98 ZJ Intermittent Misfire - Page 2 - JeepForum.com
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post #16 of 20 Old 11-18-2018, 06:42 PM
RedRiverT
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1997 ZJ 
 
Join Date: Nov 2014
Posts: 678
Quote:
Originally Posted by GOLDWING View Post
OP stated that he gained 20 psi by adding a cap full of oil to the cylinder which indicates rings losing compression not valves.

GW
He said he did that on Cylinder 4. He apparently didn't check compression on the other 5, which would likely all do the same thing.

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post #17 of 20 Old 11-18-2018, 10:22 PM Thread Starter
dotahoe
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1998 ZJ 
 
Join Date: Jul 2016
Location: Nashville
Posts: 24
Quote:
Originally Posted by RedRiverT View Post
He said he did that on Cylinder 4. He apparently didn't check compression on the other 5, which would likely all do the same thing.
I checked compression on 3 and 5 too both where 130-135. Didn't really see the need to check further due to me already knowing which cylinder I have the misfire on.
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post #18 of 20 Old 11-21-2018, 01:47 AM Thread Starter
dotahoe
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1998 ZJ 
 
Join Date: Jul 2016
Location: Nashville
Posts: 24
I preformed a block test today and it passed. I'm going to verify proper timing again and if it is bad i'll adjust it/replace worn parts and if its ok i'm going to send the heads off for pressure testing. One of the techs in my shop told me what he is hearing is a premature ignition causing the misfire but that it is strange that it only does it consistently under load and at 2k rpm. Checked the wave form data of the O2 sensors and the Crankshaft and Cam sensor. Everything seems to be operating correctly signal wise.
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post #19 of 20 Old 12-08-2018, 03:05 AM Thread Starter
dotahoe
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1998 ZJ 
 
Join Date: Jul 2016
Location: Nashville
Posts: 24
TPS was fried. Swapped it with one of my friends and the misfire went away. It was still sluggish after swapping the tps so i swapped my fuel pump relay with a/c clutch relay and it started running fine after that. Due to it being at my work and having a bad battery after all the testing i have to wait til the morning to give it a good road test and call it fixed but we will see.
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post #20 of 20 Old 12-08-2018, 05:56 PM Thread Starter
dotahoe
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1998 ZJ 
 
Join Date: Jul 2016
Location: Nashville
Posts: 24
When I road tested it today it was feeling very sluggish around 50 mph. I decided to drop the tank and lo and behold I found the issue. The lock ring had popped off of the fuel pump and the pump was just sitting there in the tank sideways. I took it out and dumped the fuel out of it and of course found a bit of water inside my gas tank. I ordered and new lock ring on amazon and an new Bosch fuel pump parts will be in Wednesday.
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carbon build up , diagnose , intermittent , misfire

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