6.9 motorhome giving new grief

[Rattlenbang]

A few weeks ago I got help getting my project motorhome going (thanks again). We took it camping a few days ago and drove it about 160Km (75 miles) and it ran pretty good except the common and annoying issue of occasionally stalling after dropping the throttle too quickly. I adjusted the idle up a bit and it no longer does this. I got about 12mpg, which is pretty good I think for a 26' motorhome.

But after sitting a few days when I headed out this morning I got a few clicks and it started losing power, like it was running out of fuel. I pulled over and it stalled. I hit the starter expecting the inevitable starter grind of a diesel that has lost injector prime. But it started right up and seemed fine. I took off again and didn't get nearly as far before it started stumbling, losing power and eventually died again.

Each time after restarting it seems ok but eventually got to the point where I could only go a few hundred yards before it acted up again.

I fuelled up to make sure my gauge wasn't loopy and replaced the fuel line to the filter with a piece of clear tubing, and there is no air getting to the filter. The filter is new. Fuel pump is new. Lots of pressure, lots of fuel squirting out of the schrader valve. Checked the voltage to shutoff solenoid and that's ok. Its like pressure or vacuum is building while its running until it can't run anymore. Shutting it off seems to release this until it's been run awhile. It will do this even just at idle.

After remove the clear vinyl tube and re-installing the normal fuel line, it seemed to idle much longer, about 20 minutes before it finally died again. Before doing this it would stall after a couple of min of idle. Coincidence?


I'm wondering now about the check ball on the outlet and whether if that was stuck if it would give those symptoms? Any other ideas? Again, no air getting the the filter.

 

[gandalf]

... it ran pretty good except the common and annoying issue of occasionally stalling after dropping the throttle too quickly. ...

That sounds very much like the metering valve is sticking. Its located in the IP. This is generally an indication that the IP is getting old and in need of replacement soon. To hold that off for a while you might use a really good fuel system cleaner. I can't remember the name, but some one will come alone with it.

 

[riphip]

Hotshots Secret Extreme. Can find it most anywhere even Amazon

 

[aggiediesel01]

Nothing wrong with the suggestions above but I'd start by taking that new fuel filter off and double check that it's not clogged up already. Seems from your early description that the truck sat for a while before you got it going again. Very likely that algae has taken hold in your tank and the new diesel and trips down the road are shaking it loose and sending it to the fuel filter. Pull the filter and pour it out into a paper towel and look for a grainy reddish substance or other sludgy condition. If there's a bunch there, treat the tank, buy a few filters and just keep driving and changing them until you've filtered it all out. Also take a close look at the fuel filter light on your dash while it's acting up, if the circuit is working it will light up while you're having issues but then it will go out while just idling.

 

[Rattlenbang]

Also take a close look at the fuel filter light on your dash while it's acting up, if the circuit is working it will light up while you're having issues but then it will go out while just idling.

I thought that light was just to indicate water in the system, although the water separator doesn't exist in my rig...

I've run two cans of seafoam through the IP, and FYI it only has about 100k miles on it. Do they really need rebuilding after such little use?

The original fault that kept it from starting was indeed a stuck metering valve. After running the seafoam through it stopped the stalling after throttle issue for awhile, but then it came back.

I forgot to mention I installed a cheap inline fuel filter and it looks clean still after my latest run. But engine still stalls if I switch to rear tank, so it's not that filter, and since it was already there to catch gunk, I doubt much of anything made it to the main filter. I don't know what micron setting a small gas filter is, but I've seen organic gunk in diesel before and there's none of that in it.

 

[aggiediesel01]

I guess I don't know for sure what the pre '87 vehicles had for indicators but '87 and on trucks had 2 fuel related lights, "Water in Fuel" and "Fuel Filter". The Fuel Filter light is connected to a pressure switch on the side of the filter header that grounds when the injection pump is sucking fuel faster than the lift pump can provide which typically is clogged fuel filter. If you've got a pre-filter that you can look through and see nothing then algae isn't your problem.

 

[chillman88]

Seafoam is very mild compared to Hotshot's. I'd try the Hotshot's myself, the seafoam may have helped a little but still left some gunk in there.

If I was really concerned about the IP I'd get some LiquiMoly Diesel Purge and run the truck on that straight in a closed system with the returns running into the same container as the diesel purge is in. I've heard running like that will clean a lot of crap out of the system, and from what I've read it's pretty noticable if you watch it running from a clear container like a 2 liter soda bottle.

 

[Philip1]

I thought that light was just to indicate water in the system, although the water separator doesn't exist in my rig...

I've run two cans of seafoam through the IP, and FYI it only has about 100k miles on it. Do they really need rebuilding after such little use?

The original fault that kept it from starting was indeed a stuck metering valve. After running the seafoam through it stopped the stalling after throttle issue for awhile, but then it came back.

I forgot to mention I installed a cheap inline fuel filter and it looks clean still after my latest run. But engine still stalls if I switch to rear tank, so it's not that filter, and since it was already there to catch gunk, I doubt much of anything made it to the main filter. I don't know what micron setting a small gas filter is, but I've seen organic gunk in diesel before and there's none of that in it.

The average lifespan of the injector pump with modern diesel is around 125000 miles or so.

 

[typ4]

Gas filters dont like diesel.

 

[Rattlenbang]

Well, things got complicated. I decided to pull the outlet ball valve, because since it determines pump internal pressure, if it sticks, pressure will build in the pump until the internal transfer pump can no longer drive the plungers. As it turned out, it was full of a bunch of crap. The ball itself appears to be glass and I couldn't see through it when I first pulled it out. I knocked and flushed out a big pile of crud.

Hoping this was the issue, I reinstalled it and fired up the truck, this time on the rear tank (I honestly don't know why I switched tanks) it idled for a long time but then suddenly stalled. Big disappointment. I decided to pull the fuel filter and was surprised to see it 2/3 empty. Well then, I figgered the filter must be plugged after all, and so I popped out and bought a new one. On a hunch I also put back on the clear tubing fuel line, and was surprised to see air intrusion happening. Not regularly, but occasionally a big gurgle of air. I switched back to front tank, and it was okay, as I had seen before.

This time truck died because of the rear tank air intrusion, not the same problem I've been having. I've never really run the engine any length of time on the rear tank.
The engine seems to be running ok for now, But I don't know if the filter was the cause or my cleaning out the pressure regulating valve.
Obviously I need to find out where that air is coming in when switched to rear tank. The rear tank is full. Where do they usually cause problems? Everything from the selector valve forward is ok.

 

[IDIBRONCO]

My first guess was the lift pump is going bad. Since you now can run on the front tank just fine, my next guess would be the fuel tank selector valve (fsv) may be sticking internally. When this happens, they can do some funny things.

 

[IDIBRONCO]

I got about 12mpg, which is pretty good I think for a 26' motorhome.

I'd say so. Cubey has a 1985 RV. I think it's 27 or 28 feet. I think that he said that he gets about 7MPG after installing a new Motorcraft fan clutch.

 

[pastorjeep]

7-8mpg in my 1989 Winnie 26'with the 460.

 

[dan-o]

Stanadyne fuel additive did wonders for my '89 7.3 IDI. Not that the other stuff is worse, but it was recommended on this forum. I dumped about a quart of it in each tank. Ran it for about 30 minutes and it was like a new truck. It's about $40 a jug at Autozone, but it says it will treat something like 250 gallons.

 

[Cubey]

I thought that light was just to indicate water in the system, although the water separator doesn't exist in my rig...

It should be under the driver's seat with a plastic hatch with a pull handle/cable, if the W/S hasn't been removed (like on mine). I put a Racor W/S filter under there intsead.

Odds are you need to do the return line o-rings if it's air intrusion. Also check the short hose at the mechanical fuel pump, since that let in air if it's leaking.

Try bypassing the tank selector valve while troubleshooting to be sure that's not the problem.