But with the no cost gauge I'll put on I think I'll lengthen the spring. A posting indicated original length at .550". Must I remove the whole bolt or can I just take out the end nut and remove the spring leaving the ball inside?Can you confirm this? But if it is weak then maybe a little longer to compensate for age and fatigue. I ask my wife to compensate me for my age and fatigue too.
 

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Don't know if shipping to Canada will make it slower or more expensive but here's the same OF valve that Cummins sells for $30 USD
eBay Cummins Overflow Valve

You can remove just the top nut to get at the spring. Be careful, sometimes the ball sticks to the spring just long enough for you to pull it out and have it fall on the ground.

New design OF valves don't have the top nut. Guess they didn't want people stretching the spring.

Think you'll find pulling FP from the top of the filter is quite congested. The IP inlet is wide open.
Do make sure to use a needle valve or you'll never get a good reading before the gauge breaks.
 

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Discussion Starter #7
It's alive! Got the new fuel and return line in this morning. I thought I would put a little pressure in the tank and save some pumping. Good thing, my rubber gasket on the bottom of the pre fuel filter was leaking. Solved that, and it primed okay and fired after some cranking.

No fuel pressure gauge yet. I was just happy to get it going. Rain again tomorrow but I might have a chance to put the FP gauge in. I'm coming off the banjo with a needle valve into an oil pressure gauge I have here with the small hose. Really liked the idea of puting that fragile little hose inside 1/4" tube, which I just bought. Going in the cab with the gauge. How would you suggest I route the tube?

I thought about just leaving it under the hood. Changed my mind I thought if the truck dies while towing and I still have pressure on the in cab gauge well I at least know that the first half of the fuel system is okay.

This morning just after I got it running for about 20 minutes I remembered the specs for fuel pressure, in the teens at idle and 30's for 2500rpm no load. So I increased the rpm to 1500 and held it -was smooth, incresed to 2000 and held it -was smooth, increased to 2500 -started to flutter. I'm thinking that relief valve is a problem. Can't wait to ge the gauge on to see the numbers.

So what did the old guy learn. Presssurize the tank a little to find air leaks that become fuel leaks. Man does not live by fuel lines alone, you must have a FP gauge. Performance on these Cummins rely on correct fuel pressure delivered to the injector pump. I could not have done this without this forum. Thanks.
 

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How would you suggest I route the tube?
On auto like you have there is a rubber plug on the firewall where the clutch rod would have come though.
I just poke a slit in it with my pocket knife and push the tubing though.
The slit seals up very well against the tube.
 

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Discussion Starter #9
Bill:
Great, in it goes first of the week. Raining heavy today. I'll get back with some numbers.
 

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Discussion Starter #10
Got gauge in today. Went off banjo with needle valve into oil pressure gauge thin tube inside 1/4 tube for protection. Mounted gauge under lip of dash near 4x4 shift lever.

Opened needle slow and got nice steady readings. Bingo! Idle 15psi, after an increase to 2,500rpm no load, only goes to 18-19psi. I'll have a little help tomorrow to pinch the return line and find the culprit.

Bill, would 15-16psi at around 1750rpm (my towing rpm for trailer) kill my power? I just got the truck in the summer and towed with it to Florida and back and thought it a little dogie in the hills. Trailer around 7000# loaded.
 

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You will really feel it any time the pressure drops below 25 psi while driving.
Many times you'll also have white smoke.
 

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Discussion Starter #12
Had my help arrive early tonight while still light. Got some interesting pressures. At idle around 15psi. With the return line rubber pinched shut the pressure climbs slowly to 26-27psi. What say you doctors?
 

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Discussion Starter #13
Took the truck for a ride last night and here is what happened.
On start up: truck stumbled with blue white smoke and no fuel pressure in the new gauge. It took maybe 20 seconds for pressure to build to about 15-17psi.

After 30minute drive at highway speed pressure never went over 17psi. Then when I got home with no load in park ran it up to 2500rpm still the same, 17psi.

As mentioned in the last post with the line pinched off all I got max was 27psi and it was a slow crawl up to that.

I will stretch the spring a little and try that but now I'm thinking lift pump.

On start up is it normal for pump pressure to rise slow or is it bang right up?
 

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Sounds like you need a new lift pump and maybe after that a new OF valve.
 

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Discussion Starter #15
Factory manual says remove starter to replace lift pump. Can it be done without starter removal?
 

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Discussion Starter #16
Hey, I goofed! Never thought I'd be happy to say that.

Was thinking lift pump but thought I'd pinch off the return line one more time with a different set of vise grips. Bingo, pressure spiked to over 80psi. So, on to the relief valve. Took the nut off measure the spring it was under 1/2", stretched it a tad, around 1/2". Put it back and pressure at idle was just over 20 and at 2,500rpm no load 35-37. With the gauge on I think I'll leave it as is. I suspect the spring is lazy and if pressures drop I'll replace the relief valve.

Man, replacement parts sure are silvery: I checked Case IH and the same lift pump (must change fittings) was $150 cheaper.

Thanks to all for the help with this.
 

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If you ever do need a LP Cummins has the best deal, $79
 
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