GC ZJ 5.9 misfire - JeepForum.com
 2Likes
Reply
 
LinkBack Thread Tools
post #1 of 18 Old 07-08-2020, 04:36 PM Thread Starter
pelle2
Registered User
1998 ZJ 
 
Join Date: Jul 2020
Location: Sweden
Posts: 15
GC ZJ 5.9 misfire

My 5.9 runs really bad, and it feels like it's misfiring or not running on all cylinders. The problem has gotten gradually worse, and now I don't want to drive it longer than ~1 km for testing due to the jerky behavior of the engine. The problem appears to worsen after the first few minutes of driving. Indication of heat being involved?

In addition to all oils/filters and serpentine belt (and other stuff unrelated to the engine), I've replaced:

All spark plugs, multiple times
All spark plug wires
Distributor cap
Distributor rotor
Ignition coil
Throttle position sensor
Camshaft position sensor
Thermostat
PCV-valve + grommet
Both oxygen sensors (Kolak)
Battery
Crankshaft position sensor

Hughes engines plenum kit installed

Cylinder heads have been replaced by previous owner in 2008

The jeep has ~240000 km on it (~150000 miles)
No major oil or coolant leaks
Trans appears to be in great condition

Feels like I've replaced most things that could be the problem. I don't think it's the fuel pump or filter since it doesn't run any worse if I give it some gas.
I really thought it was the CPS, but replacing it had absolutely no effect despite the fact that the old sensor had cables where the plastic isolators had melted and visible leads.

Any ideas what to try next? Feels like a waste since the car is in pretty good condition except for this weird behavior.

pelle2 is offline  
Sponsored Links
Advertisement
 
post #2 of 18 Old 07-08-2020, 05:22 PM
hilljacknm
Registered User
1996 ZJ 
 
Join Date: Nov 2019
Location: Albuquerque
Posts: 54
Garage
Double check the spark plug wires are in the correct firing order.

Was the engine running poorly before changing all the parts?

1996 ZJ 5.2
Doug Thorley Headers, Kolak exhaust

BFG KM3 30x9.50"
hilljacknm is offline  
post #3 of 18 Old 07-08-2020, 11:28 PM
Timo_90xj
Web Wheeler
 
Timo_90xj's Avatar
1998 ZJ 
 
Join Date: Mar 2006
Location: Helsinki, Finland - on the European side of the Atlantic
Posts: 10,520
How is the fuel pressure? It needs to be within specification and steady.

If you have a code reader/ scanner that shows live data, it helps a TON in diagnosing issues like this. You want to at least look at upstream O2- sensor readings, coolant and intake temp readings, spark timing, throttle position, manifold pressure.
It'd be even better if you can datalog to see what is happening/ causing the issue.

All the wire harnesses in good condition, no damaged/ melted insulators on wires?

1998 Grand Cherokee 5.9 LX daily driver, 1.75" BB, 32" KM2s, HPD30 Eaton e-locker/D44a stock LSD, 4.56 gears, custom- fabbed tube bumpers and tube fenders,...


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.



1990 XJ Limited (4-door), 4.0 I6, AW4, NP242, ***rolled and totalled @ 165k miles***

***Under construction***
1990 XJ (4-door), 4.0 I6, AW4, NP242, PBR 42" tires, Unimog 404 portal axles, 110" WB, full cage + uniframe completely rebuilt, front 3-link + panhard / double triangulated 4-link rear,... ***SOLD***
Timo_90xj is offline  
 
post #4 of 18 Old 07-09-2020, 03:28 AM Thread Starter
pelle2
Registered User
1998 ZJ 
 
Join Date: Jul 2020
Location: Sweden
Posts: 15
Quote:
Originally Posted by hilljacknm View Post
Double check the spark plug wires are in the correct firing order.
Done, they are!

Quote:
Originally Posted by hilljacknm View Post
Was the engine running poorly before changing all the parts?
Some of the parts were changed some years ago before it started running this bad. The Cam/crankshaft sensors, coil and battery were replaced after it got really bad. It's been a gradual increase of these symptoms the last ~2 years or so. In the beginning, it only started jerking after about 15-20 minutes into the drive, now it can be felt even on idle, but gets worse after a couple of minutes already.

Quote:
Originally Posted by Timo_90xj View Post
How is the fuel pressure? It needs to be within specification and steady.
Unknown, I don't have the tools/experience to check it. It feels more like it's an issue with the ignition system itself rather than shortage of fuel. But that's just a hunch so not much worth.

Quote:
Originally Posted by Timo_90xj View Post
If you have a code reader/ scanner that shows live data, it helps a TON in diagnosing issues like this. You want to at least look at upstream O2- sensor readings, coolant and intake temp readings, spark timing, throttle position, manifold pressure.
It'd be even better if you can datalog to see what is happening/ causing the issue.
I have an OBDII-reader for use with my phone, I guess that's not the kind of reader you mean, but I'll try to log as much data as possible and take it for a short ride again today. The problem with the OBDII-reader seems to be that the bus speed is so slow in the jeep that it can't really log quick voltage changes for the O2-sensors for example.

Quote:
Originally Posted by Timo_90xj View Post
All the wire harnesses in good condition, no damaged/ melted insulators on wires?
There's a lot of them, but as far as I've been able to see, no damage on any of them. I'll check again.
pelle2 is offline  
post #5 of 18 Old 07-09-2020, 04:52 AM
V8GCZJ
Registered User
 
Join Date: Sep 2018
Posts: 572
Quote:
All spark plugs, multiple times
Brand/type?
Quote:
Distributor cap
Aluminum or brass(oem style) inserts?
What brand sensors (especially the cps)? How bad was the plenum gasket? If it was real bad it can clog up the cat. Does it act up more under acceleration?
V8GCZJ is offline  
post #6 of 18 Old 07-09-2020, 08:50 AM Thread Starter
pelle2
Registered User
1998 ZJ 
 
Join Date: Jul 2020
Location: Sweden
Posts: 15
Quote:
Originally Posted by V8GCZJ View Post
Brand/type?
Champion, called "436-2" at the dealer. Copper electrode.

Quote:
Originally Posted by V8GCZJ View Post
Aluminum or brass(oem style) inserts?
That's a good question, I don't remember. It might have been this one: https://www.amazon.com/Standard-Moto.../dp/B000C7Y4AI

Quote:
Originally Posted by V8GCZJ View Post
What brand sensors (especially the cps)? How bad was the plenum gasket? If it was real bad it can clog up the cat. Does it act up more under acceleration?
The CPS was Mopar, the other sensors probably Standard Motor or some other aftermarket brand.

I mean, it feels worse when accelerating, but that might just be because there's more revolutions and more power being put through = more violent vibrations. When the problem was less pronounced, accelerating didn't seem to make it worse.

Plenum looked like this:


Bad?
pelle2 is offline  
post #7 of 18 Old 07-09-2020, 09:17 AM
jtec
Web Wheeler
 
jtec's Avatar
2014 JK Wrangler 
 
Join Date: Oct 2017
Posts: 8,445
any chance you have looked for DTC codes?
1998 is OBDII so the app should be able to read the DATA, more likely a app/scanner issue than the jeep's system for limited DATA.

Do you have a vacuum gauge?
have you done a compression test?

'quickly' removing plug wire can you ID which cyls are misfiring- Which ones do not make a difference when removed.

Have you trouble shot for an exhaust restriction?

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
jtec is offline  
post #8 of 18 Old 07-10-2020, 08:23 AM Thread Starter
pelle2
Registered User
1998 ZJ 
 
Join Date: Jul 2020
Location: Sweden
Posts: 15
Triple checked the spark plug wires and discovered that one of them was slightly off the connector at the distributor cap. Now the car runs without misfires! There's a very very small jerking behavior intermittently when driving, but that might be completely unrelated to the original problem.

I'm guessing that the CPS replacement fixed the original problem, and that I managed to push the cable out of it's connector slightly when installing the sensor.

Gonna run some strong fuel system cleaning stuff through the system now in case there's been carbon buildup while it was running like crap. Ordered a "Autel Diaglink OBDII Code Reader(DIY Version of MD802)" before discovering the wire. But I guess that will come in handy when the car breaks down again in a week or two..



Thanks for all the help!
hilljacknm likes this.
pelle2 is offline  
post #9 of 18 Old 07-10-2020, 10:08 AM
Timo_90xj
Web Wheeler
 
Timo_90xj's Avatar
1998 ZJ 
 
Join Date: Mar 2006
Location: Helsinki, Finland - on the European side of the Atlantic
Posts: 10,520
Quote:
Originally Posted by pelle2 View Post
Gonna run some strong fuel system cleaning stuff through the system now in case there's been carbon buildup while it was running like crap.

Run a gas mixture of ~50/50 of E85 and 95E10. Might be a bit sluggish to fire up, but that will dissolve some of the crap off the engine. Run the engine at highway speeds on 3rd for 20-30 minutes, it'll burn some of the carbon buildup away.

Then just fill up as usual with 95E10.
pelle2 likes this.

1998 Grand Cherokee 5.9 LX daily driver, 1.75" BB, 32" KM2s, HPD30 Eaton e-locker/D44a stock LSD, 4.56 gears, custom- fabbed tube bumpers and tube fenders,...


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.



1990 XJ Limited (4-door), 4.0 I6, AW4, NP242, ***rolled and totalled @ 165k miles***

***Under construction***
1990 XJ (4-door), 4.0 I6, AW4, NP242, PBR 42" tires, Unimog 404 portal axles, 110" WB, full cage + uniframe completely rebuilt, front 3-link + panhard / double triangulated 4-link rear,... ***SOLD***
Timo_90xj is offline  
post #10 of 18 Old 07-11-2020, 09:57 AM
V8GCZJ
Registered User
 
Join Date: Sep 2018
Posts: 572
Quote:
Plenum looked like this:


Bad?
Was referring to the gasket fix...
http://www.hughesengines.com/Index/p...p?partid=27091
By all the oil on the plate i would say it's bad!
V8GCZJ is offline  
post #11 of 18 Old 07-13-2020, 08:07 AM
LordHobbit
Registered User
 
LordHobbit's Avatar
1993 ZJ 
 
Join Date: Aug 2009
Location: Utah
Posts: 2,614
Get a couple cans of Mopar Combustion Chamber Cleaner (CCC) from the dealer. Follow the directions on the can. If the first one produces a lot of smoke, run the second can.

93 red ZJ 196k 4.0. Spent more money than I should have ...
LordHobbit is offline  
post #12 of 18 Old 07-13-2020, 10:35 AM Thread Starter
pelle2
Registered User
1998 ZJ 
 
Join Date: Jul 2020
Location: Sweden
Posts: 15
Quote:
Originally Posted by LordHobbit View Post
Get a couple cans of Mopar Combustion Chamber Cleaner (CCC) from the dealer. Follow the directions on the can. If the first one produces a lot of smoke, run the second can.
I've tried to get those in Sweden, doesn't seem to be available and Amazon wouldn't send it, or if it was an ebay seller..
pelle2 is offline  
post #13 of 18 Old 07-13-2020, 10:42 AM
Timo_90xj
Web Wheeler
 
Timo_90xj's Avatar
1998 ZJ 
 
Join Date: Mar 2006
Location: Helsinki, Finland - on the European side of the Atlantic
Posts: 10,520
Quote:
Originally Posted by pelle2 View Post
I've tried to get those in Sweden, doesn't seem to be available and Amazon wouldn't send it, or if it was an ebay seller..
Probably the same reason certain engine paints etc. aren't sold here - they are forbidden in EU countries for at least non-professional use.

1998 Grand Cherokee 5.9 LX daily driver, 1.75" BB, 32" KM2s, HPD30 Eaton e-locker/D44a stock LSD, 4.56 gears, custom- fabbed tube bumpers and tube fenders,...


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.



1990 XJ Limited (4-door), 4.0 I6, AW4, NP242, ***rolled and totalled @ 165k miles***

***Under construction***
1990 XJ (4-door), 4.0 I6, AW4, NP242, PBR 42" tires, Unimog 404 portal axles, 110" WB, full cage + uniframe completely rebuilt, front 3-link + panhard / double triangulated 4-link rear,... ***SOLD***
Timo_90xj is offline  
post #14 of 18 Old 07-15-2020, 08:05 AM Thread Starter
pelle2
Registered User
1998 ZJ 
 
Join Date: Jul 2020
Location: Sweden
Posts: 15
Ok, so the misfire is still definitely there. Gets worse after the first few minutes it appears. It's like it's missing intermittently.

After I changed the crankshaft position sensor (as well as the camshaft position sensor earlier), I deleted the fault code for the CPS. It's back again, I guess meaning that the problem isn't fixed?

pelle2 is offline  
post #15 of 18 Old 07-27-2020, 07:46 AM
Philippsen
Registered User
 
Join Date: Aug 2019
Posts: 10
It seems like CPS... But you have it changed...
Philippsen is offline  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the JeepForum.com forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid e-mail address for yourself.



Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome