I got a 5.2 Dakota 5-spd that seems to run fine at idle, but under load it won't rev over ~1900RPM. It'll accelerate fine until about 1900rpm then make this loud "hissing noise" and bog down. It's just enough for me to shift on a flat land, not going anywhere uphill. When I depress the gas pedal, the noise goes away.

I thought it was the cat, so I took that off and it ran a little better but no cigar. I thought it was the TPS but not that either. I'm running out of ideas and money here. I was wondering if you guys had any ideas. I checked and have no vaccum leaks.

The only thing I could thing of was what I read off another forum where the o2 is shot (reading too rich) and causing the IAC to suck in air. Did anyone else have this problem or could maybe help me with this? It sounds legit but I'm running out of money here. It feels like it runs fine but the PCM isn't giving enough gas to the engine. It'll drive on a flat surface up til like 2000rpm then get "Stuck" there and make a hissing noise. When going uphill, it'll barely make it there.

I guess I'm just praying for a miracle here....

 

Up early today like me

I dont know the V8 engines all that well but it sounds like a common problem Im thinking the plenum is leaking

read this link

but im only guessing

If the other forum regs say thats it this will give you a look at what you will need to do LINK

 

I found this today Laughed my head off.

Redneck DIY

 

I actually just got done doing the plenum and it didn't fix the problem.

 

I know you ruled out the cat, but it still sounds like plugged exhaust to me. Did you look inside the cat? Maybe it came apart and some pieces clogged the muffler?

Also, check your fuel pressure. I've seen clogged fuel filters cause the same symptoms (never on a Dodge, though).

 

What year and do you have any codes?

I'd be curious as to the MAP sensor.

 

It's a 97 with no codes flashing. I know it's not the cat cause I took it completely off. Got an open pipe ATM.

Next step will have to be the MAP sensor. IAC valve is good.

Does the Haynes manual tell you how to test the MAP and O2? I figure I should go buy a multimeter and rule those out of the way.

 

When's the last time you cleaned the throttle body, as in pulled it off and cleaned it all up?

There's a little rubber fitting under the MAP sensor, check it.

The MAP sensor changes resistance as barometric pressure changes. It is the the primary source of information on injector pulse width.

Here is some info on the MAP sensor:

A 5 volt reference is supplied from the PCM and returns a voltage signal to the PCM that reflects manifold pressure. The zero pressure reading is 0.5V and full scale is 4.5V. For a pressure swing of 0–15 psi, the voltage changes 4.0V. To operate the sensor, it is supplied a regulated 4.8 to 5.1 volts. Ground is provided through the low-noise, sensor return circuit at the PCM.

 

Thanks, I'll go out and check the hose on the MAP, didn't think about that. Would make some sense if the hose cracked or something of the like.

As for the TB, I cleaned it out not too long ago and looked good when I did the plenum but I guess it won't hurt to check and see if the MAP port is clogged by some odd reason.

 

I would think if that MAP connector was bad it would run like crap all the time. I still think you have some big air leak in a manifold gasket to have that loud hissing sound.