1994 6.5 Turbo Diesel stalling issue

[kennyrodgers]

Hi Guys,
I have a customers RV in at the moment for some sealing work but she told me today that if she doesn't leave it idling for at least 5 minutes the engine will cut out within two miles of leaving home. No issues if she lets it warm up first.
This is quite recent and only started showing itself last month.
Thanks in advance for any pointers.
Cheers.

[Rickf1985]

Sounds like it is getting air in the fuel line. Check the suction line from the tank to the filter and from the filter to the lift pump for any cracks in the line that could be allowing air in and letting fuel drain back to the tank. If no cracks check the filter for leaks around the gasket. They used many types of filters but if it has the rectangular filter they were notorious for leaks. I have also seen lift pumps cause this same issue by losing the prime. At idle they can catch up before the air gets to the injectors but under load more fuel is needed and air is sent to the injector instead of bypassing. If this is a high mileage motor then have a look at the injection pump since it also can allow fuel to drain back thought the fuel return. That will usually cause a no start or start and instant stall though.

[kennyrodgers]

Cheers Rick and how are things, all good I hope.
I had a look under there yesterday, There's an inline tubular filter along the chassis rail in more or less the same place as my gas coach ( chevy petrol) and that looks to be fine and I can't see any leaks anywhere. It looks the same as my filter but there are two wires going to it.
I'll lift the doghouse and see what I can see under there.
Cheers Buddy.

[Rickf1985]

That sounds more like a fuel pump than a filter. That could also be a problem if it is a pump that is not running.

[tmsnyder]

Yep that's the lift pump.

Check the lift pump by cracking open the air bleed on top of the fuel filter and turning on the key.  It should shoot fuel up and out of the top for something like 10 seconds.   Also there should be a t-valve near the front of the engine for bleeding off water from the bottom of the fuel filter housing.  Cycle the key and you should hear the pump ticking if it's working, and fuel pumping out of those two valves.


If you've got fuel coming out it's good.  If no fuel coming out, and you can't hear the pump running then you need a new lift pump.  It's that thing you thought was an inline fuel filter with two wires coming out of it on the frame under the driver seat.  They die all the time, I've been through at least 2 of them in the 8 years I've had my truck.


If it's got good fuel then it might be the PMD, those cause intermittent stalling.   Usually more when they get hot but honestly there's not much else that can go wrong with them. 


When was the last time the fuel filter was changed?  They should be changed every other oil change or so.  Is the owner doing this?


Is the owner never checking or bleeding off water in the fuel from the T-valve?  They should have noticed that no fuel was coming out if the lift pump died. 

[tmsnyder]

You should be able to hear the lift pump running when you turn the key while the 'wait to start' light is on.

[kennyrodgers]

Hi all.
Many thanks for the replies and apologies for not getting back sooner. I just got back from a few days away at the  Drags.
The thing I thought was a filter with the wires is approx halfway down the chassis. It's a 30ft coach so at least 10ft away from under the seats. Is that what it is ?  It looks the same as the one on my gas coach...apart from the wires.
I'll run through the checks when it's in the shop next time and thanks again for the replies.
Pete.

[Rickf1985]

That is the lift pump, if it goes out the injection pump will pull fuel as long as it does not lose prime but that is what it sound like is happening. Since there is no fuel leaking while it is running I am betting on a suction side leak that may be pulling a small amount of air while running but it is allowing the fuel to run back to the tank when shut off. That would be between that pump and the tank.

[kennyrodgers]

That's interesting then and something very weird is going on.....this is a bit of a long one.
The customer reported a strange sound when on shore power.
Sure enough, when I plugged it in at the workshop I heard what sounded like a motor or pump running. I got underneath and the thing that we're saying is the lift pump was vibrating like hell. I pulled the battery cover (batteries under the steps) and there is a P/O fitted relay wired from the coach batteries (not the engine battery) with a wire going to this little pump that is also joined to the factory wire connector that then goes to the factory wires above the tank.
I then traced the switched wire of the relay all the way to the front of the coach and it is retro fitted to the "Radio Aux/Main battery switch. I flipped the switch and hey presto, the little gizmo went quiet again.

Now couple all that with this.  As is the norm on older coaches...the intellitec converter has failed..  ( this is the third one I'll be changing in as many months ) When I tested the converter it was humming like crazy and the output voltage 12.6v at the supply side and the battery side, not the 13.6v it should be. a sure sign that it's toast. Here's the strange part...When on shore power and the aforementioned relay is triggered the voltage at the battery side of the converter shows 15.5v  Hm? It's obviously back feeding from that relay but how the heck is it reading 15.5v.
Any ideas on that one and what would be the purpose of the retro fitted relay.
It's all good fun and thanks in advance.

[Rickf1985]

My friend, YOU have your work cut out for you!!!! Bubba has been there big time. Does this thing have house batteries and separate starting batteries? If so are the starting batteries any good? That would be the place to start, It has to have good starting batteries and then get that house battery circuit out of the loop. You need to be working with ONLY the vehicle system. If that pump has been running the whole time it was plugged in without have proper flow through it then it is toast. Once you get the electric squared away check that pump for pressure, and volume next.

[tmsnyder]

Sounds like the lift pump wasn't running when the PO wanted it to, so he hard wired it to a switch.   I _think_ that lift pump is powered through an oil pressure switch maybe? 


Yup, confirmed here:  http://www.ssdieselsupply.com/p11_6.5_diesel_ops_switch_oil_pressure_switch.html  "This is the switch that commonly fails on these engines. This switch is dual purpose. It not only is a sending unit for your oil pressure gauge, but it also turns your lift/transfer pump on and off. When it fails, your lift pump will not run. The truck may be difficult to start, but will run. You will notice a hesitation on hard acceleration-most common symptom."


And the oil pressure switch is a common failure (although mine has never died).   So, just conjecture here, but maybe the oil pressure switch died, the PO couldn't get the lift pump to run, so he wired it direct off that switch.   Instead of fixing the original problem. 


Btw, that website is run by Walt, and most of their business is 6.5L diesels.   If you have any questions about that engine he would be a good person to call. 

[kennyrodgers]

Cheers, you guys are fantastic !!

We have decided on a new battery as it will go flat if the coach is parked for a few days,   I was also planning on fitting a manual disconnect for her so that would stop any drains whilst the coach is parked.


Thanks tmsnyder, that sounds exactly right how you've called it. Wouldn't you think that whoever wired it this way would have fitted an idiot light then you know when it's running or not.
I'll pass this on to the customer and we'll see what she wants to do.


Thanks again guys, priceless info on here.
Pete.

[tmsnyder]

Just reposting this so I can see the tiny font...

Cheers, you guys are fantastic !!

We have decided on a new battery as it will go flat if the coach is parked for a few days,   I was also planning on fitting a manual disconnect for her so that would stop any drains whilst the coach is parked.


Thanks tmsnyder, that sounds exactly right how you've called it. Wouldn't you think that whoever wired it this way would have fitted an idiot light then you know when it's running or not.
I'll pass this on to the customer and we'll see what she wants to do.


Thanks again guys, priceless info on here.
Pete.

[kennyrodgers]

That's weird, it looks fine my end.
Aah well.