Partial reset / Electrical surge ?

[noisymime]

Hey All,

So my MS3 has been running pretty well for quite a while now. Still dialling in the map correctly at the top end with the turbo, but all in all very happy with things. Driving along the other day though, something very odd occurred where the engine simply cutout. The tacho dropped to ~0 rpm and it was clear that it had cut out. 4 seconds later, the whole thing just fired back up (The car was still rolling along at this point) and proceeded to drive like nothing had ever happened.

A few minutes later though I realised that, whatever had happened had did something odd to the O2 readings. The values were all of a sudden dramatically different and the signal itself looks very different in the log, being smooth now rather than the jumpy readings that it has always been (It's a fairly standard Innovate O2 sensor). Fortunately I happened to have a log running at the time, so can see what happened. The ECU doesn't appear to have reset at all as SecL is unaffected:



So, other than the O2 reading, everything appears to be running perfectly normally again. The hall sensor on the crank has never given as any issues with sync and this is the first time in 3+ years with it that something like this has occurred, so I don't believe it's a typical sync loss issue.

Anyone got any ideas as to what could cause something like this?

[Matt Cramer]

What sort of O2 sensor / controller are you using?

[noisymime]

Innovate lc-1. Just using the sensor it came with, I it's a Bosch?

[Matt Cramer]

Try doing a new free air calibration.

[noisymime]

Cheers, I'll give that a go. Any idea what could cause this type of issue in the first place?

[Matt Cramer]

A voltage spike can throw the LC-1's calibration out of whack. They are a bit sensitive to electrical noise. Grounding them to the engine block can help.

[noisymime]

Thanks again Matt. Anything I can do to prevent the engine cutoff in a situation like this? Is it likely to have been something like the crank sensor (powered off the vref on the relay box) that temporarily died?

[Matt Cramer]

There is definitely SOME sort of sync loss issue. Would you be able to catch it in a tooth log?

[noisymime]

I'll see if it happens again. First time it's ever occurred in 3+ years with the MS3 on, so no idea if it will happen again, but I'll have the tooth log turned on. After it happened I got a little nervous I'd get stuck with a non-running car, so I high-tailed it home and haven't had it out again since. I'll do the free air calibration this weekend and go for another drive .

Thanks again for your help.