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HELP!!! 93 Cherokee wont start


 
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thebearman
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Joined: 16 Dec 2006

PostPosted: Sat Dec 16, 2006 7:26 am    Post subject: HELP!!! 93 Cherokee wont start Reply with quote

Hello,All. I have bought a 1993 Jeep Cherokee.It is a 4.0 auto 2 door. It will not start. Engine turns over.I have a good spark. I have good fuel presure.Battieryand timing check out good.I checked the OBD and am getting a code 76.This code is Fuel Pump Resistor Bypass Relay Circuit.The only thing the manual says is to take it in and have it diagnosed.I have check all the fuses,relays and wiring.Everything is good. The guy i bouight it from was having this problem.He put it up for sale when it was not running then as he was cleaning it out he tried to start it and it started up.I test drive it drove it home my wife drove it around and it ran fine.I pulled it in and out of the garage many time with no problem.Then it wont start now.I have been going throw everything I can think of.Please Help.Thanks
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TheBrat97
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Joined: 28 Jul 2006
Location: Dallas, TX

PostPosted: Sat Dec 16, 2006 4:57 pm    Post subject: Reply with quote

Check your head gasket...could be losing compression.
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thebearman
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Joined: 16 Dec 2006

PostPosted: Mon Dec 18, 2006 4:40 am    Post subject: Reply with quote

I checked out the head gasket.Its keeping good compresion.No leaking. Is there other relays besides the ones under the hood??? Thanks Bear
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94z07
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Joined: 09 Dec 2006

PostPosted: Tue Dec 19, 2006 12:11 pm    Post subject: Reply with quote

The fuel pump resistor is there to keep the fuel pump from wearing out prematurely. The by-pass circuit is there so that the jeep will start with enough pressure. When you turn the key to run do you hear the fuel pump run for 1 second? When you try to start the jeep does it turn over but never start?


If it turns over and you have spark and you have fuel pressure are you sure the injectors are firing? If you have a stethoscope listen to one as someone turns the engine over see is you hear it clicking open and shut. You can use a short length of garden hose or just rest the tip of your finger on an injector to see if it is firing.

If the crank position sensor is inop then there will not be spark.

Oh yeah if you see oil in your distributor then it's time to replace the distributor any way. A reman dist from NAPA comes with a new sensor and is only a few dollars more than a cam sensor alone.

If the cam position sensor is inop then there will be no fuel injector pulse.

If the timing gears have lost some of their plastic coating and the valves are now in the wrong place, everything will seem to be ok but the jeep will never start until the gears and chain are replaced and the cam is indexed to the crank properly.

Testing the cam and crank sensors are basically the same. Back probe the connectors and you should observe 0 and 5 volts between the B (ground) and C (signal out) terminals as the engine is cranked over. The crank sensor will give two 5 volt pulses per revolution of the engine while the cam sensor will only give one pulse per revolution.

The cranks sensor is sometimes called: “CPS” or “Ignition pickup – Crank”
The cam sensor is sometimes called: “CPS” or “Ignition pickup –Cam” or “Stator”

Both sensors have part numbers on them that the parts stores can cross reference to make sure you buy the correct replacement part so take them with you if you are replacing them.

If you are testing with a DVM turn the engine over slowly or you may not see the pulse. The needle swings are much easier to see on an analogue volt meter.
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