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Author: Subject: Tuning with a wideband Lamda Sensor
brown_d9

posted on 26/5/15 at 09:12 AM Reply With Quote
Tuning with a wideband Lamda Sensor

Hi all,

So we have bitten the bullet and bought a wideband lambda sensor to tune the 1.8 Zetec running on ZX9 carbs.

My question now is how do we go about starting.

From what I can tell we should be starting with full throttle (main jets) and working downwards, am I right in thinking we should find a nice straight piece of tarmac, floor it and start reading?
What would an ideal reading be for foot to the floor?

When working down to the needles, how do we go about this, cruise around half - 75% throttle and play around with the needles until we get a good reading, again what would a good reading be?

I think the idle jets are fairly simple, but again and tips on a good reading?

Apologies, I appreciate this is a bit of an open question, but having never attempted anything like this (and having the old man saying we don't need this sensor I can do it by ear blah blah) I would love an idiots guide because after all that's what I am :-)

Thanks so much in advance.

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dave_424

posted on 26/5/15 at 09:41 AM Reply With Quote
Foot to the floor you should aim for 12.5

Cruise can be leaner, around 14-16 should be a good place to be.

Idle wants to be as close to 14.7 as you can when all fully warmed up

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brown_d9

posted on 26/5/15 at 11:29 AM Reply With Quote
Thanks for your reply, much appreciated.

One thing I don't really understand is I can see that we can get it set up nicely for 2 points, idle and foot to the floor.
But how do you tune everywhere in between, for example cruise could be set doing 60mph at 3000rpm but cruising at 70mph and 3500rpm the fuel air ratio could be different, or does it not work like that?

Also surely when the needles are metering the fuel, can the same thing happen? As in when the needles lift slightly we could get the A/F spot on, but when they lift a bit more when your pressing that little bit harder the A/F goes a bit wrong.



Thanks

Dan

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coozer

posted on 26/5/15 at 01:00 PM Reply With Quote
I would try just holding the revs steady at 1000 rev intervals and write down the AFR. A hand off someone who can concentrate on the gauge is better than trying to do it while driving.

Adjust each rev range until your in the ball park. You will soon get the hang of what affects what.

When you press the pedal to go a bit faster the slider lifts to give some extra acceleration fuel so its important to hold a steady rev to let the AFR settle down.

May be quicker to go to, or phone Bogg Brothers....





1972 V8 Jago

1980 Z750

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brown_d9

posted on 26/5/15 at 03:16 PM Reply With Quote
quote:
Originally posted by coozer
I would try just holding the revs steady at 1000 rev intervals and write down the AFR. A hand off someone who can concentrate on the gauge is better than trying to do it while driving.

Adjust each rev range until your in the ball park. You will soon get the hang of what affects what.

When you press the pedal to go a bit faster the slider lifts to give some extra acceleration fuel so its important to hold a steady rev to let the AFR settle down.

May be quicker to go to, or phone Bogg Brothers....



Thanks!

Does load not make any difference to the A/F ratio, as in surely at 3000RPM in 3rd gear compared to 3000RPM in 6th gear the A/F ratio would read differently?

Or am I still missing something.

I would love to pay Bogg brothers a visit, but unfortunately they are so far away.

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dave_424

posted on 26/5/15 at 03:36 PM Reply With Quote
Look up an Air fuel vs load map on google images for a non turbo car, that should show you how the AFR changes with loads and RPM
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coozer

posted on 26/5/15 at 04:45 PM Reply With Quote
There will be a difference but carbs are fixed really.

I would do it all in fourth 1:1 to get a good balance..

If you want the afr to be constantly adapting to the conditions you will have to go over to injection.... like me... DONT WASTE YOUR MONEY!!!

Hindsight is wonderful.....





1972 V8 Jago

1980 Z750

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baz-R

posted on 26/5/15 at 05:39 PM Reply With Quote
quote:
Originally posted by dave_424
Foot to the floor you should aim for 12.5

Cruise can be leaner, around 14-16 should be a good place to be.

Idle wants to be as close to 14.7 as you can when all fully warmed up


I think you're going too struggle too get a good idle and reasonable cold start and idle that lean in a carb idle circuit.

Beauty of fuel injection is you just tweek the number's to get in to work right in every aspect.
Just can't be done the same way with carbs so you just have to make a best compromise

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