xj misfire cylinder 1 and multiple.
Thread Starter
Newbie
Joined: Jun 2018
Posts: 17
Likes: 0
Model: Cherokee (XJ)
xj misfire cylinder 1 and multiple.
i have a 96 cherokee and for a little bit now I’ve been getting a cel for a misfire on cylinder 1 and also multiple cylinders. Checked for spark, compression. Both seemed good. When checking operating fuel pressure it was good as well (50psi range). I decided to do another fuel pressure test today and noticed while bleeding the air out of the gauge, air continuously kept coming out. When I turned the engine off, fuel pressure dropped to 0 in less than 5 minutes. Tried clamping the fuel line (back behind the filter to isolate if it was coming from the tank or not) and it held fuel pressure a little longer but still went down to about 27 psi until I let go of the clamp and then pressure immediately dropped to 0. I’m thinking this is a check valve/pump problem. Would this really cause cylinder 1 to completely misfire though?
Senior Member
Joined: Nov 2010
Posts: 682
Likes: 134
From: Good 'ol WI
Year: 1987
Model: Cherokee
Engine: 4.0
Did you check your distributor cap and rotor? There could be crusties built up on the contacts on the underside of the cap.
Also double-check grounds (engine & body) and distributor connectors (and all other engine connectors).
Also double-check grounds (engine & body) and distributor connectors (and all other engine connectors).
Thread Starter
Newbie
Joined: Jun 2018
Posts: 17
Likes: 0
Model: Cherokee (XJ)
I did swap out the rotor, distributor cap, plugs, wires ect. Haven’t checked grounds. With the amount of air that was coming out from fuel pressure testing and the psi drop I think Im having more of a fuel problem, I just don’t know 1. If this would actually be cause this misfire/low rpm problem
2. If you have continuous air coming out while bleeding the fuel pressure gauge, could it Elbe coming from the tank or would it be a cracked fuel line or injector?
2. If you have continuous air coming out while bleeding the fuel pressure gauge, could it Elbe coming from the tank or would it be a cracked fuel line or injector?
Last edited by Xjmurr; Nov 13, 2018 at 05:34 PM.
CF Veteran
Joined: Nov 2010
Posts: 5,840
Likes: 117
From: In the middle of Minnesota!
Year: 1999
Model: Cherokee
Engine: 4.0
To confirm your codes to be sure we are all on the same page, you are getting a P0301 and a P0300? The devil is in the details with OBD codes. Post each and every one of them.
You likely do have a check valve failure within the fuel pump assembly that is shot and that is what is causing the rapid pressure drop. However, if you are holding around 50 psi while at idle and your 96 is the new style (with fuel pressure regulator on the pump inside the tank, not under the hood.....96 was a year of change for fuel systems), then it's very possible that fuel is not the root cause of your misfires. If you have a 96 with the old style fuel system, then 50 psi is too high and you need more troubleshooting; should be around 31 psi.
What exactly is your compression? Best to run it on all cylinders. The compression spec on the 4.0 is 120-150 psi, with no more than a 30 psi variation between cylinders.
Test your "ignition coil". This can be done with a meter and a manual testing for both primary and secondary resistances. You are looking for a strong, BLUE, snapping spark. Yellow/orange/white spark indicates a weak spark which can cause misfires.
You likely do have a check valve failure within the fuel pump assembly that is shot and that is what is causing the rapid pressure drop. However, if you are holding around 50 psi while at idle and your 96 is the new style (with fuel pressure regulator on the pump inside the tank, not under the hood.....96 was a year of change for fuel systems), then it's very possible that fuel is not the root cause of your misfires. If you have a 96 with the old style fuel system, then 50 psi is too high and you need more troubleshooting; should be around 31 psi.
What exactly is your compression? Best to run it on all cylinders. The compression spec on the 4.0 is 120-150 psi, with no more than a 30 psi variation between cylinders.
Test your "ignition coil". This can be done with a meter and a manual testing for both primary and secondary resistances. You are looking for a strong, BLUE, snapping spark. Yellow/orange/white spark indicates a weak spark which can cause misfires.
Last edited by tjwalker; Nov 13, 2018 at 05:55 PM.
Thread Starter
Newbie
Joined: Jun 2018
Posts: 17
Likes: 0
Model: Cherokee (XJ)
Compression was right around 120 psi for that one cylinder, probably should have the rest when I did the test, but I always can later. I did check the coil and it’s fine, even swapped for a minute with one I knew was good. Now I was only under the assumption that the fuel pressure regulator was inside the tank and I’ll have to do more research and look around for that.
CF Veteran
Joined: Nov 2010
Posts: 5,840
Likes: 117
From: In the middle of Minnesota!
Year: 1999
Model: Cherokee
Engine: 4.0
Compression was right around 120 psi for that one cylinder, probably should have the rest when I did the test, but I always can later. I did check the coil and it’s fine, even swapped for a minute with one I knew was good. Now I was only under the assumption that the fuel pressure regulator was inside the tank and I’ll have to do more research and look around for that.
Trending Topics
Thread
Thread Starter
Forum
Replies
Last Post
fonty493
Stock XJ Cherokee Tech. All XJ Non-modified/stock questions go here
17
Dec 22, 2021 05:07 PM
dave1123
Stock Grand Cherokee Tech. All ZJ/WJ/WK Non-modified/stock questions go here!
0
Jul 4, 2015 06:51 AM
Mcgorty
Stock Grand Cherokee Tech. All ZJ/WJ/WK Non-modified/stock questions go here!
7
Jan 12, 2015 06:21 PM
HudsonN
Stock XJ Cherokee Tech. All XJ Non-modified/stock questions go here
5
Aug 18, 2014 04:36 PM
super20g
Stock Grand Cherokee Tech. All ZJ/WJ/WK Non-modified/stock questions go here!
4
Apr 22, 2014 10:34 AM
Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)