[T3] Bad day at the (FI) office

[Daniel Nohejl]

> One of your readings is low by a factor of 10. Looks like you got 
> your scales mixed up, below, but I can't tell which reading is 
> mistaken because I don't know which is which. If what you typed is 
> correct, that may be part of your problem.

My multimeter (Fluke digital) doesn’t throw out decimal readings unless resistance goes into the highest scale so there isn’t any way I could have misread what I saw. I got a straight up reading of 64 ohms for each temp sensor yesterday. I removed the 100 ohm resistor from the CHTS for this reading. If you’re expecting that one of these should be 640, then perhaps this relates to my issue? Again I took these readings after I’d been driving for close to an hour so the motor was well-warmed up, not just initially warmed up and I expect the resistance would be quite low. I just don’t if it's too low or not. I don’t have any reason to doubt the multimeter but I could try another one and see what it says. 

In general, is 64 ohms too low for the CHTS when fully warm? 

Is 64 ohms too low for the air temp sensor when fully warm? 

> Keep in mind that we don't have any actual F/A data on the '68-9 
> D-jet engines, so, even assuming that your meter is accurate, you may 
> be going astray on an assumption of what to expect for F/A. And, BTW, 
> this is D-jet, not K-jet, so stick with the D-jet manual.

I’m not using a K-jet manual….I was talking about  the manual that Russ Wolfe often posted pages of on The Samba and on his website. Tram uses it as well and refers to it as a workshop manual they used at the dealership. All the section headings I’ve seen begin with “K” so I just called it the K manual. Like these for example (they should link to Photobucket):

VWFIwiringT3troubleshoot.jpg <http://i260.photobucket.com/albums/ii33/tramandbixrule/VWFIwiringT3troubleshoot.jpg> 

VWFIwiringT3.jpg <http://i260.photobucket.com/albums/ii33/tramandbixrule/VWFIwiringT3.jpg>


> Right now I'd say that you're caught between 2 sets of conflicting 
> data. Your F/A meter is telling you that you're too lean; your gas 
> consumption is telling you that you're too rich. Your temp sensors 
> seem to be saying that they think things are still not getting fully 
> warmed up, so it's running rich.  What should you believe? Unless 
> you're leaking fuel out on the ground somewhere, the fuel consumption 
> calculation is so straightforward that there's little chance of 
> significant error.
> 

I think that in my frustration I might not have been clear. The meter isn’t giving conflicting info. It’s telling me I’m rich with the resistor installed at the CHTS and this is in accord with my poor fuel consumption. 99.9% of my driving the last month has been in this state: resistor installed, bad MPG, rich AFR readings.

The meter only tells me I’m lean when I remove the resistor and I don’t drive for very long under those conditions both because it isn’t enjoyable (underpowered, hesitating, sometimes bucking) and it isn't inadvisable (too hot). Since I don’t drive for more than a few minutes without the resistor, I don’t have any fuel consumption records for that condition. While it might not be scientifically precise, the meter is in synch with my experience.  

The only reading I’m actually confused about is the one at the CHTS with the 100 ohms added. If I remove the resistor from the CHTS, then I can say with relative confidence that the resistance readings at both temp sensors suggest that they’re fully warmed up, though, like I said above, I’m not sure if the non-resisted readings are too low or not. Since my resistor isn’t even providing a full 100 ohms of resistance (more like 70-90 depending), I’m struggling to accept that 70-90 ohms of extra resistance is preventing the sensor from reading as fully warmed up when the resistor is installed. However, the difference between poor fuel consumption and too lean to drive seems to be this 70 to 90 ohms of extra resistance.

Keith and William have both affirmed that the CHTS should get below 100 ohms. However, I’ve read conflicting things about the role of the CHTS after warm up. Some say it only influences warm up and signals to the ECU that the engine is warm while others suggest that it continues to influence the fuel mixture at all times.  Both make sense to me but the latter would certainly explain why sometimes in the summer the idle can be a little rough after a long highway run. 




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