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Startng truck after replacing a fuel line.


Jim Gell

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I believe I have a fuel line to replace that weeps fuel oil. It's getting on the wires to my engines computer. I thought I would remove the aproximatly 18 inch line, take it it to a hydraulic hose maker, and have them make a new one to put back on myself. I read someplace here that even though it looks like a hydraulic line, it would be important that the hose material is compatable with diesel fuel.

 

Before I do this, I want to ask if I will need to bleed the air out before I restart, and how I would do that on my Detroit 60 Series with the Davco filter? (filter is on far side of engine from hose to fuel pump I am replacing)

 

Is this something I might be better off taking into a $hop?

 

Jim

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Sibernut,

 

I didn't think about topping off the tanks first. I will do that. Thanks.

 

I wish I understood the fuel system plumbing better including how to bleed the air out of fuel line. I'm thinking I should know that before I pull this line off. The leak has not effected how the truck runs, yet. There is dampness, but not enough leaking to drip on the ground. I do have a little oil coming out the air dryer ? located on firewall. I was wondering if the compressor located right by the leaking fuel line was sucking in fuel oil.

 

Jim

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I don't know Davco. But I'd check fuel level in the tank (almost empty= harder to pull fuel up). Then I'd fill the Davco if possible & give it a shot.

Is it a high-mounted fuel pump that creates a partial vacuum? Theoretical max lift on a vacuum pump is 30', and with potentially just one coupling (hose to pump) reality is probably still better than 26'. 3' of fuel tank should be a cakewalk for any pump.

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I don't know how long my minor leak can go without causing trouble. It is possible that the fuel oil waterproofs the wires going into the engine computer, and is a good thing. Then again, it may degrade the insulation over time and cause problems. I am taking a wild uneducated guess that the fuel from the leak is entering the air supply compressor somehow simply because the wet part of the line is right near the compressor. What else would cause oil to be expressed out the round rubber "reed" on the air dryer? I doubt that having oil in the air supply is a good thing, and is something I need to fix.


The Davco is on the passenger side of engine about frame high. It appears to have a system to heat the fuel as there are what look like coolant lines coming and going on the bottom. The fuel lines are routed to the driver side under the radiator fan, but then appear to go down the frame beyond the firewall (apparently to the fuel tanks). Similar lines come back from that direction and lead to what I think is the fuel pump.


I put three photos in a Google+ "collection". I never really learned how to use the previous versions of Google+ and now it looks like they changed it. Hopefully the link I will include a link at the end of this post will work.


Photos are from the driver side of engine. I might be assuming wrong that it is a fuel line, but I think that is what I was told by someone at the Nat'l Rally. I am surprised a fuel line would appear to screw into the upper front of the engine as shown in one photo. I assume it either passes through for pre-heating or connects internally to the injectors. If it's not a fuel line then my next guess is a engine oil circulation line. Someone please educate me and advise me if it could wait until the ECR.


Here are the photos. Note: I added comments describing the photos a few minutes after original post.


Jim

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Hi Jim, I can't help you on the line you are asking about shown in the photos. The black reed valve you show on the firewall is your "Treddle" valve. When you push on your brake peddle, a rod comes through the fire wall and pushes open a valve inside it to let air go out to your air brakes. That's the reason for all the air lines attached to it. The oil residue around that air relief/discharge valve indicates to me you are getting some oil into your compressed air supply, probably from an aging air compressor and/or a dirty air dryer filter.

 

While we're discussing this "treddle" valve, according to Bendix... with truck air pressure up and engine shut off, you can spray some soapy water on that black rubber disc and watch for any bubbles. According to Bendix, if you see more than a one inch bubble during one minute.... the valve needs to be replaced. That's not much air bypassing is it? After seeing several bubbles around mine, I twisted the wrist area of a surgical glove tight around mine and within one minute the glove looked like a young milk cow. I changed mine out. Hope this helps some.

 

Ed

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That rubber "reed" you're referring to is just a dust cover for the treadle/brake valve. If you remove the center screw and look behind it you can probably determine if the "oil" is coming from the valve or being blown back onto the outside surface. If coming from the internals of the treadle there may be other problems than just a leaking hose. Oil in air in bad juju (compressor or overdue dryer service most likely). The problem is how long it's been like this and where else the "oil" has migrated in the system.

Hopefully it's just blowback from your leaking hose.

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in the picture you have labeled as "It's not clear in photo, but the lower end of the leaking line comes down around the air compressor and connects to a fitting near in top right of photo. It looks higher than it is. it appears the leaking line connects to the front (left) area of this horizontal pump like unit, and the line coming out the rear probably goes to fuel tanks. "...

 

thats Detroits lift pump on the end of those fuel lines.

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Hi Jim, I can't help you on the line you are asking about shown in the photos. The black reed valve you show on the firewall is your "Treddle" valve. When you push on your brake peddle, a rod comes through the fire wall and pushes open a valve inside it to let air go out to your air brakes. That's the reason for all the air lines attached to it. The oil residue around that air relief/discharge valve indicates to me you are getting some oil into your compressed air supply, probably from an aging air compressor and/or a dirty air dryer filter.

 

While we're discussing this "treddle" valve, according to Bendix... with truck air pressure up and engine shut off, you can spray some soapy water on that black rubber disc and watch for any bubbles. According to Bendix, if you see more than a one inch bubble during one minute.... the valve needs to be replaced. That's not much air bypassing is it? After seeing several bubbles around mine, I twisted the wrist area of a surgical glove tight around mine and within one minute the glove looked like a young milk cow. I changed mine out. Hope this helps some.

 

Ed

i have to 2nd your comments about either a dirty air dryer filter or aging air compressor.

 

RE: treddle valve. id wipe off the residue and see what it smells like... if it smells like diesel , its from the leak. if it smells otherwise and you have it covered in 1k miles

since you wiped it off, your best off replacing it.

 

id check your air tanks and drain them and see how much comes out.

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I drained the air tanks and there was very little liquid in them. Perhaps and ounce or two total for all three tanks. However, it was a thin but oily black liquid. Probably mostly water, but certainly a fair amount of oil too. Is that normal? I don't remember if it is any different from before, but as best I recall, it has been the same since I owned the truck.

 

Back to the fuel line, I don't have leaking fuel oil spraying in a big way. The computer wiring connections are just behind and below the wet (leaking) line. I would guess the leaked fluid builds up in the area (on compressor , etc) then drips down and sprays onto the wires. It does not go far though, and definitely not up onto the treadle valve.

 

The area around the treadle valve looked oil free, except for that round black rubber reed. I think it coming from within. It sounds like my next step would be to smell the oil on it, and take it off and look inside. Hopefully my nose will know what the fuel smells like. I could stick my nose over an open fuel tank to compare.

 

Maybe I should replace the air dryer filter even if it's not causing any problem. It's not been done in the 5,000 miles I have owned the truck. Sorry to be so naive, but where would I look for the air dryer and the filter? Will it be obvious how to replace it?

 

Thanks for all your help.

 

Jim

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On mine it is located under the truck behind the transmission, be sure you drain all air from the tanks as you will get a surprise if you don't.

It's very easy to change, just unscrews like any of the filters you have on the truck, Mine was blowing so much oil into the system, I have a Cummins M-11 that I had to replace the dryer.

Found that the air system on mine needed a hold back valve ( check valve) to keep air pressure on the compressor to keep from by-passing oil, did this and no more oil in the dryer or tanks for me, but that's probably not your problem.

 

Roger

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I drained the air tanks and there was very little liquid in them. Perhaps and ounce or two total for all three tanks. However, it was a thin but oily black liquid. Probably mostly water, but certainly a fair amount of oil too. Is that normal? I don't remember if it is any different from before, but as best I recall, it has been the same since I owned the truck.

 

Back to the fuel line, I don't have leaking fuel oil spraying in a big way. The computer wiring connections are just behind and below the wet (leaking) line. I would guess the leaked fluid builds up in the area (on compressor , etc) then drips down and sprays onto the wires. It does not go far though, and definitely not up onto the treadle valve.

 

The area around the treadle valve looked oil free, except for that round black rubber reed. I think it coming from within. It sounds like my next step would be to smell the oil on it, and take it off and look inside. Hopefully my nose will know what the fuel smells like. I could stick my nose over an open fuel tank to compare.

 

Maybe I should replace the air dryer filter even if it's not causing any problem. It's not been done in the 5,000 miles I have owned the truck. Sorry to be so naive, but where would I look for the air dryer and the filter? Will it be obvious how to replace it?

 

Thanks for all your help.

 

Jim

the Air Dryer / filter is on the crossmember UNDER the sleeper. find the air compressor which is above the lift pump in that one picture and follow the big air line back under the cab/sleeper to the air dryer. depending on which air dryer you have . most of them you unbolt a bunch of bolts and peel the cover off and change the filter. sometimes there bad enough you end up changing the whole air dryer. just beware if you replace the dryer and its a Bendix branded theres a PILE of clones and they are garbage. so make sure you get genuine bendix.

 

*ANY* fuel leak isnt a good thing and having it spray onto the computer wiring by the ECM is Definitely not Good. .. once you get your fuel leak fixed , you probably want to clean the wiring at the ECM and unbolt the connectors on that end of the ECM and check and see if you have any oily residue in the connector that needs to be cleaned out. be careful if you decide to take that route and mark the connectors to where they belong.

to do this yourself.

 

*I* know the Detroit Series 60 well (pre-egr motor). feel free to shoot me a PM if you need more info.

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Thank you Lou! Sounds like I should be able to find the air dryer.

 

I could not detect any odor at all in the oil on the black round dust cover/reed on the treadle valve. Might need my wife to do the smell test.

 

We are heading out to diner with family soon, so I won't get to do anything else today.

 

Jim

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Thank you Lou! Sounds like I should be able to find the air dryer.

 

I could not detect any odor at all in the oil on the black round dust cover/reed on the treadle valve. Might need my wife to do the smell test.

 

We are heading out to diner with family soon, so I won't get to do anything else today.

 

Jim

Jim,

 

Not a problem.

 

good luck with your project. let us know how you make out.

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