After getting the car tuned and sorting out the cooling issues, the car was running as expected for two weeks until today.

I went to fill up at a higher quality E85 pump and jumped from 65% to 75% E. Immediately after, when trying to drive out of the lot, the engine began breaking up and bucking with some backfires when trying to accelerate. I pulled it into a spot, looked at the logs, decided just to get a ride, come back, switch the plugs, and try to drive it. Switching the plugs let me cruise home, but the breaking up continued to occur at anything from 20% throttle to 5k into a WOT pull. Fairly inconsistent but always hitting what felt/sounded like a soft limiter.

My tuner opted to use a percentage multiplier for flex instead of dual tables and it appears to be working correctly in the logs. I also don't see how a 10% bump in E content would cause misfiring/blowout by itself so my best guess is that my Toyota COPs are somehow failing. There are also a few things I should note.

- The old plugs looked fine
- Gapped at .02
- When the car would break up, there were usually sync losses (code 39)
- The RPMs and PW would momentarily read zero
- The ECU would register in "cranking" state
- Cranking dwell would be applied
- I felt this issue once or twice before bumping up the E% but not nearly as bad or consistent

I've only read up on tuning MS3 enough to solve most simple drivability issues, but a more experienced set of eyes would help here. Im wary of dropping money on a better ignition system yet so any additional observations are greatly appreciated. I've attached a log and the tune where around 187 seconds into the log is a good example of the breakup.

 

Rpm 0 = crank sensor issue. Everything else in the log you’re seeing is related to 0 RPM.

 

I'll double check the CAS and wiring tonight after work. Logically you're absolutely right, but the symptoms seem to suggest to my (maybe lacking) intuition that the sensor/crank signal isn't the root issue.

Is there a way for the ignition system to somehow cause those sync losses?

 

Ok, more reading suggests I take a composite log and see if that reveals anything. Ill have to do that another day but my quick look over of the CAS and wiring didn't spot anything obvious.

I just find it really odd that this was basically a non-issue until immediately after I changed E%. Seems almost unrelated.

 

could just be bad luck. I had a crank position sensor wire get tagged by the WP pulley, just enough to short and cause extra readings. The composite log will indicate if it's dropping or adding extra pulse on the crank or cam, go from there once you've determined if it's a sensor issue.

 

Turns out the issue was a mix of bad and good luck.

The bad luck being that it indeed had nothing to do with ethanol.

The good luck being that it was my cam angle sensors connector which apparently had vibrated itself just loose enough to occasionally lose connection.

I triple-checked the wiring, including unplugging and plugging the sensor back in, went to take a composite log, and the sync loss issues were gone. Easiest fix I've had in 3 years. Thanks for checking my sanity.