[Vwdiesel] Cold starting procedure?

James Hansen jhsg at sasktel.net
Thu Dec 23 23:43:47 PST 2010

If you don't have a clamp meter, measure voltage drop across the bus bar,
should show a drop across each plug.  Ones that don't show a drop in voltage
after the plug as measured on the bar aren't consuming power. Pretty easy.

As Val suggests, a clamp meter for this is the way to go is you want to
measure current.  Most vom's are limited to 10a unfused passthrough current,
as in you place the meter in the circuit, and will release the smoke if you
exceed that 10 a rating. 

-----Original Message-----
From: vwdiesel-bounces at vwfans.com [mailto:vwdiesel-bounces at vwfans.com] On
Behalf Of Val Christian
Sent: December-23-10 10:11 PM
To: vwdiesel at vwfans.com
Subject: Re: [Vwdiesel] Cold starting procedure?

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
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
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
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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