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1998 jeep grand cherokee limited: crank sensor..the fuel pressure psi

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i have a 1998 jeep...
i have a 1998 jeep grand cherokee limted with a 5.2l that has no codes i replaced the coil the cam sensor and the crank sensor and checked the fuel pressure psi ok the coil wire has power at key on but shuts off and wont go hot while its cranking i have been checking it aginst my friends identical jeep and still cant find the problem
Submitted: 6 years ago.Category: Jeep
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Answered in 16 minutes by:
2/19/2011
Jeep Mechanic: Chad, Lead Master Tech replied 6 years ago
Chad
Chad, Lead Master Tech
Category: Jeep
Satisfied Customers: 1,114
Experience: Electrical master,Diesel Specialist,Lead Tech/shop foreman
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Have you checked the ASD relay and all fuses?
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Customer reply replied 6 years ago
yes sir
Jeep Mechanic: Chad, Lead Master Tech replied 6 years ago
How did you check the fuses?
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Customer reply replied 6 years ago
by eye and with a test light after no sucess
Jeep Mechanic: Chad, Lead Master Tech replied 6 years ago
OK, I'm going to have to go over the wire diagrams for a few minutes. But I might come back and ask you questions during. And knowing that you have a test light, I will need you to do some testing.
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Customer reply replied 6 years ago
ok im not shure how late i will be abel to work this is my first time here can we pick up in the morning
Jeep Mechanic: Chad, Lead Master Tech replied 6 years ago
Yea, thats fine. I will leave you some stuff to check for me. I will be at work tomorrow, but will check the site from time to time.
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Customer reply replied 6 years ago
thank you
Jeep Mechanic: Chad, Lead Master Tech replied 6 years ago
ASD Diagrams
graphicgraphicgraphicgraphicgraphic
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Jeep Mechanic: Chad, Lead Master Tech replied 6 years ago
I also need you to check with the test light, remove the ASD relay, while cranking, which pins have power?
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Customer reply replied 6 years ago
i have the info you need but i dont k now what the pin numbers are one prong has power constant and one pin constant while cranking
Jeep Mechanic: Chad, Lead Master Tech replied 6 years ago
OK, that is what is suppose to happen.The one that has power while cranking, is also suppose to have power when it is running.Do you know how to remove the cover on the relay? When you remove the cover on the relay, with it installed, while cranking it will actuate and move the lever over.It should stay engaged while running.
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Customer reply replied 6 years ago
it wont run at all and not shure if i bought the right new one im looking for the old one i will take apart and check now
Customer reply replied 6 years ago
it disconects at key on for 1-2 seconds then makes contact when it looses power is the pcm keeping it shut down is there a way to bypass it(the relay)to see if it will start my brand new battery is getting low i have a truck charging it d
Jeep Mechanic: Chad, Lead Master Tech replied 6 years ago
If you fold a paper business card in half you can hold the contacts closed inside the relay with the cap off of it. Also you can try swapping the ASD relay with the starter relay. You know the starter relay works.
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Customer reply replied 6 years ago
ive tried that with the contact seperated first cause thats how it is at key on then with it closed and i tried jumping the power to the coil with the relay removed and with it installed also i can send power to the coil plug from the relay
Jeep Mechanic: Chad, Lead Master Tech replied 6 years ago
I would like you to try something for me real quick. Unplug all the O2 sensors and try to start it.
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Customer reply replied 6 years ago
nothing
Jeep Mechanic: Chad, Lead Master Tech replied 6 years ago
OK, I am missing something.I have seen this before.And I am having CRS right now.I am going to go back over the diagrams and everything you have said and think about it for a few minutes. I'll get back to you as soon as my CRS goes away.
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Customer reply replied 6 years ago
:) i hate when i get that lol thanks for the little laugh
Jeep Mechanic: Chad, Lead Master Tech replied 6 years ago
No problem. Right now I am leaning towards the PCM is bad. But I don't want to say that yet. Bad thing is I had one just like yours in the shop a few months ago doing the same thing. Just can't remember what the repair was.
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Customer reply replied 6 years ago
ya is the pcm on the firewall by the coolant tank is it the same thing as the ecm or is there a ecm and pcm would the pcm allow power to go to the coil at initial key on if it was bad
Jeep Mechanic: Chad, Lead Master Tech replied 6 years ago
Yea, the PCM is the ecm. It is on the firewall by the coolant tank.Yea, if it's not seeing the ASD output on the initial key on, it will stop power to the coil fuel pump and everything else.
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Customer reply replied 6 years ago
oh ya my fuel pump works about 45 psi was the first thing i tested would it kill spark and not the fuel pump if its the asd
Jeep Mechanic: Chad, Lead Master Tech replied 6 years ago
No ASD should kill both.But let me double check that.
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Customer reply replied 6 years ago
ok
Jeep Mechanic: Chad, Lead Master Tech replied 6 years ago
But I just found this.
The ASD supplies battery voltage to the fuel injectors, ignition coil and oxygen (O2S) sensor heating elements. The ground circuit for the coil in the ASD relay is controlled by the powertrain control module (PCM) The PCM operates the relay by switching the ground circuit on and off.
So, the PCM is most probably the cause.
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Customer reply replied 6 years ago
ok ill get one orderd
Jeep Mechanic: Chad, Lead Master Tech replied 6 years ago
alright.
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Customer reply replied 6 years ago
hey one more thing alot of people on the internet have tried all of this all of the sensors and the pcm and still had troubles what do i do if it doesent work
Jeep Mechanic: Chad, Lead Master Tech replied 6 years ago
Then you will have to start opening up wire harness and looking for wire damage.
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Chad
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