Boost Problem

[Cam2006]

Hello everyone! I'm new here and I have a question.

Today while i was waiting (for class to start: about 10 min) in my truck this morning in the parking lot i felt my truck shake (and heard a clunk type noise) like someone hit my truck with their door or something... but nothing... Truck was running fine, gauges all good.

But now here is the problem (might be from that noise). When about 3/4 throttle or going over 65 mph, I gain boost to about 11 then kicks down to 4 - 5, then it would go up to about 7 or 8 and kick back down to 3 - 4. And it keeps kicking down until I let off of throttle or go under 65 mpg. I feel the loss of power when it kicks down. When I start out from a stop the truck drives fine and builds boost fine.

I don't know what to check or where to start... My exhaust is off underneath the passenger floor board because it snapped off (previous owner didn't know what to do i guess, was held together with sheet metal screws). I don't think that is the problem though because it's been like that for about 500+ miles with no problems, I am going to get stacks for it, but don't have the money to make repairs or get the stacks yet.

Any suggestions or help would be greatly appreciated.

~Mike~

[gmctd]

Welcome to the forum Mike...............

Symptom could be fuel related, or FSD\PMD related, where engine stalls briefly, then resumes - would jar the truck at idle.

When you get a chance search for stalling and FSD\PMD threads, and lift pump threads for more info

[JohnC]

Mike:

Check your DTC Codes. Your boost issue sounds like a sticky wastegate solenoid or something similar.

[Mark Rinker]

The noise you heard and the new boost problem could be caused by the failed exhaust crossover.

If the crossover pipe joints fail and leak exhaust pressure, your turbocharger will 'surge' and will not produce boost predictably. This happened to one of my '94s last fall right after replacing the turbo to tailpipe exhaust componants with a Pinnacle 4". While it would still run and drive (back to the repair shop...) it surged as if the boost was coming and going - as you describe in your post.

I ordered the crossover from www.heathdiesel.com. www.kennedydiesel.com sells complete kits and crossovers. The Pinnacle kit (no crossover included) can be found at http://cgi.ebay.com/ebaymotors/Chevy-6-5-GMC-1994-2000-4-Diesel-Exhaust-J-Jardine_W0QQcmdZViewItemQQcategoryZ33630QQihZ008QQ itemZ180080751710QQrdZ1QQsspagenameZWDVW

I really liked the look and sound of the Pinnacle kit.

If this is not the cause, by all means follow the suggestions listed above...if you search on 'wastegate' on this forum you can read for hours on that topic alone... www.heathdiesel.com has a simple approach to solving 6.5 wastegate control.

[Kennedy]

Mike:

Check your DTC Codes. Your boost issue sounds like a sticky wastegate solenoid or something similar.

Yep, shoot some wd-40 in the wastegate hose wile idling. A sticky solenoid will cause boost to drift.

[Cam2006]

Checked my DTC codes and it came up with 99.

[Cam2006]

Sorry about the double post...

How hard is it to replace the crossover pipe on my truck? I am probably going to look at some things after work today. But if I can't get into my schools shop then I'll be working in the cold.

[gmctd]

DTC99 is APP module fault - clear it, if it reoccurs, you migh spend some time on the various PCM harness connectors and grounds

[sailun]

I got a big clunk and a shake on starting one morning last fall. Thought one of the daughter's cats went thru the fan belt.

A few days later is when the rest of the crank pulley bolts sheared off.

Just about the same mileage as yours, too. 155k.

Didn't throw any codes, just the belt.