Re: DIACOM Errors

[Roger Heflin <rah@horizon.hit.net>]

On Sat, 6 May 2000, Scot Sealander wrote:

> Have you noticed any DIACOM errors?  Besides O2?
> 
> I have been tuning my TGP and am having trouble getting the 
> error below an integrator spread of 120 to 138 or so....  
> Most of it is reasonably close, but positive transients seem 
> to cause some (temporary) integrator increases, and negative 
> transients can cause some integrator (temporary) lean outs.
> I am assuming maybe some plenum filling, etc going on here?
> The added MAF also reports bigger VE numbers during this 

You have noticed that the car computer is not setup to reduce the
integrators to while it is adjusting the BLM?

I noticed on mine that when the BLM is adjusted because of the ints
being off enough that the ints aren't adjust to compensate for the now
higher BLM and keep the fuel mixture constant.

> time.
> 
> But back to DIACOM, the first error is in the two bar MAP 
> reading.  DIACOM does not report the two bar MAP correctly.  It 
> handles the 2 bar MAP as if it was a one bar MAP reading.  This 
> prompted a change in the ALDL stream to put the one bar MAP value 
> in there to at least get some more data points in the one bar VE maps.
> 
What is being put into the datastream?   I know for rpm they put in
rpm/25 so if you go faster than 6375 the reading is wrong, it would
not suprise me if there are other readings that are very similar.

> But moving stuff around by DIACOM readings was not fixing things.
> So while watching DIACOM, I noticed that it went into PE at 89 kPa.
> Knowing that the min PE load was set to 94 kPa, this meant some 
> investigation.  Putting the "MapInKpa" value in the ALDL stream for
> airflow revealed that PE was indeed triggered at 94 kPa per that
> reading.

Are these all values from the A/D convertor or are they the "filtered"
values?   Have you actually checked the math for diacom as compared to
what the ALDL data spec is, it probably would not be suprising if
there were a few off by one erors.

 > 
> At key on, engine off today, DIACOM reported 94 kPA as baro, and
> 94 kPA as manifold pressure.  The MapInKpa variable was reading
> 99 kPa.  At idle, manifold pressure was about 39 kPa, and the
> MapInKpa reading was 40 kPa.
> 
> So it seems that at least the one bar MAP and baro readings may 
> be off by about 5% at the high end.  The lower end seems to be
> much closer.
> 
> Scot Sealander
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