hey 2000 xj, stock 4.0, head and block has 50K, everything else, ie sensors, throttle etc have 150K..
has developped a cold start misfire on #6, P0306.. usually after a few minutes it clears up.
i installed new autolite plugs gapped to .35, a new coil rail, the fuel pump is less than a year old pushing 53 psi at key on, swapped the #3 injector for #6 injector, still skips on #6.. i have not done a compression check, because the skip goes away..
scan tool freeze frame info all looks normal, except the IAT temp reading is -185F. the data stream IAT reading shows whatever the ambient air temp is, if its 50F outside the IAT reads 50F.. I would think, if the problem was related to the IAT id have multiple cylinders misfiring, not justone in the middle ofthe firing order..
since it clears up after a few minutes, am i experiencing a crusty/carbed up exhaust valve? or is there another electrical/sensor gremlin i should be looking for? should i do a seafoam steam-clean treatment on my jeep?
If it is getting fuel and spark, Id check the compression. Perhaps cylinder #6 is weak enough cold to disrupt the momentum of the engine however after warming up it would be sealing better. If it has good compression then we look back into the sensors. Pull out that plug and take a look at it, see if it is wet or fouled already.
Is this something new or has it been a problem for a while?
I'm just curious due to the recent temps we've been seeing lately.
Garage kept or sitting outside? Just asking since you said it clears up after a few minutes
The cold if f'in with everything here in PA. And when you toss electronics into the mix...
this all started sometime in october.. my jeep is an "outside toy", since i dont have a garage.. and its getting progressivly worse.. although, the last two mornings at -4F it started pretty good considering the temp..
i didnt get to mess with it today, no compression test, no seafoam treatment.. ive got too many buses to fix and be DOT ready..
finally buses are taken care of.. so, i started it, ran it around a bit, to the bank, etc.. finally seafoamed the intake.. still starting the same..
cold start skip. had to start it to pull it into the garage, started with the same skip. pulled the plugs. looked just as nice as they did back in mid september when i put them in. not wet. not burned. not fould. 'cold' compression test showed an even 150 on all 6 cyls. vacuum gauge on the intake showed steady, no fluctuation.. the cel is still flashing, still have cyl 6 misfire, and i can still hear an irregular pop from the exhaust, and the engine is obviously skipping..
If your CEL is on then there will likely be codes. Pull them and let us know what they are.
That will tell a great deal and lead to a speedier recovery..
If your ambitious you can clean your throttle body. I did this today and had positive results.
It was filthy in there.. This is just good PM anyway... http://www.jeepforum.com/forum/f9/cl...mmies-1114849/
I know you have a new fuel pump but just for giggles cycle the key on/off a few times before starting and see if this helps. I would perhaps look into testing the crank sensor to see what it's doing when cyl #6 fires. If the plug isn't fouled and the cylinder is holding 150psi then combustion is taking place. Thinking into a fuel restriction issue or a faulty cps... then after that you need to research how the cps, iat, and ecu work together.
straightsix; why would it only effect one cylinder? when you say cps, most people seem to be refering to the crank sensor.. butit seems that when the crank sensor goes, it wont start or run, or will run then quit and not want to restart till it gets cold again..
when i replaced the motor five years ago, i destinctly remember usuing a scan tool to zero the cam. so i had rechecked it to make sure the reading was still correct..
but if you mean cam sensor, could the shaft to the cam sensor have a wobble like they would develop in older distributor models? but if it did, wouldnt i see a fluctuation in my tach?