Greetings all,
I picked up an 82, C code, C/20 a couple of weeks ago. I'm new to diesels, but I've done an awful lot of reading on the Chevys/Fords/Dodges up to this point. I stumbled across a deal (we'll see about that in the long run but I had enough cash to get this) on this truck and went for it.

When I got the truck the primary filter was bypassed and the guy said he couldn't get it to stay running, that it would just die on him out of the blue. I replaced both filters and replumbed the primary back into the circuit. Bled the air out of the system & got it started. Drove it around the block. All's great so far. I took it out to the barn (8ish miles) for the 1st road trip with it. All was well on the way out but it died about 10 times on the way home. Lots of air in the lines at that point (installed the clear hose for the return from the ip before I did the fuel filters).

Here's what I know and what I've tried:
New fuel cap, drilled out & mounted a tire valve stem in it. Pressurized the fuel system to about 5 pounds. Zero leaks anywhere in the system after 2 days. Checked, rechecked, re-rechecked all the hose clamps. Verified correct operation of the lift pump. Pulled both filters back off to see if the gaskets had any issues and/or if I messed something up on them. Everything seems OK.

I took it for another test drive out to the feed store for alfalfa & delivered it to the barn & made it home just fine. Cool! I fixed it! Not. Went out again and about 10 miles from the house it started losing power again and died. Popped the hood, major air in the clear hose again :(

So, my question is: does anyone have any idea what the hell is going on? Is there anything in the ip that could expand enough to create an air leak once it's hot? How about the mechanical fuel pump on the block? Whatever it is seems like it's directly related to heat.

The only thing I can think of that I haven't tried yet is to run it without a fuel cap on the system to see if it's creating a vacuum somewhere along the line.

Sorry for the length of the post, I wanted to try to get all the info out there the first time.

Thoughts?

Thanks,
Mike

Supply pump is supposed to keep the pump pressurized. Do you have plenty of fuel pressure. Quite sure it's not the inj. pump.

I have not plumbed in a gauge to monitor the fuel pressure yet. Sounds like I should. Where in the system should I hook it up?

Thanks,
Mike

I had a problem like that in a '75 Plymout Fury (my 1st car). Turned out to be a rusted out fuel pickup in the fuel tank--if you check the lift pump fuel pressure output, you should see it. But if you see faulty pressure from the lift pump, try rigging a suction line into a fuel can to see if the problem aint upstream from the lift pump.

Alternately, the return line system is supposed to provide a certain amount of backpressure but if there's a blockage, it would shut the motor down. But that wouldnt explain air in the return lines... But a vacuum in the fuel tank might do it. Next time it starts dying 10 times on you, try cracking the fuel cap and see if you release a big vacuum? If it seems directly related to heat, it might also be directly related to "time".

Update:
I bought a vacuum/pressure gauge and plumbed it on the gazout side of the primary fuel filter. Unplugged the pink wire and left the ignition on. The lift pump was putting out between 40 & 45 psi with the ignition on. I replaced the piece of fuel hose from there with clear 3/8" line to see where the air was getting in. I fired it up and it looked like my tee was letting air in maybe...It also showed that it was pulling about 4" of mercury in vacuum instead of pressure.

Removed the gauge from the system & took it for a test ride out to the feed store (4 miles). Ran great on the way out but started to die on the way home. I pulled off the road & popped the hood before it had a chance to die all the way and the piece of clear hose was sucked down to nothing and there was a *lot* of air through the system. Got it home after bleeding etc and here I am.

So, the gazin side is not supplying the gazout side with enough fuel. Is there any way for me to figure out if it's a plugged up fuel pickup in the tank as sblair mentions above, or if it's my lift pump is not putting out enough?

Where do you guys buy lift pumps if that's the culprit?

Thanks for any info,
Mike

The lift pump was putting out between 40 & 45 psi with the ignition on.

you sure about that? they are only supposed to put out 6.5-8psi for the mechanical pump.

Argh! What a dumass I am....yes, between 6 & 7 psi, between 40 & 50 KPA...Sorry about that :(

Update:
Dropped the tank, no problems on the pickup side of things. I did notice that when whomever switched this over from a dual tank to a single tank setup that they plumbed the fuel from the WIF line instead of the main pickup with the little filter on it. I replaced all the fuel lines, re-plumbed in the WIF drain to the side that the tank lives on and put new hose clamps on every fitting.

I purged the air, got it started and watched (I still have the clear hose from the output of the primary filter to the mechanical fuel pump). It ran for about 15 minutes before I started to see air in the line from the filter. A minute or two later there was air in the return line from the IP and she sputtered & died.

Essentially back to square one. I've got an air leak *somewhere* in the system :(

I thought that about the only thing suspect from that side of the delivery system was the lift pump. I took some Saran type wrap and sealed off the lift pump on either end so I could narrow down where on the pump the leak was. Fired it up and waited...it doesn't appear to be sucking air from the lift pump either.

Thoughts? Ideas? Should I take the thing to the shop and pay them to trouble shoot it? Sell the thing and buy something newer?

Thanks for any insights,
Mike

Hi
at that point before starting to gess you can pressurize your systeme 3-4 pds MAX .Block the filler cap ,remove the return line on top of the IP,put the pressure on the return line and hold it at 3-4 pds.


With a mix of dishwasher soap and water spary all the systeme and you will find the probleme for sure . Pay special attention at the small dark hard to reach corner most of the time the leak hide in those corner.;)

Good hunt Ed

Another update:
I pressurized the system to 4 psi, let it sit for 48 hours, it dropped maybe .1 or .2 pounds. I found one tiny droplet of fuel on the "in" side of the lift pump and a bit of a wet spot on the secondary filter. I wouldn't expect the leak to be on the secondary filter as I'm seeing the air on the "out" side of the primary filter (still have the clear hose there).

I took the lift pump off, disassembled the suspect fittings, cleaned everything up & reassembled with teflon tape on the threads even though the fittings look like compression type where the teflon wouldn't do any good anyway (is teflon OK with diesel?). I took the housing for the secondary filter off, cleaned all of those threads up, teflon'd those threads too and put it all back together.
Bled the system again (317 times & counting I think) and fired it up. It actually seemed like it ran a bit longer this time before really sucking a lot of air into the system. Maybe 20 minutes of idling in the driveway before I noticed the air.

I bought some dye for the fuel system and am going to put that in the tank tomorrow, repressurize the system back to 4 psi or so & let it sit overnight at least. I can borrow an ultraviolet light source from work for the weekend to try to track down this problem. If that doesn't work, or doesn't show me where the possible leak is, I'm thinking of putting some of that dye in a squirt bottle and doing a systematic spray of the system. I'll do one run at a time when it does start sucking air. I'm not sure how much of the dye needs to be in the lines for me to see it with a UV light, hopefully I don't have to find out :-)

On the plus side: I know the fuel lines/tank/pickup/fittings on this truck like I haven't known on any vehicles I've ever owned & I can get an air-filled system bled & fired up with the best of 'em :-)

Thanks for all the input guys, I'll let you know how it goes in round 27!

Mike

I had a problem like that in a '75 Plymout Fury (my 1st car). Turned out to be a rusted out fuel pickup in the fuel tank--if you check the lift pump fuel pressure output, you should see it. But if you see faulty pressure from the lift pump, try rigging a suction line into a fuel can to see if the problem aint upstream from the lift pump

When you drop your tank ,do you open to have a look at your pickup in the fuel tank .maybe there is a rag blocking your strainer in the bottom of your tank.

Tigman,
I pulled the entire pickup assembly out of the tank after I dropped the tank. The only thing I found was that the previous owner had bypassed the main pickup tube , the one with the little filter sock type thing on it, and had plumbed the Water In Fuel pickup to the lift pump (this was a dual tank truck that somewhere along the line was converted to single tank). The main pickup was plugged at the top with a piece of hose, a bolt & a hose clamp.

Everything inside looked good. I rerouted the hoses so the real pickup was feeding the lines, replumbed the WIF line to the correct line at the back of the frame (after plugging all the lines and pressure testing the seal) and remounted the tank.

Mike

I know I'm kinda late to the show, but you could always put a electric fuel pump in. That fixes all sorta fuel leak problems.

Guipo

Guipo,
I just read through all the posts with "electric fuel pumps" in them to get a better feel for the conversion. I may just go ahead and bypass both pumps and go that route this weekend. I'll probably go with blocking off the mechanical pump and removing the electric pump under the passenger's seat route, use a coupler for the fuel line where the electric lived and mount the new pump up in the engine compartment somewhere to feed the primary filter/water separator there.

Thanks for the tip!

Mike

Sounds like you should look to the filter originally bypassed by previous owner. He bypassed it to stop this problem and now that you re-plumbed it you have the problem back.

Update to the updates:
I went ahead and bought an electric pump this afternoon & installed it in place of the old electrical lift pump. It ran for 30 minutes or so with no air at all! I'll road test it tomorrow and let y'all know how it goes.

Next on the list: fuel gauge. I'll start a new thread on that, but, fwiw, the sender is working & is nicely grounded. I have the gauge out of the dash, it's a 3 pronged guy, if I manually move the needle back to near empty (where the tank is right now) it immediately moves to the 1 1/2 tank range as soon as I plug it back in. The manuals I have here have more of a block diagram than a schematic so I don't know which pins should see what at this point.

Thanks again for all of the input/help/advice!

Mike

Mike, you dont have all your fuel wire's hooked up. The same thing happened to me.

There's only 1 wire running from the fuel tank. make sure that bad boy is hooked up.

Guipo

" How about the mechanical fuel pump on the block? "

I have seen a mechanical lift pump "make" air in the system several times on 6.2/6.5's, replaced with new and alls well.Try it.

Mike, you dont have all your fuel wire's hooked up. The same thing happened to me.


:exactly:

The wire to your sending unit is cut, broken, or disconnected somewhere. Common problem, and easy to fix.

I had the same problem today. The truck would run fine for a couple of minutes and then splutter and die.

At first i changed the fuel pupme, which was a waste of time as looking around the tank area i could see fuel dripping onto the exhaust pipe.

The corner with the leak is very difficult to get to, but from underneath i could see that a build up of sand etc in the area where a side rail joins a cross rail fuel was dripping down from a rusted out fuel pipe.

I re-plumbed the fuel pickup from on top of the tank, forward to the next rubber hose point.

Unfortunately i have a new problem as i flattened the batteries in my previous starting attempts and no amount of jump-starting will bring it back to life. I've got the batteries on charge now, so hopefully i'll have better luck tomorrow.

Moral of the story? Check for rusted out fuel lines before replacing components . . . .