Guys,
I have recently re-established a friendship with an old school mate of mine
who just happens to work for Cosworth in Northampton in the UK. I have asked
him about getting the EPROM / ECU re-mapped and these are his comments. No
very encouraging, but I will keep digging.
Regards,
David "working slowly towards a surge free GTS"
.......
Hi David,
Gosh - this sounds serious!
I would be a little hesitant to totally replace the EPROM and have to map
every value back into a new one yourself with just the one change to remove
the surging problem!
Ideally you will need to interrogate the original EPROM and establish
exactly which numbers control what.
Most ECU data is based upon temperature, speed and load inputs , processing
of these parameters outputs a fuel injector duration - usually fired once
per rev if non timed injection (injection point not related to any engine /
cam position - just an expensive carburettor!) or fired once per cycle if
sequential (usually timed to fire onto a close inlet valve just before inlet
valve opening, fuel evaporates on the valve so good mixture preparation and
emissions - open valve injection usually better for power)
I would start by looking what inputs the ECU receives , i.e. engine speed,
engine load (throttle position or inlet manifold vacuum), engine coolant
temp, air intake temp etc!
These would probably tell you what sort of tables to look for in the EPROM
data - usually a fuel injector duration in milliseconds with axis of engine
speed and load. these will be corrected by various other tables to add fuel
for cold starts, or to shut off fuel on the overrun, or transiently add fuel
on rapid throttle inputs.
Ideally you would just want to find the maps that may relate to steady state
operation at 3.5krpm play with these, leaving well alone all the maps for
"correction" of the fuelling. It's a pretty big job to guess which chip
address relates to which "map" or parameter.
Does the ECU also control ignition timing or is it just fuel - this could
also affect drivability seriously.
A good automotive book is "Automotive Fuel Injection systems - A technical
guide" by Jan P. Norbye - published by Haynes publishing group - ISBN
0-85429-755-3 don't worry it's not actual too technical!
Ideally it would be nice to find out the cause of the hesitation - could be
wrong fuelling - too rich or too lean or wrong spark - too advanced or
retarded - or maybe to fix it people have just over fuelled the engine at
this point to override a badly calibrated transient correction. Or maybe by
retarding the spark or over fuelling people just slow the response /
acceleration of the engine and so move the frequency of the response to road
load feedback to such a point that the surging does not occur!
As you can see this sort of thing is a nightmare!!!!
But look on the bright side - the engine I'm working on has 14,700
calibratable maps or parameters - including fly - by - wire, traction and
stability control, abs , gearbox control, ECD stage 3 emissions, and full
OBDII diagnostics.
By the time this lot all relates its a night mare to get the engine to
start!
I'll have a dig round see if you can find out any more info.
See Ya,
Paul.
