[Supras] boost pulling timing

[Jim Jobe]

Boost (MAP, Speed Density), AFM, are ways to measure air volume,
commonly referred to as "load".  In the case of the 7MGTE ECU,
air volume is calculated using the AFM and IAT sensors as inputs.

Yes, any ECU should retard and advance ign timing vs load either
via a function or a pre-programmed table.  RPM, coolant and intake
air temp, as well as of any number of variables inputs are used 
when calculating ign timing.  Ign timing is usually retarded
as temps pass the normal operating range in an attempt to
control cylinder temperatures.

Something like this: (numbers are arbitrary for example)

Ign Timing table.  Note the dip at higher boost. 

  10| 17 16 14 13 14 15 16 17
  9 | 18 17 15 13 14 15 16 17
  8 | 19 17 14 14 15 16 17 18
P 7 | 20 19 17 15 16 17 19 22
S 6 | 20 21 19 16 17 19 21 24
I 5 | 22 21 20 19 19 20 22 24
  4 | 22 23 22 21 22 23 24 25
  3 | 24 24 24 24 25 26 27 28
  2 | 26 26 26 26 27 28 29 30
  1 | 26 26 27 28 29 30 31 32
    -------------------------
      3  3  4  4  5  5  6  6 
      0  5  0  5  0  5  0  5
      0  0  0  0  0  0  0  0
      0  0  0  0  0  0  0  0
              RPM

Ign Timing vs temp

 +2.0 +1.5 +1.0 +.5 0  -.5 -1.0 -1.5 -2.0
 ------------------------------------
 1    1    1    1   1  2   2    2    2
 5    6    7    8   9  0   1    2    3
 0    0    0    0   0  0   0    0    4
              Coolant Temp (F)

The "knock sensor" code is triggered when the ECU
does not receive any signal at all from the knock
sensors.  The knock sensors are essentially microphones
with a bandpass filter applied.  Any time the engine
is running there will be some noise.  The CE code is
to tell you that the knock sensor circuit is malfunctioning
because no signal has been received, not because it is
reading above the threshold suggesting there is knocking.

On Thu, Dec 20, 2007 at 09:07:32AM -0500, Walker, Brian (Rich. Dist) wrote:
> I'm not aware of a feature that would cause boost to pull timing, I
> believe that circuit is open loop as I don't recall the ecu receiving a
> pressure signal from the sensor. Perhaps it's related to an airflow
> signal that pulls timing? (from my understanding the ecu should retard
> timing at higher boost for safety and power reasons, I'm imaging that's
> a function of airflow in the maps?)
> 
> I wonder if anyone out there has datalogs showing timing vs. boost? The
> MAFT is supposed to show this info, but I haven't had a chance to mess
> with mine since install. FWIW, I've never had a code for knock, even
> when one sensor crumbled apart as I went to remove it.
> Brian W
> 
> -----Original Message-----
> From: berniek at technicaldevelop.com [mailto:berniek at technicaldevelop.com]
> 
> Sent: Thursday, December 20, 2007 12:58 AM
> To: Walker, Brian (Rich. Dist); cthommes at adelphia.net; Jim Jobe;
> Supras at supras.com; Jeff Mohler; Jeff Corbat
> Subject: Re: boost pulling timing
> 
> I've wrestled with this issue too, running a Lex and 550cc injectors, 57
> trim CT26, 3" turbo back exhaust, 15-17 PSI boost, IC upgrade to come,
> some hardpipes, all with the stock ECU, trimming fuel pressure and the
> Lex bypass.  In a word, the pressure transducer at least in '90 and '91
> applications only operates the dash gauge, nothing more (it will operate
> up to almost 15 PSI at about 14.9V output if you rescale the gauge
> circuitry to match it).  That leaves the knock sensors to retard timing
> if and when needed under higher boost.  I believe Jeff Corbat is running
> a setup like this with a stock turbo and has had no problems.  I've had
> no codes set ever (in all of 500 miles, lol, but some of it before the
> snow under really punishing conditions.
> 
> 
>     Bernie
> 
> 
> PS:  I believe I might have an earlier ECU which might explain slight
> mixture dependence upon temperature and faster idle with the lights on.
> 
> Once when I did not catch second gear upshifting in time, it spun to
> 6500 RPM, which '91's with fully counterweighted crankshafts are not
> supposed to do.  My '90 stuttered at 6200.