6.9 IDI questions

[Dustyman]

OK, new here but not new to diesels. Had several Cummins. I just bought an 87 F350 Air Force Ambulance/6.9 with 9400 miles, not a misprint. I tried to drive it home 200 miles and made it 57, had it towed the rest of the way. It was running perfect and then the last few miles it would occasionally sound different, smoother, and pick up a bit of power. Then it died. Restarted a couple of times, but not for long. I had no flashlight, few tools and the windchill was below zero, so I just called a wrecker to take it the rest of the way. Would appreciate suggestions for this particular animal as far as what to look for.

Next day I plugged it in and it started after a few revolutions. today I was going to take it to the shop to work on and it will not run above idle for long. Backed back up to my hose and ordered a filter, fuel is old, they said last summer but who knows. No leaks. When I removed the filter it was only half full? Live a long way from town and have no other wheels as someone crossed the centerline last week and wrecked my daily F150.

Also, I want to buy a paper service manual for this truck so would appreciate suggestions for the best one that is available. I plan on getting this sorted out and driving it to Alaska, want a paper manual in the truck.

 

[Clb]

Long list of possibilities...
Try the atf trick first.
Then look at...

Air intrusion
Fuel drain back
Gummed up Fuel system
Any possibility of Fuel gell?

Helm used to reprint oem manuals be sure to get all the reprints possible.

 

[asmith]

@Clb is right. There are a few possiblities of what is could be. What is the fuel level in the tank? 1/4 or below the shower heads could have broken off and you are sucking air.
It could be pieces of the old shower heads or algae are stuck in the pick up tube and blocking flow.
fuel filters could be clogged, lift pump could be bad.
One way to start diagnosing is get a clean jug and fill it with diesel and run the truck on that, if it fixes the problem you know the issue is behind the lift pump. If it does not fix the issue then you are probably looking at the lift pump of the injection pump.

 

[gandalf]

The"ATF trick" Clb mentioned:

Open the fuel filter, dump the fuel, and fill it with ATF, This would be an ideal time to change the fuel filter if you plan that. Put the ATF filled filter back in place and start the engine, assuming it starts. Let it run a minute or two, until you can hear a different sound to the engine, then shut it off. You now have ATF throughout the injection pump. Let it sit overnight, at least, then start it and drive it hard. This last, "drive it hard", is assuming that the ATF had a positive effective.

 

[Dustyman]

Ok, I put a new Fuel Filter on and although it did not cure the problem it changed it. I managed to limp the truck 15 miles to the shop where it was warmer. -21 degrees wind chill here. There is what looks like a water separator on the far drivers firewall, and it does not look like a factory install. May be because this has an ambulance body? Anyway it looks like hell, and two of the hoses are kinked. Is this where the separator normally is? Bad spot to work on it. If it is I would just like to buy a whole new unit. Sorry, forgot to take a picture.

 

[gandalf]

The earlier IDIs did have a water separator on the fender wall, driver's side, in front of the firewall. It was always a problem. Does yours have a pull ring on the top, and probably a hose out the bottom as a drain? Once you pull that ring you are too often subject to air intrusion because the valve does not seat properly. If that is what you have, get rid of it, splice in some new fuel line to go around it, bypass it.

 

[IDIBRONCO]

The earlier IDIs did have a water separator on the fender wall, driver's side, in front of the firewall. It was always a problem. Does yours have a pull ring on the top, and probably a hose out the bottom as a drain? Once you pull that ring you are too often subject to air intrusion because the valve does not seat properly. If that is what you have, get rid of it, splice in some new fuel line to go around it, bypass it.

I agree. The symptoms sound like air intrusion to me. It's the picking up of power that gives it away.

 

[Dustyman]

The earlier IDIs did have a water separator on the fender wall, driver's side, in front of the firewall. It was always a problem. Does yours have a pull ring on the top, and probably a hose out the bottom as a drain? Once you pull that ring you are too often subject to air intrusion because the valve does not seat properly. If that is what you have, get rid of it, splice in some new fuel line to go around it, bypass it.

It does not have a pull ring, has a plastic hand nut on the top. I may see if I can get it working but what a pain. Ford must have been practicing unserviceability for the trucks they make now. The lines are kinked like I said, and that may be the problem, should have had ells as they are all jambed up. Rubber lines, I'm thinking replacements. This was an Air Force truck in North Dakota so who knows what was done in the last 39 years.

I agree. The symptoms sound like air intrusion to me. It's the picking up of power that gives it away.

Not arguing, just trying to understand. When you have air intrusion and it picks up power what is happening? I had Cummins, but to be honest, they never broke so I didn't learn much. Is it a lean condition like how a 2 stroke runs best just before it blows?

 

[Brian VT]

...a lean condition like how a 2 stroke runs best just before it blows?

Been there, done that. Track bikes used to (still do?) have a way to lean the mix out near the end of the race for more power. If you didn't melt the piston(s) down at the finish line then you didn't give it everything you had. ;-)

Fwiw, I have the OEM water filter on my firewall with the pull-ring drain . Luckily, I came here before ever touching it and it hasn't given me any trouble yet. But I do have a Racor assembly that I may try to replace it with some day.

 

[IDIBRONCO]

I had Cummins, but to be honest, they never broke so I didn't learn much.

They do break. I have a friend who got a "good" deal on a truck with a Cummins only to find out that it not only needs a turbo, it also needs an engine. I know of another guy who fairly recently spent $12,000 to have a shop get his '91 and '04 Cummins trucks running again. Neither one had run for over a year and they both had the entire fuel systems gone though.

When you have air intrusion and it picks up power what is happening?

When this happens, the injector pump is advancing the timing to try to compensate for the air. Since I don't know much about the internals of a pump, that's about the only way that I can describe it. I don't know how a Cummins pump works. Those may act differently.

 

[Clb]

Op hit the poster
"Amgen"
Read his earlier tech 101 postings on any diesel forum for much beneficial insights...

 

[franklin2]

When this happens, the injector pump is advancing the timing to try to compensate for the air. Since I don't know much about the internals of a pump, that's about the only way that I can describe it. I don't know how a Cummins pump works. Those may act differently.

That is sort of what I understand. The IP uses the incoming fuel to operate the timing advance mechanism inside the pump. When it loses the incoming fuel, it can't control the timing correctly. So you get this "surge" from the timing going wacky.

 

[Dustyman]

When this happens, the injector pump is advancing the timing to try to compensate for the air. Since I don't know much about the internals of a pump, that's about the only way that I can describe it. I don't know how a Cummins pump works. Those may act differently.

Thanks.
I was buying the dodges new, and trading at 160Kish, then came High pressure and Def and I went back to gas. This 87 rig is my attempt to have a retirement rig I can depend on and fix myself, no computers, no satellite tracking, just an old man and his camper.

 

[Dustyman]

OK, worked on it today. It is a racor filter /separator so has been replaced. Could not find a filter in any parts store within driving distance so will have to order one. Cleaned the old filter as best I could in the parts washer and put it back together rerouting the hose so it was not binding/kinking. ran out of battery before it would fire so threw a charger on it and came home. Should have filled the filters first but had no diesel and no siphon hose. After a couple of tries I went to town and got some diesel. Batteries started getting weaker so I called it a day. Batteries are new, but have not been fully charged yet, only 57 miles on them.
Thinking an electric pump would be good for these times when you are molesting the fuel system but I would want an electric and a mechanical both, can you do that? I go to a lot of remote places and I like redundancy. What say you?

 

[miked]

I have used a cheap, brake vacuum bleeder, to pull the fuel up to the filter, emptied the bleeder cup a number of times making sure no air was left, undid the inlet line to the filter and hooked it up there, I did fill the filter ahead of time. Seemed to help save time cranking. In fact, it fired up with almost no hesitation. but the injection pump had not been run out of fuel.
I had put new tanks in my truck and all the lines had drained when I did this