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Turbo Issues

Big T

Big T

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Location
Fullerton, CA
My son's '94 is having turbo issues as he returns to SoCal from a trip to Lake Shasta with a boat in tow. During the trip the boost would be off and on and I tried to diagnose via iPhone from afar as I was attending a wedding in Los Gatos, CA.

Stock GM Turbo with Vacuum wastegate. Turbo boost not working at time and kicking out wastegate error code. I had him change out the wastegate solenoid, after which it would see boost up to 7 psi, then completely dump off to 0 psi as it the wastegate was stuck open. Apparently the turbo worked most of the trip down the flat central valley, only to stop working as he proceeded up the Grapevine (Tejon Pass). He's stuck at 25 going up it with the Buddy 4 position tune on the tow setting. He says that at every fill up when he undoes the fuel cap there is an incredible vacuum. So I had him turn the tune down to the lowest setting and pull over to loosen the fuel cap. He said the the vacuum was so strong that it wanted to suck the fuel cap back on.

He started back up and proceeded on, with the turbo working on the on-ramp then stopping on the highway.

I have yet to drive it to experience the problem, so I'm diagnosing via texts he vocalizes to his wife who's riding shot gun. With the problem persisting after replacing the solenoid, I was thinking a sticky wastegate problem. Now I'm thinking fuel delivery problem. A little over a week ago, he had towed the boat up to Big Bear Lake taking a route that went from 1,500' to 8,400' with no problems. He says it's not over heating, and he's keeping the EGTs at 950 to 1000 (Pyro in crossover at the Driver's side manifold). Not sure if it's defueling or there's some issue with the fuel tank.
 
I've considered cracked vacuum lines and asked him to conduct a test where you pull the lines from the solenoid, suck on the lines to create a vacuum and watch the wastegate actuator while doing so. Not clear whether he ever did this test.
 
I always had lots of black smoke when I had vac problems. Probably sensors.
 
sctrailrider said:
Tell him to leave the cap loose for a while anyway.

I suspect cracked hoses or a vac pump going bad, and maybe the sensors..
Click to expand...

Loosening the cap was one of my first instructions last night and he said the vacuum in the tank was so strong it wanted to pull the cap back on. Next instruction was to turn down the 4 position buddy tune to the lowest setting to lessen the fuel draw. He said after doing this, boost got to 9 psi going up the on ramp then dropped to Zero. It's dumping black smoke with no boost.

They made it home after 1:00 AM PST. I'll go take a look at it today. I have vacuum lines I can pull from the wrecked '95.
 
Tank vacuum appears to be somewhat 'normal' and you need a good cap to pass emissions.

:nonod: You are towing with the factory turbo? :mad2: And the GRAPEVINE at that!?!? :mad2:

Under high load (towing) the back pressure gets high to drive the GMx. If the vacuum pump is weak or the actuator diaphragm has a leak backpressure can blow off the waste gate. It appears to happen when it starts to throttle the boost so I am thinking pinhole in actuator. Check the vacuum reading off the pump and then as suggested look for cracked boots etc. on the vac lines.

Pull a vacuum on the actuator with a hand tester and see if it bleeds itself off.

Fuel issues would be low boost - not 0 boost. The ECM hitting a trip point via high IAT or other protection mode could be cutting off the fuel and boost. But you are getting black smoke so I doubt this.

:D I don't have waste gate issues anymore...
 
WarWagon said:
Tank vacuum appears to be somewhat 'normal' and you need a good cap to pass emissions.

:nonod: You are towing with the factory turbo? :mad2: And the GRAPEVINE at that!?!? :mad2:

ATT is on the list of things to buy. It's my son and he tends to learn by trial and error. I would never do that trip with a boat behind me unless I knew the truck was operating perfectly. I've towed boats all the way down the Baja during August. I have such respect for that Baja Highway, I've never towed it with the 6.5. The engine overheat issues on the wrecked '95 are what brought me here to TTS in the first place. Before my son left, I threw him two spare trailer tires on rims for the trip. He had two trailer tires go on the trip.

Under high load (towing) the back pressure gets high to drive the GMx. If the vacuum pump is weak or the actuator diaphragm has a leak backpressure can blow off the waste gate. It appears to happen when it starts to throttle the boost so I am thinking pinhole in actuator. Check the vacuum reading off the pump and then as suggested look for cracked boots etc. on the vac lines.

Pull a vacuum on the actuator with a hand tester and see if it bleeds itself off.

Just came back from inspection and test. Vac lines are intact. I sucked on vac lines to create a vacuum and it locks up the actuator and it does not leak down. The vac lines look to be in excellent condition and must be the new set that's missing on the '95. Hooked up GMTDScan and it has a DTC 78 Wastegate Solenoid fault, yet the solenoid is brand new.

Fuel issues would be low boost - not 0 boost. The ECM hitting a trip point via high IAT or other protection mode could be cutting off the fuel and boost. But you are getting black smoke so I doubt this.

:D I don't have waste gate issues anymore...
Click to expand...

I know, this should all be rectified by an ATT. Would like to solve this problem first.

He said that after loosening the fuel cap, the turbo pretty much worked the rest of the way. He said that the new wastegate solenoid significantly improved the situation, but it still occurred. He noted a strong correlation of the turbo working when the tank was full, then increasing episodes of lost boost as the tank level got lower. Fuel filter was installed fairly recently. Stock lift pump, though a FRC-10 is waiting to be installed.

Truck worked fine pulling the boat up to Big Bear as in no loss of turbo boost. Issue appeared on this trip. He has said that periodically he's lost the functionality of the adjustable Buddy tuner.

BTW the gauge panel has gone haywire again, sometimes working, sometimes not, sometimes just pegged at 80 mph. It has to be a ground problem. He says the problem surfaced when he connected pillar gauges. I told him to take it into the speedo shop as I hate troubleshooting other people's electrical work.
 
What about the air filter? I know mine looked clean but wouldn't flow enough air under boost and gauge went to zero and a massive black cloud followed me.... a quick removal of the air filter for a few minutes would see if it helps..
 
Big T said:


I know, this should all be rectified by an ATT. Would like to solve this problem first.

He said that after loosening the fuel cap, the turbo pretty much worked the rest of the way. He said that the new wastegate solenoid significantly improved the situation, but it still occurred. He noted a strong correlation of the turbo working when the tank was full, then increasing episodes of lost boost as the tank level got lower. Fuel filter was installed fairly recently. Stock lift pump, though a FRC-10 is waiting to be installed.

Truck worked fine pulling the boat up to Big Bear as in no loss of turbo boost. Issue appeared on this trip. He has said that periodically he's lost the functionality of the adjustable Buddy tuner.

BTW the gauge panel has gone haywire again, sometimes working, sometimes not, sometimes just pegged at 80 mph. It has to be a ground problem. He says the problem surfaced when he connected pillar gauges. I told him to take it into the speedo shop as I hate troubleshooting other people's electrical work.
Click to expand...

GROUNDS I think this is where you should start. The ones on the intake and the one to the firewall then to the frame.
 
Possible the cap has failed. Tank sock and just a plain undersized factory lift pump for the tune are also concerns.

Do you have a new 'extra' ground strap from the body to the engine and frame to engine? You should...
 
No extra ground strap. I'll work on that. I really need to drive the truck. They were still unloading and had the boat hooked up.
 
Doesn't seem like I'm getting definitive answers here. Should I swap the turbo from the wrecked '95 onto the '94?
 
Big T said:
Doesn't seem like I'm getting definitive answers here. Should I swap the turbo from the wrecked '95 onto the '94?
Click to expand...

No.
Test vac system for leaks and proper vacuum.
Test fuel system incl tank cap.
Test and add grounds.
Know why Bill Heath called the vac system a "mess" other than selling a TM.
 
WarWagon said:
No.
Test vac system for leaks and proper vacuum.

Did this and it did not leak down.

Test fuel system incl tank cap.

How do I do this?


Test and add grounds.

May sound stupid, but how do I test grounds? Ohm meter from frame to engine?

Know why Bill Heath called the vac system a "mess" other than selling a TM.
Click to expand...

Yep, which is why this is headed towards an ATT.
 
Search 6.5 grounds. That is name of thread with pics from Turbinedoc that I used when I was throwing weird codes and guages were going wacko. Sorry don't know how to link it for you. I added extra set of straps. I'm pretty sure he gave ohm readings. Hope this helps.
 
Update:

Son drove it around today without boat behind it and could not replicated the turbo boost drop off. I drove it around and experienced the same.

Son had said that his Buddy 4 position tuner had periodically not changed when the switch was operated. I noted the truck was chirping the rear tires and had a lot of grunt. I checked the tune and it was on position 1 (economy). I switch it to position 4 (race) and there was no change. I went through all positions and no change in performance.

After reading how the ECM sends signals to the wastegate solenoid causing it to open and apply a vacuum to the actuator, I'm thinking the problem is related to the ECM. The vacuum lines checked out and hold the wastegate open without leaking down when a vacuum is applied. Colby said he'd be cruising at 65 with the boost at 5 psi and it would just drop off to 0 psi for no apparent reason. He said that prior to installing the new wastegate solenoid, it was doing this on side trips without the boat in tow. I've asked Colby to send an e-mail to Tom on this.
 
Follow-on: Son said that when he lost boost and shut down, it would still be the same after a restart. Only after sitting awhile, like overnight, would the full boost return after a loss event.
 
Big T said:
Yep, which is why this is headed towards an ATT.
Click to expand...

ATT :hihi::thumbsup: I have a boost code now and then on Buddy's tune. Not been in a long while though.

Test fuel system incl tank cap.

How do I do this? Test fuel pressure at water drain idle and at WOT rev limiter. Anything over 0 PSI is good.
You need to stop by an emissions shop and have them test the fuel cap with a pressure vacuum device. Or just get a new one. I get a good hiss on the burb every time as the temp swings are extreme.

Possible kinked fuel line behind fuel filter (visual inspection) firewall side, plugged tank sock, failing lift pump, water in fuel (Drain some fuel and let settle from water drain and Pull and inspect fuel filter).


Test and add grounds.

May sound stupid, but how do I test grounds? Ohm meter from frame to engine?

Digital voltmeter. Ohms are worthless with wire size and currents involved. Anything over 0.25v needs more wire. Test frame/engine/body/battery. Test frame to engine by reading voltage between the frame and engine. (with lights on fans on high more or less everything on...) Then read voltage body to frame, engine to frame... I had the ground strap start to go bad and my EGT gauge started to flutter from 0-full scale like a airplane prop. Added a body to engine strap and it went away. Only took 0.4v body to engine. And it failed in Sunny AZ no less...

The power window speedometer episode indicates the grounds are weak as fuses/breakers/fusible links should have popped...

The root cause of your issue was me being too close to your 6.5 the other day when I visited... :hihi:
 
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