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Re: [T3] 68 Fastback FI (?) Issues - Diagnostic Help Requested

On 27 Mar 2006 at 17:35, Mike Smith wrote:

> The >14.5 V reading was taken from the VR's battery (double prong) side.

That's right for engine off or at idle, but it should rise with RPM 
until it regulates and levels off between 14.1 and 14.4. The latter 
voltages will be low if the battery is discharged, so I recommend 
making this measurement after driving around a bit.

> Per my other message - I picked up both a "new generation" Bosch (solid
> state) 30-019 VR from my VW jobber and Niehoff unit from my local parts
> store.

So Bosch sells the new version under the same old part #? That seems 
odd, but maybe not too odd.

Read on below....

> To start this episode, I started the car and backed out of the garage - at
> that point, the car started right up and was idling fine; so I turned off
> the car and pulled the battery ground cable.
> I pull off the VR that was installed in the car and put in the "new" Bosch
> unit, making sure all wires were on the correct connectors.  It was a bit of
> tight fit against the heater channel, but there was no risk of shorting the
> connection and the thick card stock that folds up over the VR is still in
> place.
> I reconnected the battery ground cable and started the car.
> At this point, the car ran very badly - certainly not as well as when I
> started.  It was running at a very low RPM, nearly stalling idle, with light
> backfire "pops" out the tail pipe...  I opened the throttle - there was a
> significant hesitation and more backfire.
> I put on the dwell/tach and my timing light - the RPM was sitting around
> 600, but I was still showing timing at 0 TDC.  I tried to pick up the idle a
> bit by backing out the idle adjust screw on the throttle body, but that had
> no effect in that direction and screwing it in would just drop the RPM to
> near stall.
> I then checked the voltage off the "new" VR - on the battery side (big
> double spade connectors), it was reading 12V... sheesh... turned off the
> car.

12V at idle could have been okay. The test is to see what the voltage 
does as the RPMs increase. At idle, the generator isn't putting 
anything out, regardless of what kind of VR is in there.

> After venting a long blue streak, I collected myself, and pulled the Bosch
> VR and replaced it with the Niehoff VR - that VR looks very much like the
> Bosch unit I pulled out of the car.
> I then started the car again - it seemed to start a bit better, but the idle
> seems a bit "iffy" - but the voltage coming off the battery side was a
> steady 14.5V... I took the car around the block - but it's still bogging.
> I'll probably get some time tomorrow to take it out and have my son watch
> the voltmeter on a somewhat longer drive and see how that looks.

I'm assuming that the 14.5V figure was at higher RPM. That number is 
a bit on the high side, but still within the margin of error.

> I hope I didn't fry the brain in some fashion with that new-fangled "solid
> state" Bosch 30-019 VR...

I've also heard some bad reports on the new VR, but I don't really 
trust those reports since they come from people who don't really 
understand generators, VRs, and charging systems. They could still be 
right, however. They just told me they had more trouble with the new 
ones than with the old ones.

Low voltage certainly won't hurt the brain, and I think it would take 
something above 20 V to damage it. I don't know where that might 
actually occur. I've never "tested" that limit.

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

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