4L80E slipping from idle?

[dbryans]

I've started noticing some slipping when going from idle, in gear, brake on to brake off, moving on my '94 K2500 6.5TD 4x4 Suburban. I notice my problem when stoping on an upward slope while in gear but with the brake on. Sometimes (irregular, not hot or under load, yet) shifting into reverse and back will re-engage, sometimes I need to shift to park wait a sec and then back to drive before it will engage.

I just read the codes (grounded the diag terminal, watched the service light) and got the following:
35, 36, 78

I expected to get a 12 to start (based on the service manual and other references online), but never got it.

35 and 36 seem to be Idle Speed and Idle Air controller issues, not sure exactly what to look at there further.

78 looks like a wastegate solenoid problem

Obviously, I'm not a mechanic, nor even remotely familiar with working on my vehicles, but I'm tired of taking it in to have noone actully work with me on diagnosing it, or even taking it for a drive with me. So until I find a place that works with me and I can trust, I'm going to try my hand at this, with y'alls help of course.

Shane...

[dbryans]

Ok, after a bit more searching, I found the "code 35" (http://forum.thedieselpage.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=1;t=004386#000000) thread by Moondoggie. Very helpful read, especially WRT finding the ground locations.

Now, can someone help me figure out how to find and inspect the wastegate solenoid so I can determine what is causing my code 78? The book I have is the "consumer" retail store version that does not have any of the diesel specific info in it.

Shane...

[TJ Moose]

Do you have the 6.5 troubleshooting manual? Good, quick and simple procedure in it. I just cured a low boost problem (signalled by a 78 code and black smoke out the tailpipe)on my '95 using duct tape. Found a hole rubbed in a vacuum line where the line rubbed behind the A/C compressor. Was going to get a new line, but the duct tape seems to work - and as soon as I get my boost and pyro gauges installed, I'll probably go to the Heath turbo boost controller and chip anyway - so I may not need a new vacuum hose in the near future. Look for poor vacuum from vac pump, or hung up waste gate cannister at arm attahcing to turbo wastegate, or hole in one of the vacuum lines, or bad wastegate solenoid. Apparently 15 lbs or higher is the magical number for the vac measurement. I had 22 from the pump and 10 at the wastegate cannister. Post-duct tape, went back up to 15 at the cannister. If vacuum lower - figure out what's leaking or not working and repair or replace it. Again - if you don't have the TDP troubleshooting book - consider getting it. Its already paid for itself at my house.

[dbryans]

No, I'm not familiar with the book your refering to. Pointers to where I can find it?

Anyway, thanks for the other suggestions on the 78 issue. I'll post any findings and results.

Shane...

[dbryans]

After more research, I found and have looked through the Online 6.2/6.5 Troubleshooting Guide (http://www.thedieselpage.com/members/guide.htm), is this what you were refering to? I failed to find anything specific about the wastegate so I think I may not be looking at the right thing.

More specifically, can anyone guide me (picture would be nice) to where under the hood the wastegate solenoid is located and what it looks like? I'd really appreciate the help for this GROSS newbie.

Shane...

[rjwest]

on the side of turbo there is a small metal 'can' with a lever and a black hose. follow the black hose back to a little black plactic thing with a plug and wires on it.

.... that is the vacuum solenoid that controls the turbo boost...

[dbryans]

I found the wastegate solenoid, no problems with the hoses from a visual inspection. I still need to check pressure.

More immediate though, I am no getting a code 87 (High Ratio Error). I started looking when the truck failed to shift up to 3rd or 4th on the highway this afternoon. The previous codes (35, 36, 78) are now gone.

I'm trying to get it in to the shop this weekend. This is over my head. Any suggestions on talking to the shop?

Shane...