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97 Burb 6.5 stumbling problem

crashandburn

crashandburn

1/2 ton status
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Dec 6, 2007
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Location
Colorado Springs, CO
Picked up an immaculate Burb a couple months ago. Has a new injection pump, rebuilt marine injectors, and a spring on the wastegate for a few more psi of boost. Someone (me) may or may not have hollowed the cat out.
About 2 weeks ago it started running a little funny on the highway and the SES light came on. Code came up Boost Sensor. Cleared it and it never came back. Truck seems to be getting worse, it seems to be worst under light to moderate throttle. It stumbles and comes back, maybe it is defueling?

I disconnected the map sensor, no change. Tried the IAT just cause it was right there, no change.
It seems like it would not be a boost/vacuum issue as it happens under low boost levels and does not seem as bad under WOT.
Any ideas?
 
When you say they put a spring on the waste gate, do you mean a turbo master? As in they blocked the vacuum line coming from the vacuum pump and the waste gate is totally spring controlled now?
http://shop.heathdiesel.com/Turbo-Master-GM96-GM96.htm

That's what I've got, and a few weeks back I also got the turbo speed, boost circuit code.
Same thing, cleared it and it's been driving fine since.
 
No, I just put a throttle return spring on the actuator to get a few more psi. Let me clarify that when I cleared the code, it did not come back, but the problem has not resolved, in fact it is getting worse. Should I block off the line to the wastegate?

It ran fine for a couple months, I don't know why that would be an issue now, unless it takes a while for the computer to figure it out?
 
Well I don't know how it works having both the vacuum and the spring. I have my vacuum totally disconnected and the line blocked off completely.
 
I don't know if maybe your getting the code because the computer is seeing one speed but the waste gate is seeing another with the spring?
 
Maybe, but like I said it seems much worse under light to moderate load, when the boost isn't very high. And it seems like an awfully long time before it started giving me trouble.

I'll try ditching the spring and see what happens.
 
Well I'm also not saying for sure that is the problem. Maybe it's a different problem unrelated to the wastegate. Cuz when I got the code there were no drivability issues. Just the light
 
I don't see the boost adjustment affecting the runability of the engine. You say the injector & pump are new, what about the PMD? A flaky PMD can do some interesting things, rough running included.
 
I'm with Ethan. It almost sounds like a PMD issue that they almost always encounter.
 
I think that would make more sense as well a fuel issue would make a lot more sense than the wastegate.
 
Smokinthehippies said:
I think that would make more sense as well a fuel issue would make a lot more sense than the wastegate.
Click to expand...

My thought is driven by the observation that a wastegate can fail in either position (open or closed), and the engine will still run smoothly. If closed, head gasket failure is the most likely issue. If open, you'll have no boost, and you'll find yourself rolling some serious coal. But in neither case would the engine stumble.

You don't have many options when it comes to diagnosing a combustion issue on a 6.5TD. You have no plugs to foul, wires to fail, gaps to set, timing advance to adjust (unless you're hot-rodding), and no air/fuel ratio headaches. Most of the typical issues you can have with rough running aren't relevant here.

You DO, however, have a PMD with a very high failure rate. If it still is in stock location with stock cooling issues, it's just a matter of time before the truck ceases to be driveable.

Checking the lift pump is another good suggestion.
 
Put in a new map sensor, ran good for 2 days, and the right back to running stupid.

Pmd has been relocated, but from experience that doesn't mean they last forever.
But in my experience, when they fail, (I've had 2 or 3 fail on a different rig) they make the truck abruptly stall.
Come to think of it, my brother had a 94 and when his pmd went, I think he said the truck ran like crap.
Mine idles smooth, and seems to run ok, or a least better under heavy load.

Maybe I should try a pmd.
 
Last edited:
black dawg said:
What year 6.5?
can you hear the lift pump? Do you have a boost gauge?
Click to expand...
It's a 97. Last time I checked boost I was running about 11 psi. I do hear the lift pump.
Lack of fuel volume or boost would cause loss of power under heavy load, this problem is more under light to moderate load.

I do appreciate the responses and suggestions though.
 
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