89 cherokee problems

mxr429 · #1 03-26-2005, 12:56 AM

I have an 89 cherokee laredo and I am having hesitation problems. I can not figure it out. It only does it around 2000 rpm and under when lightly accelrating. I have changed the plug wires and coil to msd and new bosh 4s plugs. Also changed the tps and the o2 and the crankshaft position sensor. Also the fuel pump and fuel filter. It was doing this befor all the changes. Shop does not know what it is. Any help PLEASE.

tblack · #2 03-26-2005, 02:08 AM

I hope you didn't get two replys from me, my PC dumped on me. Anyway, I was writing that I assume you have the 4.0L with the AW4 tranny. That AW4 is a very good transmission, but it has an overdrive that kicks in at about that RPM you describe. This causes the RPMs to drop. This is a fuel saving thing that is built in. Have a transmission specialist check it to assure it isn't malfunctioning, it may be you have a normally operating engine and trans. The engine is American and married to a Japanese transmission that while very reliable has a rudementary way about it including the overdrive system. One way to check it yourself is to stomp on the accelerator pedal when you feel it start to hesitate. Does it downshift and lurch forward and maintain a steadily rising RPM? if so, everything is normal. If it dies out then you have a sick Jeep and I would think it is in the fuel system. Try cleaning that first.
If you determine it is the engine, Try taking it to a shop to have a fuel system cleaning. I think the 89s had the fuel injection by then and these need to have their thorottle bodys cleaned every 15,000 miles or so.
tb

mxr429 · #3 03-26-2005, 09:34 PM

IT does down shift and take off and yes it is the 4.0 sorry I didnt say that. I checked the map sensor today and the imput voltage is 5 but the out put is nothing. It is weird I am going to look in to it a little bit more. A friend let me borrow a dealer service repair manual. But if any body has had any problems with this any input would be great.

89ltd · #4 03-26-2005, 10:42 PM

find the egr valve and pull the vacum line off it and plug it, if it runs better you have found the probem. The egr opening to early will make it hesitate.

mxr429 · #5 03-27-2005, 01:34 AM

I have already tried that and it didnt help. seemed to make it worse when going up hills. I am going to go and put a whole new ground system on it has just the stock ground straps and they suck. but the map sensor thing could be the problem but I dont know. Thanks for the tip and any more ideas would be great.

jwalden · #6 03-27-2005, 08:28 AM

It could be the map sensor.Also if it wasn't doing any of these things before you did all of those things to it, maybe its one of those.
Are the spark plugs gapped right. Maybe the porcelain on one of the plugs is cracked.

mxr429 · #7 03-27-2005, 05:37 PM

It had this problem before I changed all of those parts. So I dont know what the problem is. I checked the map sensor voltage and it was fine but I dont have a vac pump I need one to check the vacum on the sensor. thp is set perfect .830. I dont know I am about ready to give up.

Dale Aeppli · #8 03-27-2005, 06:16 PM

Quote:

Originally Posted by mxr429

IT does down shift and take off and yes it is the 4.0 sorry I didnt say that. I checked the map sensor today and the imput voltage is 5 but the out put is nothing. It is weird I am going to look in to it a little bit more. A friend let me borrow a dealer service repair manual. But if any body has had any problems with this any input would be great.

check for voltage outputis tested at connector terminal B as marked on sensor body, with key on, engine off. Output voltage should be 4-5 volts. Voltage should drop to 0.5-1.5 volts with a hot neutral idle speed condition. Dale

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