6.4 with DPF delete, tuned

The turbos simply will not go past 20 PSI, no matter how hard I try. Additionally, travelling at high speeds for extended periods (70 MPH on the interstate for over an hour or so) causes the wrench light to appear. I'm thinking the big turbo isn't engaging and because the little one is trying to compensate it's overheating the oil, but I don't know.

Any advice?

 

You need a real time monitoring tool to monitor ECT and EOT, and scan for codes, and to monitor Exhaust Back Presure. 20psi is what I see as I get onto the freeway, I only see higher if I'm pushing it hard up a hill. DPF Delete and tune also w 4.30 gearing. I can set the cruise control at 75/80mph and travel from Seattle to Salt Lake City without any concern.

 

the turbo might not be the problem....a worn hpfp could be limiting the fuel flow...or clogged fuel filters. what codes are coming back with the wrench light? have you ever seen metal particles in your fuel filters?

 

Just wondering, if you are empty/towing or not, and what mpg you are seeing. We have a similar truck. I seem to be in the 12s at that speed.

 

At that speed, empty, I'm getting 14~12 depending on headwinds.

 

I've replaced every filter on the truck other than the tranny filter, I don't tow with it because of the problem, and I've checked for codes with the wrench light on and nothing came up. My oil filters have been metal free as far as I could tell, I took the last one apart checking for metal bits and didn't see any.

My MPG is 13.2, according to the dash.

Since the last post I have gotten the turbo past 20 psi but it only went to the mid 20s while nearly flooring it. this was going on a flat road on the interstate without any weight in the bed or towing anything.

 

That is about right, my truck will not go above 20psi unless I'm accelerating up a grade.

 

Even up hills it struggles to go higher. And even if the turbo was fine it doesn't explain the wrench light.

 

What did the fuel filters look like? Do you have a way to monitor the High Pressure Fuel Pump? I have an Edge Insight CTS. I can set it to monitor about any sensor on the truck. And it reads codes, and can reset them too.

How many miles are on the truck?

Any exhaust leaks? Broken manifold bolts? Up pipes to the turbos leaking? What about the pipes from the turbos to the air-to-air cooler and back to the intake?

 

The fuel filters were worn but I have no idea how old they were. They were the filters that came with the truck when I bought it. No, I don't have any way to monitor the fuel pump.

Roughly 89K miles.

I don't know how to check the exhaust for leaks when I can't get to the pipes.

 

Bit of an update, I had the codes checked, the only two that came up were P1000 and P0480.

 

P1000
It means the truck hasn't been driven enough to run all of the internal tests since the last time the codes were cleared or the batteries were disconnected. Disconnect both batteries, leave the cab door open to trigger a voltage drain, let the truck sit for twenty minutes before re-connecting the batteries, take the truck for a long drive like 1/4 tank.

P0480
Fan response is not correct, Check the wiring harness and the connections.
2008 Fan Clutch Wiring diagram
Pin #1 – Control signal – PWM signal which is hard to measure with a volt meter
Pin #2 – VPWR – 12 volts from fuse (F74)
Pin #3 – Ground
Pin #4 – speed signal back to PCM (feed back)
Pin #5 – VBPWR – power back to PCM

 

Again, buy your own scan tool so you can monitor real-time data - or just take it to a dealership.