[Vwdiesel] Cold starting procedure?
val at mongo.mongobird.com
Thu Dec 23 20:10:40 PST 2010
Actually, a good DC clamp ampmeter is very valuable. A series ampmeter
isn't as helpful, and as quick, especially if you are faced with harnesses
that don't come apart as easily as the glowplug harness on an 82.
For example on a TDI, you can clamp the sensor over different parts of
the glow plug harness to see what the current is to each plug. Within
about a minute, you get accurate readings.
I had a intermittent problem which was causing a (non-diesel) engine to die,
and it was tied in with the fuel pump, ECU, ignition harness. Took me a while
to find it. But in the end, pulling out the clamp meter, tagging
the individual wires, and nailing down was was happening at each point
allowed me to find the ultimate problem. (Which was the insulation of a
wire which had chaffed on a valve cover edge, through the insulation,
intermittently grounding that signal.)
Five years ago, I got a couple of these meters, and they were about $110 each.
Now I see them for about $40 on eBay. I have one which auto-zeros with a
button, and one which is zeroed out with a side mounted thumb operated
pot. Get the auto-zero one if you can. For 40 amp measurements, it doesn't
matter, but much of the debugging you'll do on a car is less than an
amp. Sure, an in-line ampmeter would be better with a couple of milliamps,
but the DC clamp is good enough for 95% of what you will need to do on
cars, houses, etc.
AC only clamp meters (usually capable of measuring DC Volts) are in
the $10-$13 range. The DC Amp ones are more, so don't buy the wrong one.
While most of the clamp meters top out at 200 amps, some run to 400 amps.
Generally, they aren't suitable for starter motor diagnostics on a diesel,
because the currents are higher. But they work great for lighting,
alternators, etc. Want to know how much charge is getting into your battery?
Just put the clampmeter on a battery cable while the engine is running,
and you can readily see.
They are the bees knees for hunting down parasitic drains on batteries, as
End of rant.
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