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97 grand cherokee crank - no start ,blows f21 & f20 fuse,

Customer Question
97 grand cherokee...

97 grand cherokee crank - no start ,blows f21 & f20 fuse, dont have a diagram or info on what the fuses are for,

Mechanic's Assistant: Will the headlights turn on? Is the battery fully charged?

Have it hooked to a charger, battery was low, had a short to ground unpluged the lights and it wasn't shorted anymore

Mechanic's Assistant: Are you fixing your Grand Cherokee yourself? What have you tried so far?

I got the jeep knowing it had problems, the guy was throwing parts at it, starter, alternator, wires, then I got it, the coil was cracked and the engine ground rusty fixed that, he said it blew those fuses but it started & ran 2-3 min then turned off & will not start back up, has blown the fuses a few times, the fuel pump is running all the time, like the pressure relieve not working, good fuel pressure though,

Mechanic's Assistant: Anything else you want the mechanic to know before I connect you?

I don't have a diagram, thanks

Submitted: 9 months ago.Category: Jeep
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Answered in 22 minutes by:
9/17/2017
Jeep Mechanic: kalamykid, Shop Owner/ Tech replied 9 months ago
kalamykid
kalamykid, Shop Owner/ Tech
Category: Jeep
Satisfied Customers: 5,342
Experience: I HAVE OWNED MY OWN SHOP FOR OVER THREE YEARS. I HAVE THE TOOLS AND SOFTWARE TO ANSWERE ALMOST ANY Q
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What size engine does your jeep have in it?

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Customer reply replied 9 months ago
4.0
Jeep Mechanic: kalamykid, Shop Owner/ Tech replied 9 months ago

2 or 4 wd?

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Customer reply replied 9 months ago
4 wd 97 4.0
Jeep Mechanic: kalamykid, Shop Owner/ Tech replied 9 months ago

Look on the drivers side of the engine. The O2 sensor wires run through a wire loop on the side of the block. See if the wires are shorted out.

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Customer reply replied 9 months ago
they look fine have unpluged the sensor and looked at the wires
Jeep Mechanic: kalamykid, Shop Owner/ Tech replied 9 months ago

Did you find the metal wire loop the wires run through? It will be towards the front of the engine on the drivers side just in front of the engine mount.

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Customer reply replied 9 months ago
let me double ck,
Jeep Mechanic: kalamykid, Shop Owner/ Tech replied 9 months ago

Thank you.

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Customer reply replied 9 months ago
yea everything fine with those wires, OEM loom still good shape & wires look like new,
what the 2 fuses for, thanks
Jeep Mechanic: kalamykid, Shop Owner/ Tech replied 9 months ago

The fuses run to the asd relay as well as the heated circuts for the O2 sensors. Double check the wires for both O2 sensors and not just the wires from the O2 sensors to the plug, look over the wires from the plug back to the pcm as well.

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Customer reply replied 9 months ago
ok, but we need to take this back up tomorrow, its dark and the jeep is outside, can I contact you somehow after I get all that checked out, tomorrow?
Jeep Mechanic: kalamykid, Shop Owner/ Tech replied 9 months ago

Yes. Just book mark this chat page so you can come right back to this page tomorrow.

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Customer reply replied 9 months ago
ok thanks
Jeep Mechanic: kalamykid, Shop Owner/ Tech replied 9 months ago

You are very welcome. Chat with you tomorrow.

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Customer reply replied 9 months ago
hello, rear co2 sensor looked to be damaged, got it unpluged, one wire pin corroded-green, cked wires could not find any problems, tried to start it (both sensors unpluged) fired right up, was able to move the jeep to concrete pad, then I turned it off, turned key back on, fuel pump shut off like it suppose to,fuel gauge working & low fuel light out, so I started it back up, ran for 45 seconds and it turned itself off but did not blow any fuses, ASD relay was warm, it will not start back up, cranks but no start,
Jeep Mechanic: kalamykid, Shop Owner/ Tech replied 9 months ago

Did you try putting another asd relay in it?

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Customer reply replied 9 months ago
I just switched them and still no start, but just with one, i'll try anotherone tomorrow, do you have a diagram showing wire pin numbers for ecm and , power distrabution box relay--fuse Identifaction,
Jeep Mechanic: kalamykid, Shop Owner/ Tech replied 9 months ago

I do have a pin out for the pcm, but for the fuses all I can do is look up the wire diagrams to see what fuse does what. The asd relay is connected to the f21 fuse, and feeds power to the o2 sensors.

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Customer reply replied 9 months ago
yea, ok it didnot blow any fuses this time, I would like the pin out for the ecm if that is possible, I do think the rear co2 sensor is bad, was causing lots of problem, but there is still something going on, we're getting closer to the problem
Jeep Mechanic: kalamykid, Shop Owner/ Tech replied 9 months ago

I will get you the pin out asap. I am not at my desk right now.

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Customer reply replied 9 months ago
sounds good, I'll be working on it again tomorrow, try asd relay first and let you know, thanks
Customer reply replied 9 months ago
hello, thanks for the pinout, OK I took another relay, same p/n put in asd, tried to start, did not start, then as I was walking back to front of jeep I heard a hissing & saw smoke over at PCM, I pulled the asd & disconnected the battery all in about one second, wow, checked all fuses did not blow any, don't know what could have made it do that, came right in to let you know,
Jeep Mechanic: kalamykid, Shop Owner/ Tech replied 9 months ago

You have to have a dead short some where near the pcm. Was the smoke coming from the pcm itself or the wires to it?

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Customer reply replied 9 months ago
I'm not positive, looked like lower left side of pcm, but i unhooked everything so fast smoke wasn't much and was gone before I could pin point it
Jeep Mechanic: kalamykid, Shop Owner/ Tech replied 9 months ago

Can you remove the pcm and see if it smells like smoke?

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Customer reply replied 9 months ago
i'll do that & get back, thanks
Jeep Mechanic: kalamykid, Shop Owner/ Tech replied 9 months ago

Also check the plugs for the pcm and see if you see any melted wires.

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Customer reply replied 9 months ago
ok, i'll look it over good, anything else, while i'm out there
Jeep Mechanic: kalamykid, Shop Owner/ Tech replied 9 months ago

That is all for now.

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Customer reply replied 9 months ago
smells a little burned, looked around did not see any wire problem,
Jeep Mechanic: kalamykid, Shop Owner/ Tech replied 9 months ago

I hate to say it but there has to be a short in the wire harness that has back feed into the pcm and burnt it out. The pcm will need to be replaced, but you will need to find the short first.

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Customer reply replied 9 months ago
just as i thought,any wireing diagrams that you might have that you think might help, would be appreciated, thanks for all your help, these electrical problems are a pain, thanks again
Jeep Mechanic: kalamykid, Shop Owner/ Tech replied 9 months ago

The best thing to do will be to unplug all the sensors on the engine and The run an ohms test on all the wires at the pcm plug to ground. All of them should read OL as long as they are not running to a ground. Let me know what pins have a reading other then OL and I will look them up and see what is going on for you.

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Jeep Mechanic: kalamykid, Shop Owner/ Tech replied 9 months ago

For all the wires you get a reading on, please tell me what color the wire is with the color of the strip, as well as what pin location it is.

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Customer reply replied 9 months ago
yea thats what i'll do, soon as i find out anything i'll let you know
Jeep Mechanic: kalamykid, Shop Owner/ Tech replied 9 months ago

Thank you.

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