87 zj intermitent cylinder 8 misfire - JeepForum.com
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Unread 04-19-2013, 03:58 PM   #1
johnyc
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1997 ZJ 
 
Join Date: Mar 2011
Location: dieppe, NB
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87 zj intermitent cylinder 8 misfire

"edit" its a 97 my fat fingers hit the 8 by mistake oops

Hello im having a problem I cant seem to figure out with my 97 zj.
It has a 5.2L and it keeps misfiring on cylinder 8 but its always only 8.

I checked the wires plug and distributor all seem ok and are only a few months old, I did a compression test and everything seemed ok.
I also checked the injectors there ok and are only a year old I changed them last spring.

The only code im getting is cylinder 8 misfire.
What really confuses me is I changed my tps last night and reset the computer and all of a sudden it ran great problem solved all night.
Until this morning when its back and a computer reset did nothing this time.

I'm out of ideas on were to go next the fact that it comes and goes is really confusing me.
any help would be greatly appreciated, thanks.


Last edited by johnyc; 04-19-2013 at 07:19 PM..
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Unread 04-22-2013, 07:03 AM   #2
johnyc
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Well the starter died on me this weekend changing it tonight so havent been able to try anything else.
Altho I dont even know were to look next

Any sugestions from any one?
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Unread 04-22-2013, 08:32 AM   #3
ratmonkey
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Try routing the plug wires according to the dodge tsb.
That plug wire commonly cross fires by induction from overlapping wires.
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Unread 04-22-2013, 09:45 AM   #4
johnyc
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Alright il take a look at that as soon as I get home from work thanks
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Unread 04-22-2013, 07:33 PM   #5
abraham743
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1997 ZJ 
 
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Location: greenwood, indiana
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Also be sure and check your coil wire. I had a 5.9 ram with the same issue when I checked cylinder 8 it always had spark. So I used a spark tester attached to cylinder 8 wire and started the engine about every 4 revolutions there would be no spark. It was the coil wire I have no explanation for why it only missed on #8 but I did find where the coil wire was arcing.
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Unread 04-23-2013, 07:07 AM   #6
johnyc
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I made sure the wires were aranged the way they should be and still the same thing I looked at it running in the dark and couldent see any spark but I never really looked at the coil wire very close il take a look at that one next
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Unread 04-23-2013, 07:41 AM   #7
johnyc
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I was also just thinking about when it started doing this.
It was right right after the relay for the starter died on me in the box under the hood, I replaced it with the one for the intermitent wipers and havent put a new one in yet.

I dont see how it would but could that posibly affect anything?
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Unread 04-24-2013, 06:09 PM   #8
johnyc
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so after a hole lot of playing around with it i decided to do another compression test for the hell of it. this time i got right around 90 psi per cylinder, that seems low to me what should it normally be at 120 ish?
i still cant find any arcing anywhere after checking everything multiple times, the injector is still firing just fine as well. i did how ever pull out a few plugs and check them by grounding them and looking at the spark. none were skipping that i could see but the spark did look rather dim on all of them, could a weak coil cause a misfire in only one cylinder tho?
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Unread 04-24-2013, 07:20 PM   #9
SpenceAK
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If its intermittent its gonna be hard to find this is where a labscope would come in handy ( intermittent issue with cam or crank sensor) I'd put a Noid light on inj. 8 harness let it run watch for a glitch same with cyl. 8 plug wire put a spark tester on it watch for a glitch. Also make sure the inj is actually squirting there's is a inj. Tester that lights up with mechanical pulses waekon makes one.
When doing these test's I'd put a load on the engine, have a friend brake torque it. Do you have access to a scanner?
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Unread 04-24-2013, 07:24 PM   #10
ratmonkey
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Compression should be above 130, 165 is near new. Anything lower than 120 is cause for a rebuild. Below 90 is not enough to combust the air fuel charge properly.

Are you sure you did the test right?
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Unread 04-25-2013, 06:16 AM   #11
johnyc
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I have a tester for the plug wires I couldent find a skip in any of them was a nice steady pulse if not kind of a dim one, same from the plug.
The end of the plug is covered in fuel so the injector must be firing, but il see if I can get it tested just to see.

I thought those compresion tests I did were off il try again tonight my tester has a long rubber tube on it that screws into were the plugs go but im having a hard time geting it on very good with the metal tubes over the plugs on there.
Any advice for making sure its on there good? Or just try to get it as good as I can.
I can only get it on I cant get it turned in tight at all right now

Last edited by johnyc; 04-25-2013 at 07:04 AM..
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Unread 04-25-2013, 01:05 PM   #12
johnyc
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This vehicle is my dd and all I have at the moment so I still need to drive it to work every day could i unplug the injector just to go to work and such so its not washing down the cylinder?
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