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Old 08-13-2010, 09:09 AM
maxsdad maxsdad is offline
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Default Need Cherokee troubleshooting help

I know, I know...it's a J**p....
But it's my daughters, and she got it free, and it's all she can afford.
It's an 89 cherokee laredo with the 4.0 liter renix based injection sytem. It all of a sudden started running really rough and we had it towed home about a month ago. Since then, we've been trying to figure it out...new cat, new tps, new cps, new o2 sensor, new bunch of other sensors...cleaned out throttle body and injectors, new plugs, new bunch of other stuff....we thought maybe it was bad gas, so we drained the tank and replaced with new gas...let it run for about an hour...still no luck...
This pos has no check engine light..there is a proprietary tool that can read codes but hardly anyone has one anymore....some dealers have them, but I don't want to pay more for a diagnosis than the car is worth.
Anyway...I was hoping there might be a Cherokee pro out there who could help us diagnose the problem.
Can't afford much in the way of payment, but can certainly provide and food!!
Thanks in advance for any help.
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Old 08-13-2010, 09:30 AM
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Fuel Filter? Vacum? Check all your wires and lines. That old something may have come loose or kinked. I have a buddy that knows them better i will ask and see if he has any ideas.
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Old 08-13-2010, 09:42 AM
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Thanks!
New fuel filter and pump...checked the vacuum lines a million times in the last month...can't see any wires disconnected or melted. No fuses blown, we also changed the map sensor...unhooked the battery after changing out the sensors, gave it time to reset. Compression is OK, as is fuel pressure. EGR valve seems to be working ok.
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Fuel Filter? Vacum? Check all your wires and lines. That old something may have come loose or kinked. I have a buddy that knows them better i will ask and see if he has any ideas.
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Old 08-13-2010, 09:50 AM
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OK left him a message. I will see what he has to say. Can't remember but isnt there two fuel filters?
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Old 08-13-2010, 10:04 AM
maxsdad maxsdad is offline
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Hmmm - That I'm not sure about...I'll check.
And thanks for your help!
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OK left him a message. I will see what he has to say. Can't remember but isnt there two fuel filters?
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Old 08-13-2010, 01:16 PM
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Hey Rob, I'm not sure what the problem is (starting? running? etc) but this may be the solution you're looking for or maybe give you some leads to check.

Starting Problem Solved
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Old 08-13-2010, 01:36 PM
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Thanks Chris - I'll look at it closer this afternoon. Just got back from a little more troubleshooting and this is what I found this round - I unplugged the map sensor and I could not get the car to start. I plugged it back in and unplugged the map sensor vacuum line and the car ran 100% better with the vacuum line just sitting there - the minute I plugged the line (I could feel vacuum) the engine started to die???
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Hey Rob, I'm not sure what the problem is (starting? running? etc) but this may be the solution you're looking for or maybe give you some leads to check.

Starting Problem Solved
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Old 08-13-2010, 01:54 PM
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Beats me Rob but I know some people that may be able to help. I can pass on some phone numbers if you'd like to toss it around with someone else.
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Old 08-13-2010, 01:55 PM
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Hey Chris - Thanks - that would be great - it's apparently a commonish problem with the 87-90 Renix 4.0 litre engines - Rob
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Beats me Rob but I know some people that may be able to help. I can pass on some phone numbers if you'd like to toss it around with someone else.
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Old 08-13-2010, 01:58 PM
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Weird...

Can you test the MAP sensor to make sure the thing is putting out the right range of voltages for the vacuum it is seeing?

We have a 2000 Cherokee with what is probably a similar setup (maybe not) and it intermittently runs REALLY rough. Usually it clears up within a few minutes or after shutting it off. no help i know.

I'll pull the vacuum line off of mine (drove it to work today) and see what happens just for comparison's sake.
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