TJ Engine Misfire

[keithc]

Wow, bad week for BigBird. 2000 TJ, 4.0. No engine mods other than a K&N filter. Think she has about 75K miles.

Monday on way to work, she started running rough. Check engine light and then started stalling and really knocking by the time I left work, so towed her to AutoZone. Computer said cyl #1 misfire. Got home and ripped her apart and the #1 plug was missing the electrode. Like gone, snapped off at the base. All of them were sorta brown, but the rest not eroded (25K miles and 6 years on the plugs Bosch Platinum plugs). Replaced all plugs tonight and didnt improve.

Will fire up and run smooth for 15 seconds, then start bucking. Even will run a bit (sometimes stalling), and then smooth out for another 10 seconds, then back to rough... pulled the coils rail and checked all the connections, more di-elec grease and reconnect. Nothing better.

Factory service manual doesn't really list any way to test the coil rail, but she is a $130 non returnable part at AutoZone. Hate to be wrong.

Also doesn't list a way to test the crank position sensor (those connectors also look OK).

There is of course the chance than a cylinder problem (stuck valve, etc) led to the bad plug and code, but before I tear the head off and really dig deep, I figured I would consult the oracles...

Any thoughts are appreciated. Thanks all.

-Keith

[ZAEDOCK]

Sounds like the coil for that cylinder is toast. That's my guess as to why it burned out the spark plug.

You could check compression to verify that the cylinder is OK. You already know that you have fuel. The last ingredient is spark.

See if someone here with a 2000+ TJ can stop by your house and swap coil rails to test. I'd pull the rail off my buggy and lend it to you, but it's currently at my mom's house.

[Opie]

I had a similar problem, after the plugs and coil rail were replaced - it ran for about 30 seconds, then died. Then 2 injectors were replaced - same problem, so theh mechanic put the old rail back on to start the diagnostics over again, and POOF - everything runs fine again !! Paid for the injectors & plugs, but they were nice enough to send the coil rail back for me no charge. Been fine for 6 months and counting.

[keithc]

Joe, that is exactly the thought I had... check with another known running smooth pack. Anyone close by with a 2000-02 (I think they changed in 03) 4.0 TJ? HA HA! Maybe I will just leave notes on TJ's in parking lots and see who calls me...

The working for a few seconds, not for a few seconds thing is weird. Next stop is to drain the fuel rail and take a look at the injectors too...

Ug.

[Hoodoo Man]

Joe, that is exactly the thought I had... check with another known running smooth pack. Anyone close by with a 2000-02 (I think they changed in 03) 4.0 TJ? HA HA! Maybe I will just leave notes on TJ's in parking lots and see who calls me...

The working for a few seconds, not for a few seconds thing is weird. Next stop is to drain the fuel rail and take a look at the injectors too...

Ug.

I expect there may be a few heeps in Nashua tomorrow at Udoit. come on by! mines a 97 so no joy there...

[Eve]

I have an 01 TJ 4.0, I may or may not have an issue with cyl #3 but it starts/runs no prob, cyl #1 is fine and I'll be at u-do-it tomorrow...

[keithc]

Worst part is I don't know about "Udoit". I may be that old and non-forum-ed. Sorry all.

Anyone near Springfield, MA can connect, and use our garage with air tools, etc. I got so much help for the BSJI folks back when I started, I am happy to return the favor. And at this point I have the compression check gauge, to be used in the morning to see if I am fooling myself with the problem. (BTW, I will cry so hard you will feel it on the forum if I have to rip the head apart....).

More tomorrow. Wish me luck.

[johnsxj]

It's not that bad! Heck you can even leave the manifolds bolted to the head and still pull it!

[keithc]

OK, so got through the compression testing.... but seems a bit odd relative to the FSM. Got dead on 105 on all cylinder on 3-4 trys each. Except for #5, which was consistently 85. FSM says should have 120-150? And the #5 was not the problem cylinder....

Ripped apart the fuel rail, just for ha ha's, and the #1 seems cruddy, but not damaged. So I am assuming it was giving gas and just got gummed up from not firing with the bad plug.

Back to assuming its the coil pack or CPS, but cant seem to test either of those....

Really looking at the option of borrowing a coil from a running truck to test before buying.... Anyone in the 00-02 TJ range close to Springfield, MA?