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Old 05-29-2020, 07:55 PM   #1
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Join Date: Oct 2011
Location: fortwayne, indiana
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6.5 turbo diesel issues

I just recently bought a 93 3500hd. I was told it been setting for 10 years being used as storage seeing it is a box truck it didn't surprise me, just gave me a reason to lowball them lol. I replaced the power steering pump and brake hoses and it ran like a top and stopped too lol ... at least around town but when I get it on the highway it gets a hesitation. I read somewhere it is called fish biting. I've checked everything. the tank looks brand new on the inside as well as the pickup screen, lift pump works 5 to 7 psi at idle and down to 2 at wot. new fuel filter, last chance screen is clean, all new injectors and return lines, replaced pmd as well although it's no longer a pm just a d lol also cleaned all grounds. but the hesitation is still there at 55mph. I unplugged the optical sensor and it runs even better but the idle is high and it stalls on occasion when coming up to traffic lights. I'm starting to think this is not a fueling issue but a sensor or electrical issue causing a fuel issue. just seems to me it's cutting back too much fuel. considering going mechanical but cruise control would cost more lol.

I would appreciate any ideas or a link to get me pointed in the right direction
88 gmc v3500 bonus cab classy chassy conversion, 454, nv4500, np205, dana 60 front with spool, 14 bolt ff cac rear with locker.
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Old 06-05-2020, 09:00 AM   #2
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Location: edenton nc
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Re: 6.5 turbo diesel issues

Put a clear fuel line on going from the injection pump to the return line. It's at the front of the pump and is about six inches long. There should be no air bubbles visible while truck is running. An air bubble a top of line when truck is off is ok.
1995 k3500 cclb srw 6.5 turbo diesel.

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Old 06-06-2020, 11:55 AM   #3
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Location: West Falls, MD
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Re: 6.5 turbo diesel issues

Your '93 should be mechanical injection, DBII pump. I never had that kind of problem with fuel, but I've had lagging and stalling that was hard to figure out on a '92, same set-up. I tried everything, I figured. Maybe a year before the issue I had run new fuel lines, dropped tank, cleaned that up and rustproofed it. While I was at it I replaced the sending unit/pickup.

It was really cold, like single digit, so I suspected gelling. I rescue treated it and all seemed fine, but not for long. It might be ok for a couple days. It seemed pressurizing the tank would get it going again. I suspected some freak debris issue. Like some a-hole stuffed trash in my tank.

Tank and fuel looked perfect. I cut the sock off the pickup and look, my buddy looks, looks fine, looks new. Cut and stretched flat I blew 120 psi on it with my hand on the other side. I couldn't feel any air, only back on the hand holding the blow tip.

We sure were baffled on that, but there was no doubt there is where the problem was. One of those can tell you what but can't tell you why kind of things. Truck ran fine for a long time after replacing the unit.

That was a crap replacement part issue, I suppose. But it does go to show how funny that diesel can act. Might help your thoughts some on your problem
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