1997 XJ 4.0 Misfire Problems

[YJeXtreme]

My XJ has started having a slight miss recently... Yesterday CEL came on... Scanned it with P0301 Code... 1cyl misfire... Plugs, wires, cap & button have less than 2000miles on them... 1st idea was #1 injector, swapped it witha Good used spare, still has slight mis, haven't rescanned to see if it moved to a different cylinder. Jeep was extremely difficult to start after i reinstalled the rail... Going to wait until the weekend so I can work in the daylight... Will pull the plugs, run compression check... Any other suggestions? Mileage on motor is around 150k

[4.3LXJ]

Plugs would be my first thing to check

[YJeXtreme]

They'll be checked, however no reason for plugs with less than 2k miles to fail, esp for a quality brand. Going to also run Data stream on it this week...

[4.3LXJ]

Have you verified it is number one?

[nickxj94]

I've bought bad plugs out the box before.. it was Bosch plugs too, I have ran champions in both my xjs for two years now never had a problem with them.. also I would check the wires just to make sure take a old one and replace the one in question see what happens..

[YJeXtreme]

Per scanning to trouble codes only... My shop is occupied by another project so to really dive into the XJ will have to wait until Friday...

The fault code throwing the CEL was P0301... Which is cylinder 1 misfire

[YJeXtreme]

Running Autolites in this right now... Bosch can be tempermental ugs depending on application, i ran 'em in my old big-block Ford FE motors withno issues, but had problems out of other engines...

Jeep has ran great but with a big drop in MPG over the last 2 1/2 months. Has gone from 16.8 MPG avg in town to 14.4 MPG avg in town, now the mis & CEL

[nickxj94]

Running Autolites in this right now... Bosch can be tempermental ugs depending on application, i ran 'em in my old big-block Ford FE motors withno issues, but had problems out of other engines...

Jeep has ran great but with a big drop in MPG over the last 2 1/2 months. Has gone from 16.8 MPG avg in town to 14.4 MPG avg in town, now the mis & CEL

Its a pita to diag these things IMO I fought with my 00 xj for 6 months finally got it worked out, tps, both O2 sensors, plugs, coil rail, turbine input Sensor, rewired cps connection it was melted to each other, found a few shorted wires on parking lamps its running great no misfires and getting 17.5 MPG on the hwy ..

[YJeXtreme]

Its a pita to diag these things IMO I fought with my 00 xj for 6 months finally got it worked out, tps, both O2 sensors, plugs, coil rail, turbine input Sensor, rewired cps connection it was melted to each other, found a few shorted wires on parking lamps its running great no misfires and getting 17.5 MPG on the hwy ..

I agree it can be a PITA... I'm lucky to have a buddy with a shop disgnostic scanner, which helps... I refuse to just toss $$$ and parts at a problem. The O2 sensors were replaced within last 2k miles as well as Catalytic (this was due to prev. owner's decision to gut the cat & attempt to bypass the sensors...

My 1st guess is still bad injectors... Will post more later this week

[nickxj94]

I agree it can be a PITA... I'm lucky to have a buddy with a shop disgnostic scanner, which helps... I refuse to just toss $$$ and parts at a problem. The O2 sensors were replaced within last 2k miles as well as Catalytic (this was due to prev. owner's decision to gut the cat & attempt to bypass the sensors...

My 1st guess is still bad injectors... Will post more later this week

Could be injectors it would be a great time to upgrade to neon injectors, that's my next mod on the 00 xj I still get the #3 misfire every once in a while (heat soak) hopefully it will help

[YJeXtreme]

My misfire code was cleared & hasn't come back... However after running Data Stream, my rear o2 is on it's way out... Likely culprit of decreased MPG & roughidle...

[cantab27]

My misfire code was cleared & hasn't come back... However after running Data Stream, my rear o2 is on it's way out... Likely culprit of decreased MPG & roughidle...

yes sir.......when i swapped mine over better gas mileage and running

[YJeXtreme]

Still got misfire... New downstream o2, checked plugs... Still clean & properly gapped, new injector O-rings... Mis still with my spare working ECM. I'm beginning to wonder about valve springs. Read alot about 97s having issues with them... Any other suggestions? I hate throwing $$$ and parts at a problen with a reliable diagnosis

[4.3LXJ]

Done a compression check yet?

[YJeXtreme]

Was sick over weekend... Will have to do that friday on my say off..

[YJeXtreme]

Problem solved with decarbonizing the combustion chambers... 1/2can of Seafoam, and a 20-30min heatsoak. Jeep runs better than it has in the year I've owned it... Now if I can just solve the obnoxious lifter tick...