Looking at a 99 f-350 EX cab bone stock with 140,000 rough miles on her, ZF6 tranny. Runs good, but the owner says in the last couple of weeks around 2500 RPM he hears a hissing noise and feels a decrease in power. I rode with him and confirmed the above statements, I believe it is a waste gate malfunction, or leak. Is this possible, and if so how can I trouble shoot it to identify and replace the affected component. If any body has any other line of thought please feel free to enlighten me.

 

check i.c. boots and clamps, also check up pipes for leaks.

 

I should've thought of that, will do, does the malfunction waste gate seem crazy?

 

No, not really but it is usually an IC boot based on the description. Does it build boost/power fine right up to that point? At what boost does it begin to hiss?

 

There are no guages, so boost pressure cannot be measured, it is consistent at 2500 RPM, but doesn't do it when it is cold.

 

Hmmm, check all the boots. If the CCV mod has not been done they are likely oily and probably become more leak prone as they warm up. As for the up pipes, look for soot as evidence of leaking exhaust. If you still think it is the WG, pull the red line off the WG and plug it onto a IC boot clamp bolt and see what happens.

 

Bryan, you are a stone's throw away from me. If you don't get it sorted out, send me a PM and I'll be glad to look at it or even scan it with AE if needed. I am in Clarksville and off today. Let me know if you want to bring it by.
Mike

 

Could the warm up valve be closing?

 

Not likely. As soon as you touch the pedal, the EBPV opens back up. And he's talking about tooling down the highway mashing the pedal. The EBPV can get stuck, but it wouldn't be spontaneously closing while moving.

 

Wastegate rarely has issues... I would bet a boost leak or surge... the early 99 turbos can start to surge bad once they get wore out...