I've got a 91 with a 5 speed, around 15 lbs of boost I hear a noise that sounds like an exhaust leak and my boost pressure fluctuates. I can't see any soot on the turbo housing or downpipe, any idea what may be causing this?

 

Blown manifold gasket on the bottom side? That would be more difficult to find as it is a hard to see location.

 

I'll check that today and let ya know what I find.

 

You have compressor surge. It's very common on 5 speed 1st gens that have been turned up a lot or have a smaller turbine housing installed, it's due to the turbo being out of it efficiency range. The '94 and newer trucks have a slot in the compressor housing that allows air to recirculate at low RPM and high boost. If you have access to a big enough lathe, you can cut the slot yourself. Or you can get a used 2nd gen turbo off Ebay or the site classifieds. Your third option is to upgrade the compressor side of the turbo. HTT is the place that built my turbo.

http://www.htturbo.com/

 

After checking all the exhaust connections, I think you're right Dave. I haven't found any leaks anywhere visually or by feel. Should I turn my fuel back down a little to stop this or will it not do any damage just sound real bad? I readjusted the power screw on my pump this morning and did not notice it but it seemed only do it once hot. I'll keep you updated.

 

You can drive around the surge by shifting late to keep the RPM's up. It'll only surge at low/mid RPM and high boost. I drove mine surging for about 6 months and it didn't blow (I installed a WH1C off a '94 at that point). I did try to drive around it as much as possible though. You can run it as is until you fix the problem by whichever way fits you abilities and budget.

 

I turned the power screw down a little today and it doesn't do it as much. Every once in a while, it will do it when I let off the throttle. The guy who had the truck before me messed with the ?alderson? spring, could this encourage the problem? My pump isn't turned up much, I'm maxing about 23 pounds. Also, I noticed in another forum that the smoke screw adjusts initial fuel, could that screw being in too far cause this, I've never messed with it but my truck smokes as soon as you step on the go pedal and on start up.

 

When you let off the throttle suddenly, that's known as "barking". That's the noise made by the built up pressure in the intake rushing back past the compressor. It's not good for the turbo because it makes the turbo slow down suddenly and puts a lot of torque on the shaft. The cure is to let off the throttle gradually when possible - obviously situations arise where you have to jump off the gas immediately.

Turning down the power will cut down on the surge. If the AFC system has been played with (fuel pin, star wheel, smoke screw), that will add fuel and aggravate the problem as well. If it was me I'd find a used turbo off a 2nd gen and fix it that way instead of turning the truck down. That's no fun.

All 1st gen trucks put out a puff on startup, nature of the beast.

 

Thanks for the info, it's made everything alot clearer to me as to what exactly is going on.