Hi, im new to this site and new to 12 valves. Just bought a 1998 dodge 12 valve cummins, 4x4, 3.55 axle gear ratio, 265/75/r15 mud tires. I havent done much to it, seems to run good. New oil, oil filter, fuel filter, and spectra performance air filter. I put C foam through it and it ran much better. the only thing i dont understand is the truck gets only 15 mpg. I drove like grandpa and got 15 and then drove normal and got 15 and drove crazy and got 14. Everyone who has these trucks report getting 17-20 easy. Need some advice please, thanks.

 

That milage dosn't seem right especially with the 3.55's, jack her up and make sure you don't have brakes hanging up. Can't think of anything else off the top of my head

 

Yeah, that's what I get with a trailer. Stick or auto?

 

X2

 

that or valve lash is an easy killer!!! Id toss the spectre filter while your at it...

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Is the spectre filter one of them tiny Ones, you need a decent size one to feed a diesel... to much air restriction will kill you mpg, can you hear valve rattle on top or while your driving!

 

Wait, what?

 

Puncuation something im not good at

Here wait Im saying, do you know if Valve Lash has ever been performed on your truck if not, it needs to be done. Poor valve lash leads to poor perfomance, bad fuel milage, and excessive valve train rattle. Another thing I was trying to ask is How big is your air filter, spectre is not a good brand at all IMHO, I would junk it and buy a BHAF filter, if the filter is to small it can restrict to much air and your truck cant breathe!

 

the air filter is spectra big one. which isn't that big. where can i get a BHAF? and i have no idea about the valve lash.

 

I would also get the timing checked. and while your at it, get the timing advance about 16* and you will see good performance and you mpg's will go up. My average all summer was 24-26 mpg, Highway driving, with no load at 60 to 65 mph.

But make sure that the person knows what they are doing if they are going to work on your 12 valve.

Corb

 

What would be better? advance the timing or retard the timing? Im looking to get better mpg and more performance.