87.5 CGT Trip computer & MC swaps, do they get along?

Joshua Van Tol josh at spiny.com
Wed Jan 14 00:13:09 EST 2004

On my megasquirt conversion, which will be done one of these days, I'm 
planning on synthesizing the air flow plate signal. I'm going to data 
log the air flow plate, as well as the other engine parameters (MAP, 
throttle position, coolant temp, rpm,  etc) and figure out what the 
correlation is. Hopefully it's linearly related to air flow, which 
would be great, because that's pretty easy to extract from the MS.

Then, I'll be adding a D/A converter to he MS, and that'll output a 
"fake" signal to replace the lost air flow plate signal.

If I get it working I'll share.

On Jan 13, 2004, at 10:12 PM, Huw Powell wrote:

>> So in summary, the orange digidash was used in 87.5 CGTs and later 
>> urqs. .....   But
>> for the most part, the orange digidash only needs speed and fuel 
>> level to calculate fuel consumption and does not require either the 
>> airflow pot OR the fuel enrichment signal from the ecu.  Neither is 
>> provided for on the urq.
> There is no way to possible calculate fuel consumption (instantaneous, 
> especially) without more inputs.  The trip computer must have some 
> sort of engine load info in order to do the math.  I suspect it is 
> just getting the data via a different path, ie, it's hooked up in some 
> other way than the earlier ones.
> As far as unused wires/connectors, I'd venture to say that *all* 
> vehicles will have them - because complex harnesses are usually built 
> to support a range of options.
> Anyway, I still think there is no way you're going to get one of these 
> old CIS trip computers to fully work after an EFI conversion.  On the 
> later UrQ's which are EFI, the TC is surely getting air flow data from 
> *somewhere* - probably the engine ECU, which gets it from some sort of 
> sensor other than the old CIS airflow pot.
> As far as the appropriate dash for an 87.5 (etc.) CGT, this could be 
> useful info.  Though, I'd swear the one I have (87.5) is a red dash - 
> and the TC works, as little as I've run it.  I'd go out and check in 
> teh field now, except the temps just dropped below 0 F again... and 
> won't be back up above that for a couple of days... brrrrrrr
> -- 
> Huw Powell
> http://www.humanspeakers.com/audi
> http://www.humanthoughts.org/
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