87' will crank but dies after about 5 seconds - JeepForum.com
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post #1 of 38 Old 12-24-2009, 01:04 PM Thread Starter
coastiemike
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1987 MJ Comanche 
 
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87' will crank but dies after about 5 seconds

I drove my 87' 4.0L MJ to work the other day and left it there for three days and when I returned and started it up the truck died when I put it in reverse. It started back up but now will not stay running. I thought the CPS switch could be bad, so I replaced that with negitive results. I replaced the cap and rotor 3+ months ago and yes I have good gas in the truck. Could I be dealing with a ground issue or is it something easy? I am trying to use the KISS method on this problem. Any help would be great. Thanks

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post #2 of 38 Old 12-24-2009, 04:13 PM
maddzz
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Will it stay running if you hold the key forward in the start position? But stall when you release the key back to the run position? or will it stay running with the key released and then eventually stall?
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post #3 of 38 Old 12-25-2009, 03:20 PM Thread Starter
coastiemike
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it does run after the key is released
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post #4 of 38 Old 12-25-2009, 10:37 PM
AMCSportTruck
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Dose it fire up run a few seconds die then fire right back up and run fine ? mine dose that . . . Now that it's getting ran more then once a year it's starting to go away. . .

Maybe letting it sit goofed with it some ?

Mike
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post #5 of 38 Old 12-26-2009, 06:41 AM
DIVERHERB
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If I remember right there is a balast resistor for the fuel pump on the left front fender that used to go out from time to time and caused these same siymptoms. Just jump across it and see if it will run okay. On the later years this was not used. I have heard of people just bypassing it permanently, but they are cheap and I would just replace it if it is bad.
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post #6 of 38 Old 12-26-2009, 02:28 PM
cruiser54
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You've received some good advice here. But let me remind you that you NEED to clean, shine, and tighten your grounds no matter what!!!!!!!!!!! There are the ones at the engine dipstick tube and the one from the driver side firewall to the back of the head. These grounds were problematic when your vehicle was new. I can assure you they haven't gotten better over time. Also remove the center bolt from the black box on your driver side firewall that all those wires run through, take the two halves apart and clean the black tar crap out of it and spray the connecters with contact cleaner before reassembling.
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post #7 of 38 Old 12-26-2009, 05:40 PM
Pete M
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If his is an 87, then it wouldn't have gotten the ballast resistor from the factory, but could have had it installed as customer complaint work (the resistor quiets down the fuel pump). the ballast resistor was made standard in 88. If it was installed, then I can only guess that it will be on the drivers side fender and is a whitish ceramic unit with 2 wires coming off of it.

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post #8 of 38 Old 12-29-2009, 09:39 AM Thread Starter
coastiemike
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I checked and cleaned all the ground connections, now my mj will crank but not start. I hear the fuel pump kick on but I don't get any fuel at the fuel rail.I changed out my fuel filter less than three months ago so I dont think that is the problem. Also have chattering at the relays right behind the battery sometimes as soon as I turn the key on. I am completely lost???
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post #9 of 38 Old 12-29-2009, 10:20 AM
AMCSportTruck
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If you have some rust build up in the tank it's possible to have plugged up your filter in 3Mo i have had them plug up in 3 feet . . . that suck's . . .

Now i would just to be sure, remove the line going into the filter turn the key if it shoots fuel the pump is flowing fuel. I have them run but not push fuel.

Then reinstall the line and disconnect the other side of the filter and run pump, that way your sure all is flowing below.

that gets the pump n filter tested, If all is working as it should then the issue is on the engine side, then you'll have to check thing's like fuel REG and injector or injectors . . .

I have had engines where the fuel system was flowing fuel to the Reg and to the Injection system but it wasn't spraying any fuel because there was no Electrical signal firing the injector/s. . .

test for fuel then test for Power. hope this was of some help to ya.

Mike
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post #10 of 38 Old 12-29-2009, 12:43 PM
DIVERHERB
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When you say that you have no fuel are you checking it at the test port on the fuel rail? Like has been previously stated to check at the filter and after the filter. I have had the fuel regulator clog up on several jeeps and I actually had rust make its way up into the fuel rail on a 5.9 and cause several injectors to stop spraying.
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post #11 of 38 Old 12-30-2009, 09:48 AM Thread Starter
coastiemike
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update 12/30/09

I took all the knowledge gained here and applied my own knowledge and found the following:

1. Lose connections.
2. The chattering relay was due to a lose ground wire by the oil dip stick
3. I took 1988 MJ Comanche suggestion and removed my fuel out line from my filter and turned the key on to check the output of the fuel pump/filter and had good flow(note this didn't happen until I tightened the ground wire at the dip stick.)
4. I got my MJ started and it ran as long as I rev it up ( haven't tired to drive it yet).
5.Since it was running I thought to check the alternator output at the battery and I was only getting 12.3 VDC, so this leads me to belive that my alternator is bad.

With all that said, am I on the right track or am I missing something? I would like to clean my throttle body, but is it worth it? THanks for all the help and if anyone is ever in Key West, look for the red MJ it's the only one here!!!
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post #12 of 38 Old 12-30-2009, 12:10 PM
AMCSportTruck
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The only MJ ? or the only RED MJ ?

I don't see my MJ making such a long trip . . . But then again this truck has been amazingly impressive so far so far

I would swap out that alternator get it started again and see how it dose on a test drive, bring another driver and a set of wheels just in case it stalls out and don't restart . . . i learn this the hard way a few times

Mike
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post #13 of 38 Old 12-30-2009, 12:55 PM Thread Starter
coastiemike
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both!! the only MJ period.
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post #14 of 38 Old 12-30-2009, 01:32 PM
AMCSportTruck
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There are fine little beast's ! yours should be ok just gotta get threw this little PMSing stage its got going all is going to be fine . . .

Mike
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post #15 of 38 Old 12-30-2009, 01:57 PM
DIVERHERB
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I would definitly clean the t/body and make sure you remove and clean the IAC motor. They are the cause of a lot of idling problems.
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