Any ideas on actual cause of code? The Service Engine light is coming on while the truck is under load (going up slight hill, taking off from a stop, etc...) and goes off as soon as you take your foot off the throttle.

I checked the codes (94 suburban, 6.5 TD) and it is giving me a 78 Wastegate solenoid. I replaced the solenoid and it is still happening. Also, when checking codes, I do not get the "12 diagnostics" code before it gives me the "78" code. Could this be an indicator of other issues?

I have seen an increase in black smoke when accelerating. I just replaced the wastegate actuator a couple of weeks ago.

Would appreciate any suggestions for what to check next. I have a trip coming up in 3 weeks and really need this beast in running order.

Any suggestions, other than replacing the truck (already getting that one from the wife), are welcome.

 

Check for vaccum leaks

 

also try cleaning the gunk and build up out of the boost pressure sensor, that has given me fits before too.

 

Hoping to follow up on both the suggestions tonight. Will let you know how it goes.

Thanks.

 

Make sure wastegate arm wont move by hand when running either

 

With a wastegate solenoid code it is likely that the wastegate will move by hand untill after repairs have been made.

 

Checked the vacuum at the solenoid and I am getting 0-1". Have not been able to access the vacuum pump directly. But reading through another post, they mentioned that you cannot delete the vacuum pump if you HVAC controls are vacuum actuated. I had the AC system repaired a month ago, and it quit working again. When I look up vacuum pumps for a 94 suburban with a F vin, it shows a pump for "without AC" and one for "with AC". Am I correct in thinking that I need a new Vacuum Pump? Really didn't want to spend my weekend under the truck.

 

Check the vac lines themselves-it is common for them to crack or break from age.
they can be replaced with rubber.

On a 94 the hvac controls should be electric so there should not be any correlation or connection with the engine vac pump.

Also if it ends up that you have/want to replace the vac pump-get AC delco,the aftermarket pumps are failing after only 1 year in many cases.

 

Didn't understand what they were talking about with the vacuum pump and hvac, as I could only locate the line from the pump to the solenoid, and line from solenoid to wastegate.

Pump was shot, only pulling 5" at the pump, so that is getting replaced today, along with new lines (might as well do it all, if I am going to be in it)

AC was the compressor self-destructing. Like how these things tend to happen in groups, just to throw you off a little.

Thanks for the suggestions and input. Got a long way to go before this beast is done. Got a 4" Diamond Eye exhaust ready to go in, but I may wait until I replace the Turbo.