SPARKY WRX

Hi,

When I was at Well Lane on sunday I was slightly worried about my Air/Fuel Ratio readings from my dawes AFR since I had decat downpipe. It was suspected that the fuel pump wasnt supplying enough fuel at the top end. It was begining to reading lean on full boost after a few hard blasts.

any way, on the way home I planted my foot and the dawes AFR (which has four lights red, yellow, green, blue from lean to rich) went green, then at the same time I switched my lights on!!! The readings from my dawes went to red (lean) and when I switched them off it went back to rich!!!

Very confusing !!!

Any sort of electrical load seams to affect my readings, weather it be the lights, fans or climate controll. Could it be affecting my fueling via a problem with the battery or is it just electrical interferance.

Has anyone experiance the same problems?


cheers

Mark Shield

iain atkins

You really need to take the feed for the AFM (power supply) directly from the battery, and also make sure you get a good clean earth as well.

This should clear up your readings.

Regards



Iain

SPARKY WRX

Cheers Ian,

I have run two thick gauge wires straight from the batery, the kind you would use for an amplifier, to the AFR and ran a thin gauge wire from the ecu to under the drivers side dash.

Mark

Myk

Might be the fact you've usd thick guage wire??

As the fuse at the battery needs to be 2amps, i'd have thought 5amp wire would be more than sufficent.

I fitted mine over the weekend, fingers crossed all working well so far!

I hope this helps

Myk

SPARKY WRX

cheers

Ill change my wire and see what happends, I think iv got some lying around, I never got round to putting a fuse in line so I'd better do that at the same time !!

Mark

NotoriousREV

I guess ideally you want to use the same gauge wire as the lambda sensor uses so you're not altering the reading.

SPARKY WRX

NotoriousREV,

I think i use the same gauge to tap the signal from the ecu to the dawes AFR meter but like I say the Power supply to my Dawes Meter Is via two large gauge wires. Im going to change the power supply wires and see if it makes a difference.

Also Iv been looking at your post on bosh coil packs for the early impreza,s. Do they take much fitting. Im not looking for some right now but when you get them fitted I would be interested to know how you got on.

Cheers Mark

NotoriousREV

I'll let you know how I get on, I'll try and take loads of pics, but it shouldn't be too hard. I'll probably do the 5 point earth mod while I'm at it.

SPARKY WRX

Brillient, 5 point earth mod, just what I was about to do!

What gauge of wire are you using and what model do you have ,and which five points are you using, sus turret, manifold, dip stick etc etc?

So far Iv got a couple of earth leads from halfords and one from car stereo shop but carnt remember the gauge.

My car is a 94 wrx

Cheers Mark

SPARKY WRX

I Have a spare lambda which I might just stick into the spare lambda hole in my revolution down pipe which at the moment is blanked of.

This will anable me to leave my origonal lambda alone and use the spare for the AFR.

My spare has two black wires and a white one i think, can i wire it up independantly, is it just a case of +ve wire, -Ve wire and signal wire. or is it more complicated than that?

Thanks Mark

markwild

I've the same problem - The lights or any heavy electrical load cause the AFR to under read....

Did you find a fix for this ?

Mark

SPARKY WRX

I Havent had chace to sort it out yet, iv been to busy with other problems.

The only thing I can think of is maybe some sort of earthing problem.

What have you tried so far.

cheers

Mark

markwild

I've had it fitted for 2 weeks, but didn't use my lights till yesterday - so that's when I found it !

I've tested it now and can easily prove the issue by switching the screen heater (rear) on and off - flicking the led from blue to yellow !!!!!

I've not tried anything yet, but I have 3 options:
1) try connecting the earth to the body of the sensor -
2) connect the earth to the sensor wire at the ECU (If I can find it)
3) connect the earth to one of the ECU screws in the floor - I could then run a thick earth cable from here to the battery....

Unfortunately, all of these are a bit of a pain - particularly in the evening, when its dark and raining !

I'll try and locate the sensor earth at the ECU first I think, as this should show a measurement that the ECU is seeing. If this makes a difference, I'll fit an earth from the ECU to the battery

I'll keep you posted, but let me know if you have any ideas / find any solutions !

Cheers,

Mark

SPARKY WRX

I have an ECU pin out diagram for for my 94 wrx if you want it

dont know if it will be the same as yours, what year car do you have?

Mark

markwild

sorry - its a 98my UK turbo - I'm also going to measure the voltage between the battery -ve terminal and the ECU ground point. Maybe I can detect some fluctuation when the rear screen heater is on....

Mark

SPARKY WRX

what worries me is that if the lights etc are effecting the dawes, are they effecting the signal to the ecu which means every time i use my lights does it make my car run lean!!!!

maybe its worth checking that the actual signal to the ECU from the lambda isnt afeected.

But I think its something to do with the dawes earth. maybe its worth checking that the actual signal to the ECU from the lambda isnt afeected.

markwild

I think that the Sensor and ECU are using the same ground level, (I think that the sensor has both ground and signal wires).

Therefore, the only mis-reading is because the afr is relative to the battery earth, not the ECU earth - these should be the same, but appear to float under load due to bad earth wiring ....

I'll let you know my findings, but it may be the weekend before I can get the car in daylight...

Mark

markwild

I've located the wiring diagram and the pin for the ECU ground, so I'll compare voltage here and at the battery ... Also, I may try moving the AFR ground to this location....

Mark

greasemonkey

Mark (Sparky), have a look at my comments in response to the "other" Mark's identical problem here.

Seems there's a lot of it about!

markwild

aargghh . We've created an infinite loop !





GM / Sparky, I'll try all these on Saturday and post the findings here.....





Ta,





Mark

SPARKY WRX

cheers lads, Ill have a go at the weekend as well

Mark

markwild

OK - Looked good to start with. Measured between -ve battery terminal and -ve ECU stud (The one with a black/silver wire attached to it). (at bottom of ECU)

With Engine running, no screen heater/lights, ~5mv.

Switch on lights etc, ~25-30mv. Therefore, 20-30mv difference, i.e. 1,2 or 3 leds on AFR...

However, having moved the earth to the ECU pin, THE LEDS ARE THE SAME - THEY STILL GO TO 2 LESS WHEN I SWITCH ON THE SCREEN HEATER !!!!

**** !

This, coupled with my knocklink prob, has completely b0lloxd my night !

Mark

markwild

FIXED !

I've taken the connection to gnd straight to the ECU feedback from the O2 sensor (which is the second pin from the right, bottom row on my 98my).

I measured the voltage between this pin and the earth pin stud first and this varied depending on the other electrics switched on.

Anyhow, I now am measuring directly across the sensor, and the reading DO NOT change when I switch on the lights or rear screen heater....

Mark, I suggest that you do the same...

Thanks to GM and everyone for their assistance (AND my DAD)

Mark

PS _ Looks like my knocklink Is OK - I've done the 'tap the sensor' trick and I get the lights, so EXCELLENT !!

SPARKY WRX

Thanks Mark,

Didnt get chance to have a look, to busy fitting coil packs and mapping my boost controller.

Will give give that a try at the weekend

Thanks again

Mark

p.s. What do you think is causing the difference between the ecu stud and battery earth, should that be happening and is it just the engine earth, would a earth mod fix this.

[Edited by SPARKY WRX - 9/30/2003 8:11:07 AM]

markwild

Yes, I think that the current for heavy usage items is tracking via the incorrect places - the earth mod ought to fix it, but I'll do that as a project for another day !

As its only milli-volts, it shouldn't affect any item that uses 12v, only sensors that use electronics, due to their sensitivity. As long as the sensors on the ECU use both feed out and back (i.e. at least 2 wires) it should be ok



Mark

SPARKY WRX

Mark,

What about the knock sensor, I have my -ve wire bolted to an earthing nut under the drivers side dash, the knocklink seams to be working ok but rarther speradic at times. Do you think that the lights, heater etc. will have the same affect on that.

Cheers

markwild

Is it a knocklink ?

If so, I assume you mean the -ve for the power .

This will be OK, as it uses + and - 12v for power, BUT uses feed to and from the sensor for the electronic reading, therefore, only the 12v feed will be affected, which various by +/- 1 volt anyhow when you use lights, increase revs etc..

Should be no prob..

Mark