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Unread 01-07-2014, 05:43 PM   #1
skidj2x
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cold start skip

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?

any thoughts?

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Unread 01-07-2014, 09:27 PM   #2
straightsixjeep
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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.
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Unread 01-07-2014, 09:39 PM   #3
skidj2x
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im hoping #6 will be ok.. ill be pulling the plugs and doing compression test tomorrow.. ill post up my findings
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Unread 01-07-2014, 10:40 PM   #4
landude
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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...
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Unread 01-08-2014, 05:53 PM   #5
skidj2x
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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..
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Unread 01-11-2014, 07:17 PM   #6
skidj2x
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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..

now what
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Unread 01-11-2014, 07:29 PM   #7
landude
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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/
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Unread 01-11-2014, 08:02 PM   #8
skidj2x
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trouble code p0306, cyl 6 misfire.. i cleaned the throttle body yesterday..
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Unread 01-11-2014, 08:43 PM   #9
straightsixjeep
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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.
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Unread 01-11-2014, 10:17 PM   #10
landude
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How about an intake leak?
Maybe spray some starting fluid around intake components with it running.
See if it picks up rpm while you're spraying..
Just a thought..
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Unread 01-11-2014, 10:26 PM   #11
skidj2x
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i sprayed the intake at the head, around the base of the injecors, and around the vacuum lines going into the intake.. no change; still ran like a ford
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Unread 01-11-2014, 10:34 PM   #12
straightsixjeep
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Quote:
Originally Posted by skidj2x View Post
i sprayed the intake at the head, around the base of the injecors, and around the vacuum lines going into the intake.. no change; still ran like a ford
Can you flip flop coil packs? Also clean any grounds you can find. Look into the injector wiring for any breaks or dirty grounds.
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Unread 01-11-2014, 10:36 PM   #13
skidj2x
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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?
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Unread 01-11-2014, 10:37 PM   #14
skidj2x
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i did change coil rails.. i moved spark plugs and moved injectors
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Unread 01-11-2014, 10:39 PM   #15
landude
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Seems like you've covered many things.
How about cleaning the Throttle body. Dude, I did this today and was pretty impressed.
And as posted above the CPS in these thing can be a PITA...
http://www.jeepforum.com/forum/f9/cl...mmies-1114849/
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