I just bought an RV, it is the 6.2L w/ THM400 tranny and I would love a little assistance on getting it running well.


Short Story:

My problem is that it seems to start just fine when cold and idles well for about 10minutes. Then, it will idle up and down and cut-off. When I check the fuel filter; it will be only about 1/4 full. Then, when i manually fill the fuel filter, it will start fine, run for a little and then do the same thing again.

Any ideas on what this could be? lift pump or something like this?

Also, it has a good leak around one injector and very light leak around another. Any quick tips on how to fix this before I start at it. I am used to gasoline engines, so this diesel is a new frontier for me.

http://i17.photobucket.com/albums/b60/E36bmer/Mobile%20Uploads/1008091830a.jpg

For a longer story:

I tested it out and it seemed to run great and for at least 20 min, however when I was looking at it the previous owner got it stuck in a ditch, I mean we were flooring it trying to get it out for a few minutes, and leaving it running, it still ran fine. So, I left to come back another day. When I now bought the thing and drove away for about 15min, I am pretty sure it ran out of fuel on the way to the station. Then I filled it up and got to the station, left and it died again. So, I remembered to try to fill the fuel filter with fuel and then it seemed to start this whole thing. Now, it seems like it will only move about 100yards before dieing. Whereas before it didn't seem to have any issues.

sounds like your lift pump died. their a bit** to get at in a truck let alone a RV. another thing you could do is put a clear hose on the injection pump return port so you can see if theres air bubbles getting into the system.

being an rv, i don't know if theres a sock on the pick up in the tank. if there is it could have plugged up with crap when it ran out of fuel. or a line may be sucking air to the tank from something getting jarred when stuck in the ditch. you could try disconnecting line from lp tp filter, crank it a bit and see if its pushing fuel

those injectors leaking where line connects or where rubber hose connects? if line, you could loosen nut and clean connection and retighten. more than likely its a bad or cracked end on the line and will need to be replaced

Run the truck from a 5 gal pail of fuel. You could have any of a few issues. If it has the factory mech lift pump, put an electric LP on. The mech ones suck anyway. As was stated site glassing it could show if your sucking air. Could be the pickup tube. Could be the truck is out of fuel and the fuel gauge is broken. Just ran into that with a 94 6.5. I ran the truck on an IV to diagnose it...I used a separate elec fuel pump with a 5 gal jug full of fuel.

The low level in the fuel filter tells me air is getting into the system, AND likely your lift pump is not working. They can be one and the same issue. Bear with me for a second...

For your filter to not be full, air has to get in there. If your lift pump was pumping enough fuel to satisfy engine demand, the fuel filter would be full and there would be pressure on the line, either sealing a leak or causing an external fuel leak. If the lift pump is bad, AND you have an air leak, then the injection pump will pull fuel from the filter, which is then being replaced by air from the leak, instead of fuel from the lift pump. Makes sense, I promise. Check for air leaks & lift pump functioning, if lift pump is bad then get yourself a block-off plate and an electric lift pump, you'll thank yourself later.

if it was run out of fuel, the filter could be plugged up and the pump can barely fill it.

on a 6.2, the ip should be able to suck enough fuel to keep going

Could be a Injector Pump Problem I know mine used to run for 20 Min Rev up & down, up & down then stall & hard starting after that. i had leaking return lines & the housing on my pump is gone so that was my problem. how much Km or Miles is on that 6.2 & is it a 1500 ( C-code) or 2500 & up( J-code) Diesel?? u deninatly have air in your system & i would re do all 8 injectors on that truck while your at it

JL :cool:

There is actually only about 40k miles on the motor that was replaced for some reason when the original motor went at 52k miles. I have the whole log book from previous owners, they even went so far as to note when they filled up, how much and where. Then, just a note, no explanation "Engine blew, replaced with rebuilt 6.2L motor"

Where is the lift pump? Is it in the tank, or is that on the backside of the motor? I see where the IP is on the front side, and I am kinda thinking that it works fine, just from the symptoms.

I hate sounding dumb, but just started learning about this motor. If it isn't the lift pump, what is that on the backside of the motor anyway?(behind the air filter, between the two back cylinders) It looks like fuel lines are running to it and there is a spot where a clear line is there, and an arrow on this plastic T, I actually don't see anything moving through this clear line. I will try to get pictures, as I am sure this description is difficult.

I found out that there is a spare electrical pump installed in-line, between the tank and fuel filter (the previous owner told me that) to help fix any air problems in the fuel line. But, it isn't hooked up now b/c it isn't supposed to be hooked up when running, it is just for clearing air from the lines??? So, I was thinking of turning that sucker on, and loosening the drain on the fuel filter, and running a gallon or two through into a bucket. Then, there shouldn't be any air in the lines at all, I am guessing. Or, should I disconnect a hose closer to the engine to run fuel through the entire line, or all the way through the injectors, if that is possible?


Now to the injector leak, I guess I will just take them off and inspect them to see what is going on. Here's where they are leaking from: (between the seal where I circled in red)
http://i17.photobucket.com/albums/b60/E36bmer/1008091830a.jpg

that thign at the back is the vacuum pump. it runs the emissions stuff and the cruise and a TH400 autmatic transmission. the shaft that goes down into the engine from it also drives the engine oil pump much like a distributor on a gasser

Where is the lift pump? Front of the motor, passenger side. You'll see it if you crawl under and look up on that side.
I hate sounding dumb, but just started learning about this motor. If it isn't the lift pump, what is that on the backside of the motor anyway?(behind the air filter, between the two back cylinders) That's your vacuum pump. It runs your a/c controls, and since you have a TH400 transmission it's used to control the trans (you'll find one of those lines goes to the IP and then to the trans)

I found out that there is a spare electrical pump installed in-line, between the tank and fuel filter (the previous owner told me that) to help fix any air problems in the fuel line. But, it isn't hooked up now b/c it isn't supposed to be hooked up when running, it is just for clearing air from the lines??? So, I was thinking of turning that sucker on, and loosening the drain on the fuel filter, and running a gallon or two through into a bucket. Then, there shouldn't be any air in the lines at all, I am guessing. Is it a 12v electric fuel pump? If so, I would remove your mechanical lift pump and block it off (blockoff plates are easily found at your neighborhood auto shop), and just use the electric one. They're more reliable anyhow. If it's some kind of 120v pump that someone decided to install and use to purge the system now and then, having it plumbed in the line and not powered could be causing issues all its own. In fact, that's true if its a 12v pump too; it shoudln't be plumbed in if it isn't used.

If you do use the electric pump to 'prime' your system, it will solve any air issues you have -- so long as there isn't an air leak. If your fuel lines are leaking air into the system, having that pump purge it isn't going to solve the issue, as your system will just pull more air in as you drive.

that thign at the back is the vacuum pump. it runs the emissions stuff and the cruise and a TH400 autmatic transmission. the shaft that goes down into the engine from it also drives the engine oil pump much like a distributor on a gasser

Interesting how our answers differ based on our trucks, 4320. I was saying the vacuum pump controlled the a/c and the trans, you say emissions, cruise, and trans.

My truck has no emissions and I can't use the cruise as the wrong steering column is installed....your has emissions, no a/c, and I'm guessing cruise control? heh.

Thanks for all the help guys. I got it running yesterday. Just hooked up the electric pump to a switch and it made it the 2-hr drive home last night. I forgot to check the model of the pump and everything, but it was an in-line pump that said "automotive fuel pump." I will look into that lift pump block-off plate and removing that and just using the electric pump that is there.

The only thing I need to figure out now is just how fast I can go in this thing. It seemed to be turning pretty high rpms at like 50mph. So, I was afraid to go much faster than that, even though plenty of throttle was left. I need to get an RPM gauge hooked up and start playing around with some other things.

My goal is to get this thing running on waste veg. oil and travel around the country this summer. Hopefully I can get it running well for that.

Hey that sounds like alot of fun. That's kinda my retirement dream. too bad I'll never retire.

An RV with a Turbo 400 transmission will probably run close to redline at 65, depending on your rear gearing which I'd bet is 4.10 or higher. The best thing you could do would be to upgrade to a manual, such as the NV3500/NV4500 which is a bolt-in swap for our trucks (4500 in your case, you could make the 3500 fit with some mods tho). 2nd best choice for highway cruising is replacing the TH400 with a 4L80E, which is essentially just a 400 with an extra gear and electronic control. This is a more involved swap requiring a few sensors your rig doesn't have.

Interesting how our answers differ based on our trucks, 4320. I was saying the vacuum pump controlled the a/c and the trans, you say emissions, cruise, and trans.

My truck has no emissions and I can't use the cruise as the wrong steering column is installed....your has emissions, no a/c, and I'm guessing cruise control? heh.

i forgot about the A/C controls. mine are all cable driven i only said the tranny because ive heard of the shifts being bad because of a leaking vacuum line.

An RV with a Turbo 400 transmission will probably run close to redline at 65, depending on your rear gearing which I'd bet is 4.10 or higher. The best thing you could do would be to upgrade to a manual, such as the NV3500/NV4500 which is a bolt-in swap for our trucks (4500 in your case, you could make the 3500 fit with some mods tho). 2nd best choice for highway cruising is replacing the TH400 with a 4L80E, which is essentially just a 400 with an extra gear and electronic control. This is a more involved swap requiring a few sensors your rig doesn't have.

Yeah, it has 4:10 gears. Think I could find a truck or something in a junk yard that I could just grab a taller rear end from? It seems to accelerate plenty fast, but I would hate to run at 55-60mph for 15+hrs, non-stop across the deserts of the US, near redline. Surely that can't be healthy. I am not going to swap in a manual as that is a little more than I want to modify right now. But, would be willing to change the rear diff.

Yeah, it has 4:10 gears. Think I could find a truck or something in a junk yard that I could just grab a taller rear end from? It seems to accelerate plenty fast, but I would hate to run at 55-60mph for 15+hrs, non-stop across the deserts of the US, near redline. Surely that can't be healthy. I am not going to swap in a manual as that is a little more than I want to modify right now. But, would be willing to change the rear diff.

If you have a 14 bolt rear, you'd need a new carrier to go down below 4.10. You might have a hard time finding them below 4.10 as well, it seems to me most 14 bolts came in 4.10, might find a 3.73 but that won't help your problem by a really significant amount. You'll lose just about any towing capacity your RV had, as well; part of the purpose of getting my truck was to put a camper on it and tow a boat, which almost makes me want to go to 4.56s if/when I do this, for extra grunt. I would definitely get a 5-speed if I were to do this tho.

If you find a 14 bolt with 3.42s, well, it would fix your top speed problem but your truck will be entirely gutless. And I mean, 0-60 in 'sometime next week.'

If you have a 14 bolt rear, you'd need a new carrier to go down below 4.10. You might have a hard time finding them below 4.10 as well, it seems to me most 14 bolts came in 4.10, might find a 3.73 but that won't help your problem by a really significant amount. You'll lose just about any towing capacity your RV had, as well; part of the purpose of getting my truck was to put a camper on it and tow a boat, which almost makes me want to go to 4.56s if/when I do this, for extra grunt. I would definitely get a 5-speed if I were to do this tho.

If you find a 14 bolt with 3.42s, well, it would fix your top speed problem but your truck will be entirely gutless. And I mean, 0-60 in 'sometime next week.'

haha, thanks. I guess I will just leave it then. I mean I'm not too sure how safe this thing would be at interstate speeds anyway. I'll just target an average speed in the 50mph range, cruise and have fun during the long drive.