94 YJ 4.0L ignition problems, I've replaced everything I can think of - JeepForum.com
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Unread 04-19-2009, 04:43 PM   #1
ltjblalo
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2000 XJ Cherokee 
 
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94 YJ 4.0L ignition problems, I've replaced everything I can think of

I looked through the forum for too long, and have spent too much time on this, but I'm stuck.

I'll start from the beginning. Bought this YJ two weeks ago, and it started and ran beautifully when I test drove it and on the drive home. Later that afternoon, I go to start it, and nothing. I check a few things, and determine the fuel pump is shot, not getting any fuel out of the tank.

Last weekend I replaced the fuel pump, then waited a week for new fuel tank straps, and re-hung the fuel tank this morning. The only thing I can think of that may have happened is that one of the breather hoses on the top of the tank may have been pulled out during the last bit of hanging.

I get in, try to start it up, and nothing, no spark. Test spark at the plugs, nothing. I replace the cap and rotor (they were in bad shape, needed to be done anyway), and nothing. Now I test the spark at the ignition coil, nothing, and it's cracked, so I replace that. Still no spark. I test the resistance at the plug for the CPS and I'm getting varied readings from 4.5ish (on the 20K ohm scale) to infinite. So I play it safe and replace the CPS too. Still no spark.

So my question now is, what else could it be, and how can I test it? Is it possible that a disconnected breather hose on the fuel tank could case the computer to not send spark? I need help before I set this thing on fire.

Thanks.

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Unread 04-19-2009, 04:48 PM   #2
ltjblalo
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Forgot to add, I did check that I am getting fuel after replacing the pump, and have double and triple checked all fuses and relays.
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Unread 04-19-2009, 05:50 PM   #3
ltjblalo
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I also tried to do the key trick to check codes, but I'm not getting the check engine light at all. Could this be a sign of a bad computer or bad ignition switch?
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Unread 04-19-2009, 06:40 PM   #4
TSEJEEPERS
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Wow alot of problems. When you said you checked the fuses and relays did you check the ones under the dash or the ones under the hood?
I really do not think the vent line would have anything to do with it. The tank is vented through the cap. The other lines you see are for the charcol canister, which has nothing to do with it.
The only other thing I can tell you is make sure you have a good ground to your pump.
After reading your post again you say you have no spark. Is your battery good?
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Unread 04-19-2009, 06:43 PM   #5
ltjblalo
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I checked both sets of fuses. I'm reading more and I think the tell tale sign now is that the check engine light doesn't come on when I put the key at the "ON" position. This points to a possibly bad computer. Any way to test it for sure? Should I take it out and have the dealership test it? Another $300 to get this thing running again wouldn't surprise me.
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Unread 04-19-2009, 06:55 PM   #6
TSEJEEPERS
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Did you check for spark at the plug wires?
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Unread 04-19-2009, 06:56 PM   #7
idaholtby
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Quote:
Originally Posted by ltjblalo View Post
I checked both sets of fuses. I'm reading more and I think the tell tale sign now is that the check engine light doesn't come on when I put the key at the "ON" position. This points to a possibly bad computer. Any way to test it for sure? Should I take it out and have the dealership test it? Another $300 to get this thing running again wouldn't surprise me.
The typical problem with a bad ecm is usually seen in cold weather. The CEL does not come on initially because the computer takes awhile to power up due to bad capacitors. When this happens the ASD relay does not actuate so your fuel pump in turn will not come on. You say that you do have fuel. When you depress the schrader valve on the fuel rail, gas squirts out? Your CEL should come on when the ignition is first turned on, so this is a problem, but may not be related to your problem. I would check to see if the CEL lamp is good. The PO may have removed it to help make the sale. The only other sensor that comes to mind that may cause your problem could be the camshaft position sensor in the distributer.
Check your CEL light first and see what is up with that.
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Unread 04-19-2009, 07:32 PM   #8
ltjblalo
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Yea, the valve on the fuel rail squirts out gas.

Just pulled out the dash and swapped the CEL bulb with the seatbelt bulb, which I know is good. Old CEL bulb lights up in seatbelt slot, so the bulb is good.

Before I did that I had the key in the "ON" position for about 45 minutes to an hour and the CEL never went on. So could this be a bad ground to the PCM? I plan on checking that out tomorrow after work when the sun is up.
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Unread 04-20-2009, 06:47 AM   #9
idaholtby
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Quote:
Originally Posted by ltjblalo View Post
Yea, the valve on the fuel rail squirts out gas.

Just pulled out the dash and swapped the CEL bulb with the seatbelt bulb, which I know is good. Old CEL bulb lights up in seatbelt slot, so the bulb is good.

Before I did that I had the key in the "ON" position for about 45 minutes to an hour and the CEL never went on. So could this be a bad ground to the PCM? I plan on checking that out tomorrow after work when the sun is up.
pin -32 on the ecm connector supplies the ground to the CEL light. I see you found the ecm t/s'ing thread. Good luck.
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Unread 04-20-2009, 09:02 AM   #10
ltjblalo
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Next thing I'm going to test is the ignition switch. I tested for voltage across the "Dome" and "Ign-lps" fuses, 5V across the Dome and 12V across the Ign-lps. It was dark and late, so I didn't test power to the ignition switch wires, but the low voltage on the Dome fuse could indicate a faulty ignition switch.
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Unread 04-21-2009, 07:40 AM   #11
ltjblalo
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Well, I got it running. When I went to test the harness to the ignition coil, I noticed the CEL start flickering on and off while I was moving the harness. I did my best to get it seated better, to the point where the CEL stayed on. After a few more tries cranking, it fired up and ran a little rough, I'm guessing there was some air in the fuel lines.

I also noticed that there was a 10A fuse in the Dome slot, which calls for a 20A. Oddly, the fuse wasn't blown, but I replaced it anyway right before it fired up.
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