catflap

LOL, arg you buggers thinks catflap, sitting on the fence not realy understanding, but finding it all very facinating and learning while


Sooon he ponders to himself " i will understand all of this, soon."

puting my car on a select monitor on wednesday, will this show me if my setup resonably accurate?

john banks

see what you are saying.

If you have a ground with a resistance then it will have a potential difference across it though = offset?

paulwadams_my99

Yes, but there is no resistance going directly to the battery as there are no other cicuits in the way to take any current.

If anyone knows Darrens email adress then can they post it to me or mail me cos i would appreciate his input into this and why he made such a point about earthing at the battery.

Cheers

Paul.

john banks

The select monitor will read the Lambda relative to its ground LOL! This is what the ECU gets.

paulwadams_my99

and ifts wrong i wonder what things they will check?

[Edited by paulwadams_my99 - 3/10/2002 11:44:24 PM]

john banks

the heater grounds separately, so shouldn't be an issue, so I hear you again. (slowly being convinced )

is Darren's address on the website?

paulwadams_my99

cant find it anyehere on there.

dowser

Paul/John - methinks you should both sort out star-point earthing and be done with it

Richard

john banks

Use that then, otherwise the Link manual on the MRT site gives you ECU pinouts. Or there is a full ECU diagram on Ravensblade.

[Edited by john banks - 3/5/2002 3:24:58 PM]

paulwadams_my99

to where though? Can't see enough metal in the hole/plug, or did you strip the insulating and solder and tape up?

[Edited by paulwadams_my99 - 3/5/2002 5:22:34 PM]

john banks

Don't know. Your car is probably OK and it is the setup or the installation of the meter.

It is somewhere in the DIY AFR thread.

[Edited by john banks - 3/5/2002 7:25:17 PM]

paulwadams_my99

hmm i can find this in there John:
<600 <1% >15:1
720 1% 14:1
760 2%
800 3%
840 5% 13:1
860 6% 12:1
880 >8% 11:1

I was really after some kind of info which detailed what is recomended through the rev range on WOT, something to base my readings against.

oh this bit " Recommendations I have are that for 3-9PSI boost you should see 830mV - just under 5% CO 13:1 AFR. Between 9-15PSI boost you should see 850mV - 5.5% CO 12.5:1 AFR. Over 15PSI boost you should see 870mV - 7% CO 11.5:1 AFR."

Where did you get that info from?

The original thread also has people stating they taped into wire 21, yet ravensblade shows you to do it to 18.
No 18 on my blue plug is a white wire with silver dots down it. Thats what I have connected to. Thats the right one isn't it?

edited to try and avoid confusion

[Edited by paulwadams_my99 - 3/5/2002 8:36:01 PM]

T-uk

edit to add-taken from the possumlink version 5 manual
note-this is looking into the mouth of the plug

I used on my MY00,
pin21-signal
pin9-power




[Edited by T-uk - 3/5/2002 9:21:13 PM]

paulwadams_my99

oops posted the wrong link there I have the right one anyhow

Guess I better find out what the voltages are set to then, I take it I can just strap on a voltmeter to the connection and see what I am getting?

edited to say thank you t-uk

[Edited by paulwadams_my99 - 3/5/2002 8:42:41 PM]

paulwadams_my99

well i was getting blue to start with then as the engine really heated up it seemed to settle on orange?

[Edited by paulwadams_my99 - 3/5/2002 11:31:27 PM]

paulwadams_my99

oh right, i'll check tomorrow then on way to work.

I could get it to stay on red by doing half boost after i had booted it. I'll give it a full test tomorrow and possibly stick a voltmeter on.

Thanks again everyone for your patience, i do appreciate it a lot!

[Edited by paulwadams_my99 - 3/5/2002 11:46:13 PM]

tonymy01

I tend to agree with John (am also an Elec Eng). The sensor has two wires going to the ECU, one for signal, and one for "earth reference", and so taking the readings across these two points at the ECU is probably the best. However.... The LM3914 (this is the circuit you guys are using, right??) does draw current (and the LEDs of course!), so this current will now be flowing via the 12V feed (of course) and returning via the earth that you are connecting to the ECU, so perhaps upsetting the ECU O2 input pair with extra current that it wasn't expecting? Of course, as a guess, all the sensor earths are tied together in the ECU, along with the main ECU power earth, and so this may not have this problem doing it this way.
I have tried two different meters, both build it yourself kits (one with PIC, one with LM3914). I hacked the LM3914 kit, it has 10LEDs with the high/low mixtures indicated with red or orange, and put the LEDs vertically in the spot next to the clock in the MY01. (They just fit with a bit of filing..) The power and earth (and LED dimming) comes from the clock, but this does have its problems. When my headlights are turned on, the indicated level drops a couple of LEDs (indicating leaner), this also occurred with the PIC meter which was fed from the cig. lighter. Thinking about it now, the earth return current from all the dash lighting probably shares these earths....
I have also made 2 large earth connections in the engine bay, one to the chassis, and one to the turbo side of the inlet manifold (figuring many of the important sensors like the 2 O2s, AFM, etc are on this side), so thought that this may have helped, but it didn't!
Yes, earthing is critical when measuring such tiny changes of voltage (especially anything above or below stoich..).
You can check out what my setup looks like here:
http://users.bigpond.net.au/tony_h/subaru
R's
Tony

babber

I don't want to argue with anyone, but I know that when I wired my AFM up I ran all the cable from the ECU. Live from the ECU live, signal wire from the Lambda signal wire and earth from the lambda earth. I got Blue on WOT (occasionally green) and that's what I expected to see.

I tend to agree with John, surely the ECU will get the voltage from the sensor, so it's best to read it at that point

Cheers Phill C

PS Electronic engineers have been known to be wrong before!!

john banks

OMG who dredged this one up

babber

Not me, but think it makes funny reading

Cheers Phill C

Leeroy

I tend to agree with John on this one (I too am an Electrical Engineer!). What you are trying to monitor is the lambda sensor signal input to the ECU, as this is precisely what the ECU is acting on, and hence any measuring device (AFR Meter) is pointless if it is not showing an accurate representation of this signal.

Grounding the AFR back to the battery can only be a bad thing as the voltages to be measured are of the mV order, and taking the impedance of the required 2 metres or so of 1.5mm single core cable into account, the voltage dropped will be x mV (can't remember the exact value, will check in 16th Edition volt drop tables). This will then result in error.

However, if the sensor ground IS at some potential above 0V, it is probably more advisable to rectify this to prevent any earth currents circulating. This can be easily measured with a DVM.

That'll do for now 'cos its late and i'm getting stick off the missus, so if anyone has a question/quierie please feel free to slag me off/praise me etc.!

Katana

Gah, I can't seem to stand electronics. Come to think of it, I've got a phobia when dealing with it. Laplace transfer, the weird shaped truth tables, etc are just way too confusing.

On another note, has anyone else installed a Dawes AFR in an early model car? I need to know which wire to connect it to for the ECU. Ta.

Darren Dawes

Hello Everybody,
At the request of Jamie Whitfield, I'll insert my $0.02(US, of course) and try to give you some insight as to where my suggestions for grounding came from. I should know better than to get involved in this dispute (ah, I mean, DISCUSSION), but here goes ;-)
I think everyone can agree that you do not want to ground to the chassis of the vehicle, due to minor differences in potential that occur throughout the vehicle. It does not appear to me that this matter is up for dispute, but it bears repeating. DON'T GROUND TO THE CHASSIS, unless you fancy a feedback display that is calibrated by turning on your vehicle accessories.
Now for the good part: The grounding suggestion for my meters initially called for connection to the lambda sensor return (or "ground") wire. All factors being equal, this is the logical point to connect to as you are looking for the potential difference across the sensor. (Please note that I use "potential" in the engineering sense, being another word for "voltage", rather than in the example: "you have the potential to date Samantha Fox" ). On vehicles with no specific lambda ground wire, I suggested a point on the engine, near to the sensor, as this set-up grounds through the exhaust manifold bung.
Then along comes the respected Gus Mahon (father of our boost controller), with a string of vehicles that he claims give higher readings on the meter, after he grounds them to the battery. Since you are probably not familiar with Gus, he is the "show me" type who proves things, rather than trusting the theorists (me). It's hard to dispute theories when presented with physical evidence. Gus gave me a few examples of cases where the meter readings were not what was expected, based on EGTs and known fueling factors. In most of the cases, it was a Chrysler product with the problem, and a vehicle type that we both have extensive experience with. To make a very long story a bit shorter, it was discovered that in instances where the lambda ground was a bit spotty, it's connection was not robust enough to provide a current return for the meter. In spite of what may be claimed on the National Semiconductor data sheet about the reference voltage being stable, the internal regulator of the LM3914 is a bit slow to react (or varies) if not provided with a proper ground path (especially when the display maxes out the available current source). In their defense (defence for some of you ;-) a good ground is one of those "duh!" things that is assumed by the chip maker. I then made measurements on a variety of vehicles and discovered the same case on number of them and reluctantly conceded defeat of my theory in light of the practical evidence. It appears that this type of problem is likely to occur on a number of vehicles whose lambda ground is faulty, or was never intended to provide a return path for such a device. I decided that the battery recommendation was the best compromise for the wide variety of vehicles my customers tune. From that point onward, I suggested use of the battery as a grounding point. Please note that this situation is possible with any A/F meter that uses the lambda sensor, which is pretty much every one of them. All of the meters are similar in design, with differences in display, calibration, and filtering. There will of course be exceptions, where the lambda return is very robust and the connectors "first rate". If that seems to be the case in your vehicles, then by all means, use it. However, you have to understand that the majority of customers are not as attentive or educated as some of the members of this forum, so we try to make suggestions that will aid the majority.
As usual, I'll add my comment here that I may not be able to follow this thread. The volume of email I receive does not always allow it. However, you are welcome to email me directly at Darren@DawesDevices.com , with your specific questions. If you would like to debate theoretical problems, then I'll ask that you be satisfied with my opinion on the topic, when direct physical evidence is not present. I don't always have the time for a debate, unless it involves a couple o' pints.

Thank you for your business!
Darren Dawes
==Dawes Devices

Jamie Whitfield

Thank you Darren!

LOL @ "you have the potential to date Samantha Fox!"

That response certainly deserves a pint!

Jamie

www.j-w-racing.com

paulwadams_my99

Trouble is that I need confidence that what the afr is reporting is accurate to start with. I don't particularly fancy messing about with the sensor but say i did do you reckon that spacer is anything more than washers? It says to angle it in the manual so is it a "special" spacer?

Say it is accurate and the dawes is configured correctly as below then a green light (3) through rev range at wot is ok yes with a hint of blue ?

1st light (red) .81v - .83v
2nd light (yellow) .83v - .85v
3rd light (green) .85v - .87v
4th light (blue) .87v to limit of O2 sensor

Regards Paul

P.S.

I will post an image of my install this afternoon for peoples ref and cos i think it looks quite good and am quite proud of it

How much is a new lamda sensor anyway?

[Edited by paulwadams_my99 - 3/6/2002 2:25:37 PM]

paulwadams_my99

Thank u Darren for the comments.

The point about dodgy earths and the reading of, was exactly the point i tried to make. As i said there is probably little differnce connecting to lamda vs battery in a perfect working model but it is a safer earth to the battery.

Thanks anyway and for whoever did drag this up

Regards

Paul.

Katana

Cheers. Now only one more thing to find out, does anyone know what colour/color wire for the lambda signal for an MY93? I want to cut it near the ECU.

Tone Loc

iTrader: (1)

Hi Katana,

I've got a diagnostic manual for the early cars at home so i'll try to dig out the ECU pinouts for you. I should be fitting my AFR soon too, as soon as Jamie puts it in the post with my clear indicators .

Tony.

Katana

Cheers Tone. Jamie's called me this morning and said that he's sending it all out today. He's got problems with my postcode on the computer. 20 quid says that he typed Zero-X-2 instead of OX2.

Tone Loc

iTrader: (1)

No problems m8. Is he sending the clear indicators from the group buy out too? Hope so .

Tony.