[Supras] boost pulling timing

[Walker, Brian (Rich. Dist)]

Great explanation Jim. Seems like this could be a problem some folks run
into (ecu retarding timing more than mapped as coolant temps rise.) I'm
assuming this is where a lower temp T-stat would have an advantage?

For a while I've suspected the stock clutch as my car pulls pretty hard
on an auto-x course (high 2nd, low 3rd gear) but feels slow on straights
(only catches lower powered cars) at the track once it has some heat
built up (high 3rd/4th gear it revs but just doesn't want to accelerate
as hard.) Could be a combination of things and not just the clutch.

Your comment about knock code is why I was surprised I never got one,
the sensor literally fell apart after removing the KS wire connector. I
guess it must have been receiving a signal, although probably not an
accurate one. Acceleration was much improved after replacing the KS and
wiring, yet no code was thrown because a signal must have been present.

Brian W

-----Original Message-----
From: Jim Jobe [mailto:jjobe2 at supratech.org] 
Sent: Thursday, December 20, 2007 9:55 AM
To: Walker, Brian (Rich. Dist)
Cc: berniek at technicaldevelop.com; cthommes at adelphia.net;
Supras at supras.com; Jeff Mohler; Jeff Corbat
Subject: Re: boost pulling timing


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.