It's been a while since I've posted, lots of stuff happening lately. Car is good though.
I didn't post the tensioner repair images further up in the thread, just realized. Using drill bits with pliers is my favorite thing (can you sense the sarcasm):
The car slowly but surely started having the same issue again that it had while on the dyno in SC. Symptom was breaking up under load around VTEC crossover when the boost really started coming in. This was also tightly coupled with the tach bouncing and seizure activity.
It took me some time to properly diagnose it, but was able to trace the issue with my oscilloscope and driving the car every day to work for about a week. Each day I would stage the scope leads to a different set of inputs/outputs, to hopefully catch a glimpse of the gremlin that might lead me to the root cause.
With a low amp clamp coupled around coil ground lead (had to make a longer wire from the ICM, leading outside of the dist, then back inside to the coil negative) so I could watch the current ramp profile of the coil charging behavior. This is where things got weird. I noticed that the ramp profile was clean and normal during idle and cruise, but under boost and higher RPM, the current peak would begin to drop, then randomly the charging profile was less of a curve and more of a striaght ramp. Basically the coil wasn't able to charge properly during it's on-time, and randomly wouldn't reach peak current fast enough in the primary, so when the primary turned off, it had less magnetic field energy available to collapse over the secondary windings, leading to weak spark output during those times.
This was also confirmed through primary side waveform analysis... I could visually see the peak KV drop off, and even outright misfires when synced against the TDC sensor in the distributor. The misfires were random, coil charging behavior was random, some pulls did it while others did not.
Good news was that all of my distributor position sensors (TDC, CKP and CYP) all generate AC voltage properly, and none of them were dropping out, all the way to the ECM. ICM signal from ECM to the ICM was also good and consistent during the problem (checked at the ICM), so the ECU was receiving rotation sensor inputs and attempting to properly command the ICM, so those circuits were proved out as not being part of the issue.
This lead to the issue being ICM coil driver output related, coil related or power/ground to the ICM/Coil related. I decided to try and stress test the distributor ignition components on the bench, in and around the RPM area that the problem was most prevalent, 4-5000 RPM.
To find out how fast I would need to pulse the ICM/coil, simple maths and engine theory knowledge are required:
- 5000 revs per minute at the crankshaft, divided by 60 to determine revs per second = 83.3 RPS crank
- Thats crank speed, so divide by 2 to find camshaft RPS = 41.65 RPS cam
- Within one revolution of the camshaft, there are 4 firing events, one per cylinder, so multiply cam speed by 4 (since there are 4 firing events per cam revolution) to find ICM/coil driven frequency = 166.6 Hz
So I needed to turn the ICM/coil on and off at 166.6 times per second to simulate the conditions on the car at 5K. Easy peasy
This was testing the PWM setup between 4 and 5K RPM, at around 140hz:
Nothing during my testing showed out of ordinary, coil amp ramp and firing KV looked beautiful on the bench, even at 7.5K RPM, 250Hz (I've experienced 200 Hz on AC with my TIG welder doing aluminum work, but that extra 50 cycles per second sounded like an alien coming in to land lmao).
That's when it hit me. Before all of this, I did run 3 full lengths of 10 gauge wire from the battery ground post all the way up to the engine, with each one getting a ring terminal and attached to the valve cover, distributor case and the thermostat ground bundle, to try and remedy the misfiring, thinking it was a ground issue. Then it hit me, could it be the power circuit?
Instead of trying to replace things one by one to trace the root cause, I had a pretty good idea of how to remedy things. As long as ICM and coil received proper power and ground, it appeared that things worked correctly. I figured now was a good time to go ahead and just convert the civic to external coil. I've had some old Prelude parts laying around for just this purpose, including a coil, ICM, coil noise condenser and distributor cap:
Bench tested the Prelude ICM and coil first, before installing to the car. It all seemed to work well.
Went ahead and ran dedicated power, fuses and grounds to the Prelude ICM and coil, completely bypassing the car harness for those things. The ICM stays on when given power and ground, so I now have to regularly use my master disconnect switch. The only thing I still used in the engine harness was tach signal wire and ECM to ICM driver signal wire.
Without a good place to mount the coil (since this was more or less just a test) I put a rubber strip against the side of the coil and ziptied to the strut tower brace lol.
Testing and initial proof of concept:
I electrical taped everything up for testing, and drove the piss out of it. ZERO misfires and NO tach seizures!
Feeling satisfied, went ahead and made the install more or less permanent. Still don't have a good place to mount the coil, but I kinda like it on the strut tower brace lol:
Oh yeah, I also installed these quick release bumper elastics. For some reason, my bumper fasteners that hold the bumper to the fender keep vibrating out of the hole that is in the bumper, or just outright loosen themselves. This gets rid of all the stupid fasteners and is vibration proof lol:
Update over
