john banks

At atmospheric the MAP sensor reads about 2.3 volts, which is a bit too high for a simulated MAF signal and makes the car incredibly rich and misfires as soon as it starts.

However, if you start the car with the MAF disconnected and then a second or two later connect the MAP signal to the MAF input it idles beautifully with a reading of about 1.3 volts, which is just right for my engine. With a little blip of the throttle it accesses some sensible areas of the map that with a little work could make this workable.

When the car is started with the MAF disconnected there is a CEL, but this disappears once the MAP signal is connected.

Obviously the maps will need to be totally rewritten, and it doesn't take account of charge temperature, but neither does the Link ECU for my model year.

Need a short delay circuit which switches out the MAP to MAF link during cranking until a vacuum is established and it could be workable.

jgevers

Hi John,

It would be quite safe to run your engine with just MAP and Throttle position sensors as load sensors. Lot's of other turbo engines do. However, in my opinion, an inlet air temperature sensor becomes more important. Air density does have a dramatic effect on fuel/air mixture. I know your IA temperature seems to be quite low at all times but on prolonged high boost runs it will climb suddenly and a lot. Various manufacturer's motorsport teams have tested this, and that's why a lot of manufacturer's race/rally teams have boost mapped with IA temp as a parameter.

If you want I can dig some of the paperwork out on this subject.

regards,

Job

john banks

That would be handy Job. I was going to use a microcontroller to do this see http://bbs.22b.com/ubb/Forum7/HTML/000240.html but it got a little complex and I got distracted

I could try to get it running with pressure only first and then alter the signal with a little circuit at a later date to compensate for temperature?

I suppose there would be a 10% change in density for 27 degrees approx (0C = 273K, n is proportional to absolute temp).

[Edited by john banks - 12/6/2003 8:17:25 PM]

Windows

John, probably a totaly different situation, but wondered if you could give a bit of advice mate?

My car is fitted with a Link ECU just now, but, I need to remove it.
I am getting a GEMS fitted within the next couple of weeks, but the only thing I can replace the Link with at the moment is my standard ECU.
Problem is, I dont have the MAF anymore, (custom turbo inlet)
Is there way to get round running the standard ECU without a MAF short term?
Not planning on driving the car hard, could even drive it off boost, but I need to get the Link sent to the customer who has bought it ASAP.

Cheers

jgevers

You could bodge it by using a basic switch over relay, activated by something like the abs warning light? Would take 15 mins.

I think you are right on air density, but if I remember right, it is quite different under pressure.

Job

[Edited by jgevers - 12/6/2003 8:47:35 PM]

john banks

Nice thought on the relay Job.

The MAP sensor reads 0.88V in an absolute vacuum, and about 0.1V per PSI above that. So I am thinking of putting the MAP sensor signal into the non-inverting input of an op amp, 0.88V into the inverting input. The output would then be proportional to airflow. I could then use a linear thermistor to bias the gain of the op amp to correct for temperature.

I can rescale the MAF to load table in the ECU to linearise it and zero reference it

Without using temperature compensation, when the charge temperature is high the mixture would richen and the timing would retard, no bad thing in a way, but not by design.

Unfortunately Windows, when you disconnect the MAF sensor with JECS it is a very primitive limp home mode, and it can also tend to run extremely rich indeed. It would be OK for moving the car a few hundred yards, or around a garage/driveway to get it out the way, but it would be better to hire a Micra rather than drive with no MAF from what I've seen!