DIY air-fuel ratio meter

[silverbullet]

Stumbled across this while looking for more afm info for LPG tuning and optimisation, but would be useful for any practical types who don't want to waste fuel and get maximum efficiency from their engine http://www.buckeyetriumphs.org/technica ... onitor.htm If you look further down the page there's a "how to build your own led bar graph AFR meter"
RS catalogue and soldering iron at the ready...

(edited by rob to make link work..)

[jamesc76]

just had a read sounds good but lamba probes generate and use ac from the ecu????

[tonytech]

Nice idea, but I've seen rats making tidyer nests than that wiring.
T

[R0B]

blimey mr bullet.your dash will look more like an apollo spacecraft.than a t3/t25 by the time your finished

[Aidan]

lambda probes generate their own voltage due to difference in 02 level in air outside the exhaust and that inside the exhaust, but they produce very low current but it's perfectly possible to monitor the variation with a voltmeter just the same as the ECU does on the digifant, which means it's possible to check when they have failed, generally they give a low voltage that doesn't vary and in a modern car the check engine light comes on and your obd will give lambda sensor code; just had this on the scooby, and fixed it with a new £15 lambda sensor

this is interesting stuff, nice one Ian

[silverbullet]

blimey mr bullet.your dash will look more like an apollo spacecraft.than a t3/t25 by the time your finished

Is this how syncrodoug started out?
I'm more of a nuts,bolts and welding man really but will admit to an obsessive interest in the lambda output at the moment
It looks like 0.92v is the magic figure for maximum beans from your bucks.

[fairwynds]

this is great stuff, and also your recent t'other thread re the LPG set up
could a 'how to' with whys and wherefores, including where to get the parts (for us lesser mortals) be posted for Wiki...pleeeease?

Cheers

FW

.....puts on a stainless steel exhaust and has now gone all engine tuning weird!!

[silverbullet]

Good idea! I'll alert Clive to the existance of the thread with some extra info/pics etc. for the Wiki

[pionte]

Or you could save yourself ALOT of time and energy and fit one of these

http://cgi.ebay.co.uk/PLASMA-DISPLAY-AI ... 1383wt_912

[silverbullet]

Unfortunately, those cheapo AFR "gauges" are notoriously inaccurate. With LPG you want to know what's really going on "in cylinder". The good quality, calibrated ones are more like £200 and that's an expense that I was determined to avoid. Ya pays ya money, ya takes ya choice...

[CycloneMike]

Unfortunately, those cheapo AFR "gauges" are notoriously inaccurate. With LPG you want to know what's really going on "in cylinder". The good quality, calibrated ones are more like £200 and that's an expense that I was determined to avoid. Ya pays ya money, ya takes ya choice...

You won't ever really know whats going on whilst you use a narrow band sensor as the output isn't linear and it is only designed to indicate either rich or lean mixture not an acurate AFR. The good quailty guages probably use a wideband sensor and controller which give a linaer voltage output 0-5V and therefore can be accurately used to indicate AFR. They can also provide feedback to an ecu to help self map an ecu.

[silverbullet]

Fair comment and I fully appreciate the limitations of the narrowband sensor. All I was trying to do was get a better set-up of my LPG system for little outlay, since trying to do it with a CO meter had proved little better than useless. To that end, it was a success.
I'm getting near-equal mpg on gas against petrol (from the official figures in the handbook) and it goes as well as before.
The job's a good'un from where I'm sat.