Hello,
I was just given a 92 Dakota, which I plan to sell. It has the 3.9L and 3speed auto with OD. Anyway, it didn't seem to have much power and I changed the muffler as I've had other Dodges that needed different mufflers for more back pressure. After changing it, it still seems to have no power it has troubles going up hills. The exhaust on this truck look like 3 inch pipe but where the muffler attached it was 2.5 inch. So what is the factory size pipes for this, they appear to be original. Had to replace the starter and ignition switch to get it started and running.

 

I'm sick and tired of getting into this discussion, so I'll keep it short and to the point. Engines need just a little bit of backpressure to work to their maximum efficiency. Too little backpressure will disrupt the flow of the intake, causing the engine to lose power, while too much will disrupt the flow of both the intake and exhaust, causing the engine to lose power. "Just enough" backpressure insures that both systems are working efficiently together. I have headers, no cat, and a flowmaster 40 muffler on my truck... how much backpressure do you think that is creating?... and it will drive up and over anything with any amount of weight on its back. If you want backpressure, stuff a potato in your exhaust pipe and see how good it runs.

With that said, it sounds to me like you either have a clogged cat or need an ignition tune up.

 

give the cat converter a shake, i had the same problem and they told me at the exhaust shop the ceramic in it broke up (too many trips on the barrens road) and it plugged up the exhaust. should mention this was on a 90 Comanche but i think there all the same.

 

Ok thanks, if it does rattle I'll just put a pipe in its place and see how that works.

 

Thats definately the best thing to do! Especially if your area doesn't require emissions inspection.

 

Well I fixed the tranny cooling lines since they were leaking. I hit the catalytic converter and no noise, so I left it. There are no exhaust leaks. I did the key dancing thing and came up with no issues. I drove it around and seems to work fine, has troubles going up hills a little, with OD off it was better. Not sure if that is just the way the 3.9L is or what, but it was owned by someone that lived in a city. So tommorow I'll run some fuel system cleaner, and see what the top end is in attempt to clean the carbon out I will most likely drive it for a week or so to work out any bugs before I sell it.

 

your tranny lines where leaking? could be the tranny slipping from low fluid and the plates cooking. once they do the tranny will slip and it seems like low power from the engine.

 

I fixed the tranny lines and after that it felt like not much power. Never felt like it was slipping at all. Not sure if the 3.9L is just not that powerful, guess I'm just use to V8's, even though it's mostly a 318. I've just been driving it around with the overdrive off and seems to be working fine, even spun the tires a few times. I only use the overdrive on staight flat roads, which there are few around here. Drove it around for about 3 hours yesterday, gas gauge didn't move a whole lot and nothing broke. Pretty quite for a truck and drives nice. Bigger engine and I'd keep this and sell a different truck.

 

the 3.9 has lots of torque and i could cook the tires but i had the 3.90 gears in it. if your used to the v-8's with higher gears in them ( 3.55 or even the jeep 2.70 ) then it's going to seem slack, but for grunt the 3.9 and the 3.90 gears will pull a small house, just don't offer anyone on at a stop light.

ps i nicknamed the Comanche the " BULLET " it had 2.70 gears and a 4.0 HO in it. but once you left the pavement it sucked. fast but no torque.