i have a 1996 dodge ram 2500 with a 5.9l v8. i bought it with 209k miles on it and i took the engine out and took it to get it rebuilt and they bored out the cylinders a bit to make it a bit bigger and a little bit more power. however, ever since the engine has been back in, (about 6 months) i have been unable to get the check engine light off and it has been in to the shop about 4 times and no one can really seem to fix it. also, when i am at an idle, the rpms start reving up and down. usually only to about 1000 or so but its been doing that this whole time. and again no one knows whats wrong with it. any comments or ideas on what it could be?

 

I read your having problems with your idling. I know you have a different truck then mine, but I would have your iac motor checked out first to see if thats the problem first. If that checks out fine then I know it has to be your PLENTUM GASKET>on your intakemanifold in which is gone bad. You may be losing oil & wasting gas. Change to a metal gasket.[sm=icon_cheers.gif]

 

I am not an expert, but I believe the 5.9L engine still runs on a speed and density type system to determine the amount of charge entering the cylinders. This is not a mass flow meter like other OE's use to determine how much air to enter the cylinders. This could be important because your engine computer needs to know how much fuel to inject to match that charge. A speed-density system uses the engine RPM to determine the amount of air being drawn into a cylinder (because the bore and stroke are constant and known).

*If you have modified your cylinder bore or stroke, you are know taking in more air than than the engine computer knows about. And the computer will still only inject enough fuel for the factory motor. This results in a lean condition. Then the oxygen sensors will detect this and richen the fuel mixture, but they are not quick enough to detect immeadiate changes. That is why you might experience erratic idle.

 

i think you just solved my problem kuch68. last year we took out my engine and had it rebuilt and the guy bored out the cylinders a little over the standard clearance (im not certain as to what size they are now) but i do know that the computer was never changed over since then. thanks that makes a lot of sense now.

 

Call Southeast Performance at 813-503-8069 or 813-886-6166. One of the owners (can't remember his name) builds incredible engines, and knows more about Dodge motors than anyone I've ever talked to. And when I talked to him he spent quite a bit of time researching something for me that he knew he wasn't going to be making a profit on. I asked something he didn't know, and he wanted to find out so he did, even though he knew he couldn't make a sale with my problem. REALLY cool guy, and he's a DF sponsor.