My neighbor has a 93 Grand Cherokee Laredo with the 4.0 Straight six. It will start, Idle and run great for the first 20 seconds, then sputters and lopes along, and then dies and wont start again. checked the schreader valve under the hood that that didnt have any pressure, replaced the fuel pump and fuel filter, we now get a continious run of fuel and still have the same problem. it seems that it runs great when its cold, but doesnt run for a **** when its starting to warm up. The little console says the "coolant sensor bad". Does this mean its the coolant sensor on the pump or the one in the reserve tank? Any Ideas why she wont run?
My 99 sport with the I6 4.0 had the same problem, replaced the coolent pump, rad and hosing, bought a bottle of blue devil (just to make sure my head gaskets where not leaking) flush and filled the system, and it ran just great. Later models have a fail safe in the CPU that shuts the motor down should pressure or temp rise so also check the CPU.
replaced the coolant sensor, still says coolant sensor is bad in display in the truck. kept it running, it runs great at idle when it gets up to 210 degrees, wont run above 2k rpms when warm though. Compression is good in all 6 cylinders. Any Ideas Anybody?
alright if you changed the coolant sensor after you did that did unhook the negative battery cable for about 5mins. if not do that it will clear any codes in the cpu then run it again then check for codes if the code comes back check the wires going to the coolant sensor and see if there cut or chafed or the insulation is gone or torn if that is all good check the wires for a short if that checks out then ohm out the sensor unplug it and use your ohm meter when the motor off and cold the resistance should be 7000 ohms or 7k or higher if that is in range start the motor let it warm up to temp. and then ohm out the sensor again it should read 1000 ohms or 1k or less if that checks out then that is solved as for the wont run above 2k rpms and you have a new fuel pump and filter you need a fuel pressure gauge that will read 0 to 30 psi start the motor and the pressure should read 14 to 15 psi at a idle if the pressure is wrong try adjusting the fuel pressure regulator there is a screw on it you can turn to bring the pressure to the proper reading if adjusting the pressure regulator does not change the pressure then it is bad cause too low of pressure will cause it not to get enough gas at higher rpm and too much pressure will flood out the motor at a idle and cause the cpu and the o2 sensor to go all haywire and run like crap but the coolant sensor is very important to cause it tells the cpu what to do at cold or hot temps. it has to do with fuel spark advance and cause the sensor tells the cpu when cold to dump more fuel then it warms up and then the 02 sensor comes in to play to tell the cpu to lean out some man i hope this helps you if you need more help email me at email@example.com oh ps check the fuel return line for blockages
hey fitztool i all most forgot you don't need a scan tool on 1991-1997 models all you have to do is turn the key on and off three times in five seconds and the check engine light will flash in a flash and pause and then flash again the coolant sensor code is 22 so that means the check engine light should flash like this it flash then flash again then it will pause then flash two more times for code 22 OK at the end of the codes it will flash a code 55 it will flash 5 times then pause then flash 5 times again if you do this and all it gives you is a code 55 then that's the end of codes and all the sensors are fine OK turn the key as follows to get codes ON,OFF,ON,OFF,AND THEN ON IT WILL START TO FLASH