So i have an 86 Jeep Cherokee with a 2.5L 4 Cyl TBI engine, CEC computer controlled etc. Jeep starts fine, idles decent, engine revs great. Once the engine is under load (in gear) it has a hard time accelerating, almost like it is lacking fuel or air. I've dropped the gas tank and replaced the gas, the sock is clean, the filter has been replaced, i can see the injector pumping fuel into the throttle body. Ignition timing is non-adjustable, but correct according to spec, and advancing correctly. All vacuum tubes have been replaced and verified to be hooked up to the right stuff. the EGR will not hold a vacuum, but im' not sure that it would cause this problem. Compression is good and even across all cylinders. air filter clean. TPS registers good. O2 sensor registers good, and MAP registers good (they are all withtin the allowable voltages according to the service manual. New plugs, wires and dist. cap.

So, any ideas why this thing feels like the parking brake is on (it's not)

9/11/2006 12:40:18 AM

Quote :

"the EGR will not hold a vacuum"

if you could elaborate...

Quote :

"So, any ideas why this thing feels like the parking brake is on "

so does it bog/stumble/miss, or does it feel like it's making full power but something is just restricing it/holding back? if it's the later, i would put my money on the cat. convertor, which could also possibly explain the egr issue depending on what you mean by not holding vacuum.

9/11/2006 12:54:25 AM

ah i forget to mention the exhaust is gone from the header back... To test the egr you can push under it with your finger and it's supposed to stall the engine...i can tell a difference in the engine, but not much. When i put vacuum pressure on the egr with a hand vacuum pump, it does not maintain the vacuum...in other words, i'm pretty sure there's a hole in the diaphram

9/11/2006 1:03:32 AM

Quote :

"in other words, i'm pretty sure there's a hole in the diaphram"

doubtful that's your issue then, as long as the seal where it mounts is good. on simple FI systems like yours, egr valves can even be completely eliminated with basically no noticeable effects.

Quote :

"ah i forget to mention the exhaust is gone from the header back"

this is where i'd start. put some exhaust on it and go from there. basically complete lack of backpressure is going to definitely affect things, your computer doesn't even nearly have the parameters to compensate the fuel/air mixture and timing for such an extreme change. that's even assuming the o2 is in the manifold, if it happens to be in the missing downpipe that would even further point to lack of exhaust being the issue. i haven't worked on enough of those motors to recall where it's located.

9/11/2006 1:20:58 AM

that's the next thing for sure is an exhaust...the o2 is right on the manifold, it appears to be throwing a good reading at this point. thanks for the input this far

9/11/2006 1:24:14 AM

gas filter!!!

9/11/2006 1:29:53 AM

Quote :

"it appears to be throwing a good reading at this point"

doesn't really matter... your main issue imo is the lack of back pressure. even the more sophisticated obdII systems can have trouble compensating for such a drastic change without supporting actions in the fuel/intake department beyond the stock parameters. your particular injection system doesn't rely heavily on o2 input. while you would notice some changes, you could have a non operative o2 and it would still run/drive fairly decent (assuming everything else was in proper working order).

9/11/2006 1:44:41 AM

FAS GILTER!!!!!!

9/11/2006 2:46:25 AM

Quote :

"Ignition timing is non-adjustable, but correct according to spec, and advancing correctly"

still sounds like an ignition issue to me, what is the static timing and how much is the total advance?

9/11/2006 8:00:28 AM

Could a bad cat cause a misfire in one cylinder?

9/11/2006 9:15:35 AM

Quote :

"no"

9/11/2006 9:32:55 AM

Ignition timing is 12° BTDC idle and advances to 26° @ 2000 RPM i think...close to that. I'm not sure why it's so far btdc, most cars i've worked on are around 6-8 btdc

9/11/2006 9:52:38 AM

That's not unacceptable in the least.

9/11/2006 9:54:38 AM

maybe a bad MAP sensor or no vacuum getting to it

9/12/2006 7:58:24 AM

Quote :

"maybe a bad MAP sensor or no vacuum getting to it"

damn it there are some ignorant idiots that post around here...

Quote :

"MAP registers good"

Quote :

"All vacuum tubes have been replaced and verified to be hooked up to the right stuff."

this guy has obviously done his homework, has a clue what he's doing, and is taking/has taken all of the proper diagnostic steps so far. he doesn't need any stupid out of your ass haven't even read the thread answers.

9/12/2006 3:53:02 PM

you'd be far better asking this question on http://www.naxja.org/forum

9/12/2006 9:20:42 PM

torque converter or some shit like that?

9/12/2006 10:31:24 PM