1993 jeep grand cherokee laredo won't crank

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landonsdad2511

New member
I have a 1993 jeep grand cherokee 4.0 straight 6. New fuel pump. New coil. New crank sensor and replaced the engine control module And a new neutral safty switch. The fuel pump has power going to it but it does not pump gas. The coil has power going to it but had no fire coming from the the coil to the distributor. The crank sensor has no power on the plug. I checked the grounds and they seem to be ok. Does anyone have any idea that will be the reason for all of these. The jeep shut off while driving it. The engine will spin over but will not fire up. Not even with starting fluid
 

Welcome to Jeepz.com . Two items come to mind , relays and fuses. First check any blown fuses in the power distribution center under the hood. You can check under the dash or where the fuses are located on a grand just to be sure too. Also , there should be a fuel pump resister under the hood , but I know you posted that the pump is getting power . If you must , verify at the harness disconnect near the fuel tank that there is power if you have not already . One more item that should not be missed, the auto shutdown relay in the PDC . This relay will kill power to ignition and fuel pump should the PCM tell it to like if the engine is running too hot. Check these items and hoping that your problem is here . Post your findings when able. Also , feel free to check similar threads on this subject in our forum for more possibilities . When we post POR findings and fixes , we pass on to a member who may on their mis fortune be in need. Best of luck and thank you for your membership here at Jeepz.com . Greg
 

I don't hear the fuel pump itself. Also still don't have fire coming from the coil. I tested that with a screwdriver
 
Before we check if injector harness is firing , we need to know that terminals 30 for the auto shutdown relay and fuel pump are hot . Once voltage is found , you'll need a fused jumper to jump terminals 30 and 87 in both auto shutdown relay and fuel pump relay. Your not getting spark and I believe power is not being fed to PCM which fires injectors and coil. Keep in mind that the Fuel pump relay is fed by the auto shutdown relay as well . It is important to know if any terminals are not hot in start and run for these two . Will search more wiring diagrams soonest to find where your power is for the PCM . If you can verify that power actually moves across terminals of all related fuses , ignition and fuel pump , this is a good start. If you can check relay start and run by making jumper wires with male and female spade connectors to plug into relay prongs and connect to socket terminals to read voltage , this will help verify what is live and what's not in start and run. I know the jeep is not starting but when I say run , I mean ignition on . Please keep in mind that some of these wires feed back to PCM so you will want to use a computer safe test light ( not expensive ) and measure voltage with a 10 mega ohm digital multimeter to avoid over drawing on computer circuits . Circuits that flow a maximum of 5 volts for example were not meant to power a 12 volt test light . 12 volt demand from non-computer safe equiptment will have you replacing the PCM again.
 

landonsdad2511 said:
What would keep power from getting to the fuel rail? And how can I test the fuel rail for power?
Click to expand...
The injectors are fired in a sequential firing order by the PCM directly . To check for power , you will at least need a computer safe test light to probe the power terminals , which are live at start up but the ground terminals re controlled by the PCM to complete the circuit to fire the injector(s) in a sequential order . It is preferred to use a noid light which plugs directly onto the injector harness plug but for diagnostic purposes in this no start condition , let us keep it simple.
I cannot find a reliable wiring diagram for your '93 as my CHILTON book is not telling me what I need to know . However I do have a 1992 Chrysler shop manual with complete diagrams and I believe the harness and PCM , while not identical by part # are similar for our purpose.
The important thing is to find if your getting a signal at the injectors to,see if the PCM is communicating to its sensors , injectors and ignition. The computer safe test light is inexpensive and a must for this job or any time you want to read voltage on a computer circuit which any auto has many . This light can read voltage as any test light but only requires .21 volt for light the diode ( red for positive and green for negative ) which makes it computer safe . Let us find this first to,see where we proceed . Please check repair manual how to read voltage from the ignition coil to,determine if PCM,is firing it . The wiring harness will have to be back,probed on the weather proof connection to verify PCM activity but please check the manual for proper procedure as to avoid " spiking " the PCM . This is why I emphasize a computer safe test light and a 10 mega ohm impedance multimeter. If no voltage is found at the injectors which are supplied by relay but grounded by PCM and the coil is not being fired directly by PCM , we will know where to proceed and I will have to hit the books . Please post your findings as you can .
Appreciate your fast reply and thank you for your membership at Jeepz.com . Greg
 
Also on the 93 jeep grand cherokee. There are 2 wires to the coil. Should both of them have power and it grounds out on the engine or should only one of them have power. Right now only one wire has power on it
 
Will have to study more on my wiring diagram tonite when I return home but the 18 gauge grey wire ( according to my diagram ) is fed from the PCM and the 16 gauge dark green w/orange tracer is fed from the alternator . BTW , my error , the power wires for the fuel,injectors are fed from the ignition coil , not a relay. Although power to the PCM should be confirmed , the ignition seems to be key in diagnostics to troubleshoot and the injectors will follow suit. If the wire from the PCM is live , that's a good thing .
 

Further examination of my '92 Chrysler shop manual wiring diagram shows a wire 18 gauge dark green w/ orange tracer that splices to a 16 gauge dark green w/orange tracer that powers the fuel injector harness for all injectors and the ignition coil. This wire feeds from the field on the back of the alternator. Please check the field for damage or if it is burned out as this may contribute to the no start problem .

please be advised that I am quoting from a '92 jeep XJ diagram and color code may be different but the wiring should be very similar however I cannot verify this without a '93 ZJ diagram .
Both jeeps are 4.0 I6 and will have very similar wiring .
 
First I want to say thank you for all the help you have giving me on my jeep. It has been a blessing. I've learned a lot. But it's still not fixed but have narrowed it down to the power distribution center. I ended up jumping the terminals for the fuel pump relay and the ASD relay and found out that I am not getting power to the #30 terminals. I jumped the power from the #86 terminals to the #30 terminal and the jeep crank for a second but I guess flooded out from the all time hot on the injectors.

What at would cause my #30 terminals to lose power on the relay connectors? And what do I do to fix it?
 
Does the asd relay power the alternator or does the alternator power the asd. I seen on a wire diagram that there is a wire that goes from the alternator that splices off to the asd and fuel pump relays that powers the #30 terminals.
 

As shown
 

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Brother , your the man ! A lesser man would have caved and took it to a flunky mechanic , charged a diagnostic fee and probably still not found it and tell you to take it to the dealer . That's why we do our own. Terminal 30 of the ASD goes to fuse #2 in PDC and in turn , a splice of which goes to cavity #3 on PCM , trans control unit and also to a fuse #15. Not yet ready to blame the trans control unit but if it narrows down to it , hope someone got a spare ?
The fuel pump relay terminal 30 also feeds to the same splice so conversely is powered by the same as the ASD . It seems that what is causing the fuel pump to lose power is causing the ASD as well and resulting in your no start. With key on , look for power on both sides of the fuses ( both terminals ) . Fuse 15 feeds fuse 4 to the cooling fan relay ( auxiliary condenser fan) .
Seems like a lot to investigate but really happy you got this far in your diagnostics . You the man!
The trans control unit is under the dash . On my XJ it is on a lower dash panel that's removeable , would have to check that on a GC dash . The wire from the trans controller is a 14 gauge red wire ( '92 MJ/XJ diagram) . Leaning toward that control unit since there are two more ( in this diagram ) wires that feed back to the ASD and fuel pump relays . If you cannot find anything burned as far as wiring , blown fuses , bad field on alternator , bad aux fan , see if you can score a TCU from the boneyard . We must feel confident that all inspection turns up good wiring and relays . As long as the wiring to the aux fan is not charred , a bad fan shouldn't cause this no start but ground a wire that feeds back to a relay will cause interruption in these circuits .
Almost there brother , hoping you'll nail this real soon. I hope my shop manual was of great service , it collects dust more often . Was REAL useful when I had to diagnose no power to my a/c compressor several years ago . Would up being the a/c thermostat wiring shorted with the blower motor wiring to blower motor resistor . You see how when wiring is bundled together in a harness that these problem arise ? Lovely , just wonderful . Jeeps are GREAT but we still got chase after them like a two year old . Sometimes you can't take them no where ! Ruttin ' for ya brother . Greg . Just wanypt to see you get 'er fixed , don't need to like me on Facebook or nothin' . Just kidding , lol
 
landonsdad2511 said:
Does the asd relay power the alternator or does the alternator power the asd. I seen on a wire diagram that there is a wire that goes from the alternator that splices off to the asd and fuel pump relays that powers the #30 terminals.
Click to expand...
Man , you are right in top of this , top dog , white on rice !
The alternator will power the ASD which feeds through the ASD and fuel,pump relay to charge the ignition coil and fuel injector harness , but I don't have that going to the alternator.
In my shop manual ('92 MJ/XJ/YJ) , the alternator field feeds ignition coil and injectors .
Perhaps there is a difference in XJ versus ZJ wiring but the outcome will be the same . Alternator will power virtually all directly or via the PCM.

P.S. - not to confuse things today since we are working with two different diagrams (?) , but see if my first post today agrees with your diagram as far as the fuses and relays . Want to be sure there is no major difference .
 
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Hey brother , got to return to work , wishing best of luck and looking forward to your post soonest . Will be following along on your progress .
 
I took a test light to the wires that run to the alternator field and I'm getting power through them. The relays still don't work on #30 terminals. Also now I learned that the tcu fuse (3) and the ignition control (2) both located in the pdc does not have power to them.
 
Now I am as intrigued as you , I must jump on this tomorrow and research more. Getting closer now , process of ILLimenation is working in your favor.
 

Is there a way to read the code that may be faulty while the jeep isn't running? I know it will show quite a few of them but maybe I could write them all down and start marking stuff off the list. I have a obd 1 and 2 reader but I have never done it without the engine running.
 
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