6.5TD, no vacuum line to turbo, wastegate wide open, correct?

[urbex]

Went to check out a '96 K2500 with the 6.5 turbo diesel last night. One of the issues I noted was that the vacuum line to the turbo was missing. The rubber connector was on the hard line on top of the turbo, but the rest was no where to be found. The vacuum pot is holding vacuum OK (pushed it up by hand, blocked vacuum port with finger, vacuum pot held position). Granted, I didn't spend a huge amount of time trying to track this down during the inspection, or attempt to repair the truck on site before making an offer on it, lol.

Test drive showed little power in the motor, and flooring the throttle resulted in rolling coal every time.

Obviously the black smoke is the result of over fueling, presumably due to the wastegate now being wide open at all times? Wastegate being open would also explain lack of power, due to zero boost being built.

I just want to make sure I'm understanding the operation of this turbo/wastegate arrangement, and verify my assumptions to be generally correct, before potentially buying myself in to a major can of unexpected worms, lol. I'm familiar with turbocharger systems in general, have been through several turbocharged cars and the Banks on my 7.3, but am used to systems that work off of boost pressure to control the wastegate, not vacuum.

 

[red EOD]

Sounds like you're on the right track. If you want to test it you can basically wire tie the waste gate controller closed (temporary only) and replace it with a mechanical controller if you decide to buy the truck. The stock turbos on these were never that great

 

[KirsL]

I second what Red has said.

Mechanical setups for the wastegate are pretty cheap and adjustable. Just keep it under 15lbs on a stock engine and it'll be very happy.

 

[urbex]

I had posted this after I got home from looking at that truck. Hadn't occurred to me at the time to try to tie it shut, but then I also wasn't 100% sure how the system worked, and didn't want to try to start hacking on something that wasn't mine.

Ended up putting in an offer on the truck anyways, and the seller accepted, now just waiting for her to get the title to it...so it may or may not end up being mine, lol.

 

[BadDog]

I may be off my rocker, and don't know any specifics about the 6.5 TD, but I don't think I've ever run across a wastegate controller that works off vacuum. And it doesn't make sense to me. They have a spring in them that holds the waste gate closed until boost on the diaphragm head reaches sufficient level to overcome the spring and open the wastegate.

Unless the 6.5 is substantially different than the norm, it seems that the problems exhibited would more accurately be supported by a wastegate stuck open, or a fuel side problem.

 

[urbex]

Unless the 6.5 is substantially different than the norm,

It appears that it is - http://www.dieselhub.com/maintenance/6.5-diesel-wastegate-solenoid.html

There's a vacuum pot on the side of the housing that looks an awful lot like the vacuum pots on HVAC boxes that control the outside air flap or coolant diverters for rerouting coolant around the heater core when the AC is selected. There's a vacuum line that runs from the turbo to a PCM controlled solenoid that meters vacuum to the wastegate pot.

Threw me for a loop when I first popped the hood....as in a "WTF did some hilljack redneck try to rig up here?!?!!?" kind of way

Problem for me was that I was out in the middle of nowhere, where I didn't even have signal to make a phone call, much less pull up Google to figure out how this thing worked out there. Thus, I didn't know if no vacuum defaults to wide open or completely closed. If it was in fact completely closed, low power, and STILL overfueling, then I know I would have potentially had much bigger issues on my hands.

 

[BadDog]

Ahh, that makes sense. The PCM has input from a boost sensor and makes the decision to trigger the solenoid sending power (vacuum) to the wastegate diaphragm/head and pulls open the wastegate. And it's better than direct electrical control because you don't need a remote gate or to have a solenoid mounted on/near the turbo hot side. I hadn't thought about it, but that actually makes sense so that the PCM can command open and dropping boost when the boost pressure itself may not be at some pre-set level to open the traditional direct boost referenced wastegate. That's the only way the PCM would have complete control of the boost pressure. Thanks for the clarification.

 

[red EOD]

Yea it's an odd turbo setup that GM had, but it defaults to basically the wastegate always open with no signal.

If it turns out that the turbo needs more than just the wastegate control fixed (usually fine unless it's worn out) then swap out to a hx35, hx40, or one of the other turbos. The 35 and 40 are cheaper, will also greatly increase the performance of the truck. The GM series of turbos were nice in that they spool up damn near instantly if adjusted right which was good for around town traffic, but that's it. Turbo was past efficiency before even reaching peak torque and is a big choke point for EGT's.

 

[urbex]

Turbo felt fine when I pulled the intake boot off...minimal play, no contact with the housing, spun easily and smoothly, compressor wheel looked clean. I suppose it's possible that the turbine side is shot, but I doubt it. I'm fairly confident it's just the wastegate control that needs attention.

 

[urbex]

Turned out the vacuum line just pulled out of the rubber connector. Eventually found it buried down in the intake, with the split loom having walked forward a bit, concealing it. Just looked like part of the wiring harness at first...pushed it back into the rubber connector, power back and coal rolling gone. Just a small puff of black smoke when flooring it, like it should be.

I think I'm still going to look at either a standalone MBC or EBC for it though.

 

[imiceman44]

Turned out the vacuum line just pulled out of the rubber connector. Eventually found it buried down in the intake, with the split loom having walked forward a bit, concealing it. Just looked like part of the wiring harness at first...pushed it back into the rubber connector, power back and coal rolling gone. Just a small puff of black smoke when flooring it, like it should be.

I think I'm still going to look at either a standalone MBC or EBC for it though.

So it's now a good deal if it does run good

 

[urbex]

It's appearing that way...The trans is still a bit iffy, but I think it might just be a fluid leak issue, though it's not leaving any obvious puddles. Maybe a really slow leak that's just soaking into existing road grime built up under the chassis (I haven't had it up on the lift yet to really inspect the under side). Might have mentioned it in one of the other threads...short of it is delayed engagement into 1st and reverse, but otherwise feels good once it's going. Fluid was just barely kissing the end of the dipstick the first time I went to look at it, and we added a couple quarts of ATF to it then. It improved, but was still delayed, and backing it up a hill was interesting as it kept disengaging reverse going up. Revving it up a bit got it going again, but then it felt like it wanted to slam into gear, and I was trying to avoid tearing up the guy's gravel driveway.

I just added another quart or so last night, and the situation improved quite a bit. I'm going to drop the pan this weekend to put a new filter kit in, verify the dipstick is set at the correct height, refill with fresh fluid, and do a thorough leak inspection. Also going to start looking for a 4L80E core to rebuild, and have it sitting here just in case the trans does let go.