Critique my diagnostics. Coil rail?
Thread Starter
Member
Joined: Aug 2015
Posts: 183
Likes: 2
From: Florida
Year: 2001
Model: Cherokee
Engine: 4.0
Critique my diagnostics. Coil rail?
Hi all,
While charging the AC today the 4.0 started running like it had a dead cyl.
Pulled individual injector wires and cyl #2 made no change whatsoever while all others made a very noticeable difference.
Swapped injector 1 and 2 with each other. I also turned the engine over while rail was out - both injectors sent fuel.
Reinstalled rail and same result, cyl #2.
On to compression test - Did a couple runs with about 5 seconds of turning over - 120 and 150 psi.
Then onto trying to check spark with the COP.
I tried my best to ground plugs 1 and 2, I could see 1 sparking but not 2. Swapped them, same result.
From my understanding, 1 and 2 share the same coil. If so, how can 1 work but not number 2?
While charging the AC today the 4.0 started running like it had a dead cyl.
Pulled individual injector wires and cyl #2 made no change whatsoever while all others made a very noticeable difference.
Swapped injector 1 and 2 with each other. I also turned the engine over while rail was out - both injectors sent fuel.
Reinstalled rail and same result, cyl #2.
On to compression test - Did a couple runs with about 5 seconds of turning over - 120 and 150 psi.
Then onto trying to check spark with the COP.
I tried my best to ground plugs 1 and 2, I could see 1 sparking but not 2. Swapped them, same result.
From my understanding, 1 and 2 share the same coil. If so, how can 1 work but not number 2?
CF Veteran
Joined: Jan 2017
Posts: 3,402
Likes: 394
From: Connecticut
Year: 2000
Model: Cherokee (XJ)
Engine: 4.0
Thread Starter
Member
Joined: Aug 2015
Posts: 183
Likes: 2
From: Florida
Year: 2001
Model: Cherokee
Engine: 4.0
CF Veteran
Joined: Jan 2017
Posts: 3,402
Likes: 394
From: Connecticut
Year: 2000
Model: Cherokee (XJ)
Engine: 4.0
Old fart with a wrench
Joined: Nov 2010
Posts: 14,398
Likes: 740
From: Manlius, east of Syracuse, NY
Year: 2000 XJ Sport & WJ Laredo
Model: Grand Cherokee (WJ)
Engine: 4.0L
How do the plug boots and springs look? The boots can carbon-trail inside and cause a misfire. I would advise you NOT to check spark unless you have plugs in ALL 6 boots and grounded, otherwise the voltage can back up and short coils internally. I'm seriously planning on going to a Dodge 3.8 V6 coil and plug wires. You can check out a complete kit from ksuspension.com
CF Veteran
Joined: Jan 2017
Posts: 3,402
Likes: 394
From: Connecticut
Year: 2000
Model: Cherokee (XJ)
Engine: 4.0
Because 2000+ post-cat O2 sensors actually do something other than just monitor the condition of the cats:
Downstream Sensors (California Emissions): Two downstream sensors are used (1/2 and 2/2). The downstream sensors are located in the exhaust downpipes just after the mini-catalytic convertors. The downstream is also used to determine the correct air fuel ratio. As the oxygen content changes at the downstream the PCM calculates how much air fuel ratio change is required. The PCM then looks at the upstream oxygen sensor voltage and changes fuel delivery until the upstream sensor voltage changes enough to correct the downstream sensor voltage (oxygen content). The downstream oxygen sensors also provide an input to determine mini-catalyst efficiency.
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Thread Starter
Member
Joined: Aug 2015
Posts: 183
Likes: 2
From: Florida
Year: 2001
Model: Cherokee
Engine: 4.0
How do the plug boots and springs look? The boots can carbon-trail inside and cause a misfire. I would advise you NOT to check spark unless you have plugs in ALL 6 boots and grounded, otherwise the voltage can back up and short coils internally. I'm seriously planning on going to a Dodge 3.8 V6 coil and plug wires. You can check out a complete kit from ksuspension.com
Springs looked great as well as the boots.
Again tho, Ive had it like this for at least 4 years. This recent issue is just that, recent.
CF Veteran
Joined: Jan 2017
Posts: 3,402
Likes: 394
From: Connecticut
Year: 2000
Model: Cherokee (XJ)
Engine: 4.0
Thread Starter
Member
Joined: Aug 2015
Posts: 183
Likes: 2
From: Florida
Year: 2001
Model: Cherokee
Engine: 4.0
As soon as I pull the injector lead the engine stumbles really bad.
Luckily my brother has a 02 WJ so Im going to borrow his coil pack for a day.
Just a matter of getting over to him.
Thread Starter
Member
Joined: Aug 2015
Posts: 183
Likes: 2
From: Florida
Year: 2001
Model: Cherokee
Engine: 4.0
The WJ ran like poo with my coil.
So i...
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