BenS

I have a manual transmission 1996 Cherokee se 2.5. When I push the gas pedal all the way down it bogs down, but if I let off a little it accelerates. What should I check? Is it probably a clogged fuel filter or something more like a TPS or a vacuum problem?

BenS

I don't know if it is related or not, but my speedometer is also wrong. It shows that I'm going around 10-15 mph faster than I am actually going at normal speeds.

Roler

I'd have a look at the TPS to begin with....test it, preferably with an analogue (non digital) meter, looking for gaps in the smooth swing of the meter whilst you go from closed to full open throttle.

captainwoot

How does the exhaust sound? a restricted / plugged exhaust will make it fall on its face at wot.......

BenS

I kinda doubt the exhaust is clogged. I recently bought it very cheap and the muffler has holes in it. It does make the 2.5 sound pretty badass though!

I'll test the TPS tomorrow

cruiser54

Just bought it?

How are the plugs, wires, cap and rotor?

Catalytic converter can be clogged.

BenS

The plugs, wires, cap, and rotor seem fine. I pulled the plugs and they seem fine. They've turned a little yellow or light brown, but the gap looks normal. These are on my list of things to replace in the near future though. I am having a hard time figuring out how they would only have problems when the gas pedal is all the way down.

I don't really know how to check the catalytic converter to see if it is clogged for sure, but it seems fine and I don't have a cel.

When I got the jeep it had a cel for the downstream oxygen sensor, speed sensor, and the pcv valve. The speed sensor was unplugged for some reason, so I just plugged it back in and everything worked. I replaced the rear oxygen sensor and the pcv valve. I have also replaced the thermostat, radiator hoses, front brakes, clutch master and slave cylinder, serpentine belt and probably a few other things I can't remember right now. The front driveshaft is out right now until I replace the u-joint.

I've just been fixing the problems based on their importance and now I've at least gotten the jeep to where it passed emissions and I can drive it every day. I'm planning on draining and refilling all of the fluid, replacing all of the vacuum lines and fittings, getting new plugs, wires, etc and replacing the fuel filter. I just want to make sure I fix this problem before I move on. The jeep has a rebuilt engine and around 275,000 miles in case you're wondering. The kid who owned it for two years before me didn't take care of it very well, but they kept the oil changed and the body is in good shape.

cruiser54

CRUISER’S VACUUM TEST FOR EXHAUST RESTRICTION
Your vacuum gauge should come with an instruction booklet outlining the procedure. Hook the vacuum gauge up to a source on the intake manifold. Start the engine and note the vacuum reading. Usually 17 to 21 inches of vacuum. Throttle the engine up to 2,000 to 2,500 RPM for 20 seconds or so and the vacuum reading should stabilize to the same reading you got at idle. Let the throttle snap shut. The vacuum reading should shoot up about 5 inches of vacuum higher for a second and then come quickly down to the original reading. If the vacuum reading stays high and comes down slowly with jerky needle movements, you have an exhaust restriction.

BenS

Ok my catalytic converter had blown its guts back into the muffler and clogged it basically. I still have the problem where it bogs down at full throttle though. I let a local mechanic drive it and he suggested vacuum or map sensor. At this point I'm pretty sure that my manifold gasket is blown, so I'll replace that first and then if the jeep still isn't fixed I'll replace the map sensor. I replaced my IAC and CPS while I was working on it. My IAC was stuck and the CPS looked pretty nasty and I thought it couldn't hurt to replace it.

BenS

I went to buy a new map sensor today and realized that my Jeep has the wrong one. Apparently it has the throttle body from a 1996 Jeep grand Cherokee v6. The wiring looks good, so I'm wondering if it was just a fluke and came from the factory like that or if someone pulled a junkyard part or something. Would that different map sensor cause it to bog down at full throttle?