know speed sensor inside out? EA82 efi

[steptoe]

Does anyone have and care to share an intiment knowledge of speed sensor circuit contribution towards EGR on our subies, especially EA82 efi ?

There are those who have converted to efi either EA or EJ, some have been able to use onboard speed sensor of the L series to connect to the new engines ecu. There are others who have not got it connected because it was an MY converted or an L without the speed sensor reed switch built in the speedo head uniit.

Those that have not connected have reported no drive issues.

My studies of factory manuals indicates that to test speed sensor all you need to do is just a few kph , they say 3 or 4 kph ! I recall so looks just to ensure it is rolling not actually at a travelling speed.

Elsewhere in the manual it says that the EGR control is disabled at 45kph and the vacuum to the EGR is then bled off by the EGR vacuum solenoid switch (on RHS of throttle on inlet manifold) , bled off to the intake duct from air box

Question is : Is it the same speed switch or vehicle speed sensor that provides info to the ecu for both above functions ? Last time I looked at L speedo was not looking for two reeds. Only found one circuit understood to be VSS. Whether the voltage changes from rest to moving then to 45kph will take some testing.

It sort of blows the theory out of the water that if you block of the EGR on EA82 turbos you can gain 10kW, unless those kW are found under 45 kph AND it is all functioning as designed


comment please......

[Gannon]

The VSS simply supplies a pulsing signal to the ECU.

The ECU is responsible for calculating the vehicle speed depending on the number of pulses received per second.

So yes the VSS is only one device with one output.

[steptoe]

OK so it is a pulse being continuously supplied so long as it is moving and speedo works ? and the pulse is driven by the magnet/spring bit of the needle

ringing some bells here. Thanks Gannon. I was thinking it was single funtion as in NO or NC type reed switch, not continuous supply of pulses, now thinking same as cruise control signal. Same pulse wire I used to find if lucky when fitting cruise controls 15 years ago for a parts shops customers - meant no magnets to tie up

The ideas behind this question is the intention to run EA82T in the Brumby....without an ECU and all its associated wiring. The fuel of choice being dedictaed LPG so no fuel management is required of the factory ECU just emissions which is only the EGR solenoid.

Spark and knock control is by the early non optic dizzy and its knock control module ( I found it Craig!), fuel is by LPG Impco using its own module controlling mixtures rich/ lean signalled by O2 sensor, so only need an ECU powered up and earthed and wired to control EGR to operate under 45kph. Can tinker with a cruise control magnet or two and pick-up to achieve this. Then the engineer certificate should be a breeze, not having to wirte up injectors, sensors, fuel pump relays etc, etc. Brumberty took this option of LPG to avoid ecu some time back with his Wonder Brumby.


It is located extreme LHS behind dash next to glovebox, can actually see its 2 mounting screws when open door LHS)

[Gannon]

Why not use the EA82 carby's EGR control system? And get rid of the ECU altogether

[steptoe]

Now this is a good reason to think out loud on a forum.

Intelligent suggestion Gannon

I have replaced the original solenoid vacuum switch with one off a carby unit to clear the solenoid stick on or off trouble code, so they are the same to that point. OK , to save me pouring over manuals for long time, can you share with me what it is that controls the EGR vacuum bleed off solenoid on EA82 carby? Whatever it is I hope it is not pressure sensitive to BOOST

[Gannon]

It isnt really clear in the manual i have, but it seems that it uses either orifice vacuum modulation, or thermo valve vacuum modulation.

From the diagram, the line is tee'd from the EGR valve, one line goes to above the throttle of the carby, (vacuum increases with load) and the other line goes to the thermo vac valve and to the air cleaner.

Im not sure how you would accompanish this on a non carby car as there is no vac on load with just a throttle and no venturi.

edit:

I just thought of it....

Have an adjustable vacuum switch that activates a soleniod valve to the EGR valve at between -10 inHg and 0 inHg, (cruising vacuum) and have a one way valve to prevent it working while you are on boost. Maybe also incorporate a thermo vacuum thingy so it only happens once the engine is warm

I'll draw you a pic if my explanation isnt real clear.

[steptoe]

Thanks again for your efforts and apologise for my laziness.

I have looked at factory manuals. There is one set up for Swiss and Swedes and one for others with carbies. Two others for turbo and plain efi.

If the diaphragm on the EGR valve itself can handle boost vapour should be OK coz it just won't open and work as required when low load and high vacuum is present.

I think I may have discovered an answer to what I recall as a 'discussion' as to only efi L series had a reed switch speed sensor and others claimed they had carbied L's with a speed sensor. Found a diagram of a carby L with a speed sensor in the diagram and comment that the speed sensor was used to disable the EGR function above 80kph. The turbo efi 3 plugger ecu is designed to disable the EGR at speeds above 45kph.

The thermo vac switch is used to disable the EGR if the engine is not at basic operating temp.on Oz carbied L's, possibly in combo with the speed sensor.

It seems the theory of EGR function is to keep combustion temps lower, but I guess the disable function that means not required at higher speeds and that it goes against eficiency and power if it does. So..... I guess I could hook up vacuum directly to EGR valve and loop in a switched relay off the boost light circuit to cut off the EGR vacuum supply as soon as boost comes on and rig up a circuit the responds to whatever pulse I can get from a magnetic pick up ala cruise control. A job for my electronics engineer buddy to prove himself ???

I sort of don't want the EGR to function at higher speed than necessary just because I have good vacuum indicating good econmy esp if the theory of EGR in use has an effect on economy...and there is also the idea in mind that to cut off EGR function totally the idle NOx goes through the roof

Itr was only the Oz delivered EA82T and efi ? that did not have a one way valve between the bleed off of the EGR solenoid and the pre turbo air intake - so many of us with alleged import motors may just have this valve in place !

You start to think that some of us would benefit from having a plethora of LEDs with labels on dash indicating just when what is operational within the ECU like those modern portable DVD screen sized kits you can get now to monitor all ECU function. Guess I could start with an EGR monitor LED !!j

[Gannon]

Have a read of this Autospeed - EGR Comeback

And Tweaking the EGR, Part 1 and Part 2

[steptoe]

Great response Gannon. Well spotted. I should spend more time at autospeed. I stopped buying Zoom when I worked out the style had changed (and the degree of genius) with Julian Edgar leaving/selling. I liked his McGuyver approach and ability to share in a well written way - much like our Disco! Discovered Julian and autospeed only this year. I gotta say I do HATE reading stuff like this on screen though, erk on the eyes neck etc.

I played with a spare EGR today hooked up to the Brumbys vacuum and just watched its response through the rev vacuum range on the spot. I can see it working as a basic no switch affair, yet can see it would be a bother on decel engine braking - so a cruise control style pulse pickup with magnet may have a place. I need to check my 88 wags set up when I find its keys and see if it is thermo valve and speed sensor pulse instead of plain switch voltage.

You'd think it would be enough for an engineer approval that an EGR is in place and works