Air Intrusion Redux 1994 F350 7.3 IDI

[tbrumm]

I know the subject of air intrusion in the IDI's has been beat to death, so one more thread about it probably won't hurt anything. A couple of my injector caps were leaking a bit, so I ordered out a Dipaco return kit and replaced orings, caps and hoses. I still had 2 leakers so I installed viton orings. That dried up the caps and return lines, but the truck became even harder to start. I then replaced the 3 fuel olives with new Dipaco olives just to be safe. The filter was still draining out so I started checking return lines from engine back to tanks. I did find a place where the plastic fuel return line just behind the motor has rubbed on the cab, so I replaced that. All other lines looked fine. The FSV was replaced last March because it was leaking air. The mechanical pump was replaced last October with an actual Ford unit because the old one had begun to weep. New supply hose too. And disconnecting the incoming fuel line at the filter shows the line filled right up and it is not leaking back. Checked the Schrader on the filter and found some air bubbles under the cap, so I replaced it with a viton schrader so no leak there now. The water bowl on the filter was replaced last fall with new WIF sensor, new schrader and new drain valve. New fuel heater and oring at that time as well. Also just replaced the filter return fitting with new check ball and spring. I thought maybe the filter gasket might have a leak, so I installed a new filter. So, I have done all of this work to try and solve my extended cranking times only to now have extremely long crank times. The filter is really draining out and fast after shut down. The truck runs great once the filter fills back up. To try and pinpoint the problem, I installed some clear line between the IP return fitting and the return cap on No. 2. The clear line fills up completely with fuel and stays there with no bubbles even after truck is shut down. I installed a clear line between the filter return and the cap on No. 1. When running, fuel runs out the filter return and down the the cap. The clear line fills up with fuel for about two inches up form the cap when the engine is running. The fuel stays there in the line for a few minutes after shutdown, but then the bubbles start to show up and the fuel quickly drains away. I would say that within 10-15 minutes the filter has been drained and very long cranking is needed to start back up. The return from the IP still stays full of fuel regardless of time elapsed. I should note that this is happening with both fuel tanks full and with the truck on level ground. This happens when switched to either tank too. I have double checked all the return caps and all appear to seated correctly - they "clicked" into place when I installed them- and caps and hoses are still dry. I am about to the point where I am going to remove all the return lines, caps and orings and start over. I hope someone has some suggestions, or at least moral support that will help keep me searching for the leak. Thanks in advance guys! Todd

 

[Iowa 73]

Add an electric fuel pump and you will be good to go. While it will not fix the drain-back issue, it will prime the system without all of the engine cranking.

 

[Wyreth]

Hit everything I would have suggested already.

My only thought would be, replace the back return lines (where it T's into the tank return) with clear. Then if bubbles come UP into the caps, then your caps are ok, and the leak is further down the return system.

 

[tbrumm]

Thanks for your input. Tonight I installed a clear line after the return tee at the back of the motor. The good news is no bubbles are trying to migrate to the front, so it appears the lines to the tanks and the FSV are not leaking air. Still haven't found where the air is getting in, but at least that narrows it down to somewhere under the hood. The lines at the No.1 cap are looking really wet. I did spill a little fuel when I reomed the clear line, but I didn't think I got he lines that wet. I have some o rings coming so I guess I will try again and replace orings. I read Mel's great tech write up on the idi fuel system so I used a little vaseline to slide them on without damage (or so I thought).

 

[Optikalillushun]

Good luck is all i can say, i fought this same issue with mine until i did what u have done and replaced every rubber part i can get. Seems to have cleared up finally.

I had wetness everywhere from the fuel filter heater, WIF sensor, olives, return caps (two times), etc. Its a total ******, i feel ur pain. Here is one tip i read or was suggested to me as a temp fix, use an o-ring on top of the return cap to make sure the caps are fully seated. shouldnt disturb anything as u are just unscrewing the injector line nut.

 

[Wyreth]

Make sure to check the insides of the caps for burrs, or sliding them on will shread the o-rings. Thanks to modern manufacturing even Russ' kits arn't completely free from this.

 

[Optikalillushun]

x2 what he said, i had to debur mine from Russ. Good call.

 

[tbrumm]

Thanks a lot, guys! I hadn't thought about burrs in the caps being an issue. When my viton orings get here, I will pull the caps back off and inspect them. With your help, I may get to the bottom of this yet!

 

[tbrumm]

Update - Well, I finally seem to have my air intrusion issues solved. Whew! Per your suggestions, I removed the return fittings and carefully inspected them for burrs. Sure enough, I had to clean a few of them up. The main culprit, however, was one of the tees (new) that actaully had a very fine crack in it. I replaced that with another tee and changed out all the orings yet again. The truck starts so fast now I can hardly get off the key quick enough. Again, I appreciate all the helpful suggestions!

 

[icanfixall]

Sometimes when we replace something with a new part we feel it going to be fine. But in your case you had a flawed cap. Did it come that way or did you do that when you installed it.. Who knows for sure. Its a good feeling to finally beat the problem. And an even better feeling finding out what all the trouble was. Any wet area is going to be a diesel fuel leak. That stuff creeps into the tinyest of cracks and usually makes a mes. Glad you got it working correct. Nice to know it fires off so quickly.... Gives me a warm fuzzy feeling when they lite off like that..

 

[Brad S.]

Update - Well, I finally seem to have my air intrusion issues solved. Whew! Per your suggestions, I removed the return fittings and carefully inspected them for burrs. Sure enough, I had to clean a few of them up. The main culprit, however, was one of the tees (new) that actaully had a very fine crack in it. I replaced that with another tee and changed out all the orings yet again. The truck starts so fast now I can hardly get off the key quick enough. Again, I appreciate all the helpful suggestions!

I'm fighting the same long cranking time, that tee was not leaking the fuel to the outside where you could see it??

 

[tbrumm]

The tee that had the fine crack was not leaking any fuel to the outside. The only reason I found it was I was putting clear lines in the various return hose locations and looking for air bubbles. That, and the fact that I was looking for any little thing that might be the problem. Apparently, the crack was so fine that air could get in, but fuel could not leak out. Since it was a new tee, that was not something I was looking for or expected. I see you have a Carrier electric pump on your truck. From what I have read, shouldn't the electric pump prime the fuel system and overcome the drainback caused by the air intrusion? I wonder if maybe your starter is getting slow? Last year, the crank times on my truck gradually began to get longer and longer (over a couple of months) until the truck almost refused to start. It is not really even all that noticable as the you kind of get used to it. I put in a Powemaster 9050 starter and the truck turns over very fast. I know there are other threads on here discussing starter draw, and somebody will probablt chime in with some good suggestions too. I certainly feel your pain, as I feel like I have just won some sort of a battle! It is definately worth it to keeping working to solve the problem. Imagine what is would cost to have a service department try to find the problem? They might be faster, but they still have to search like we do.

 

[Agnem]

...shouldn't the electric pump prime the fuel system and overcome the drainback caused by the air intrusion?

Only if your cold idle advance is functional.

 

[tbrumm]

After about 6 months of nearly instant starts after solving my original air intrusion problem, I am again having a bit of trouble. I don't always have the problem either. I will drive the truck to work in the morning, then it will sit parked all day (on a level area). When I start it to go home at night, it will instantly fire up and run smooth for about 10 seconds. Then it will start to miss just like there is some air in the lines. No tailpipe smoke though - at least not that I can tell in the rearview mirror. Then it will smooth back out and be fine. This happens every few cold starts, but not every one. Seems to occur an either fuel tank regardless of fuel level. The fact that it happens about 10 seconds after the truck is running, then runs rough and then smooths out quickly may provide a clue as to problem - but I am unsure where to begin looking. Anybody else ever have these symptoms? Thanks in advance for any insight!