PO303 Misfire on cylinder 3

[speedyWS6]

Hi Guys,

Been a good while since I posted but always having a look to see what is going on.

As the title suggests.... I have code PO303 showing on the OB2 reader. This is cylinder three, as I am sure you know!
The car idles pretty good and if not getting heaving on the gas pedal and just driving at low revs it drives fine.
If I get on the gas to, for example, use a slip road to get on the motorway it gives light pops from the back but
never jerks or bucks or makes driving dodgy!! Once steady at 70MPH or so it drives fine with the odd very light
little pop every once in a while?

I have changed the Coil pack of number three for another with the same part number on it. I've got a bud with a couple of spare LS1 motors!!
A used coil pack from one of these motors has been used but what are the odds of that also being bad?! I did this work with my bud and we both are sure
that if you go in and clear the code it idles better?? Maybe wishful thinking?! A lively drive today after switching the coil, of
about six miles, saw no code appear on the dash but the same PO303 pending code in the OB2 reader.

Tomorrow when the motor is cold i'll have a look at the plug condition and maybe change the lead. Again a used lead ( for the short term)
as stuff is not on our doorstep like you guys have it. The plugs only have about 2000 miles on them and they are TR55's

Any ideas welcomed!!

[Whamhammer]

Hi Guys,

Been a good while since I posted but always having a look to see what is going on.

As the title suggests.... I have code PO303 showing on the OB2 reader. This is cylinder three, as I am sure you know!
The car idles pretty good and if not getting heaving on the gas pedal and just driving at low revs it drives fine.
If I get on the gas to, for example, use a slip road to get on the motorway it gives light pops from the back but
never jerks or bucks or makes driving dodgy!! Once steady at 70MPH or so it drives fine with the odd very light
little pop every once in a while?

I have changed the Coil pack of number three for another with the same part number on it. I've got a bud with a couple of spare LS1 motors!!
A used coil pack from one of these motors has been used but what are the odds of that also being bad?! I did this work with my bud and we both are sure
that if you go in and clear the code it idles better?? Maybe wishful thinking?! A lively drive today after switching the coil, of
about six miles, saw no code appear on the dash but the same PO303 pending code in the OB2 reader.

Tomorrow when the motor is cold i'll have a look at the plug condition and maybe change the lead. Again a used lead ( for the short term)
as stuff is not on our doorstep like you guys have it. The plugs only have about 2000 miles on them and they are TR55's

Any ideas welcomed!!

Could it be a leak just around cylinder three (perhaps injector O-rings) ?

Have you made sure that the plug wire is good, the spark plug doesn't have cracked ceramics, and that the wire harnesses for the injector and coil haven't been chewed on by Mickey?

[speedyWS6]

Thanks for weighing in with some good thoughts, Scott...

I will get to the car this weekend and I have 8 plugs and leads heading my way.

[speedyWS6]

Eight spark plugs and eight leads found their way across to me over here and yesterday I fitted them.

Drivers side... no big deal but the passenger side... jeeez, Number eight is a pain, eh? I knew that going in
and happily the rearmost coil rail bolt was already missing from doing the headers and I knew to leave it out
and boy did that help. Still bled though!!

I will fire here up tomorrow and i really hope this cures the miss on number three!!

[Whamhammer]

Eight spark plugs and eight leads found their way across to me over here and yesterday I fitted them.

Drivers side... no big deal but the passenger side... jeeez, Number eight is a pain, eh? I knew that going in
and happily the rearmost coil rail bolt was already missing from doing the headers and I knew to leave it out
and boy did that help. Still bled though!!

I will fire here up tomorrow and i really hope this cures the miss on number three!!

Yeah, passenger rearmost plug is a PITA, I remember getting to it from the bottom.

[speedyWS6]

Well......

The new plugs and leads seemed to have cured the missing problem on 3.

I ordered NGK TR5 plugs and these leads https://shorturl.at/dipYM which are
SMP Blue Streak. Had no real idea about the leads and bought what looked like
a reasonable set!! But I was adamant I wanted the NGK TR5 plugs. After a
good look around and also having the TR55 in the car to replace, Rockauto
never had these but it appears the TR5 are the same but with a smaller gap
so I got these and opened them up from the 0.040 to the recommended
0.050

I was nervous but it fired right up and idled noticeably more smoothly and
showed no codes. Actually it idled a little faster at about 600 from the previous
500 revs.

Yet to have a drive but it seems good!