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6.5L Diesel Engine Discuss the 6.5 GM diesel engine & associated components. Automatic transmission questions & problems belong in the 4L80/85 - 4L60E - 6L90 Transmission Forum

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Old 09-11-2019, 07:27 PM   #1 (permalink)
MikeRoss
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Fuel leak, substantial

I need a some help with a fuel leak on a 98 Suburban HD. It's got 202,000 miles on it but runs fine. I just suddenly started leaving a trail of diesel behind me and a puddle where I park. It only leaks when it's running, and for a short while after it's stopped. I can't see or feel anything wrong with the FFM, but the fuel is coming down the bell housing, more on the right side. What is up there that I should be checking and how do I get to it?

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Old 09-11-2019, 07:39 PM   #2 (permalink)
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Quote:
Originally Posted by MikeRoss View Post
I need a some help with a fuel leak on a 98 Suburban HD. It's got 202,000 miles on it but runs fine. I just suddenly started leaving a trail of diesel behind me and a puddle where I park. It only leaks when it's running, and for a short while after it's stopped. I can't see or feel anything wrong with the FFM, but the fuel is coming down the bell housing, more on the right side. What is up there that I should be checking and how do I get to it?
You will need to unbolt the FFM and look and the 3 lines connected to it.
1 Fuel inlet from LP to FFM
2 Fuel inlet line from FFM to IP
3 Water in Fuel Drain line ( Runs from the FFM to the T Valve)

These lines will leak with age/heat

Inspect the 2 (two) O Rings on the FFM

1. Fuel heater on the bottom has an O RING seal
2. Water In Fuel sensor located on the side of the FFM has an Oring seal.


Both will leak with age

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Last edited by OkDually; 09-11-2019 at 07:40 PM.
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Old 09-11-2019, 09:01 PM   #3 (permalink)
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Thank you, I’ll do that tomorrow.
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Old 09-11-2019, 10:29 PM   #4 (permalink)
jnlperformance
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Is the fuel all in the valley or just at the rear of the engine near the ffm?

If its just at the rear of the valley then... it's just the ffm. If it's all up in the valley...

The return fuel rail runs up underneath the intake on the passenger side of the engine valley. Those can degrade over time. If that's it run a new rubber return line from the primary return rail (runs across the front - left and right bank injector returns to this rail) to the return line behind the engine over the transmission.

Check under the injection pump as well. (May need a small mirror to check underneath it)

May need to take the lower intake off to check all that. Dont fret. You can achieve it in 15 mins or less. You'll need a 15mm deep well and an extension. Torque spec is 31? Ft lbs I believe for the lower intake. Upper plenum bolts (6) 17ft lbs? IIRC.

5/16th socket for the turbo connection boot. 1/2 or 13mm wrench for the connection arm between the upper intake plenum and the turbo housing.

hope this helps.
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Old 09-12-2019, 09:22 AM   #5 (permalink)
MikeRoss
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Fortunately it’s at the rear.
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Old 09-12-2019, 09:54 AM   #6 (permalink)
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Old 09-12-2019, 10:25 AM   #7 (permalink)
EppNation
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Have you happened to have changed your fuel filter in the FFM recently? If the filter isn't aligned to housing and/or cap isn't screwed back on correctly or all the way, it will leak substantially but truck will still run.
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Old 09-12-2019, 12:16 PM   #8 (permalink)
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No, it’s been fine since the filter was changed some time ago. I was trying to take it out, but there isn’t any slack in the hoses, is that normal? I didn’t want to pull too hard. There’s diesel on the bottom of the FFM and the hoses, I was thinking the o-ring for the heater might be bad? Is that and the water in fuel sensor o-rings easy parts to find? I see Leroy has them if I have to order them.
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Old 09-12-2019, 12:23 PM   #9 (permalink)
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Quote:
Originally Posted by MikeRoss View Post
No, itís been fine since the filter was changed some time ago. I was trying to take it out, but there isnít any slack in the hoses, is that normal? I didnít want to pull too hard. Thereís diesel on the bottom of the FFM and the hoses, I was thinking the o-ring for the heater might be bad? Is that and the water in fuel sensor o-rings easy parts to find? I see Leroy has them if I have to order them.
Space will be limited but is doable.

The Oring part numbers can be found in the FAQ located in the parts list section:
Fuel Filter Heater O Ring - GM: 12511962
Water In Fuel O Ring - GM: 12511959

For local or online reference and yes Leroy carries them on his site.

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1996 K3500 6.5L,( "F" Eng #141 cast block) 5 speed manual, crewcab, dually longbed: 208,000mi.
Diamond Eye 4" Turbo Back Exhaust w/2.5" Flo-Pro Crossover
AirDog II DF165 w/ tank sock delete - XDP
TD-Max boost controller - Kennedy Diesel
OPS extension hose - Leroy Diesel
Glow Plug Harness- PT Wiring Solutions
Glowshift Maxtow EGT,Boost, Fuel gauges
Boost & Fuel Pressure Bolts - Leroy Diesel
2/0 Battery Cable Upgrade - PT Wiring Solutions
PMD w/#9 resistor and Re-Location Kit, mounted to bumper - Leroy Diesel
GM-5 Turbocharger
4.10 gear ratio
OptiLube summer + Formula


Proud member #1039 of The 3500 Dually Club

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Old 09-12-2019, 01:04 PM   #10 (permalink)
scasanova
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Why not use this as an excuse to replace the FFM with 2 filters instead. I put a 12 micron fuel water separator on the frame before the LP and a 2 micron fuel filter after the LP. This will let you delete the filter sock in the tank. This will eliminate a lot of fuel leak issues.

It could also be an injector return line leaking. This happened to me. The trail of diesel that only gets worse. my return lines between 6-8 and 5-7 both went bad.

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