Power loss-Falling flat on her face

[acoen]

My 86 factory original GN seems to run pretty good for the most part, but she seems to fall flat on her face through the power band. The car is completely stock down to the exhaust tips with 62k miles and in fantastic condition. She just seems to have difficulty building boost past 10-12 psi. No missing, backfiring, hickups or farts, just doesn't want to pull hard through the power band, a little slow to spool. I completed a compression test....148psi plus or minus one psi through all cylinders, fuel filter clean, air filter clean, plugs gapped at .035, plugs are whitish grey in color no fouling of any type, no exhaust leaks, trans not slipping and not running rich. I checked the turbo inlet and the compressor portion turns free and doesn't seem to have any slop what-so-ever. She will spool up in first chirp second then the slowly build boost to around 10-12 psi (sounds like the engine is working pretty hard, not slowing down just difficulty building boost). Should just keep pulling.....Could you folks give me some pointers. I'm going to check the Y tubing tomorrow moring to make sure is connected properly, check the pluck and see if it is sealing properly or the wastegate rod is in a bind. My gut feeling is that my catylatic converter is getting plugged.

The thing that leads me to believe that the converter is plugged is that this car is quitier at the tail pipe than my last GN (WE4). Just as my last GN this car is factory original and my previous car pulled very hard. Another thing that leads me to believe my converter is plugged is the lack of water that is being produced by the catylist. My last car would drip water just after start up (not a bunch, just drips), this car will produce some water but only after about 10 minutes of running.

I know I may have already answered my question, I was just wondering if I have left anything out.....Thanks in advance for the help.

Btw how can you tell that a converter is bad by just looking at it. can it be tested while off the car?

Aaron

 

[XLR8]

My guess would be a restircted exhaust or plugged cat. I don't know of a way to check it by just looking. You can try disconnecting the downpipe from the exhaust housing and see if the performance comes back.

Other things to consider, when my GN was stock original 4 years ago and I relaced the fuel pump, my upper rpm performace improved. Then after I replaced the valve springs, upper rpm performance improved again.

 

[pacecarta]

ditto on the cat being obstructed

 

[BJM]

Are you still using the factory fabric MAF tube? Is it getting sucked flat, it will do the same as a plugged exhaust.

 

[acoen]

Thanks guys, well I think I found my problem. I check my Y tubes they were cracked but not broken. So while replacing those I thought I would check my turbo shaft again, this time with the bell off. I checked it not long ago but the bell was on, (big mistake). When I removed the bell, I checked the shaft for side to side movement, sure enough I have some side to side slop in the shaft. You can just start to feel the impeller rubbing against the housing. Stupid question, would this lead to the loss in performance that I'm experiencing? Everything else looks good. Does anyone know where I can get this thing rebuilt to orginal specs? I want to retain as much originality as possible. Does someone know where I can pick up a good low mileage used turbo assembly? Any help would be great.

 

[acoen]

Question, how much end play is too much (I may have 1/32th inch of play, maybe a little more). Is a little ok. I can hear (not feel) a very very slight rubbing (doesn't appear to be the housing) but the compressor turns freely. No oil or other shavings in the intake pipe (pretty clean for the most part).

 

[acoen]

Man, I'm sorry guys. I guess I'm in a panic. I think I'm going to answer my own question. I usually end up doing this. I've been doing a bunch of research for shaft end play on my turbo, my turbo is probably fine. I haven't started the car in almost two weeks. There is no thrust play just a little end play. I have no shavings in the bell and absolutely no oil leaking. The play is no doubt around 1/64th inch maybe less (after checking again), enough to feel. I bet if I ran it a little I would not notice any end play movement at all (Oil will take up the slack and center the turbine). I still think my cat is plugged up. But I will check my inlet and IC hoses as well. I will also replace my vacuum lines.

 

[Spongebob]

My high mileage motor had the same problem....valve springs did the trick.