cold start skip

[skidj2x]

2000 late build 4.0, stock.. 50k on block and heads..everything else (sensors, etc) have 150k on them..

at cold start i get a pretty obvious skip.. usually only cyl 6 (P 0306), but more and more often its cyl 1 and 6 (P 0301 and P 0306).. usually clears up after about 30 seconds, or if its real bad, after restarting the engine. once started, she runs perfect.. at least till she cools down again.

changed the plugs, changed the coil rail, cleaned the IAC, new fuel pump pushing 55 psi, new air filter, new battery with a SG of 1300, alt charging at 14.1v

looking at the scan tool freeze frame info, the only thing out of the ordinary is the IAT temp reading.. says the IAT temp is -185 f..

so is the ecm trying to change the fuel mixture so much to compensate for such a cold reading that its causing a misfire? or is this an early indication my crank sensor is at the end of its useful life?

 

[98NWCherokee]

What type of plugs are you running? XJ's like cheap basic plugs like Champion. If you're running a fancy Bosch multi prong you may run into misfire issues.

 

[skidj2x]

autolite platinums. they were like $3 orsomething.. gapped at whatever it says on the emissions label

 

[skidj2x]

its warm out this AM, about +46 F out.. another rough start.. after getting to work, i scanned the codes (P 0306) and checked the freeze frame.. coolant temp reads +29 F, Intake Air Temp -98 F..

the datastream IAT reading is +126 F.. datastream CTS +206 F.. ill have to rescan it after it cools off to see what the IAT datastream reading is cold, to see if the IAT is the cause of my cold start skip..

Any other ideas?

 

[skidj2x]

so after going cold.. i rescan the ecm. the datastream shows the IAT at 45F, which was outside air temp. so i tried starting her up.. engine skipping, CEL comes on..

same code P 0306, cyl 6 misfire. so i check the freeze frame info.. again, the only thing that isnt right is the IAT reading.. the IAT reading is -185F.. so, what, does the ecm not really care about the IAT when youre cranking it through?

so anyway, i swapped the number 6 injector and spark plug for number three's.. so lets wait and see if the problem moves.

 

[skidj2x]

after swapping the #3 and #6 injectors, #6 still skips on a cold start. at this point im sure the freeze frame info showing the IAT reading at -185F has nothing to do with the cyl 6 misfire..

ok.. so after a little research, theres a TSB that says exhaust valves can get carbed up, and close lazily causing a misfire.. this can occur until they warm up, or the engine runs up to 3200rpm causing the valves to rotate..

so, if you were interested, im going to try some seafoam.. hopefully that will clean up any carbon deposits..

anybody have any ideas on other electrical gremlins i should be looking out for?