Code 39 and Code 78

[Kick Ass Matt]

Help.
1994 Suburban, 6.5 TD w/4L80E trans

I am tripping a code 39 and 78. I looked up www.kennedydiesel.com for their DTC codes..

39 - TCC stuck "OFF"
78 - Turbo Wastegate solenoid fault

My questions is would the TCC be stuck off cause the 4L80E to NOT get into OD? I can feel 1 - 2, 2 - 3, and thats it. There is not 3 - 4 shift. At 120 KM/H my truck would be SINGING along. I don't have at tach in my truck but it doesn't feel right at all so I have to kick in my double OD (Gear Vendors) unit just to bring the RPM down.

Turbo Wastegate Solenoid. The way I understand is that the ECU sends a signal to the solenoid to open/close allowing vaccume through the solenoid itself to open up the waste gate to to build boost. I see the vaccum pump, how much vaccum is healthy at idel? 15 inches? What else does the vaccum pump drive other than the turbo wastegate solenoid, the brakes as well? Reason I am asking is I don't want to replace the solenoid and find out that my vaccum pump is bad as well. I am going in for front end work this weekend, so I'd rather fix all the problems at once rather than go dking around in circles.

Thanks
Matt

[Robyn]

The wastegate solenoid is the little unit towards tha back of the left valve cover.
It has a set of vacuum lines coming to it.
The vacuum pump should be producing a nice steady 26 inches measured at the pump.
If the needle is flopping around toss the pump.

The vacuum at the solenoid infeed side should also be 26 as should the reading at the wastegate actuator (turbo)

The solenoids are known to go away so its probably time for a new one.

The vacuum pump runs only the waste gate. The brakes are run off the hydraulic pump (Power steering) via a hydro boost unit.
If you have less than 20 inches of suck at the pump toss it and the solenoid and get new stuff.

If you are not getting a 3-4 shift there is something going on with the tranny or the computer.

A scan with an OBD1 tool is in order to find out what is going on, or in your case not going on.

The 4L80 is an all electronic controlled tranny so it can be several things.

If I were to guess I would say possibly a shift solenoid or maybe even a bad connection.
Get it scanned and see what gives.
Guessing with these is just not the way to fly

Hope this helps some

Robyn

[gmctd]

Check your brakelite switch - controls TCC lock - prolly time fer a new one..............

Vacuum pump 26" at idle and 2000rpm, some fluctuation ok at idle

WG actuator - 15" at idle

Check plastic vacuum harness for crumbled\broke\holed

[Kick Ass Matt]

If you are not getting a 3-4 shift there is something going on with the tranny or the computer.

A scan with an OBD1 tool is in order to find out what is going on, or in your case not going on.

The 4L80 is an all electronic controlled tranny so it can be several things.

If I were to guess I would say possibly a shift solenoid or maybe even a bad connection.
Get it scanned and see what gives.
Guessing with these is just not the way to fly

Hope this helps some

Robyn

I did do a scan and code 39 is what I got.

[Kick Ass Matt]

Well I checked the vaccum pump w/a gage, and it reads 25 inches at idle. I applied vaccum w/a hand job vaccum pump to the turbo solenoid. A slight vaccum is allowed to pass through the solenoid when its NOT energized. When I energize it with 12 V, it opens up and allows vaccum through. So I "suppose" the solenoid is still good. I also measured the resistance and it checks out to be 40 - 45 ohms. Then I scaned the truck again it was still throwing the same codes. It is also starting to puff black smoke when I boot it; like WOT (wide open throttle). But then I suppose thats normal as well for a diesel truck.

As for the TCC solenoid, thats not an animal for me to touch at all...

So I guess theres nothing more I can do now other than wait till I do my front end work this weekend and let a REAL mechanic play with it; will probably take a week or 2 to get done anyways in the mean time please keep the good comments coming in.

[gmctd]

Not the solenoid, dude - the TCC brake switch, there on your brake pedal - works cruise, TCC lock and brake lites - it's hung open, which unlocks the TCC, or the fuse is bown, which unlocks the TCC.

12v on the WG solenoid is not a good test - the PCM pulses the coil to regulate vacuum - hard 12v may make it close, but it may be binding, not responsive to pulsed voltage.

And, what happened to testing it for 15" at idle?

TEST ONLY - run a hose from the pump to the wg, see what happens

[Kick Ass Matt]

Not the solenoid, dude - the TCC brake switch, there on your brake pedal - works cruise, TCC lock and brake lites - it's hung open, which unlocks the TCC, or the fuse is bown, which unlocks the TCC.

Well I know for a fact that the cruise and brake lights still work when that code was threw. To be honest I think that code was flashed when the truck was on cruise doing 50 MPH, ever since then cruise is still working. I'll see if I can even find the switch and check for continuity tonight when I get home from work.


12v on the WG solenoid is not a good test - the PCM pulses the coil to regulate vacuum - hard 12v may make it close, but it may be binding, not responsive to pulsed voltage.

So I guess I still might need a new one then.


And, what happened to testing it for 15" at idle?

What do you mean what happened? What happened to what? I tested the functionality of the vaccum pump at idle. It was pulling 25 constant. Tonight I'll rig something up so I can test vaccum between the solnoid and the WG. I have also heard that WG's can get stuck. I AM getting a puff of black smoke though which to me means too much fuel and not enough air when I am flooring it.


TEST ONLY - run a hose from the pump to the wg, see what happens

Ok....whats "suppose" to happen when I do that...wouldn't I be at full boost at idle? Assuming that the WG gets sucked open. Full boost at idle wouldn't that be bad?