2002 liberty tune up

[mark sr]

My stepson's liberty all of a sudden started running rough and the check engine light came on. It threw 2 codes [I forget the numbers :redface:] that indicated a misfire on #4 and coil issue on #4. So I plan to tune it up for him and possibly replace one coil. I've never worked on an engine set up like this. Is it as simple as removing the little coil from the top of the plug and then replacing the plug? I hope to swap out the #4 coil with a plug that is easier to get to and then see how it runs and if the light goes out.

 

[JPNinPA]

Not sure on the liberty but the tj has a coil rail. You replace the entire rail.
And yes it is plug and play whether rail or individual. Start with inspecting the wires and that the coil is plugged into the harness and on the plug. Be sure the boot on the coil that goes over the plug is not missing or cracked.

 

[mark sr]

It appears to have individual coils over top of each plug ..... took me awhile to figure out where the plugs were as I was looking on the side of the block and expecting to see ignition wires. It looks like it will be fairly easy to do once I remove the coolant jug. I'll know more after I get back from the parts store.

 

[mark sr]

I changed out the plugs and swapped the coil but it still idles rough. Assuming disconnecting the battery reset the codes, it still flashes P 0354 [it no longer shows P 0304] which indicates a #4 coil not working properly. I assume that means it must be in the wiring somewhere but I'm somewhat at a loss on how to track that part down. The connection appears to be ok.

 

[mark sr]

Did poorly on a test drive and now throws multiple codes
P0351 - #1 ign coil
P0354 - #4 ign coil
P0300 - multiple misfire
P0301 - #1 misfire
P0304 - #4 misfire
P1299 - vacuum leak

I had swapped the coil on #1 & #4 so why are both of them now not working correctly?
While working on it I noticed a disconnected vacuum line that I reconnected and now [not before] it shows a leak code ??
It's dark and I'm too tired/aggravated but I guess I dive back into it tomorrow.

 

[JPNinPA]

Ok it's strange you have two bad coils at the same time with the 1299 code. A few preventative maintenance items. Check your battery voltage. Even get it load tested. Clean terminals and connectors. Also clean the opposite end of the power and ground cables where they meet the engine and body. Press on the connectors to the PCM. I believe if you disconnect the PCM connectors the battery should be disconnected to avoid damage. Consider replacing the CPK ( crank position sensor) with a factory replacement. Anytime you replace a sensor use OEM parts. Others will cause issues.

Verify connections to the tps, IAC and map sensors.

 

[mark sr]

What is strange about 2 bad coils with the 1299 code?
I think the first thing I'll do is swap the 2 coils back. The #1 coil was good when it was on the #1 cylinder. Could swapping it have made it fail??

 

[JPNinPA]

What is strange is two failing at the same time is unlikely. And looking up the rare P1299 code and it's possible causes sounds more like a power, ground, connection issue.

You could swap it back or swap with others.

 

[mark sr]

OK, I swapped the coils back, disconnected the battery [cleaned terminals] and now it's only flashing the P0354 code. So i guess I'll buy a new coil for #4 and see what happens. What doesn't make sense to me is swapping the coils originally caused a misfire with #1 but didn't fix #4

I miss the old flathead fords - they were simple to work on!

 

[JPNinPA]

If you continue to get erratic codes finish the cleaning and checking I mentioned and invest in a new CKP.

 

[JPNinPA]

Ps what brand and part number plugs are you using? Inspect #4 coil wiring.

 

[mark sr]

I used Bosch iridium plugs. I'd have to go out to the shop to find the number although it's what AutoZone's computer listed for that engine.
I'm about convinced it has to be in the wiring to the #4 cylinder although I'm not sure what it will take to trace it down or find the bad connection or short.

My wife goes back to work tomorrow and says I've spent too much time on her son's jeep and not enough on her while she was off so I guess I'll have to put his jeep on hold until tomorrow. Nobody's in a rush since he has her car, she has my jeep and I get stuck with my 11 mpg truck.

 

[cougarlasch]

ive put bosch plugs into 3.7 and 4.7 with bad results. causing random misfire codes. i believe original in 3.7 is ngk.

 

[mark sr]

I've had good results with different Bosch plugs for years [that's the main reason I picked that brand] The plugs I pulled out were NGKs. At $45 a set I'm not inclined to swap them out again. I can't help but think the issue is with the wiring or connection somewhere leading to the #4 coil.

 

[JPNinPA]

Autolite and Champion iridium plugs seem to work best in jeeps compared to Bosch. The Bosch plugs I purchased had insulator all the way to the top with minimal wire electrode exposed. For me they did result in low mpg and rough idle.

Again if the issue shows erratically continue with the maintenance andCPK

 

[JPNinPA]

Any luck yet?

 

[mark sr]

I've been sick the last few days, that and the rain hasn't helped any either.

 

[mark sr]

My oldest son came up to help today and we've tentatively narrowed it down to either a short in the wire or computer. My son's friend has agreed to come over tomorrow afternoon and see if he can verify and help get it fixed.

 

[cougarlasch]

have you verified if there is spark by unbolting the coil and slowly lifting up on the coil while the engine is running to see or hear the ticking of spark. and if there is did you check with a noid lite to see if you are getting injector pulse.

 

[mark sr]

No, I haven't lifted the coil off of the plug while it's running .... was a little unsure about doing that as this is the first time I've ever dealt with a coil over plug set up. My son said the injector is working but thought it should have automatically shut down if the coil is working ??