z28 mysterious cylinder 3 misfire - LS1LT1 Forum : LT1, LS1, Camaro, Firebird, Trans Am, Engine Tech Forums
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  • 1 Post By cocobolo95
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post #1 of 12 (permalink) Old 10-15-2017, 07:45 PM Thread Starter
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z28 mysterious cylinder 3 misfire

Hey everyone new to the forum! 97 z28 auto 100k
it throws cylinder 3 misfire code and runs rough/rich
I changed wires/spark plugs, distributer = much better but still throws code
tested compression and came back good.
To me it smells like its running rich and somewhat hesitates at times.
It doesn't look like any of my data is off either except o2 bank 2 sensor 1 would creep down to .120 V and shot up back .600 V while o2 bank 1 sensor 1 stayed at a pretty constant .415 V
at idle the MAP kPa is 38 and spark adv 27 degrees it was kinda cold and MAF of .02 lb/s (sorry for unconventional units)
thank you!
dan!
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post #2 of 12 (permalink) Old 10-15-2017, 09:43 PM
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Swap a fuel injector with another cylinder to see if you have a leaky injector


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post #3 of 12 (permalink) Old 10-16-2017, 07:11 AM
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Having a bank 1 sensor stay at relatively the same reading is not a good thing. It's the bank 2 sensor 1 that your worried about that is acting like it should.

So your bank 1 sensor 1 is not working correctly. This can because the heater circuit is not working , or the o2 sensor is bad. If wiring is causing the problem changing the o2 won't help.

For the misfire, put front of car up in air on jack stands. At night, mist plug wires with some water. Start engine and look for spark leakage. You put car up in air so you can also check under the car. Many tomes spark leakage can't be seen from the top.

And welcome to the forum.
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post #4 of 12 (permalink) Old 10-16-2017, 09:59 AM Thread Starter
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Thank you guys!!!
I will give both things a shot this weekend and get back to you!
when you say spark leakage do you gas/air leakage or power leaking and arching?
thank you
Dan
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post #5 of 12 (permalink) Old 10-16-2017, 10:48 AM
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Spark leakage is the arching of the spark voltage before it reaches the spark plug. If you run engine at night, there's no mistaking the light show of spark leakage.
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post #6 of 12 (permalink) Old 10-16-2017, 02:17 PM
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I'd start with what you know is not working and that is the the bank 1 O2. It's on the same side as your #3 cyl.

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post #7 of 12 (permalink) Old 10-17-2017, 08:40 PM Thread Starter
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is it possible that having a leaky injector would cause the o2 sensor to malfunction due to the overload of fuel since it is on the same side?
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post #8 of 12 (permalink) Old 10-18-2017, 06:14 AM
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The O2 should still work, IMHO.
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post #9 of 12 (permalink) Old 03-03-2018, 10:10 PM Thread Starter
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in the process of removing it now! as you know its pretty tight down there. I usted pb blaster, heat, and the correct socket but started to strip it... do you guys have any prob tips for bank 1 sensor 1?
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post #10 of 12 (permalink) Old 03-15-2019, 06:33 PM Thread Starter
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Update! new o2 sensor..... o2 code gone! fought me to the end... had to take manifold off and even then had to reheat with cutting torch every 2 turns lol. honestly it does smell less rich and it took a min for the cylinder 3 misfire to come back but shes here to stay. For a sec I got a cylinder 7 misfire code but it went back to cylinder 3 and is staying there. I did put a new optispark on it too but not an ac delco one... coco I tried the water spray during night and didn't see any spark leakage so im leaning towards… (non pun intended) a bad injector or two. soon ill pull the rail off and see if I can see one leaking! Thank you for the help so far and I will report back! Just to be clear it does still smell like fuel pretty bad!

Last edited by Danomax6.6; 03-15-2019 at 06:34 PM. Reason: forgot to add
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post #11 of 12 (permalink) Old 03-15-2019, 06:35 PM Thread Starter
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also forgot to mention! had the windows and radio problem but followed a guide and resoldered the computer and it worked!
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post #12 of 12 (permalink) Old 03-17-2019, 10:56 AM Thread Starter
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update: pulled the injectors out while still connected to fuel rail... turned key on... no leak..... cycled it back and forth and left it on for 10 minutes and not a drop... I will say i think when i got the code to disappear for the longest it was after it had already warmed up and then after cold start came back.. Do you think I should try and replace the opti again?? and would you recommend the acdelco rebuild for 150/500 dollar msd? Thank you again!!

Last edited by Danomax6.6; 03-19-2019 at 11:19 AM.
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