Voltage drop and wastegate issue

[Ron_Woolerton]

Hi

Long time reader, first time post.
First up thanks for all the info over the year's. I have fixed a lot of issues from the posts here.

I have a July 94 Suburban imported new and converted to right hand drive in 94 by a factory approved converter.

I am having an electrical issue that I cannot find an answer to here. I have searched the forum extensively ... I think.

I have cleaned and tested all grounds earth straps and live straps. I have replaced the batteries. I have tested and had an auto sparky test the alternator and it is fine. I have cleaned and tested the lead from the alternator.

Problem 1.
At the batteries I am getting 14v. At the firewall junction I am getting 13.9 or there abouts volts.
On the dash and scantech tool I am getting about12v on start and for the first 20-30 minutes of driving. Then it drops to around 10v.
I am not getting a charge light or ses light on the dash.
Clearly I have a resistance issue or an ecm issue somewhere? Ideas would be good.

Problem 2.
I have a new vacuum pump and lines and a new wastegate solenoid. I have a boost gauge on the dash. Turbo boosts fine for first 20-30 minutes of driving then drops to zero and stays there. When at zero the wastegate arm can be moved easily so the solenoid must be getting a message to kill the vacuum. Some times if I drop the throttle to idle and try again the turbo will boost again for a while. Eventually I get an ses light and plenty of black smoke and no boost.
Turbo will boost fine no matter the voltage but I guess they must be related.
If I shut down and restart the turbo still will not boost. If I shut down and let everything cool off completely then good to go for another 20-30 minutes. So perhaps heat related.
Intake temp sensor reads ok according to ranges posted in threads here.
This one is very frustrating and makes the truck unusable.

I have had this vehicle almost 10 years. Voltage issue and turbo issue are recent.

Over my ownership I have replaced due to failure the following, PMD, FSS, ECM.

I have done a lot of other testing, but all ideas gladly received.

Thanks.
Ron