Misfires, A Ghost Story.

[JJacobs]

Might be worth making sure the trans is torqued to the block properly with both dowel pins in place. Movement there will certainly affect the CPS's reading. I've seen that manifested as rough running only in reverse but it could be this problem as well- worth a quick check.

 

[xjgrn]

This is getting interesting, I too have a 96, and its throwing the same missfire code, PO300, and 302. Changed the cap and rotor, then put Champion plugs back in, and had those Bosch 4 prong plugs. The codes stopped for a little bit, then came back. Tomorrow I'll try some plug wires.Whatever I find, I'll post it

 

[xjgrn]

Ok, there was a service bulliten about this misfire thing. Appearently it just may be one can of mopar combustion clearner, and 12 valve springs. With any luck, you can get a copy of this from your favorite Jeep dealer, and either give it to your mechanic, or do it at home. Either way, this has been going on since '96 in the Xj, Zj, andTj. Its nice to know we're not alone!

 

[combatcow]

its a blown head gasket, take it apart take a look if one cylinder is different looking (usually cleaner) that is you problem

 

[gradon]

It's an unsync'd cam position sensor. I sync'd mine up a few weeks ago and no more p1391 misfire code. Read:
http://motorage.search-autoparts.co...estandard//motorage/292005/169830/article.pdf
to learn sync procedure.

 

[birchlakeXJ]

This is a tough one. Random misfires can be indicative of a "lean" condition. One area to suspect would be a vacum leak at the intake manifold? Vacuum testing and exhaust gas analysis may be of value here......

 

[jtdesigns]

Any updates on the condition of these 96's???????????

 

[Camo-5]

Ok folks, I'm jumping on this thread now. I had the same issues at Nixt (and others it sounds) last summer, but I thought I solved them by replacing / cleaning one of the many things Nixt tried. Low and behold, she started acting up again this weekend after over 6,000 miles with no issues! Bucks and misses like crazy but not at start up. Only after about 3-4 minutes of running. I also noticed a loud 'sucking' sound coming from the air intake box (actually have an Airraid tube). When the rpms are held around 2000, the engine actually pulsates and surges around 500 rpms (from 1500 to 2000). At lower rpms, it bucks and pops out the air box until the rpms get up then the bucking stops but it still is not running 'smooth'.

Here are a couple thoughts and ideas that I'm going to try. Any thoughts on these?Maybe all of us with this issue may stumble upon a connection and figure it out!

-clog in the fuel line / tank / fuel pump? can't imagine it's a bad pump since I didn't have an issue for over 6K miles
-bad / clogged injector
-I sure hope not, but a computer issue?
-how about something to do with the temp sensor? My temp doesn't act normal. I get huge, quick movement in the needle. It never overheats but will jump from 120 to 210 in about 3 seconds. Maybe this is throwing something off. I'm not exactly how the chokes work on these later model engines.

I do notice after I have this issue, the metal tab on the rotor is highly fouled. Does this give anyone a hint?

Thanks! I hope we get to the bottom of this!

 

[jtdesigns]

Ok folks, I'm jumping on this thread now. I had the same issues at Nixt (and others it sounds) last summer, but I thought I solved them by replacing / cleaning one of the many things Nixt tried. Low and behold, she started acting up again this weekend after over 6,000 miles with no issues! Bucks and misses like crazy but not at start up. Only after about 3-4 minutes of running. I also noticed a loud 'sucking' sound coming from the air intake box (actually have an Airraid tube). When the rpms are held around 2000, the engine actually pulsates and surges around 500 rpms (from 1500 to 2000). At lower rpms, it bucks and pops out the air box until the rpms get up then the bucking stops but it still is not running 'smooth'.

Here are a couple thoughts and ideas that I'm going to try. Any thoughts on these?Maybe all of us with this issue may stumble upon a connection and figure it out!

-clog in the fuel line / tank / fuel pump? can't imagine it's a bad pump since I didn't have an issue for over 6K miles
-bad / clogged injector
-I sure hope not, but a computer issue?
-how about something to do with the temp sensor? My temp doesn't act normal. I get huge, quick movement in the needle. It never overheats but will jump from 120 to 210 in about 3 seconds. Maybe this is throwing something off. I'm not exactly how the chokes work on these later model engines.

I do notice after I have this issue, the metal tab on the rotor is highly fouled. Does this give anyone a hint?

Thanks! I hope we get to the bottom of this!

I just went through the exact same thing with my Renix MJ.. I changed all the injectors to the Ford 19# and was still running rough.. I found the problem in the fuel tank.. There's a 90* hose on the MJ fuel pump that had popped off.. You should try to get a fuel pressure reading, and flow rate.
My thought was the hose was still providing a small amount of pressure , but as soon as the engine needed the extra fuel it would starve until the rpm's went up.