Tom, I remember discussing with you previously the issue of fuel drainback in my truck, but did not pursue the topic with you as I should have. Thus, I'm asking for yours, and anybody else with knowledge of the subject, to provide your guidance. My truck has an issue where, if it sits without running for more than a day or so, it will crank and start and run for ~5 seconds, and then quit. Then it takes 10-15 seconds of cranking to get it running again. I've been told that this is due to fuel drainback. While I understand the concept (fuel draining out of the lines back into the tank, thus de-priming the system) I'm not exactly sure what causes it.

Do I have a leak somewhere? How do I find out?

I was just reading on another thread, and a super simple solution was discovered within: check valves. Why didn't I think of that?

Is installing a check valve, or possibly series of check valves, advisable? What else can I do to cure this issue?

 

Air intrusion. Breaks the vacuum in the system holding the fuel in place and it all drains back to the tank. If you have a return hose running from an injector cap to the fuel filter housing, pull it and cap it on both ends. If that doesnt alleviate the problem, order up some viton 111 o-rings and replace the o-rings under the injector caps. This is an ideal time to replace the hose that runs between the caps as well. This will stop air intrusion problems a solid 90% of the time.

 

Thanks for the expedient response. I'm still learning about these IDIs, what would a return hose from the injector cap to fuel filter housing look like? Why is it an "if I have one" situation? Did not all trucks come with one?

 

I dont remember if the 6.9s did, most if not all 7.3s did, then ford / IH realized that "that" hose is one of the leading culprits behind air intrusion. It gives air a high place to go to and allows the fuel to leave, effectively siphoning out half the fuel in the filter. Around 93-94 i believe there was a technical service bulletin (TSB) regarding the issue. So yours may or may not have already been fixed, or might not have come with it in the first place.
You cant miss it, if looking at the engine from the front as its in the pickup, the hose will be next to the schrader valve (tire valve looking thingy), on your right side of the filter and will loop down the the first injector cap on your left, the engines right. 1/4" or 3/16" hose i want to say.

 

Thanks, I'll give it a look this morning.

Wouldn't that hose be part of the fuel re-circulation system that helps warm the fuel in the tank when it's cold out?

 

We don't have one of those.

We just have the excess fuel from the IP and other places that needs a place to go; I don't think it was ever designed as a heating system.

As far as air intrusion, the best solution I've found is to install a primer bulb(which contains check valves) in the line between the transfer/low pressure fuel pump on the side of the engine and the filter head at the top of the engine. Typically, you just pull the steel line off, cut it with a pipe cutter(the type you twirl around it to cut), and splice the primer bulb in with little pieces of rubber fuel line.
This line has less than 10 PSI running through it, so the rubber doesn't need to hold much.

Once you have that in place, you can have as many leaks as you want in the return system and you won't have this sort of problem.

 

That makes sense, but upon further consideration I don't think it would help with my leak. Fuel remains in the filter and injector lines; I know that because it will fire right up, and then die aw seconds later. Thus, I'm inclined to believe that the fuel system downstream of the filter is what's draining.

 

Nope. Fuel is draining out of the filter. What the engine starts and runs on is the fuel in the INJECTION PUMP. Doesn't last very long then dies.

IMO a check valve will keep filter full; no draining back the incoming fuel line.

Edit: Easy way to tell: next time the truck starts then dies, try unscrewing the fuel filter and seeing how much fuel is in it. Chances are it will not be full. Obviously you would do this before trying to restart.

 

I would not assume that. It seems apparent that you have an air leak (maybe more than one) and leak(s) need to be located and fixed - that is the cure. Fuel return lines are the first suspect and yes it would start and run for some seconds. All of those connections/seals and hoses need to be checked. Most often, (almost always as far as I know), there will be a fuel leak at the location that is allowing air to get in. I think the easiest way to spot a fuel leak is in the dark with a flash light, because the light will reflect off of a wet spot and make it much more noticeable.

Check the fittings at the mechanical lift pump also - it's like the pump on gas engines, same location.

Compressed rubber olive seals and o-rings lose their elasticity over time and what happens to them in cold Alaska weather? Obviously they would shrink and possibly leak.

Old hoses can look like new until you remove a fitting or a clamp and find that under the fitting they are old, lost their elasticity and cracked. Most often (if not always) these will be leaking some fuel so that is what you'll be looking for.

When you find a leak you can fix it but I would recommend buying a return line kit which has everything you need to replace the return lines, caps and clamps - Install that when you can and be done with it.

If there is a leak between the fuel filter and the fuel tanks you'll have to trace that down the same way but I expect that you will find a leak in the return fuel lines.

 

Simply adding a check valve is not identifying and fixing the problem of return fuel lines allowing air into the system, (or fuel lines before reaching the filter) unless it's a very unusual problem that I have not heard of before - and even then, it is not fixing the actual problem.

 

As long as there is fuel in the pressure side of the system, it does not matter what you have in the return side. You may have a visible leak, or not. If you can fix the starting issue, does it matter if air gets into the return side?
I personally believe it doesn't
Fix the starting issue, then fix any visible leaks you have.

If you aren't careful, you can end up chasing a tiny leak back and forth, as in fixing one cap you may disturb the next etc.

At this point, a check valve is a very cheap solution(all told, <$20 including hose clamps and hose). If nothing else, it will help prevent you from killing a starter while trying to find the "real problem".

 

So if I go the route of a check valve in the incoming fuel lines, what would make the most sense regarding a location? I'm thinking right before the fuel filter would be easiest, no?

 

Buy this kit, and install it. It will probably solve your problem


Ford International 6 9L 7 3L IDI Diesel Injector Installation Kit 83 91 | eBay

 

Sounds like you are looking for a quick and dirty fix. A check valve is only going to keep the line full, not the filter, pump and return system.
The best band aid is an electric pump, 99% of the time just having the pump running during the glow plug cycle is enough to bleed the system unless you have s visible fuel leak.

 

Yes. On mine, I had a long loop of hose so I ended up tying it to something nearby; it seems that the distance doesn't matter too much.
The reason being is that it will stop fuel flow on both sides -- Even on the top side, as long as you don't have any air leaks at that point, it will stay full.