What Happened, Someone Tell Me Please

[zr1pete]

OK, Let me set it up for you. I have a 2005 F-350 6.0 Diesel 52000 on the clock no issues runs great. With an 4" MBRP cat back exhaust. I decided to take the catalytic converter off and put in a MBRP bypass pipe. Now this is what happened. First the highway fuel mileage went from about 18.5 to 15.5 and sometimes 14.5 then exhaust temp ran at 850 to 900 degrees pulling around 8 and 10 psi of boost while on cruise control at 70mph 2100rpm here in the flat lands of South Florida. Normally the truck runs about 650 700 degrees pulling 5psi giving 18 mpg with the cat. So do you think by pulling the cat the computer leaned out the fuel because of the very low exhaust restriction? Any thoughts? Would a tuner help? Thanks in advance

 

[Zmann ARGH]

your milage computer shouldn't reset that fast unless you manually did it ,, How are you getting those #'s?

 

[JLDickmon]

yes.. pulling the cat probably did lean it out..
tunes may help

 

[powerboatr]

if it "leaned" the fuel, then you would be using less fuel
i gained A mpg when i dropped the cat off my 06 using the same mbrp set up as you.
and lost 200 or more egts pulling, i ran around 25 psi towing and 5-8 or so empty

i know you checked already but the air filter??
and maybe your throttling it more like before....now with less restriction the spool up is a bit quicker...

you shouldn't have lost mpgs by going no cat. and egts definitely should not have gone up....
you didn't leave a rag in there did you
and by chance the muffler didnt get put back on backwards??
I have seen it done, and us old vets sometimes get twisted

 

[Dogman]

Pete,
Pull your mass air sensor and clean it with some mass air sensor cleaner then clear the computer. Anytime you change things on or truck that deals with the motors operation you should clear the computer. This is so the truck knows it has a new operation. Doing this with my truck seam to work better then the truck figring it out it's self.

 

[zr1pete]

I reset the computer while changing the pipe and the air cleaner is new. The mass air flow is clean so I did all the good stuff already. Now for the news...... I put the cat back on went for a good long run and my mileage and came back up, Egt's went back to the normal range that I'm use to seeing and the truck is running normal again, no code's thrown. I really thought that I could benefit by not running this cat but I guess I need to figure this out more.

 

[zr1pete]

if it "leaned" the fuel, then you would be using less fuel
i gained A mpg when i dropped the cat off my 06 using the same mbrp set up as you.
and lost 200 or more egts pulling, i ran around 25 psi towing and 5-8 or so empty

i know you checked already but the air filter??
and maybe your throttling it more like before....now with less restriction the spool up is a bit quicker...


you shouldn't have lost mpgs by going no cat. and egts definitely should not have gone up....
you didn't leave a rag in there did you
and by chance the muffler didnt get put back on backwards??
I have seen it done, and us old vets sometimes get twisted

HI Powerboatr, nope I did all the right things, New filter, no rags. MBRP has been on the truck for 5 years now no trouble. Disconnected both batteries for 30 minutes. But when I put that bypass pipe on the truck it didn't like it. Anybody got any clues?

 

[powerboatr]

HI Powerboatr, nope I did all the right things, New filter, no rags. MBRP has been on the truck for 5 years now no trouble. Disconnected both batteries for 30 minutes. But when I put that bypass pipe on the truck it didn't like it. Anybody got any clues?

just plain a weird one????

i thought for sure the muffler was on backwards