First 12valve cummins. Help please
 

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. :argh:

:humm: 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 :c:

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 lol

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. :tu:

Advance to 16 degrees :c:

X2

You can get a BHAF at napa I dont know what the partnumber is, but its a fleet guard filter...

pffft..... set it to 20°... :D

no, really... set it to 16,5°

replace that filter with something bigger & better...

check all your brakes & wheel bearings, are your wheel hubs hot when you stop after a trip to the store?

the wix part number 42790. any auto parts store should be able to match it up. but you will need to take out your factory air box and create a heat shield between the turbo and the filter or you will melt it. i have not installed mine yet and cant wait til i get to to see if that helps my mileage. i wish i got 15. i get 12 on a good day. its pretty much the same truck but mine is a 96.i have already done my valve lash to 8 and 18 thousandths. however i have not had my timing advanced. im kind of scared to without head studs and 276 thousand miles. some people say it will be fine yet others say be careful.

My friend has a 96 cummins and he is retarding the timing. im not sure how much but with a #6 fuel plate and timing the mechanic is expected to get 100 more horse out of it. What would be better? advancing or retarding?

Yeah if those hubs are hot after a short drive of regular cruising they are too tight and need to be adjusted

yeah the hubs do get hot. also it was pulling hard to the left when i applied the brakes, so i replaced the brake caliber but it still does the same thing, also my brakes squeak a bit.

Check your right front brake line, could be worn out and not holding form under braking pressure.

Why is he retarding the timing?

I really wish someone else would comment on this because I've never known retarded timing to be a good thing on a diesel... :humm:

I'm not sure. Who wants a retarded truck anyways?

lol

I don't think it's timing thats retarded :w2: There's no tightening or loosening on sealed unit bearings, the axle nut should be torqued to the right specs.

Much as I hate to hijack a thread, this just made me think of something.
The wheel bearings on my truck are (each) apparently a $600+ part from Chrysler, which essentially includes the whole hub assembly. We've been "saving money" by getting them from NAPA instead to the tune of around $400. In about three and a half years I've put about 170,000 miles on this truck, and both fronts have been changed at least twice each.
Then the other day I'm roaming around on RockAuto (not always the most reliable way to figure out what you need, I know) and I see a Timken front wheel bearing for my truck for under seven bucks. Now, I've never actually done the work myself, I have no idea what's involved, but our fleet mechanics always told me you have to change the whole thing. Well, the whole thing get's pretty expensive when you drive a lot. I never knew there was an option. Based on my source (RockAuto) I'm not convinced there really is an option yet. Can anyone shed some light on this? My front left is going again, and if there's a way I can change just the bearing, it would be nice.