Car misfiring, random misfire code, constant knock counts, oh my.

[Greg E]

BTW, yes I'm aware of the 91/92 sensor being mounted on the can but that photo style sensor has two outputs. One is the cam signal, the other is the crank signal. On the 93 cars they split the two into individual sensors. The method for RPM calculation is still the same.

[Toni]

Great, thanks for the clarifications. May help someone in the future.

I have a new or different symptom now and I found a log.

New symptom. I normally don't drive with my fuel pressure gauge in, I usually have my oil temp(I can hot swap the gauges in the same location). On the highway from an hr drive I notice the low light comes on and I see the needle freaking out. It was dropping below 2bar differential pressure across boost. Car was running fine but I was just cruising so not sure if I'd notice a quick blip. Could be the gauge, boost/vac signal, or actually dropping pressure. If it's dropping pressure I guess it could be the mfi/ecu, pump, or wiring. Not sure if this is connected or a separate issue.

I found a log of the knock sensor going whack. What's interesting is I get a voltage when it's showing 7-9 counts. It also shows no voltage in some sections. I need to do some logs of it working fine and also unplugged to see how the logs compare.

It does seem to follow the base, so I dunno. Might need your two cents (or a quarter) if you have it Greg.

[Greg E]

That sensor is losing power, or the connection is dropping or the sensor itself is bad. No way will you see 0v with the motor running.

[Toni]

I'm surprised that the knock sum didn't go away when it did have voltage.

[Greg E]

The zero volt counts are bringing down the average noise (knock base) so when it comes back to life, all of a sudden its out side the norm.

[Toni]

Alrighty. The new fuel pressure symptom was a false positive. Apparently my pressure sender is working fine but the gauge unit is not. Phew!

[Toni]

Misfire problem is gone. 100% the PTU.

The knock sensor issue did not resurface for a long time. I've driven some 3000 miles and two track days at Watkins Glen. However yesterday morning it came back. It was a cold morning and it came on about 2 miles going to work. Man the car dogs without timing lol. I let it cruise on the highway to see if it would go away. Ten minutes, still there. Ok so I have a new sensor with me and I figure it's not fixing itself this time and I'll plug it in when I park. Of course the damn thing goes away as I pull into work. Sure I can replace it and see if it goes away but I generally hate throwing parts at a problem.

[Toni]

There appears to be no pattern with this other than it only happens when I am on my way to work in the morning. Possible temperature thing.

It happened again today and I turned around got home and plugged in a brand new sensor. New sensor didn't change anything. I expected it to fix the problem within seconds or after a restart. Neither occurred. So I took off with the old sensor and it fixed itself within a couple miles. I'll unplug the old sensor, drive a while, and plug it back in to see how long the ecu sees the sensor again just to make sure it's as instant as I think it should be. I fear that it's the ECU being a bitch hole. Maybe I'll setup some probes at the ecu to test it with my meter when it happens to see if I'm getting anything at the harness or if it's ECU internals.

[Trevor425]

so wait, you are just plugging in a new knock sensor and not installing it? did you reset the ECU to clear the learned values?

also what flash ECU are you running, i had very strange issues with my knock sensor on my first flash ECU, but the sensor was fine.

[Toni]

Alright, I gave in and swapped in the new knock sensor I've had waiting a couple weeks ago. I've tried driving the car every day to work and so far in 2 weeks it hasn't given me troubles. A good mix of dry/humid cold/warm mornings. So far so good. I think it was either the sensor or the connector. I'm going to replace the harness end of the connector to get some new pins to ensure a good connection. So far I think I can say all my issues in this thread are fixed.