1993 Jeep zj running on three cylinders. - JeepForum.com
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Unread 10-25-2014, 10:23 PM   #1
dockrat100
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1993 Jeep zj running on three cylinders.

I just bought a 1993 Jeep ZJ a few months ago, and immediately had a head gasket job done, and the cps sensor replaced. Last week, Jeep was running fine, I shut it off for 5 minutes, and upon restart it was running terribly with a really bad miss. I limped it home and in the days since, have replaced: cap and rotor, plugs, wires, and still it runs terrible.

Unplugging the fuel injectors for 4-5-6 does not change how it runs.

I have spark on all cylinders. Sometimes when starting, I get no spark while cranking, but if I turn the key off, then try again it will usually start.

Injectors ohm good, and are getting power.

Fuel pressure is 35 lbs.

ECM? Distributor pickup coil? Plugged injectors? Ebola?

Any ideas would be appreciated.

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Unread 10-26-2014, 06:47 AM   #2
ZeeJay1997
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Originally Posted by dockrat100 View Post
Ebola?
that's probably a good diagnosis. wait three weeks and see.

maybe someone put something in your gas tank?
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Unread 10-26-2014, 06:58 AM   #3
daverode1
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Definitely ebola. ****s a jeeps worst nightmare. Check your oil sender. It should be right above your distributer cap. If not did you crack the block? I had one with the same problem and replacing these fixed it
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Unread 10-26-2014, 07:09 AM   #4
jay-h
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I'm thinking wiring harness. Three cylinders in a row, you tested the injectors for resistance but did you actually confirm that they are spraying?
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Unread 10-26-2014, 07:49 AM   #5
dockrat100
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Can't picture what the oil sender would have to do with it, but I'll look into it.

I intend to pull the fuel rail and test the injectors this afternoon.
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Unread 10-26-2014, 07:58 AM   #6
MrShaft696
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Quote:
Originally Posted by dockrat100
Can't picture what the oil sender would have to do with it, but I'll look into it. I intend to pull the fuel rail and test the injectors this afternoon.
I would start with a compression test before throwing any more parts at it
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Unread 10-26-2014, 08:06 AM   #7
Uniblurb
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Plug wires all installed back correctly when cap was replaced? Mopar crank sensor installed or a possible failing aftermarket one? Grounds all clean/good?
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Unread 10-26-2014, 08:07 AM   #8
ZeeJay1997
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seems like if it were a harness problem, the pcm would be griping about it
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Unread 10-26-2014, 08:10 AM   #9
newfieZJ
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Since you just had recent engine work , I'd look over all the vacuum lines . I check the rotor button was seated properly , not damaged , and no moisture was under the cap , at which point , I would also check for cracks .

No mention of a check engine light ? It would be nice to know if the PCM has stored and codes . Within 3-5 secs , turn the key to on , off , on , off , and then leave it on . A series of codes will flash via the check engine light by blinking . blink..blink.........blink , would be 21 for example . Series will end by flashing code 55 (end of sequence), and in most cases , start with 12 (battery disconnect last 50 starts). Let us know if anything shows up .
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Unread 10-26-2014, 08:19 AM   #10
AVR2
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Quote:
Originally Posted by ZeeJay1997 View Post
seems like if it were a harness problem, the pcm would be griping about it
Yes, if the PCM on a 93-95 ZJ decides that one or more of the injectors aren't responding, it will throw a code 27. This happened to mine entirely spontaneously. I used a stethoscope to confirm that two of the injectors weren't firing (OBD1 isn't clever enough to tell you which injectors have the problem).

Before I did anything else I decided to clean the contacts in the injector harness and on the injectors themselves, and that fixed it. The weird thing was that I hadn't gone near the injectors up till then, and two of them suddenly went down at the same time with the same problem.
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Unread 10-26-2014, 09:25 AM   #11
dockrat100
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Wires have been double checked to be installed correctly, I cannot find a vacuum leak, and the computer shows no codes.
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Unread 10-26-2014, 09:32 AM   #12
dockrat100
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Crank sensor is aftermarket, but my understanding is that when those fail, they typically have no spark at all?
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Unread 10-26-2014, 09:51 AM   #13
ZeeJay1997
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Quote:
Originally Posted by dockrat100 View Post
they typically have no spark at all?
not the case. they can mimic a bad secondary ignition system. it's not common, but they can cause random or specific cylinder misfires. there have been a couple of cases where the tip wss damaged and caused this type failure.
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Unread 10-26-2014, 09:53 AM   #14
dockrat100
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I may replace it then, if they will warranty it out.
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Unread 10-26-2014, 10:02 AM   #15
ZeeJay1997
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there are some crap aftermarket parts out there. but, i havent bought into the mopar hype that goes on this forum. anything you get is going to made by someone who brands several different iterations of quality control. then you have the markups. I've been running a sorenson crank sensor i got at NAPA for years without a problem. it wasnt as cheap as the cheapest, but not as expensive as mopar.
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