6.5 running loud and rough

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ncidi

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94 6.5 suburban randomly wouldn't start. It would crank over fine and would eventually start, sometimes 5 minutes, sometimes 5 hours. Replaced the pmd, tried unplugging the optical sensor, and neither made a difference. When it does start, it is very loud (can hear it in the video) and when it makes the loud noise the speedo goes up to 10 mph then back down, even though it's sitting still. After 5-10 minutes of idling it clears up and drives fine, but once you turn it off there is no guarantee it will start back. Thanks in advance.
Loud 6.5 diesel: http://youtu.be/tKFM4Xip-3Y
 
lindstromjd

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Sounds somewhat similar to a problem I had with my engine randomly getting louder for no reason... for me, it was my cold idle advance (the internal one) engaging and disengaging on it's own. Shortly after the injection pump died completely on me.
 
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ncidi

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Pulled the codes today, and here's what I got.
Checked the codes and got 17, 18, 34, 35, 36, and 78. I read up on them but I still have no understanding of what half of this stuff is. 78 I'm guessing is out of the window since the truck has a homemade boost control setup. The only other mod is a 10k resistor installed in the plug on top of the intake so the truck doesn't defuel with the increased boost.
 
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ncidi

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Don't have an exact mileage, they were replaced before I got the truck at 235k, it has just over 250k now and I believe the PO said he replaced them between 180k and 220k
 
lindstromjd

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I'm still suspect of them... but that may just be me. It's your call, but I think the codes are reflecting the beginning of the injection pump's internal failure.
 
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ncidi

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Going to pop test the injectors within the next couple weeks once I can get around to working on the truck. The truck has been great up until this point, not a single issue at all.
 
lindstromjd

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My issue started completely randomly on the road one day when I went to pass someone and got on it to pick up speed. No signs up to then, and acted up randomly after that until it just quit on me a few months later.
 
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ncidi

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The truck runs fine on the road, it's just at startup. The truck has been ran on biodiesel produced locally. I will continue to keep an eye on the injection pump though
 
lindstromjd

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Well, I do know that those stupid optical sensors HATE any fuel other than straight diesel, so I wonder if maybe that sensor is getting dirty... but I don't know of any ways to clean it.

Too bad you didn't get the early '94 model without the optical sensor in the pump...
 
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Unhooked the optical sensor and it wouldn't run, so that makes me believe it is something else.
 
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