DIY_EFI Digest Friday, October 8 1999 Volume 04 : Number 567 In this issue: Wastegate parameters HTML posts Re: Up Up and away RE: How completcated does Efi HAVE to be? RE: How completcated does Efi HAVE to be? Backward 02 sensor? See the end of the digest for information on subscribing to the DIY_EFI or DIY_EFI-Digest mailing lists. ---------------------------------------------------------------------- Date: Thu, 07 Oct 1999 12:29:20 -0400 From: Barry Tisdale Subject: Wastegate parameters Of all the GM ECU documents circulating on the web, none appear to contain the wastegate parameters for ECU control. My specific interest is in the '91-'93 Syclone/Typhoon, but any info would be appreciated. Thanks - Barry - Sy#26 ------------------------------ Date: Thu, 7 Oct 1999 15:34:53 -0500 (CDT) From: eclark@xxx.com Subject: HTML posts Could everyone please set thier email clients to send plain text. HTML is for websites. I hope I'm not the only one who feels this way. - - Eric ------------------------------ Date: Thu, 7 Oct 1999 16:40:50 -0700 From: "John Dammeyer" Subject: Re: Up Up and away Yikes, Phil, please turn off the HTML OK. I knew that sooner or later you'd pop in with that comment. 8-). I don't agree with you. Altitude does make a difference. I can throw a bunch of advanced Physics and Math to prove it, (I stayed up really late one night), but let's use common sense and intuition to come up with the result that Bernoulli later proved. Air is a fluid and has mass. To move air from one place to another requires force. In the case of air the force is a difference in pressure between two locations. The key element to understanding why a lower external pressure (outside the throttle plate) will move less air into the cylinder for an equivelant MAP is that the difference in air pressure results in a different air velocity. The internal combustion engine is not a static environment but one in which time plays a factor. The intake valve is open for a period of time. During that time the piston moves down and creates a low pressure area inside the cylinder. This causes the higher pressure area in the plenum to force air to move into the cylinder at a velocity dependant on the difference in pressure between the two regions. At the same time air from the atmosphere is moving past the partially open throttle plate at a velocity dependant on the atmospheric pressure and the MAP. The intake valve closes before the air pressure equalizes to the value of atmospheric pressure. Air continues to flow into the plenum past the throttle plate and the pressure would equalize to atmospheric if it were not for the next intake valve opening for the next cylinder intake stroke. So the MAP is a reflection of the velocity of the air mass flowing into the system and the velocity over time tells you how much air has actually entered the cylinder while the intake valve was open. Now because the air does have mass it doesn't stop flowing just because the valve has closed. It piles up around the intake valve and the pressure inside the manifold starts to increase at a rate faster than the difference in air pressure. When the runners are the correct length this all works together to create a sort of supercharger like puff into the next opening intake valve which actually improves the breathing of the engine. The faster the piston goes down, the more extreme the difference in pressure between the intake manifold and the inside of the cylinder and the faster the air will flow. You can simulate this with a pressure gauge and a bit of hose. Suck at the end of the hose until the gauge reads 10"Hg. and then block the hose with your tongue. If there are no leaks the pressure will stay at that value. Put a pinhole into the side of the hose and you have to continue to suck to maintain a value like 15"Hg. Suck faster and you can draw the pressure down to 10"Hg. but you're also moving more air. Now I am not saying that a Pulsewidth[MAP,RPM] table will not produce a nice clean precise fuel mixture for an engine. It does. But, the MAP and the RPM only tell you how fast the air in the intake manifold will travel into the cylinder and not how fast the replacement air moves that is drawn into the manifold past the throttle plate. Yes, on average a higher altitude will create an average lower MAP and lean off the mixture a little; but not enough simply because the Dyno runs for that MAP and RPM value had a different pressure outside the throttle plate and the replacement air moves at a higher velocity. The velocity of the airmass and the time the intake valve is open is the important part of the equation. This is why Mass Air Flow Sensors like the ones on SAABs etc have an automatic altitude compensation and work so well with Turbo Chargers; which in effect, change the pressure outside the throttle plate causing a higher velocity air flow (and a resultant higher MAP) and more air into the cylinders. Phil, a while ago you posted the comment that no one had made a case for a barometer in a vehicle. Hope this helps. Regards, John >Date: Fri, 08 Oct 1999 01:18:11 +1000 >From: Phil Lamovie >Subject: Re: Up Up and away > > > > >

Hi All, > >

Recent postings regarding MAP sensors are in need of a little >
massaging. > >

Lets start with the definition    manifold ABSOLUTE >PRESSURE >
means what it says. Not relative or delta but absolute. > >

Any ECU mapped by speed/density AUTOMATICALLY corrects >
for engine load with altitude. > >

Question 1 > >

How does the engine differentiate between part >
throttle vacuum at sea level and full throttle at 10,000 feet ? > >

Answer It doesn't. There is no difference. > >

There is no need to check and record MAP value before startup. >
As the pressure varies absolutely so should the fuel table value. > >

Speed density demands only RPM and MAP (air temp correction is >
not mapped but mathed. same for all other basic corrections) > >

If the table has 16 speed values and 16 load points you will >
have sufficient date to run the engine reasonably. > >

Pilots had to correct mixtures only with badly designed fuel systems. > >

The mech/injected engines had no such problem. > >

Phil Lamovie >
Injec Racing > ------------------------------ Date: Sun, 07 Nov 1999 19:40:45 +0100 From: Ade + Lamb Chop Subject: RE: How completcated does Efi HAVE to be? At 05:00 06/10/99 -0400, you wrote: >>I am into minis, something a lot of americans probably won't have even >>heard of never mind seen! Up until recently minis had single point throttle >>body injection. You can pick up the inlet manifold, throttle body with the >>following sensors, The system is a MAP system. I was just wondering how few >>sensors I need to make it work. Make my own ECU and keep it simple. >>Calibration would be done on a dyno using a lap top. No need for a Heated >>o2 sensor, don't need it to learn really. > >I vaguely think that you only need a throttle position sensor and a map sensor >to do a reasonable job of EFI. However, you WILL need the crankshaft position >sensor, which means you need the flywheel, transfer case and the actual >sensor. Surely it doesn't have to be *that* accurate? Why not use the coil? 2 per Rev should be enough, you only need speed not accurate position? Ade ------------------------------ Date: Thu, 07 Oct 1999 19:32:58 +0100 From: Ade + Lamb Chop Subject: RE: How completcated does Efi HAVE to be? At 05:00 06/10/99 -0400, you wrote: >>I am into minis, something a lot of americans probably won't have even >>heard of never mind seen! Up until recently minis had single point throttle >>body injection. You can pick up the inlet manifold, throttle body with the >>following sensors, The system is a MAP system. I was just wondering how few >>sensors I need to make it work. Make my own ECU and keep it simple. >>Calibration would be done on a dyno using a lap top. No need for a Heated >>o2 sensor, don't need it to learn really. > >There is a EFI Control System called the Alpha-N which calculates air flow by >measuring only engine rpm (via coil) and throttle position via a Throttle >Position sensor. Pros are simple installation and compatible with radically- >cammed engines. Cons are no closed-looped operation, inferior part-throttle >cruise metering and entire fuel map must be reprogrammed. A MAP can be >optionally >used but mainly as a input for barometric pressure for different altitudes. >This system is used for racing or heavily-modified street engines with big >cams and low vacuum. What about coolant temperature for a 'choke'? I am not bothered about closed loop stuff. I am used to carbs. I would just be nice to be able to plug a serial lead into it and tweek the mixure and the throttle pump rather than filing needles and changing the oil in the dash pot (Su carbs). Thanx, Ade ------------------------------ Date: 08 Oct 99 18:53:15 +1200 From: "Tom Parker" Subject: Backward 02 sensor? Hi, I built an EGO sensor gauge using a Jaycar kit based around the LM3914. I got my sensor off a Mitubishi 3 litre v6 car. I don't know what model, as the badges were missing in the bone yard. The gauge works as expected. The sensor does not. It seems to be backwards. As I understand it, low voltages point to a lean condition and high voltages point to rich. On the car, my guage reads about 0.85v cruise and flashes to around 0.1v when you hit the throttle. I'm running it in an out of tune mini, which is running rather lean at the moment. When I pull the choke out, the voltage drops to around 0.1v. The sensor seems to respond very quickly, and does everything that I expected from reading here, except that the voltages seem to be reversed. I had it in a flame from a butane torch, and it would read very low voltages while inside the flame, and would read 0.85v while in the air or in the flame exhaust. On occasion the voltage went negative, to about -0.1v. Is this normal? Anything to worry about? The sensor is a 4 wire unit, and I couldn't find any manufacturer's name, although there is something undneith some underseal on it. - -- Tom Parker - parkert@xxx.nz - http://www.geocities.com/MotorCity/Track/8381/ ------------------------------ End of DIY_EFI Digest V4 #567 ***************************** To subscribe to DIY_EFI-Digest, send the command: subscribe diy_efi-digest in the body of a message to "Majordomo@xxx. A non-digest (direct mail) version of this list is also available; to subscribe to that instead, replace "diy_efi-digest" in the command above with "diy_efi".