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So I bought a 99 f350 4x4 6 speed dually. I’ve had multiple 7.3s in the past. All were super strong. When I bought the truck it had a KC S300x turbo on it. Stock injectors and stock tune. It only made about 3 lbs boost at the time. I took that turbo off and put a stock turbo back on it. It now makes about 10lbs boost at 3k in 3rd gear. I’ve checked for boost leaks. Tried swapping map sensors. Checked the wastegate actuator. Swap the WG actuator with the one from the kc turbo. Bought a TS6 chip. It now smokes like a train but is still only making 10lbs boost. Any ideas? No codes.
 

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Did you check fuel pressure? With low FP it won't be able to build enough RPM to spool the turbo.
 

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He says that he gets 3k rpm. I would think that would be enough to spool the turbo.
 

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Maybe you are losing exhaust pressure. If you have the original style up pipes, there's a good chance that they are not sealing well. Look for signs of soot on the firewall around the up pipe joints. My 2003 made terrible boost that was due to leaky exhaust joints. I put on a new set of bellowed up pipes and boost went back to where it should be.
 
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