[T3] Voltage and current requirements of Cold Start Jet?

Jim Adney jadney at vwtype3.org
Sun May 1 08:44:40 PDT 2022

On 30 Apr 2022 at 15:49, Phil Hof wrote:

> Does it run on 12V? Or does the ECU feed something lower? 

The CSV gets the full 12 V from the system. I just measured the resistance 
of one, and got ~4 Ohms, so the max current should be about 3 A.

That said, I think there is probably a much better way to sort this out.

First, get a remote starting switch from your FLAPS. That connects to the 
starter terminals and has a long wire with a switch on the end that you can 
use to run the starter from anywhere you like. Of course, if you have a friend 
who can turn the key for you, you won't need this.

Then, if you have a timing light with an inductive pickup, you can use that to 
check each HV spark plug wire to see if current is going thru it. If the lamp 
flashes, you have spark. If you have spark, you can check the timing.

Finally, you said your engine dies when it gets warm.  If it still has spark 
when it dies and won't restart, I'm going to guess that this means that it's 
running too rich. There are a three things that can cause this.

One is the CSV running all the time. This can be caused by the temp sensor 
wire getting shorted to ground instead of going thru the temp switch. Or the 
temp switch being defective. The easy way to check this would be to unplug 
the CSV electrical connection and see if this cures the problem.

Second, if your car is a late '71 or a '72, it can be caused by misconnected 
wires on the starter, which often happens during a starter replacement. 
There's an easy diagnosis for this: If the fuel pump runs continuously when 
you turn the key ON, those wires are misconnected. The pump should only 
run for ~1 second when you turn the key ON, unless you start the engine.

Third, if your voltage regulator is worn out, the regulating voltage will drop 
and this makes the FI run rich. The regulating voltage should be above 14 V. 
If it drops below 13.5 V, replace the voltage regulator. The Bosch part # is 
30-019. To check this, measure the voltage across the battery while you run 
the engine speed up. The voltage will increase with RPM until it reaches a 
plateau where it flattens out. The flat part is where the voltage is being 
regulated. That's the voltage the voltage regulator is regulating at.  

You can also make these measurements at the generator, but the voltages 
will be about 1/2 V higher, so normal at the generator would be above 14.5 
V, replace the VR if below 14 V.  

A worn out VR is a VERY common, and easily fixed, problem with our FI 
cars. I have a  more complete writeup on this if you want it.  

Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA

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