Re: [T3] Coil Wire Resistance

["Jim Adney" <jadney@vwtype3.org>]

On 22 Dec 2007 at 21:18, Steve Bradley wrote:

> Jim, I'm not trying to argue you down but, why does Bentley say the 
> acceptable range of output of the regulator is 13.5 - 14.5 V. at 2K RPM 
> (Electrical System, Section 6.3)  Is the book just wrong?
> 
> Actually, I hope you are right. I'm going nuts trying to solve this problem.

The range stated in the Bentley is the standard range which is fine 
for carburated cars, where the only real consideration is whether the 
VR will keep the battery charged enough to start the car the next 
time. At the time the Bentley was originally written I don't think 
ANYONE had realized the consequences of low system voltage on the FI 
system. It's not mentioned in ANY of the BOSCH troubleshooting guides 
that I've ever seen, either.

This is just something that I discovered maybe around 1980 or so, and 
greatly to my astonishment. I was working on a friend's square and 
couldn't find the cause of his mysterious miss. Like you, I'd gone 
thru everything and still come up empty. Finally, in desperation, I 
decided to go ahead and replace the clearly failing VR, just because 
I'd run out of "reasonable" things to do. I REALLY didn't expect it 
to fix the miss problem, but it did.

Since then, we've seen this problem/solution over and over again. And 
you can find it mentioned in the occasional web site where other 
groups, concentrating on other D-Jet cars, have discovered it 
independently.

And in all honesty, I was skeptical at first, mostly because it 
seemed so counterintuitive that low system voltage would create a 
rich running condition, but it does.

I suspect that part of this was intentional. One thing that Bosch 
did, was to design this in so that the FI would richen the mixture a 
bit when the starter was cranking. It's part of the cold start 
process. I just don't think they thought about what might happen 10 
years later when the VRs started to wear out.  

-- 
*******************************
Jim Adney, jadney@vwtype3.org
Madison, Wisconsin, USA
*******************************

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