Boost leak, or something else?

[Grand_87_national]

Hello, I recently purchased a 1987 GN with many mods done. What little I've driven it, I've noticed at wot the boost gauge will drop from 18ish down to around 15ish and flutter quickly (like the needle is vibrating). This coincides with a feeling of the car falling on it's face a bit. Not a violent buck, or stall, you can feel it pulling hard, then the acceleration seems to level off, as if your slightly lifting off the throttle. I don't know if this sounds like a boost leak, or if there's something else going on. Scanmaster never pulls timing, o2 voltage seems to hang out in the lower 800 to upper 700 range at wot. Mods (that are relevant to this issue) are: turbonetics 60 series turbo, 120lb trick flow injectors, Racetronics pump, e85, ls1 maf and translator, rjc fmic, comp 212/212 cam, ported and polished stock heads. Thanks in advance for any and all advice!

 

[TURBOTIMMER]

What kind of downpipe/wastegate setup?

 

[Grand_87_national]

What kind of downpipe/wastegate setup?

Internal wastegate.... g body parts 3" downpipe.

 

[Grand_87_national]

 

[TURBOTIMMER]

First thing I thought was your wastegate puck was sticking. Never heard of that issue in a g body downpipe, but it's possible. Take your actuator rod off and see if your wastegate puck moves freely.

 

[Grand_87_national]

First thing I thought was your wastegate puck was sticking. Never heard of that issue in a g body downpipe, but it's possible. Take your actuator rod off and see if your wastegate puck moves freely.

Good call, I'm not real experienced with turbos, but when I bought it, there was no "e" clip on the actuator rod, and the jamnut was loose (as can be seen in the photo provided by the seller before I purchased it). So, while putting a clip on the actuator bracket and tightening the jamnut, I noticed it WAS hard to move, didn't know if this was normal or not. I can move it by hand, but it does take some considerable force. How do you free it up?

 

[87-WE2]

I'm going with cracked headers. Check the headers for cracks.


Sent from my iPhone using Tapatalk

 

[TURBOTIMMER]

You can spray some brake clean in there and get it to free up, but it'll tighten up again, eventually. I had the same problem with another brand of downpipe. I had to cut it apart and ream the hole out with a fine rat tail file.

 

[Grand_87_national]

I'm going with cracked headers. Check the headers for cracks.


Sent from my iPhone using Tapatalk

Wouldn't I hear the exhaust leak? It sounds quiet.

 

[Grand_87_national]

You can spray some brake clean in there and get it to free up, but it'll tighten up again, eventually. I had the same problem with another brand of downpipe. I had to cut it apart and ream the hole out with a fine rat tail file.

I'll give that a shot, at least I'll know if that's the issue. Thanks a bunch!

 

[Grand_87_national]

You can spray some brake clean in there and get it to free up, but it'll tighten up again, eventually. I had the same problem with another brand of downpipe. I had to cut it apart and ream the hole out with a fine rat tail file.

Now, I may just be ignorant, but how does the downpipe affect an internal wastegate? Isn't it completely separate from the turbo and wastegate?

 

[TURBOTIMMER]

The wastegate puck is built into the pipe. It's on the other end of that little arm your actuator is attached to.

 

[Grand_87_national]

The wastegate puck is built into the pipe. It's on the other end of that little arm your actuator is attached to.

Cool, it just appeared to be all part of the exhaust housing of the turbo. So the wastegate "door" is rubbing part of the downpipe? I'll mess with it tomorrow after work and see what I come up with. Thanks again!

 

[87-WE2]

Wouldn't I hear the exhaust leak? It sounds quiet.

Maybe, maybe not. They may be cracked, but closed during idle or low load. Then when the motor torques over under load, the crack opens up letting exhaust flow out. Worth a couple of minutes to look in there and see, even if you're relatively sure the puck is sticking.

 

[626gn]

Could also be an over enlarged wastegate hole.

 

[TurboBuRick]

Could be spark drop out on 1 cylinder. What plugs you run?

This a roller cam of flat tappet?

 

[Grand_87_national]

Could be spark drop out on 1 cylinder. What plugs you run?

This a roller cam of flat tappet?

It is a flat tappet cam. Plugs, I'm not sure, haven't had it very long.

 

[Grand_87_national]

The puck arm seemed to loosen up a bit, as I forced it back and forth. Still seems to be binding though, and the actuator arm is pulling at a slight angle, which is probably helping put it in a bind. I may try to bend the actuator bracket a bit so it will pull straight, and try to force some nickel anti seize into the arm shaft, as it is good to 2400* F.

 

[TurboBuRick]

I very much doubt the wastegate is the problem.

Change the plugs. If the condition does not change, check rocker travel. You may have a worn cam lobe.

 

[GNRick]

Do you have a fuel pressure gauge? Sounds like the pump is going south.