RTH: GTurbo got lazy after highway drive, slow to build boost, lower boost levels than normal (1 Viewer)

[IanB]

Coles notes: '93 HDJ81 auto, 140,000km, 3" from OEM dump pipe back, no IC, Gturbo grunter extreme installed about 10 days ago, main fuel screw turned up 1/2 turn total in 1/8 turn increments, truck was running great, turbo spooled quickly, great midrange and top end power, EGT's in check.

Took it on the highway yesterday, 32C, running about 120km/h, EGT's at ~900F pre-turbo (hit 1100F a few times when accelerating), came off the highway and turbo is slow to spool, runs 0-2psi at 60km/h where it used to see 5-6psi, only hitting 18psi at WOT when it used to hit 20psi set via MBC.

Now if I stab the throttle the boost is slow to rise compared to before, no black smoke though, boost does still build but something isn't right, it's not like it was previously.

I've checked the head to manifold and manifold to turbo bolts, all were still tight, no signs of leaks. The symptoms seemed to me like an exhaust leak pre-turbo might be the case, but nothing out of the ordinary. Turbo shaft has very little play and spins freely by hand. I'm at a loss, anything else I should be checking?

 

[GTSSportCoupe]

Coles notes: '93 HDJ81 auto, 140,000km, 3" from OEM dump pipe back, no IC, Gturbo grunter extreme installed about 10 days ago, main fuel screw turned up 1/2 turn total in 1/8 turn increments, truck was running great, turbo spooled quickly, great midrange and top end power, EGT's in check.

Took it on the highway yesterday, 32C, running about 120km/h, EGT's at ~900F pre-turbo (hit 1100F a few times when accelerating), came off the highway and turbo is slow to spool, runs 0-2psi at 60km/h where it used to see 5-6psi, only hitting 18psi at WOT when it used to hit 20psi set via MBC.

Now if I stab the throttle the boost is slow to rise compared to before, no black smoke though, boost does still build but something isn't right, it's not like it was previously.

I've checked the head to manifold and manifold to turbo bolts, all were still tight, no signs of leaks. The symptoms seemed to me like an exhaust leak pre-turbo might be the case, but nothing out of the ordinary. Turbo shaft has very little play and spins freely by hand. I'm at a loss, anything else I should be checking?

Sounds like a wastegate issue to me. Vacuum line leaking or popped off the boost controller or wastegate actuator?

Or, boost line popped off the boost compensator or intake manifold?

At those pressure levels, vacuum hose pops off easy. Has happened to me a number of times at far less boost. I wrapped zip ties around most of the vacuum line connections now which seems to hold them on better.

 

[IanB]

I've ziptied all connections, I'll go back and look over the lines to ensure they haven't been damaged. I had the wastegate line pop off on the stock turbo once, the turbo free revved, totally different symptom that what I'm seeing here.

This sounds more like the wastegate has stuck open...

 

[remy]

Main fuel screw not tightened?

 

[IanB]

Main fuel screw not tightened?

Just checked and confirmed main fuel screw lock nut was tight.

Wastegate stuck open seems like the most likely culprit given my symptoms, and the fact all the pre-turbo exhaust bolts are tight. The wastegate arm isn't binding on anything. Is there a way to test this, and how do I get it freed up again?

 

[gerg]

You could have an occult boost leak also. Some times the silicone hoses split and you totally cant tell until you pressurize it. Might be easier to check that than unhook the wastegate. They don't look that easy to access. You could also try pressurizing the wastegate reference line and watch the action to see if its not returning to seat properly.

 

[IanB]

You could have an occult boost leak also. Some times the silicone hoses split and you totally cant tell until you pressurize it. Might be easier to check that than unhook the wastegate. They don't look that easy to access. You could also try pressurizing the wastegate reference line and watch the action to see if its not returning to seat properly.

I have no IC, so from the turbo there's just the factory rubber connector and heavy clamps to the crossover pipe, and a gasket (new when turbo was installed 10 days ago) to the intake manifold, very few spots for boost leaks to occur, and I'd still see normal boost on the boost gauge, it just wouldn't all be making it to the engine, right?

I'm kind of settling on the wastegate being stuck open, I'll try pressurizing the wastegate reference line and see if it moves as expected. I tried removing the circlip and arm from the wastegate flapper on my old turbo, there's no way I'll be able to do that with the turbo in the engine bay at all, it would have to come back out...FML.

 

[gerg]

It doesn't take much of a leak to really diminish performance unfortunately. Might be worth it to pressurize the intake and check for leaks as its very easy to do. I use a cigarette's smoke to look for air leaks. Pretty much the only use Ive found for them. My wife was super pissed when she found a pack in my tool box. Then I explained how to look for boost leaks and how awesome it is to seal them up and she just sighed and started muttering how much she hates my truck and walked away. It almost qualified as a date.

 

[IanB]

So I've tried 2 more tests, pressurized the WG reference line with a bicycle pump, the actuator arm moves as it should, pressure holds till you disconnect the pump and release the air.

I also tried driving with the WG reference line unhooked, same lazy turbo performance, but boost would eventually climb past the 18psi mark I've been stuck at since the issue began, I saw as much as 22psi for a second. I hooked the line back up right away after the test.

I'm thinking I'll try and pull the downpipe and dump tube off the back of the turbo, pressurize the WG reference line with the bike pump to open the WG, and see if I can see and remove whatever is keeping the WG flap from sealing.

 

[gerg]

Might want to put eyes on the impeller as well if you can and feel for some play?

 

[DancesWithMutts]

Is your boost compensator working? Have you checked for tears in the diaphragm? It could be a fueling issue.

 

[IanB]

Is your boost compensator working? Have you checked for tears in the diaphragm? It could be a fueling issue.

I had the diaphram out last night, looked fine.

 

[DancesWithMutts]

I had the diaphram out last night, looked fine.

Then yeah, WG sounds like the culprit.

 

[vwluv10338]

Is your boost compensator working? Have you checked for tears in the diaphragm? It could be a fueling issue.

I had the smoke screw lock nut loosen up on me before and cause similar symptoms. It shut down the boost compensator working and messed my fuel all up and it wouldn't boost.

 

[CruiserGord]

Had a very similar issue myself one time, while highway driving. Went through all the same checks that you did till I discovered that almost all my intake manifold nuts had come loose and some had even vibrated off. So if you haven't checked them yet it wouldn't hurt to have a look.

 

[IanB]

Had a very similar issue myself one time, while highway driving. Went through all the same checks that you did till I discovered that almost all my intake manifold nuts had come loose and some had even vibrated off. So if you haven't checked them yet it wouldn't hurt to have a look.

Good thought, but I replaced the IM gaskets, gommets, and nuts last summer, and many of the nuts were only hand tight when I took it off!

 

[Tim-HJ61]

Coles notes: '93 HDJ81 auto, 140,000km, 3" from OEM dump pipe back, no IC, Gturbo grunter extreme installed about 10 days ago, main fuel screw turned up 1/2 turn total in 1/8 turn increments, truck was running great, turbo spooled quickly, great midrange and top end power, EGT's in check.

Took it on the highway yesterday, 32C, running about 120km/h, EGT's at ~900F pre-turbo (hit 1100F a few times when accelerating), came off the highway and turbo is slow to spool, runs 0-2psi at 60km/h where it used to see 5-6psi, only hitting 18psi at WOT when it used to hit 20psi set via MBC.

Now if I stab the throttle the boost is slow to rise compared to before, no black smoke though, boost does still build but something isn't right, it's not like it was previously.

I've checked the head to manifold and manifold to turbo bolts, all were still tight, no signs of leaks. The symptoms seemed to me like an exhaust leak pre-turbo might be the case, but nothing out of the ordinary. Turbo shaft has very little play and spins freely by hand. I'm at a loss, anything else I should be checking?

Might be nothing to do with the turbo. What about changing the fuel filter? Less fuel will affect performance a great deal.

 

[IanB]

Might be nothing to do with the turbo. What about changing the fuel filter? Less fuel will affect performance a great deal.

Fuel filter was replaced about 3,000kms ago. This issue came on suddenly, doesn't make sense that it isn't turbo related IMO. I'll have a chance to pull the exhaust and dump pipe off tomorrow and see what's up.

 

[arnott1t]

I'm betting fuel. unless your EGT's are climbing like mad as you have less boost to burn the fuel you had already set. Might be lazy response from a lazy amount of fuel hitting the injectors.

 

[DancesWithMutts]

I'm betting fuel. unless your EGT's are climbing like mad as you have less boost to burn the fuel you had already set. Might be lazy response from a lazy amount of fuel hitting the injectors.

Assuming his boost compensator is correctly set, he won't have excess fuel.