From: Mark J. Blair (ke6myk_mvlist@sbcglobal.net)
Date: Sun Sep 14 2003 - 19:37:03 PDT
Tom Kelly wrote:
> I'm guessing that maybe there is a pin-hole leak that lets air in the
> fuel system overnight. but don't have a clue where to look.
I haven't worked on a CUCV before, but if I'm not mistaken, it has the same
6.2 liter V8 GM diesel as my HMMWV, so maybe I can help a bit. Here's what I'd
do to narrow down the source of a potential air leak. First, I'd tee in a
pressure meter in the line feeding fuel to the injection pump, after any other
boost pump(s) or filter(s). I'd include a section of clear tubing, so that I
could see if any air bubbles are present in the fuel (after bleeding out the
air that got in while messing with the plumbing), and check the supply
pressure. On the HMMWV, which has a mechanical fuel boost pump on the lower
right corner of the engine, there should be at least 4 PSI of fuel pressure.
This is a low pressure line, and one of those vacuum gauges from Sears, Pep
boys, etc. that can also measure around 15 PSI of pressure will work fine. If
air bubbles are still present after a while, then air is getting in somewhere
between the gauge and the fuel tank. If not, then restore the plumbing, and
temporarily replace the hose coming off the top of the fuel injection pump
(which is a bypass line, returning fuel to the tank) with a short section of
clear hose. If, after a while, bubbles are still present, then there's most
likely an air leak in the fuel injection pump, and it will need to be rebuilt
or replaced. This is how I determined that my truck had a bad fuel injection pump.
Anyway, before you try any of this stuff, learn how to properly bleed the fuel
system after air has gotten in (you'll need to know this anyway if you ever
let the fuel tank run dry). I don't know the procedure on a CUCV, but it's
probably similar to the procedure for a HMMWV:
1. Open the bleed valve on the fuel filter, and crank the engine until clean
fuel flows out with no more bubbles; close the valve. (If the CUCV has an
electric in-tank pump instead of the mechanical pump that the HMMWV has, then
you may just need to turn on the ignition, rather than cranking the engine.)
Now clean up the mess you just made.
2. Temporarily remove the bleed hose from the top of the fuel injection pump,
and crank the engine until clean fuel without bubble is coming out. Use a
container to catch the fuel that comes out. Reattach the hose, then clean up
any spills.
3. Slightly loosen the flare nuts which attach the metal fuel lines to the
eight injectors, being careful to not allow the injectors to turn (two
wrenches are generally required. Crank the engine until fuel squirts out
around all eight flare nuts. Re-tighten the flare nuts, and clean up the mess.
The fuel system should be purged at this point. I typed all of this in from
memory (been there, bought the T shirt!), so somebody weigh in with
corrections if I made any mistakes.
GOod luck!
-- Mark J. Blair, NF6X <ke6myk@sbcglobal.net> PGP 2.6.2 public key available from http://www.keyserver.net/ Web page: http://www.qsl.net/ke6myk/
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