[T3] Two Tests

[Jim Adney]

On 18 Sep 2019 at 14:54, William Jahn wrote:

>  It seems to boil down to the ECU TS1 internal circuit. I would say it's
> slightly lean because of the reaction of unplugging TS1 yet I've read it
> could be either on Samba.

My guess is that it's NOT the temp sensor circuit, because of the fact that 
unplugging that sensor has exactly the effect we expect. That seems to say 
that that part of the brain is working, and making up for a fault elsewhere. 
That fault could be either inside or outside the brain, but you may have 
narrowed it down to inside.  

> If it's not the ECU then it's possible the MPS is set to lean, yet two
> of them acted the same way even though one was a 0 280 100 101 / 311
> 906 051D in the car now 0 280 100 116/ 311 906 051E. 

Testing the ECU by substitution is the only way to go, once you've tested 
everything else. You seem to have found some new loose connections and 
those are always a problem. By far, the best way to do all those tests is with 
the Bosch tester, along with someone who knows how to use it.

If you are willing to buy a buy a brain from me, I will offer to buy it back from 
you if you decide it doesn't help. You'd still end up paying for shipping both 
ways, but that would be $40 instead of $70. That's $50 for the brain and $20 
for shipping each way.

OTOH, if the temp sensor connections was intermittent, that would send a 
signal to the brain that was confusing. There's no way to know how the brain 
might respond to that. Unplugging the sensor would send a wrong signal, but 
at least it would be a constant signal.

I wondered if there was anything in the brain that might smooth out an 
intermittent signal from the temp sensor due to a bad connection. Looking at 
the schematics from Rennlist (they appear to have disappeared from 
Rennlist, but I had copies) I see no smoothing elements in that circuit. That's 
from a Porsche brain, but I'd expect your circuits to be similar.

In addition, I see that the temp sensor is in part of the circuit that drives the 
primary of the pressure sensor. An intermittent connection there might cause 
extra pulses to be generated in the pressure sensor output. That doesn't 
sound like a good thing. While we don't know that this is what's happening, it 
remains a possibility.

You asked how a worn set of trigger points could have an effect. If the 
rubbing blocks were worn or out of adjustment, that contact might fail to open 
occasionally. (If they were VERY worn they would NEVER open and the car 
would not run at all.) When just marginally worn, they can work sometimes 
and not others. I've experienced this and it's really annoying, but it happens 
under load and while driving, so this is probably not what you have.  

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