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Discussion Starter #1 (Edited)
Mystery Misfire on Cylinder 1 and 4 1.8L 2006 civic (SOLVED)

Hi Guys, I have been fixing cars for 25 years and this one has really stumped me. I have a 2006 honda civic 1.8 DX. I recently replaced the original motor with the dreaded cracked block with a motor out of a 2010 civic. The swap went fine except for the engine misfires completely on cylinder 1 and a bit on 4 whenever I go past 3000rpm. It runs perfectly at any rpm under 3000 and very quiet and smooth. The replacement engine only has about six thousand original miles or 10 000kms. I've replaced the plugs and the coils and the injectors. I've also replaced the wiring harness. I've done a compression test and I am at 180psi for all cylinders equally. At Idle it's perfect. Before I replace the computer, I'm wondering if anyone has run into this problem or something similar. Am I overlooking something? I don't think the valves need to be adjusted because at 2500RPM it's perfect. At 3000 cylinder 1 is misfiring. I did a smoke test with my smoke machine to see if there were any vacuum leaks and nothing wrong there. The oil is brand new.:badger:
 

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Discussion Starter #2
Just an update. It seems to throw the code at 3500rpm then the engine light starts flashing. If I turn off the ignition and then start the car back up I can rev the engine past 5000rpm no problem and leave it there, it will not misfire at all. As soon as it slows down to below 3500rpm it flashes and no power to the #1 coil. I am going to attempt to reflash the computer today and see what happens.
 

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Seems to be an ECU problem unless there is an issue with the SOHC inlet valve lobes of cylinder 1 which is highly unlikely.

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Discussion Starter #4
Seems to be an ECU problem unless there is an issue with the SOHC inlet valve lobes of cylinder 1 which is highly unlikely.

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Thanks for the reply. That seems to be my next move. I will try reflashing or replacing the ECU. The other thing I was thinking is that although I don't have any codes for the throttle body, I did not check what the percentage was as I'm increasing past that particular rpm. Hopefully I solve this and I can post my findings so that it may help someone else one day.
 

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Cylinder misfiring is basically a timing issue. Whatever percentage the throttle body opens, the stock ECU ensures a lean mix based on the MAF sensor readings.

Not sure if this helps but in the R18A engine, the VTech kicks in approximately between 1200 - 3100 RPM for fuel efficiency and not power as in the other Honda engines. Please check if this working as it should when you scan your ECU.

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Have you tried replacing the crank sensor? Cylinders 1 & 4 are 360 degrees (crank angle) apart in the firing order. This means the misfires occur at the same exact position of the crank shaft.
 

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Discussion Starter #7
Have you tried replacing the crank sensor? Cylinders 1 & 4 are 360 degrees (crank angle) apart in the firing order. This means the misfires occur at the same exact position of the crank shaft.
Ok here is the latest. I just swapped out the ECU with another one and the misfire now is exclusively on cylinder number 2 now.
 

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Discussion Starter #8 (Edited)
Cylinder misfiring is basically a timing issue. Whatever percentage the throttle body opens, the stock ECU ensures a lean mix based on the MAF sensor readings.

Not sure if this helps but in the R18A engine, the VTech kicks in approximately between 1200 - 3100 RPM for fuel efficiency and not power as in the other Honda engines. Please check if this working as it should when you scan your ECU.

Sent from my SM-A505F using Tapatalk
I didn't get any codes for it. I have the autel maxisys elite so it shows me all my live data as well and anything out of range is highlighted in red. I swapped out the ECU for 40 dollars and now the misfire is on cylinder number 2 only. The computer shuts off this cylinder now from firing at all until I restart the car. Maybe I'll try swapping out the VTEC solenoid from the engine I pulled out. I'll post my findings
 

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Discussion Starter #9
Have you tried replacing the crank sensor? Cylinders 1 & 4 are 360 degrees (crank angle) apart in the firing order. This means the misfires occur at the same exact position of the crank shaft.
I have not but I will. I did swap out the computer and now it only misfires on number 2.
 

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Have you tried replacing the crank sensor? Cylinders 1 & 4 are 360 degrees (crank angle) apart in the firing order. This means the misfires occur at the same exact position of the crank shaft.
If the crank sensor is faulty, the car would've starting problems, especially with cold starts.

Since the issue happens at around 3500 RPM and there is no starting issue, the crank sensor may not be faulty.

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I didn't get any codes for it. I have the autel maxisys elite so it shows me all my live data as well and anything out of range is highlighted in red. I swapped out the ECU for 40 dollars and now the misfire is on cylinder number 2 only. The computer shuts off this cylinder now from firing at all until I restart the car. Maybe I'll try swapping out the VTEC solenoid from the engine I pulled out. I'll post my findings
When you swapped the 2010 engine, did you swap with the ECU of that motor or did you use your old one?

Sometimes there maybe a small difference in the way the ECU is tuned for different years (2006 & 2010) mainly due to pollution norms and sometimes to remove any minor issues from the older model or even for some minor upgrades. So it is always recommended to swap engines along with their original ECUs.

So try using the original ECU of the swapped engine and if that's not possible, try swapping it from another 2010 model.

Just a thought.

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Discussion Starter #14
When you swapped the 2010 engine, did you swap with the ECU of that motor or did you use your old one?

Sometimes there maybe a small difference in the way the ECU is tuned for different years (2006 & 2010) mainly due to pollution norms and sometimes to remove any minor issues from the older model or even for some minor upgrades. So it is always recommended to swap engines along with their original ECUs.

So try using the original ECU of the swapped engine and if that's not possible, try swapping it from another 2010 model.

Just a thought.

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I've tried a different computer from a scrap yard with the same part number. I don't have the original ecu but I do have the new vin for the engine and I can update the computer to the new 2010 vin with the latest updates and see what happens. I'll try that thanks.
 

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Discussion Starter #17
Cylinder misfiring is basically a timing issue. Whatever percentage the throttle body opens, the stock ECU ensures a lean mix based on the MAF sensor readings.

Not sure if this helps but in the R18A engine, the VTech kicks in approximately between 1200 - 3100 RPM for fuel efficiency and not power as in the other Honda engines. Please check if this working as it should when you scan your ECU.

Sent from my SM-A505F using Tapatalk
Thanks seems to be working fine according to the scanner
 

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Agree likely an ECU sensitivity. Unplug it and replug it into the harness. An odd connector mismatch on poorly connected signal sometimes can be corrected this way.

Another thing to consider is the voltages at the various sensors across the years. Yes the ECU should be able to handle the code updates but if there is hardware changes made to address the different years then no matter what code you flash - it could still be a hardware limitation kicking in.

Sounds like you tried a different ECU but was it from a 2010? Match hardware with hardware then upgrade the software to latest image. Only then can you guarantee it’s speaking to the sensors used properly.


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Discussion Starter #19
Agree likely an ECU sensitivity. Unplug it and replug it into the harness. An odd connector mismatch on poorly connected signal sometimes can be corrected this way.

Another thing to consider is the voltages at the various sensors across the years. Yes the ECU should be able to handle the code updates but if there is hardware changes made to address the different years then no matter what code you flash - it could still be a hardware limitation kicking in.

Sounds like you tried a different ECU but was it from a 2010? Match hardware with hardware then upgrade the software to latest image. Only then can you guarantee it’s speaking to the sensors used properly.


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That makes perfect sense. I don't have the original ECU but I did verify that the 2010 ECU has the exact same part number and version number. My only hope is to flash the ECU with the VIN of the newer engine and see what happens. I will however try to unplug and plug the harness in again to the back of the ECU. I'll post my findings. Thanks for the advice. I really appreciate.
 

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Discussion Starter #20
Agree likely an ECU sensitivity. Unplug it and replug it into the harness. An odd connector mismatch on poorly connected signal sometimes can be corrected this way.

Another thing to consider is the voltages at the various sensors across the years. Yes the ECU should be able to handle the code updates but if there is hardware changes made to address the different years then no matter what code you flash - it could still be a hardware limitation kicking in.

Sounds like you tried a different ECU but was it from a 2010? Match hardware with hardware then upgrade the software to latest image. Only then can you guarantee it’s speaking to the sensors used properly.


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Thanks for all the tips. It's running great now. Even though the engine is virtually identical from 2006 to 2011 you can't just use any ECU. I called the dealership to verify the ECU part number from the newer engines VIN. Then I called the scrap yard where I had purchased the engine 4 months ago and they had it. I Installed the ECU that came from the same car with the engine and the problem disappeared. I wonder what was different about the engine.
 
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