Bad earth troubleshooting

My engine has been a bit "moody" when idling. It can idle smooth, and then suddenly change idling speed. Some of the dash gauges has also been flickering a bit. It haven't bothered me much but today I took my USB oscilloscope and started troubleshooting as I figured it must be electrical. My suspicions were the alternator as it use to haunt me.

But I was wrong. Here is the voltage between the battery negative and the engine loom ground:

I moved the loom's ground connector from a pedal box cover screw, to the engine block. Now it look like this:

The scales are different but you get the point. One could argue that bumps around 50mV won't do much harm but at least now the oil pressure gauge is more stable. It feels like the engine runs smoother too, but that might just be placebo.

Custom moulded ear plugs

I hate ear plugs. The sensation of being inside a bubble playing a video game has got me avoid them except when using power tools in the garage. I ride a motorbike to work everyday, and now when I'm getting older I can feel my ears has been taking a lot of beating over the years.

I've been testing different kind of ear plugs. From simple foam plugs to diy molded plugs. They either leak what can be described as a razor sharp noise, damp too much, or dampen the sound of the engine but not the noise from the wind.

So I decided to get a pair of custom moulded ear plugs and booked an appointment at Hörseltekniska Laboratoriet (Hearing Technology Laboratory) here in Stockholm, who often provide ear plugs for musicians and others with high demands of a good dampening curve. The plugs they recommended are from Bellman & Symfon, which sell a kind of plugs that are suitable for motorsport and that fits inside your helmet.

He filled my ear canal with some kind of foam and waited for it to cure. The silence was almost intimidating, nothing came through. Three weeks later I had the finished plugs in my mailbox.

The plugs are soft like silicone and goes in a long way in your ears. On the motorcycle they're great. I can clearly here the engine, but not the wind noise.

But in the Caterham on the other hand, the engine is just too quiet compared with the wind noise. When I drive with the plugs in at the motorway, I can't tell if the engine is running or not. I have to look at the rev counter to see if it's time to change gear.

As this year is a disaster from track day perspective, I haven't tried them on track, but I can imagine the wind noise is still so much louder than the engine noise, and no ear plug will help me there. I'll probably use them anyway, both for lowering the noise levels and for reducing the sensation of sensor overload.

UPDATE: They work great on track! I feel I even could use a bit more dampening.