AFR

[Steve_D]

Fitted an LS1 wideband sensor to the Ultima yesterday but only got to use it today.
Gauge spends most of its time around 11 or 12 but alarmingly goes to 17 under heavy acceleration.
If ever there was good reason to go EFI I think I have it.

Steve

[Pb3]

When I was in the process of my EFI conversion, I fitted the WB sensor and my ECU and logged some data before doing any engine work. What I found was a lot of light throttle work was below the minimum that could be measured ( ie 10:1) very, very rich, otherwise it was between 10 to 12+, but I didn't see any particularly lean conditions, that would be something to worry about!

[mdm123]

Steve_D said:

Fitted an LS1 wideband sensor to the Ultima yesterday but only got to use it today.
Gauge spends most of its time around 11 or 12 but alarmingly goes to 17 under heavy acceleration.
If ever there was good reason to go EFI I think I have it.

Steve

can't be right. you engine would surely be destroyed by now, most people see anything over say 14 at wot to be lean. also even my some chance you engine is still going it would be really under power. sounds like theirs a leak in the exhaust i.e. letting air in before the lambda sensor

[jschwartz]

Check for exhaust leaks.
17 is no good, except maybe if you're coasting with no throttle.
On NA wot should be 13 on an LS engine. 14-15 cruising light throttle.

[ezakimak]

Should be easy enough to adjust the carb, 1 turn either way and confirm a corresponding change in mixture with the gauge.

Jeff, is that with the knock sensors working on the LS?

[eliot]

Steve_D said:

Fitted an LS1 wideband sensor to the Ultima yesterday but only got to use it today.
Gauge spends most of its time around 11 or 12 but alarmingly goes to 17 under heavy acceleration.
If ever there was good reason to go EFI I think I have it.

Steve

Do a plug chop?
Misfires can also show up as lean conditions, as the unburnt mixture has oxygen in it.

ETA, does it go lean at the moment you floor it or does it remain lean ? (i.e., does it need a bigger accel shot)

Edited by eliot on Thursday 27th December 09:49

[ultimad]

Wow I don't see readings like that on mine and its a carb setup. Under accelleration it goes down to around 11. The only time it leans out (that's > 14.5) is at the instance you start to accelerate and it does that for a fraction of a second which I'm hoping is OK.

One annoying problem my gauge has is 'locking up' on some engine starts... wonder if it's the electrical noise generated when pressing the starter...

[GTRCLIVE]

Have a word with Pete, my modified carb I had of him, sat at a perfect 13 nearly all the time. The only time I saw it lean out was when you came off the throttle pedal it leaned out for a second or two then came back. Even on Tick-over it was sitting perfect, I would pay Pete the money ever day for one.... (That's presuming I would ever build a Series 1 SBC again, probably not...)

Cheap carbs even new off the shelf Holley's are cheap for a reason, not designed for our aplications....... Speak to PETE....

now where was I, oh that's right clearing the drive of Snow....HoHoHo..

[k wright]

What is Pete's last name and where does he work?

Anyway, you now have the most expensive tool that you need for correctly tuning your carb, a A/F meter.

The other tools that you will need are a book by David Vizard, some jets, air bleeds and accelerator pump discharge nozzles and a vacuum gauge.

If you are lean on acceleration it is likely that you need larger discharge nozzles for your accelerator pump.

If you look through my posts you should find a link for the book.

ken

[bluesatin]

Had AFR on my car for the last three years. Slight dip under hard acceleration (1/2 sec dip) but fine in all other conditions including maxing the car at Bruntingthorpe. I run a HP carb which solves the stalling under braking and generally works better. Based on this the megasquirt is going to be used for ignition only.

[Steve_D]

k wright said:

What is Pete's last name and where does he work?

I'm guessing Clive is referring to Peter Knight (PI5TON) of Knight Racing here in the UK. He has built engines for Clive and Wayne and also dynoed my engine when it was first built.
As the engine was jetted by Peter I have to suspect that I either have an air leak or the AFR itself is faulty.

When the weather improves and I have some dry roads to play on I will do some experiments.
On the list are:-
Swap the sensor to the other exhaust header.
Blank the PSV valve system.
Adjust the mixture at idle to watch the AFR go up and down and confirm it is not reading back to front somehow.
Plug chop after Hard acceleration, cruise, etc.

Steve

[CanAm Dave]

Hi Steve

Holley have recently brought out a Carburetor Installation and Tuning DVD. I bought a copy last time I did a Summit order. It is part No. 36-378. It's well put together and an interesting watch (I do spend a lot of boring nights in hotels in my job). It's $21.95 from Summit. I'm putting an order together for Summit at the moment, so spend me a mail if your interested in a copy.

Regards Dave

[ezakimak]

Steve_D said:

When the weather improves and I have some dry roads to play on I will do some experiments.
On the list are:-
Swap the sensor to the other exhaust header.
Blank the PSV valve system.
Adjust the mixture at idle to watch the AFR go up and down and confirm it is not reading back to front somehow.
Plug chop after Hard acceleration, cruise, etc.

Steve

Steve

Hopefully that will work, if it doesn’t, I’m a little short on ideas at the moment.

One option might be – if you have an oxygen/acetylene torch. You could then adjust between an oxidising and carburising flame and see if the sensor can pick it up. Not sure if it will work or be safe for the sensor, probably a last resort option.

I have heard of sensors going a bit funny if they get excessively rich conditions, resulting in a residual coating on the sensor.

Hope the weather picks up, its 35°C in Melbourne atm

Happy new year

Ryan

[Boosted LS1]

If you're using a holley then your pvcr's may be to small or the power valve it'self could be faulty and not opening (very unlikely). Don't forget that the main jets are for 3/4 throttle use, then the power valve opens at WOT allowing fuel to pass through 2 drillings from the float bowl thus bypassing the main jets. So at WOT you end up with the main jets supplying fuel as well as additional fuel from the power valve channel restrictions.

If the pvcr's are to small they can be reamed larger with a jewellers broach, or you can by conversion metering plates with changeable valves.

[Steve_D]

Quick update.
Have been out again and have cured my mixture problems.
Now have a steady 14.5 AFR.
That's 14.5 no matter if I'm on or off the throttle or ticking over...So that's the meter fcuked then.

Will have to get out the instructions and connect it to the laptop and see if anything is happening in there.

Damn

Steve

[GTRCLIVE]

http://www.chucknuytten.com/road_race.htm

750-2003RR

This was the Carb I bought from Mr Knight, even has a Road Race progressive linkage which starts to open the secondaries faster perfect for our light cars..

Edited by GTRCLIVE on Sunday 30th December 16:44

[ultimad]

Steve_D said:

Quick update.
Have been out again and have cured my mixture problems.
Now have a steady 14.5 AFR.
That's 14.5 no matter if I'm on or off the throttle or ticking over...So that's the meter fcuked then.

Will have to get out the instructions and connect it to the laptop and see if anything is happening in there.

Damn

Steve

Steve that's exactly what mine does every couple of engine starts. Not saying yours is same problem but Autometer techs said it may be noise generated from the engine start and suggested I try powering the gauge up after the engine start.

[Steve_D]

Going to put it on the computer tomorrow.
Will also try the late power up.

Steve

[davefiddes]

Sounds like it could be the calibration is maybe a bit wonky or the power isn't clean. I had an issue when I installed my Innovate LC1 where it wasn't reporting anything like sensible values. Pulled the sensor out of the exhaust and left it to air on the bench for a bit. Recalibrated it (the LC1 is an embedded device for permanent installs so I had to add a push button to the loom) and all was well thereafter.

Might also be worth checking grounds and supply but I'm guessing there's no much you can do about that if it's a handheld diagnostic meter.