OK - I got out there this afternoon to look underneath for any obvious problems. The wastegate seemed to move fine (very strong spring - used visegrip to push it towards turbo about an inch or so). The wastegate actuator thingy with the hoses seemed all intact. The intercooler pipes seemed snug and intact.

BUT - I did notice some wires that seemed UN-factory-like. A part of the harness seems disassembled, and several wires are spliced/crimped with connectors. This harness is easy to see from below, between block and radiator/fan. The images are from ABOVE. Is this the infamous now-vintage GMTU splice work?? ...for some reason, I don't think it is - but I can't tell what the harness "feeds." I've attached images below (I hope they work). If this is indeed the aforementioned splice work, I reckon I have a 90% chance of having found my problem, eh? * If you open the hood, lean in over the radiator and look down between the oil filler cap and the radiator cooling fan, that's where these wires are *


(have not gotten my MAF cleaner yet)


The image below shows radiator/fan at BOTTOM, wiring harness beneath a few hoses (to show context)



The image below here is closer up - shows more detail



And this is the most close up of the crimped wires (below)

 

I'm having a little trouble trying to figure out your pictures so I'll try to help with one of mine shot from below.

First. Disregard the crinkle black finish bracket. Your's won't have that.
The red circle is the lower Tmap sensor. If those spliced wires on yours lead directly to that sensor, then that's most likely the old style GMTU splice. Mine has the newer plug in GMTU harness.
If those splices aren't within 6-8 inches of the sensor then I doubt that it's a GMTU thing.

Thought yours was stock. If you have the GMTU(or were wondering), the upper Tmap sensor would be a blue labeled Bosch one. Easily seen. Just raise the hood and look down, on the top of the manifold.

 

It sure looks like a bowl of spaghetti, a good chance one or two of those splices are damaged, either the wire stressed and broke or the crimp was crap

 

Thanks for the quick reply, guys -


Yeah, *I* thought it was stock too! Hah - until I opened the airbox lid to see the K&N filter... (not a huge deal, of course, but I didn't expect it). Since previous owner put the K&N in, I suppose the odds are increased that it has the GMTU. I'll find the lower Tmap sensor tomorrow and trace some wires. Even if the wires AREN'T the GMTU splices, I reckon I should be soldering and shrink-wrapping them in any case.


Thanks for posting that image, FMG - it'll surely help me find that sensor. And I'll check that upper tmap sensor too... I figured those images would be tough to interpret, but I wanted to post what I could.


Another thing I noticed: I took off the "radiator cap" and see GREEN antifreeze!!! I think I read in the archived notes somewhere that they really do like DexCool. Is it significant enough that I should flush and change it back to DexCool?

 

FMG I can't heads or tails of the picture either, but, it looks like the harness that runs high across the front of the motor. I would have to look at mine to make sure. JSK back the camera up and take another shot. The GMTU connections were generally real close to the sensor itself.

 

I wouldn't stress about it, but DexCool as soon as you can.

 

It looks like the wiring harness feeds the lower Tmap sensor (thanks again fireman!), the alternator, a/c compressor, maybe other things... the upper Tmap sensor (visible below) is black with white "GM xxxx" part number, and the lower Tmap sensor viewed from above looks black as well.
(would the Chevy dealer who ran my codes see if it has a GMTU? They said nothing about it)

Below is me holding the bundle of crimped wires:


And below this is the crimped wires from below - with the starter solonoid in the foreground at the bottom:


I sure appreciate all you guys!

 

Those look like factory non-GMTU sensors. One quick observation is the use of the left hand hold down screw, 3 bar sensors I have don'e use the left hand screw.

That is a rats nest of wires. If I were you I would replace the connectors and use a sealing type heat shrink. I believe you have probably found your issue.

 

Those are the factory non GMTU sensors.

 

FMG, That's what I thought, figured you'd jump in soon. Given the location of the damaged wires, does it look like something chewed on em? Also, when the car was fixed, where was the initial damage?