RTH: GTurbo got lazy after highway drive, slow to build boost, lower boost levels than normal

[IanB]

Installed the 10mm spacers last night, a bit more than 5 washers worth, with some longer bolts. It hasn't resolved my issues of being slow to build boost, and failing to hold boost at steady loads, yet it was a further improvement as far as exhaust tone (I have no muffler so this is obvious, less "wastegate is leaking" type sound under throttle, much quieter), and max boost level. It will now hit 18psi and creep to about 21 if I stay into it.

So I'm still not resolved. I'm kinda torn as to next steps: figure out how to boost leak test, or swap back to stock turbo.

I plan on digging into the boost compensator tonight to make sure nothing has gone sideways in there, just to be sure.

 

[IanB]

All looked good in the boost compensator when I pulled it apart last night.

Today I'm boost leak testing the intake tract. I rigged something up to pressurize via the turbo compressor inlet, and used my air compressor to pressurize the intake tract. Pressure bleeds off over about 10-15sec, probably around 15psi being introduced to the system, I can hear it leak off best via the oil fill hole in the valve cover, so it's pressurizing the cylinder and getting past the rings slowly. I can't find any other leaks in the system via soapy water spray on all the joints.

Any ideas before I tear the turbo back off?

 

[jvjv]

All looked good in the boost compensator when I pulled it apart last night.

Today I'm boost leak testing the intake tract. I rigged something up to pressurize via the turbo compressor inlet, and used my air compressor to pressurize the intake tract. Pressure bleeds off over about 10-15sec, probably around 15psi being introduced to the system, I can hear it leak off best via the oil fill hole in the valve cover, so it's pressurizing the cylinder and getting past the rings slowly. I can't find any other leaks in the system via soapy water spray on all the joints.

View attachment 1779033

Any ideas before I tear the turbo back off?

 

[jvjv]

May i suggest to check the fuel strainer inside the fuel tank.

 

[IanB]

I took the weekend to mull things over, I'm not convinced my boost leak test was conclusive and points me in any one direction as far as next steps, or I just don't understand the results I've seen. I'm looking for some input.

To reiterate, when I tried to pressurize the tract from the turbo inlet to the engine, the pressure bled off quickly. I pulled the boost leak tester off and reseated/clamped it, and I started the engine for a moment hoping it would come to rest with the valves all closed, it was better than before, but pressure still bled off in 10-15 sec, the only place I could find it escaping was through the engine, it could be heard loudest with the oil fill cap removed. So air was getting into the cylinders, and presumably past the rings and venting through the valve cover. Or possibly past valve seals? The engine was cold for this test, I'm not clear if this should be concerning or not?

People suggested earlier in the thread that the valves being closed wasn't something I should worry about, it should just work out. I'm not sure how I could do a more controlled test in this instance, to ensure the valves are closed.

I ran the engine with the oil fill cap sitting loose on the valve cover, it doesn't dance around like some vids I've seen that indicate excessive blowby. The engine doesn't have issues with clouds of smoke out the exhaust, or excessive blowby pressure, I have no reason to believe there is an internal issue with the motor. It starts quickly as it always has, with a puff of black smoke that quickly clears. Other than the slow to build boost, failure to hold expected boost levels under sustained load, and general laggy turbo response the engine still runs great.

Have I seen anything here to indicate I should be taking a closer look at the engine, having compression and leakdown test performed? Or should I move forward with pulling the new turbo back off, inspecting thoroughly, and if nothing can be identified replacing the factory turbo to see if the symptoms follow the turbo or remain? It's an 8 hour job for me to re/re the turbo, so I don't want to keep doing this big job for no reason.

 

[gerg]

Did you just listen or did you smoke? Boost leaks are so very very hard to hear even when they are large. I'd reconnect your boost tester and air hose and leave it connected. It doesn't matter how much leaks inside the engine. This isn't a leak down test. It's purely to reveal leaks on connections that shouldn't leak. Once hooked up and pressurized I'd go methodically from turbo to intake manifold and everything in between checking each connection and the length of each hose or pipe. I'd pressurize to 25lbs given how much boost you run.
G

 

[IanB]

Did you just listen or did you smoke? Boost leaks are so very very hard to hear even when they are large. I'd reconnect your boost tester and air hose and leave it connected. It doesn't matter how much leaks inside the engine. This isn't a leak down test. It's purely to reveal leaks on connections that shouldn't leak. Once hooked up and pressurized I'd go methodically from turbo to intake manifold and everything in between checking each connection and the length of each hose or pipe. I'd pressurize to 25lbs given how much boost you run.
G

I expected the system to remain pressurized for much longer than I was seeing, so I ended up just listening, and feeling with my bare hands for any beak leaks, no smoke.

The fact remains that I don't THINK I'm dealing with a boost leak, so much as a reluctance to spool the turbo. A boost leak doesn't explain the "wastegate is being bypassed" sound out the exhaust, the sudden loss of wastegate pre-load pressure, etc. I'm happy to be proven wrong here, but the symptoms don't match for a boost leak IMO, it's difficult to describe convincingly when I can't let you guys take it for a drive and see for yourselves.

Of interest, I noted the turbo does spin at idle when I ran it briefly with the intake tube/boost leak tester removed.

I'll try and do the test on a warm engine one evening this week, maybe I'll have better success. I need to track down some incense sticks for smoke generation, cigarettes destroy my allergies.

 

[MonsterCruiser]

I haven't gone back and re-read things, but from memory, all the trouble shooting has been to do with the turbo, wastegate or looking for a boost leak. Now, I know the fuel settings haven't changed, and shouldn't change, but maybe try adjusting the fuelling to see if there is any difference? Check the fuel pick up in the tank like @jvjv suggested? It's something easier to play with before you go removing the turbo again.

 

[IanB]

I haven't gone back and re-read things, but from memory, all the trouble shooting has been to do with the turbo, wastegate or looking for a boost leak. Now, I know the fuel settings haven't changed, and shouldn't change, but maybe try adjusting the fuelling to see if there is any difference? Check the fuel pick up in the tank like @jvjv suggested? It's something easier to play with before you go removing the turbo again.

When the issues started, I had to back the main fuel screw off some as EGT's were getting too hot, too fast without the air it was used to seeing. I ended up setting it about halfway between where I had increased it to and my starting point. I painted the main fuel screw with a paint pen so I could keep track of things. Other than pulling apart the boost compensator to check things over, the fuelling has remained otherwise unchanged since the issues started. If I punch the throttle I can get a bit of black smoke until the turbo catches up, I have no reason to suspect a fuel delivery issue.

If this was an issue related to the fuel pickup line in the tank, or at any point between the tank and the injectors, I'd expect white smoke, or sputtering/coughing, struggling to rev, etc. I'm not seeing any of that under any conditions, revs climb as you'd expect when you give it gas, the issue is the turbo doesn't spool like you'd expect it to.

As always, I appreciate the suggestions all the same, you never know what might trigger the lightbulb in my head to go off!

 

[gerg]

I agree with the weird exhaust sound. That totally sounds like a wastegate open. I just wanted to eliminate the boost leaks. It is possible to have more than one issue I guess. What has Graeme been saying about all of this?

 

[IanB]

I agree with the weird exhaust sound. That totally sounds like a wastegate open. I just wanted to eliminate the boost leaks. It is possible to have more than one issue I guess. What has Graeme been saying about all of this?

Graeme was helpful once I got ahold of him early on in the process, but went silent around the time I felt I had it narrowed down to a faulty wastegate. I haven't been in touch with him further, he's halfway around the world, once I've got a cause in hand I'll get back in communication with him if the situation warrants.

 

[MonsterCruiser]

I remember you saying you resealed it, but could the split manifold be leaking so bad that it's causing the slow boost issue? If so, I guess it doesn't prevent you from removing everything again

 

[IanB]

I remember you saying you resealed it, but could the split manifold be leaking so bad that it's causing the slow boost issue? If so, I guess it doesn't prevent you from removing everything again

I've considered that, but couldn't see any evidence of a new leak at that point. It was leaking there before the new turbo was installed, and the turbo still spooled just fine...I'll definitely double check it again next time I'm in there all the same. If it comes back off I'll separated it to ensure the collar hasn't moved or anything.

 

[BCR4619]

You say the turbo does not spin when you have the motor in idle? correct me if I am wrong here but shortly after start-up you should hear the turbo spool up.... if not that could be the smoking gun?

 

[IanB]

You say the turbo does not spin when you have the motor in idle? correct me if I am wrong here but shortly after start-up you should hear the turbo spool up.... if not that could be the smoking gun?

False, the turbo is spinning with the engine at idle, visually confirmed this weekend.

 

[mudgudgeon]

Have you tried to wire the waste gate closed?
It would be a bit of a PITA, but a lot easier than R&R of the turbo, it only has to be good enough to help confirm or eliminate waste gate as an issue.

If the exhaust manifold was leaking enough to cause low boost, you'd hear it, or see evidence of it.
An exhaust leak can sometimes sound like a ticking our tapping sound.

A mechanics stethoscope can help locate a leak

 

[IanB]

Have you tried to wire the waste gate closed?
It would be a bit of a PITA, but a lot easier than R&R of the turbo, it only has to be good enough to help confirm or eliminate waste gate as an issue.

If the exhaust manifold was leaking enough to cause low boost, you'd hear it, or see evidence of it.
An exhaust leak can sometimes sound like a ticking our tapping sound.

A mechanics stethoscope can help locate a leak

I haven't, I have a suspicion that something else is going on there as it doesn't make a lot of sense that I'd get 2 faulty wastegate actuators in a row, I'm starting to wonder if I've got a cracked exhaust housing or something like that.

The original wastegate actuator didn't "lose it's preload" when the issues started all of a sudden, the paint pen markings on the adjustable rod confirm this. I expected to hear a broken spring rattling around inside when I got the original one off, but that was not the case, actuating by hand takes about the same effort as the warranty replacement GTurbo sent out. And the new wastegate actuator didn't improve the situation either. So I'm thinking there's some other reason the wastegate isn't sealing...

I'll see if I can get it wired shut and re-test, and I'll try boost leak testing again with a warm engine and the incense sticks I picked up last night, and report back.

 

[mudgudgeon]

hmmm, I'd forgotten you already changed the waste gate actuator.



Be careful with the incense sticks. It's a gateway drug!

Too much, and your truck will insist you start playing pan flute music, or sounds of the sea in the shop, and next thing you know, it'll be wanting vegan diesel, tie dyed seat covers and hemp tires.

 

[IanB]

Last night I tried the boost leak test again, the incense sticks were a fail and I didn't get any further with that.

I also wired the wastegate shut, and it may have actually made a small difference. The exhaust tone is the biggest indicator, less wheezy, worn out diesel sound when accelerating normally, sounds more like when I had a muffler in place, which is nice. I need to do some more testing as my 50-60km/h in traffic commute to work wasn't the best place to test things, but I feel like it may be a bit more eager to build boost when accelerating, but still runs lower than normal boost when you reach your speed and load levels off.

 

[IanB]

I've since got the WG wired shut tighter, it's tough to get all the slack out of the wire. The result is slight improvement in exhaust tone, and boost levels now creep to about 20psi, but it's not a firm max, and takes too long to get there. Boost levels are cruising load remain lower than they should be, boost is slow to build, power is down, etc.

Next logical step in my mind is putting the stock turbo back on to confirm the issue follows the Gturbo...but I broke a rib a few weeks ago and I'm unable to be hunched over the fender into the engine bay for a while. Yay.