Help! Goofy fuel guage

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krenelka@bowie-cass-ssac.com - 02 Jul 2006 04:48 GMT

I installed an elec. fuel gauge (0-30) in march, everything was fine.
average fuel pre. was 12 at idle, 18 crusing at 1750 rpm, and would clime as
high as 24 with wot. coming home a week ago, I was accelerating onto the
interstate, when the fuel pressure jumped to 28psi egt was 680, boost was
15. the fuel came back down to it "normal" range. the next morning I was
heading to town, fuel pressure climes to 27.4 after about 2 miles it shot up
to 33 before the gauge went into error mode. it has been that way since.
when I crank it up in the morning fuel pressure is 26.x, any increase in rpm
causes the gauge to top out.

I removed the sending unit from its mount on the fender and installed my
fuel injection test gauge, Bounce! the needle looked like a fan blade, up to
40psi down to 15psi, I also noticed the fuel line was throbbing. I am
thinking of replacing the fuel gauge with a manual gauge, but all that
needle sweep has me nervous.

Suggestion, Advice, & Commits requested.

Signature

Billy
1995 Ram 2500 4x4 Cummins

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Tom Lawrence - 02 Jul 2006 07:24 GMT

> interstate, when the fuel pressure jumped to 28psi egt was 680, boost was
> 15. the fuel came back down to it "normal" range.

Well, that depends on what you consider "normal". Cummins says 8-24psi at
idle, 28-36psi at 2,000RPM/no load.

> when I crank it up in the morning fuel pressure is 26.x, any increase in
> rpm
> causes the gauge to top out.

Yeah - it's a little high. I would replace the spring in your overflow
valve. Oh, and replace the gauge with a 0-60psi gauge, as >30psi is
acceptable and normal on a 12V.

> I removed the sending unit from its mount on the fender and installed my
> fuel injection test gauge, Bounce! the needle looked like a fan blade, up
> to
> 40psi down to 15psi, I also noticed the fuel line was throbbing.

Yep. As with most diesel fuel systems, you need a "snubber" - something to
damp the pressure spikes. Most guys just use a needle valve in-line, and
just open it enough to register pressure on the gauge. On my gauge, I feed
the sending unit with about 3 feet of 1/8" OD tubing - the ID is small
enough that the pressure spikes are attenuated.

> thinking of replacing the fuel gauge with a manual gauge, but all that
> needle sweep has me nervous.

I'm a fan of electric gauges inside the cab - the only mechanical gauge I
have is a boost gauge, because a little air never hurt anyone. A continuous
stream of diesel, on the other hand.... isolators are one solution, but I
spent too much time jerking around with mine, futzing with the diaphragms,
replacing lost coolant, etc. - my Autometer electric fuel pressure gauge has
served me well for 18 months.

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krenelka@bowie-cass-ssac.com - 02 Jul 2006 19:33 GMT

"normal" was 12 - 18 psi that is what I have been reading since I installed
the gauges. maybe the spring was sticking in the open position and now it is
stuck closed. how hard is it to replace?

my "conundrum" is the manual will run me $150 with a isolator and the elec
is $250.

I bought this truck in July of 05 and have spent about 7 large on
"enhancements", very little of this was related to the motor. I am in fear
of my wife finding my maintenance log. :)

Signature

Billy
1995 Ram 2500 4x4 Cummins

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Christopher Thompson - 03 Jul 2006 07:39 GMT

> "normal" was 12 - 18 psi that is what I have been reading since I installed
> the gauges. maybe the spring was sticking in the open position and now it is
[quoted text clipped - 6 lines]
> "enhancements", very little of this was related to the motor. I am in fear
> of my wife finding my maintenance log. :)

uh maybe you should run two logs? *grin*

Signature

-Chris
05 CTD
06 Liberty CRD

Real trucks don't need spark plugs

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