Vans and crashing electronics

[jospanner]

Hi, I'm a relatively new hobbyist, I'm more of a mechanic by trade, but I enjoy playing with electronics.

I'm trying to fix what is, I assume, a noise problem on my vehicle's electrical system. I know this isn't a mechanics forum, but please hear me out: In my mind this is more of a question about power supplies and noise.

The electrical system on my van ('81 VW T3/Vanagon, carburated aircooled engine, very old school) keeps doing unpleasant things to electronic devices: most notably, the new gauges I tried to install, and my Hantek USB oscilloscope. In the case of the gauges, it reboots them or makes them act erratically. In the case of the Hantek, it crashes the hardware and requires a physical reconnect to the laptop before it'll connect again (using OpenHantek software).

This problem starts as soon as the engine is started, and I did briefly manage to observe some little spikes in the 12V supply (10x probe setting) on the Hantek before it crashes.

The symptom persists with the alternator disconnected. So, I would guess ignition noise.

The question then, is, how do I approach this? As an EE hobbyist, I'm happy to try my own circuits, but considering that I'm having trouble even measuring what's going on here, I'm not sure where to start. I don't really know anything about noise or how to suppress it. I've just been trying some electrolytics across the 12V and gnd connections, a 12v linear regulator too, but no joy there - still crashes the scope etc.

A few things that could stand out:
- The signal wires for the new gauges are long (~5 metres or more) and at the engine-end are not electrically connected to the block. They have their own gnd wire that runs to the front again, forming a loop. The wiring in the van is, in general, very long because the engine is at the back and the battery + instruments etc at the front.
- Neither ignition coil nor the alternator appear to have a suppression capacitor.
- The ground connection to the engine appears to be good.
- Multimeter shows the voltages to be generally good (approx 13-14V while running).

I'm at the stage where any suggestions or pointers would be welcome, I'm a bit out of my depth on this one! 

[BrokenYugo]

Ignition parts arcing that shouldn't be would be my guess, points or electronic ignition? You can hear bad ignition on an AM radio, noise will go up in pitch with RPM. Arcing often visible in dark conditions. It usually doesn't hurt to throw a quality new cap, rotor, wire set and plugs at it.

Also, even with all wires disconnected some alternators will still make power, run it for a moment with the belt off to be sure.

[amyk]

Are you using solid-core sparkplug wires?

[mikerj]

A suitable capacitor on the ignition coil to ground would be my first move, with such a long ignition feed wire and no suppression cap it will be radiating plenty of RF.  Check cleanliness and tightness of all battery, ground and alternator power connections, an intermittent connection in these circuits can cause large voltage spikes.

[Terry Bites]

Spanner to spanner. I'd look at the Batt+ at various points with a scope powered from a separate battery. If its not ignition noise, the likely culprit is the regulator. When charging stops, the alterrnator voltage will surge. One good solution is to put a 15V "Load Dump TVS" at the points your sensive loads are connected. About 50p a pop.

[bdunham7]

Are you using solid-core sparkplug wires?

Bingo!  OP, answer this question before you even look anywhere else.  If you don't have OEM ignition wires, you should remove them and measure their resistance and report back.

[floobydust]

A car has two main grounds, check that they not broken or corroded.
The battery has a high current ground to the engine block (starter/alternator), plus a second ground wire to the chassis - usually from the battery(-) but many cars have a flat wire braid from the engine block to body/firewall. This is essential.
If the body ground is missing, you get -ve voltage spikes from accessories, such as brakelights, headlights etc. (which are typically grounded to the body) and I have seen it cause old Chevy's ALT light to come on dimly.

If the engine block-battery ground is high resistance, cranking will pull current through the body ground which again makes -ve spikes that destroys electronics.

edit: It looks like Vanagon battery(-) is solely connected to body ground, and there is a high current ground braid from transmission to body, at the rubber mount in the undercarriage, where all the water and salt is.
https://www.thesamba.com/vw/forum/viewtopic.php?t=548492