LT1 once again misfiring, new ect, plugs, wires, etc, what else?
07-05-2009, 06:46 AM
#1
LT1 once again misfiring, new ect, plugs, wires, etc, what else? Car is a 1994 Camaro Z28, 6 speed, 169,000, shorty headers, borla, moroso intake, and basically about every bolt on but a supercharger, lowere 2 inches and a few suspension mods.
About a year ago i replaced the plugs with NGK Iridiums, put in a new ECT, fixed the burnt plug wires and put heat boots on them, checked for any vac leaks, etc to narrow down this miss.
This missfire happens at all throttle positions, all engine loads but more noticeably under heavier loads (hill acceleration) but still happens even during cruise on flat roads.
I have cleaned the MAF, unplugged the maf, no realy change in drivability. The check engine light will come on intermitantly but i cant get the stupid cheapo code reader to read any codes from my data port.
So far i have checked the plug wires for burns and cant find any, all were put on with dielectric grease when i replaced them. I didnt bother pulling the plugs because they should be fine since they are 100k mile plugs with about 20k on them.
Next i want to test the ECT although i replaced it last year when trying to diagnose the missfire it had.
I'm think it could be an O2 sensor
Could it be by exhaust hitting the frame and causing false knock? it's a pretty solid missfiring. 02 sensors are new 3 years ago
The opti and water pump are 3 years old
What else should i check? I'm an LS1 guy and havent really messed around too much on the LT1s.
About a year ago i replaced the plugs with NGK Iridiums, put in a new ECT, fixed the burnt plug wires and put heat boots on them, checked for any vac leaks, etc to narrow down this miss.
This missfire happens at all throttle positions, all engine loads but more noticeably under heavier loads (hill acceleration) but still happens even during cruise on flat roads.
I have cleaned the MAF, unplugged the maf, no realy change in drivability. The check engine light will come on intermitantly but i cant get the stupid cheapo code reader to read any codes from my data port.
So far i have checked the plug wires for burns and cant find any, all were put on with dielectric grease when i replaced them. I didnt bother pulling the plugs because they should be fine since they are 100k mile plugs with about 20k on them.
Next i want to test the ECT although i replaced it last year when trying to diagnose the missfire it had.
I'm think it could be an O2 sensor
Could it be by exhaust hitting the frame and causing false knock? it's a pretty solid missfiring. 02 sensors are new 3 years ago
The opti and water pump are 3 years old
What else should i check? I'm an LS1 guy and havent really messed around too much on the LT1s.
07-05-2009, 07:33 AM
#3
Well i got around to testing the ECT. Its about 75 degrees here and i estimate the coolant temp to be about 80 degrees by the time i started the engine and pulled it onto the ramps (about 45 seconds). My ECT is reading 2380 Ohms so i am thinking i may have a bad ECT.
I am going to remove the ECT to test it this time. I couldnt get my probes to hold in place because of the odd location so i just cut the ECT sensor off of a parts car and plugged it in to read it from the wires. I'll let you know what i find out once i remove it.
I am going to remove the ECT to test it this time. I couldnt get my probes to hold in place because of the odd location so i just cut the ECT sensor off of a parts car and plugged it in to read it from the wires. I'll let you know what i find out once i remove it.
07-05-2009, 07:44 AM
#4
Ok i got it removed, no connector on it, estimate of 80-85 degrees coolant sensor temp and i got 2,280ohm resistance. According to Shoe Box's chart, this is right if you arent looking in the Celcius column LMFAO!
http://shbox.com/1/4th_gen_tech2.html#ect
http://shbox.com/1/4th_gen_tech2.html#ect
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07-05-2009, 09:47 AM
#8
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Let your car idle, take a long screw driver and stick the flat end to injector and the handle to your ear and make sure they are all clicking.
Also, Iridium plugs are terrible for fouling out. the center conductor is so small, it takes almost nothing to block it.
Stick with plane jane NGK TR55. They will last longer.
also it is possible your coil is going out. I used to say it either works or it doesnt, but I proved my self wrong when I bought my car because I had a miss, changed the coil and it went away.
Also, test your grounds. Turn the car on, turn on the ac and lights. If the car about dies. Your grounds are no good.
Also, Iridium plugs are terrible for fouling out. the center conductor is so small, it takes almost nothing to block it.
Stick with plane jane NGK TR55. They will last longer.
also it is possible your coil is going out. I used to say it either works or it doesnt, but I proved my self wrong when I bought my car because I had a miss, changed the coil and it went away.
Also, test your grounds. Turn the car on, turn on the ac and lights. If the car about dies. Your grounds are no good.
07-05-2009, 09:54 AM
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07-05-2009, 10:20 AM
#10
Grounds are fine. I also tested the coil, all 4 pins read 8140 OHMs (spec is around 8000) so the coil is good. I also tested the EGR, seems to be working fine. No vac leaks that i can find. I unplugged the PCM and let it sit for an hour but havent taken it on the road yet.
So that leaves
02 sensors
knock sensor (would this cause a bad missfire though?)
opti spark
ignition control module
This missfire has gradually gotten worse over a month or so. Last time it turned out to be burnt plug wires which i've fixed and re-checked and seem to be fine.
You guys really think i might have fouled out the iridium plugs? I put them in there so i wouldnt have to change them haha. It took me like 2 1/2 hours to replace them last time with the edelbrock shorties.
So that leaves
02 sensors
knock sensor (would this cause a bad missfire though?)
opti spark
ignition control module
This missfire has gradually gotten worse over a month or so. Last time it turned out to be burnt plug wires which i've fixed and re-checked and seem to be fine.
You guys really think i might have fouled out the iridium plugs? I put them in there so i wouldnt have to change them haha. It took me like 2 1/2 hours to replace them last time with the edelbrock shorties.
07-05-2009, 10:46 AM
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Because a coil checks out ohm wise doesn't mean it is good. Just means it passed a resistance test. Buy a 10 coil and swap it out. If it doesn't work return it.
I think its the plugs. Iridiums are junk, and they will foul out super quick if your motor has a decent amount of mileage.
Platinums are crap too. Paypal me $15 and I will send you a used set of Fusion Platinum 4's if you are into that cheesy stuff.
Standard $2 copper plugs are the way to go. trust me.
I think its the plugs. Iridiums are junk, and they will foul out super quick if your motor has a decent amount of mileage.
Platinums are crap too. Paypal me $15 and I will send you a used set of Fusion Platinum 4's if you are into that cheesy stuff.
Standard $2 copper plugs are the way to go. trust me.
07-05-2009, 02:44 PM
#13
Yeah i do use the TR55s on all my LS1s. I dont know why i thought the iridiums would last longer.
I'll buy a new coil here sometime this week and see if that helps.
I'll also buy a new set of plugs and swap to over the valve cover wires in a month or so when i can find the time to install them.
I'll buy a new coil here sometime this week and see if that helps.
I'll also buy a new set of plugs and swap to over the valve cover wires in a month or so when i can find the time to install them.
08-09-2009, 02:15 PM
#16
Well i finally got around to working on the car.
I replaced the coil, no change.
I decided to buy some NGK TR55s and spent 3 hours putting them in (stupid Edelbrock shorties) and now it's perfect!
I did find that only the passenger side plugs were fouled though. Thought that was odd. Could that be because one plug fouled then the 02 had a false reading and just fouled the whole bank or could it be because there is an injector issue on that bank or an 02 sensor issue? What do you all think? Here are the plugs i dont know which came from which cylinder but i know which bank they came from.
Passenger side plugs
I replaced the coil, no change.
I decided to buy some NGK TR55s and spent 3 hours putting them in (stupid Edelbrock shorties) and now it's perfect!
I did find that only the passenger side plugs were fouled though. Thought that was odd. Could that be because one plug fouled then the 02 had a false reading and just fouled the whole bank or could it be because there is an injector issue on that bank or an 02 sensor issue? What do you all think? Here are the plugs i dont know which came from which cylinder but i know which bank they came from.
Passenger side plugs
08-09-2009, 11:00 PM
#20
i just got all my misfiring problems fixed the other day, and had around the same issues.
mine was one fuel injector, one o2 sensor, one plug was cracked in the porcelain, and my fuel filter was just about clogged shut.
check all that and, make sure your plugs are gaped correctly at .50
the fouled plugs on one bank would probably be an o2 sensor.
mine was one fuel injector, one o2 sensor, one plug was cracked in the porcelain, and my fuel filter was just about clogged shut.
check all that and, make sure your plugs are gaped correctly at .50
the fouled plugs on one bank would probably be an o2 sensor.