possible air intrusion locations?

Some odd stuff going on here - this morning my truck fired up like normal, went into high idle like normal, idle went unstable and fluctuated for a few seconds, then engine died. Cranked it for like 15-20 seconds, it caught on and ran normal. In the evening when I was about to leave school it almost did the same thing, but this time I caught it the moment it started fluctuating, so I gave it a few taps with the throttle and it stabilized and ran fine. Beats me what's up with it, definitely seems like an air intrusion, but I ain't never had that problem before, and my return lines are only a few months old and I don't see any fuel leaks at the cap or anywhere else. Fuel/water separator drain valve is closed nice and tight. It happened all of sudden too, Saturday truck started up fine and this morning it's acting up... and I haven't done nothing to it in the mean time, it just sat parked all Sunday. Ideas?

Could the fuel pump be leaking at the weep holes or into the motor? I have to replace the short hose from the frame to the fuel pump about every 18 months. Well its a couple thoughts hope they help.

if you put a electric fuel pump close to the tank the air leak should turn into an fuel leak that will be easier to find and the trudck will still run fine.

adam g said:

Could the fuel pump be leaking at the weep holes or into the motor? I have to replace the short hose from the frame to the fuel pump about every 18 months. Well its a couple thoughts hope they help.

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Well, upon your recommendation I looked at that hose tonight after I got home, it's completely and entirely dry. I did, however, find some moisture on the #1 injector, which I find odd considering all other injectors and caps are perfectly dry. So I put new o-rings under that cap, and hopefully that will do - I dried the cap and injector and idled the truck for like 15 minutes, everything still seems dry, but we'll see soon enough.

mcbg said:

if you put a electric fuel pump close to the tank the air leak should turn into an fuel leak that will be easier to find and the trudck will still run fine.

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Yeah, I'll put an e-pump when my mechanical dies, but for now tis doing just fine.

Have a real good look around the connector for the fuel heater on the filter/separator head. Remove the electrical connection and check for any signs of fuel. That's the highest point in the fuel system and most likely to leak air. There are a couple of o-rings inside that will harden (especially with ULSD) and can leak air as well as fuel. I've seen it a number of times and mine is doing the same thing right now, just to busy to fix it.

I'll check on that tomorrow, don't think there was anything abnormal with the filter head itself, but I'll check for sure.

Well, the filter heater is fine, nice and dry. However, I think I found the problem - the big return line from the engine back was dried and cracked, but the actual leak was way back near the fuel selector valve. See, some mental midget who owned the truck before me had all of the steel return line and almost all the plastic return line removed, so the contraption I removed today consisted of about 4ft of rubber hose, then some steel tubing piece with threads on both ends to serve as a connector, then another foot of rubber hose, then a portion of the plastic line and finally the stock connector to the selector valve. I had a leak in that last piece of rubber hose where it met the plastic line, that's kinda hidden in the framerail near the tank so I never saw the leak, and quite frankly I wasn't looking for it there to begin with. So now I have a nice 6ft piece of new transmission hose from the engine all the way to the quick-disconnect fitting for the valve, no plastic and no steel line pieces, all one piece, nice and fat. Also redid the return lines around the injection pump, the line running to the filter head is now removed so even if I get another air intrusion in the return lines it will never make its way up to the filter again.

Now, here's a question - what thread is the fitting in the filter head where the return line attaches to? 1/4 NPT looks a bit large, so would that be 1/8 NPT? I'm thinking of installing a fuel pressure gauge there, liquid filled of course so it handles the diesel vibrations easier...

M.L.S.C. said:

Now, here's a question - what thread is the fitting in the filter head where the return line attaches to? 1/4 NPT looks a bit large, so would that be 1/8 NPT? I'm thinking of installing a fuel pressure gauge there, liquid filled of course so it handles the diesel vibrations easier...

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It's 1/8" and that's what I used on mine. The gauge has a 1/4" thread, so it did require an adapter.

Doug, the gauge I used on my old C10 Chevy was a 1/8 NPT, that's what I'm gonna install on the diesel too.

So, I guess mines bigger, huh?

lol, yep, but yours is bigger anyways - by two doors to be exact ;p

That's why my wife named it Moose!

I believe you have been fooled - Mel's is Moose, you may wanna ask your wife again?

Yea if you have a Moose Truck, I expect royalties.

But mine started out as a Moose with gas!