jimmyintucson

Hey all, finally registered for the forum...I've been using the archives a lot to learn about my new XJ. I have an 88 with 222,000 miles, 2.5L 4 cylinder. I got the jeep for a song, but am having trouble getting it to run. One of the first things I did was chase down all the vacuum leaks, though I think I still have one at the throttle body (I'll be getting a new gasket today) I replaced the tbi injector since the old one was partially melted (musta been runnin really rich and backfired) and was just spraying a ton of fuel in, even at idle. Now that I have the new one in, I can't get it to run right, it seems to run a bit better, definitely not as rich as before, but displaying the same MAP paradox. If I have the MAP sensor vacuum line plugged to the MAP I can get it to start and it'll run for a few seconds surging before dieing. I can stab the throttle sorta in time with the surging and get it to rev no problem, but if I hold the gas down, it'll surge a bit, then die. However, if I unplug the MAP vacuum line it'll start and run 'fine' with a high idle, though the idle drops if I put my finger over the vacuum line. What could cause the jeep to run without the MAP plugged in and run like uber crap if it's plugged in? I've had trouble finding answers, and the ones I do find don't always seem relevant as the 2.5L seems pretty rare.

Thanks in advance,

Jim

RenoXJ

Replace the MAP sensor ?

alpine.adrenaline

Your ECU isn't getting accurate readings from your MAP sensor, probably because it is clogged or contaminated. I'd recommend replacing it but you can check the voltage with a mutlimeter. Excellent diagnostic help on Renix systems here: http://www.lunghd.com/Tech_Articles/...iagnostics.htm

jimmyintucson

MAP tested out okay, and I tested it with a known good one, but all that was before the injector was replaced...I'll test it again to see if there's a difference.

chokeX

have you left the battery unplugged for a while to reset the computer after you fixed the vacuum leaks? give that a shot. It may still think theres leaks and its learned how to keep the jeep running with them.

jimmyintucson

I've disconnected the battery before, but not for more than maybe a minute or so...I just disconnected it and I'll leave it that way for a bit and see if it helps...

jimmyintucson

Well, left the battery disconnected for awhile, still no better. Seems to run like a champ as long as there's no vacuum line connected to the MAP, and when it is it's running super rich. It was suggested to me to try driving it around a bit to see if the computer might adapt, but I can't keep it running long enough with the MAP connected to make it out of the driveway. Any other suggestions?

chokeX

i had some short involving my map and ait sensor. If i disconnected the battery for a while, then disconnected the ait sensor and plugged the MAP in it would run for a while, then i could plug the ait back in and it would stay running. I never fixed the problem it just throws a code.... i should get around to that

89cherokee95

Did you ever get it running right? I am messing with my vacuum lines and the same thing is happening. It will run good (sorta... throttle hesitation) with map vacuum disconnected. then when i plug it back in the jeep dies

csmgj

In addition to my '88 Jeep Cherokee, I also have an '89 Ford Tempo. And it to won't run or idle unless the vacuum line to the MAP sensor is unplugged. Did y'all ever figure this out? Will your Jeep run if you disconnect a different vacuum line?

Hate problems like this. Find all kinds of posts with people having the same problems, but never any solutions.

freegdr

did you test the vacuum to the map does it hold it maybe theres a internal leak renix shares alot of thing with gm take the map to local u pullit yard search older gms match the connector up and see ifit cure the issue...

cruiser54

Renix era Jeeps don't respond to ECU resetting. They're not adaptive like the later models.

csmgj

Well, not knowing what else to check, I looked up a video on how to check the MAP sensor. I'm sure it's the same on my JEEP as it is my Tempo:
I was getting a flat 2.6 volts on the center pin. So I took a gamble, went to O'Rielley and bought a new MAP sensor for about $50. But I got lucky. Plugged it in, and now the car runs.

Just figured I'd reply in case others have this problem and find their way here.

cruiser54

Hey, thanks for posting up the results.