6.9 conversion fuel and return lines and hard starting

[dirtbiker]

Hello, All,

We have been progressing on a late 86 6.9 swap into a 79 f-150 4x4. Most things are fairly straight forward, but having sources like you all to answer some questions has helped take out some of the guess work.

Though we have had the truck running several times, it starts somewhat hard, and smokes a lot. Maybe some of that is because the swap was started a year ago (or more) by the previous owner, and it needs to be run and driven (not drivable, yet). Unfortunately, we have had to resort to ether (a very short shot, after GPs have cooled) to start, as a manual 10 second hit with the NEW Motorcraft glow plugs just doesn't seem to do it. I have read a lot about the return line issues, and want to be sure we are good with our fuel system. We have a fresh (compatible metal) tank, with a 3/8" line connected from the pickup to the lift pump. For the return, we have a 1/4" line running DIRECTLY into the tank. Is there supposed to be any restriction or check valve in the return line? We connected it to the grommeted opening in the top of the gasser's tank, using the "vent valve" that was attached, but removed the valve from it, so there is no restriction on the return. We just were not sure, as it seems to be so important that there are no return line leaks at the injectors.

Thanks for your input!

 

[lindstromjd]

That's a good question. On the swap I did, I just used the rear tank sending unit out of the diesel donor truck, so I didn't have any problems at all with running my return line right back to the return port on the sending unit. But then again, that was a sending unit designed for a diesel.

 

[riotwarrior]

Couple questions

Stock lift pump?

Have you replaced the OLIVES in the feed lines from pump to filter and from filter to IP? If those have gone bad it can contribute to hard starts.

Have you replaced the return line caps and O rings? If not Either Mel or Russ can provide caps and o rings and olives.

Answer those and we can proceed further.

How old is IP? Is it timed correctly?

Lots of stuff to sort out

Al

 

[dirtbiker]

Thanks for the responses. The project was started by the previous owner, so regarding the age of the injectors and pump, return lines, and olives, I am not sure. Knowing these are important, we LOOKED at those areas, and the all seem clean and dry, but I am sure looks can be deceiving. Does the fact that the return line is just dumping unrestricted into the tank sound o.k.? We are using the stock lift pump. Thanks for helping!

 

[riotwarrior]

...Does the fact that the return line is just dumping unrestricted into the tank sound o.k.? We are using the stock lift pump. Thanks for helping!

Nope how that return line dumps into the tanks should not matter however maybe push the end down into the fuel and see if that changes things.

I'm uncertain as to what to suggest without knowing more. Are the injectors GREY in colour from paint? If so likely original then and due for replacement.

I'd suggest checking the fuel pump pressure for one thing. A compression test would give some indication as to what condition this engine is in as well.

hard to say what is what without further investigation and testing.

Al

 

[67-7THREE]

sorry to thread jack.. but is it ok to run 5/16 feed and return lines?

im doing a conversion too in a 67 f100 and it already has 5/16 from the tank.

 

[77f250diesel]

Not sure if this will help, I ran 3/8 supply and return.
Welded a nipple onto the fill neck for the return line.

My opinion is 1/4 is pretty small for the return line.
If it were me I would go over everything the po did to the truck as if you were starting from scratch.
Keep in mind, he gave up !

Dennis

 

[dirtbiker]

We are going over things pretty thoroughly, as we found things like under size bolts in the motor mounts, and some things like that. I pulled an injector, and on cleaning off the recent black paint, there is gray underneath, and a mfg code of "06/06". They did not APPEAR overly dirty outside, but I am guessing they are original. The posts I have read indicate that they DO wear out with age? Looking at the lines, even though the braided casing look nice, on checking a few, they are cracked. How tight should the caps be on the injectors? Should you be able to rotate them, or should they tighten under the pressure of the line fitting? Are the "olives" that everybody talks about inside the compression nut at the end of the hard lines where they connect to the filter and ip? I am still curious if there is supposed to be any sort of pressure regulation or restriction in the return line that will prevent the return line from "draining" into the tank. Thanks everybody for your help!

 

[cpdenton]

From what I understand, there is a t fitting behind the 8 cylinder that connects the two banks of return lines and the line that goes back to the rear of the truck. That fitting is a restricted fitting, that maintains proper flow in the return line system.

I remember towcat posting something about this on another thread.

 

[icanfixall]

At the number 8 cylinder there is a return line brass manifold. I have seen it with 2 or three fittings on it. Some even had a hard 3/8 steel line running from the injection pump return to that fitting. The olives are found in both ends of the fuel line from the filter to the pump and at the lift pump to the fitler head end of that steel line. Most anyplace you find a brass nut there is a rubber seal in it called the olice. I believe they are there for vibration illimatation. It sounds like the return lines are old and worn out. Time to buy a complete kit and replace what you have.