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Discussion Starter #1
I've got an E99 350 SD that's showing some signs of decreasing performance.

It's a 7.3, factory rebuilt engine with less than 50,000 miles. I keep track of mileage on every tank and right now it's getting an average of 11½ mpg.

It's also started smoking when it's under a load, such as going up a hill when empty. Turning the chip to the heavy tow setting helps with the smoke, but drops the mpg through the basement. I don't have any hot rod settings on the chip. Just economy and tow settings. Interestingly enough, my best mileage isn't with the economy setting. It works best set on the medium tow setting.

Also, when going up a steep hill the EGT usually climbs over 1500°. When I've got a load the temp will top 1700° going uphill. LOTS of smoke too.

Boost usually runs about 8 psi under load and 1-2 on flat ground when empty.

It's also started to get a little hard to start when it's cold, though it always fires eventually.

Oil and filter are fresh.

It's a 4WD with 4:10 gears.

I really need to get this thing back in shape as I drive it a lot in my firewood business, and with the price of fuel I need every mpg I can get.
 

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If u can only hit 8psi. And you get a lot of smoke I would check for boost leaks. Check you up pipes there will be soot on the firewall if there gone. It sounds like a boost leak or turbo issue. Because if the turbo is spooling up good it won't smoke a lot. That why if u lug the engine in a high gear it will pour out smoke because no turbo psi until hit higher rpms

So I would check for boost leaks first


Sent from a Apple
 

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Discussion Starter #3
I've seen boost go as high as 14 psi at WOT, going up a hill or when carrying a very heavy load. I generally don't floor it though as the EGT tends to go a bit higher than I'm comfortable with.

Under load I can hear the turbo spool up. I did replace all the boots and wondered if I got the gasket right between the turbo and the spider. That's a tough little bugger to keep in place.
 
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