engine tuning gas analyser question

[steveo3002]

https://www.mgexp.com/article/co-afr.html

charts like above state xx afr = xyz co , is this always the case and set in stone or can certain faults make the readings skewed ?

basicly i have a wideband gauge and a co meter , both appear to work as expected but results do not match the chart

 

[Fazerruss]

What engine is it you are measuring? I'm also interested in this subject as I will soon be building a Megasquirt ecu and wide band lambda for my lotus 7 replica.
From what I've read so far the stoiciometric value can vary depending on if it's a compression ignition engine, direct injection ect. I read somewhere that the recent lean burn engines have a higher AFR than older carb and standard injection engines.

 

[steveo3002]

1988 polo retrofitted with mpi no cat

wideband says its rich at idle when the co meter says its right

 

[Shox Dr]

Are wideband any good at idle?

 

[steveo3002]

Are wideband any good at idle?

dunno lol....does seem to fluctuate more at idle that on a run

 

[8ob]

What engine is it you are measuring? I'm also interested in this subject as I will soon be building a Megasquirt ecu and wide band lambda for my lotus 7 replica.
From what I've read so far the stoiciometric value can vary depending on if it's a compression ignition engine, direct injection ect. I read somewhere that the recent lean burn engines have a higher AFR than older carb and standard injection engines.

I spent four days at rolling road sessions messing with mappable ECU`s on engine sillyness, the guy mapping did point out that some engines with wild cams, porting and high compression ratios dont necessarily make the best power at stoichiometric. Air/fuel ratios on this particular engine made the most HP running very rich, he put that down to poor combustion chamber shape and cam duration.

Bob

 

[steveo3002]

yeah this is just factory spec parts , no wild cams etc

 

[8ob]

dunno lol....does seem to fluctuate more at idle that on a run

PCV ?

Bob

 

[grim_d]

I spent four days at rolling road sessions messing with mappable ECU`s on engine sillyness, the guy mapping did point out that some engines with wild cams, porting and high compression ratios dont necessarily make the best power at stoichiometric. Air/fuel ratios on this particular engine made the most HP running very rich, he put that down to poor combustion chamber shape and cam duration.

Bob

Stoich isnt the best ratio for power, stoich is only best for emissions/clean burning because a perfect mix is so hard to achieve in an engine likely because of what you mentioned.

Between 12 and 13:1 is often where an engine will make the most power, going a bit richer on turbocharged engines for safety.

Look it up it's all very interesting, even if I don't understand a lot of it.

 

[steveo3002]

Stoich isnt the best ratio for power, stoich is only best for emissions/clean burning because a perfect mix is so hard to achieve in an engine likely because of what you mentioned.

Between 12 and 13:1 is often where an engine will make the most power, going a bit richer on turbocharged engines for safety.

Look it up it's all very interesting, even if I don't understand a lot of it.

the wideband (if its accurate) is showing good figures on the move , its just idle that im struggling with

either theres a mech issue that makes the engine need to be rich for an acceptable idle or the wideband isnt accurate

 

[dannyp]

What wideband are you running ? Ive got ms on a couple of golfs. They been converted for years now so some of the hardware is getting on a bit there using innovate lc1 and to be fair to it it’s bang on, gunstons gas testers are about useless as well. One thing to look for is a steady output from the wideband. Mine will often tell me if I have a problem with a cylinder as I’ll get a wobbly afr trace ( won’t tell me witch cyl or what it is but it will show the problem ). It reads true at idel through to flat out for me

 

[dannyp]

I’d aim to Hit about 13.5:1 afr at idel. Most engines. I don’t a steady idel very easily at that

 

[Sean]

I spent four days at rolling road sessions messing with mappable ECU`s on engine sillyness, the guy mapping did point out that some engines with wild cams, porting and high compression ratios dont necessarily make the best power at stoichiometric. Air/fuel ratios on this particular engine made the most HP running very rich, he put that down to poor combustion chamber shape and cam duration.

Bob

"Stoich" is basically a theoretical ideal.

 

[premmington]

Very difficult to ascertain if an engine is running well by measuring CO on its own.

Multi-gas analysers show O2 and HC.

Seeing how much Oxygen and unburnt fuel is another way of - looking at the cycle of combustion.

 

[steveo3002]

What wideband are you running ? Ive got ms on a couple of golfs. They been converted for years now so some of the hardware is getting on a bit there using innovate lc1 and to be fair to it it’s bang on, gunstons gas testers are about useless as well. One thing to look for is a steady output from the wideband. Mine will often tell me if I have a problem with a cylinder as I’ll get a wobbly afr trace ( won’t tell me witch cyl or what it is but it will show the problem ). It reads true at idel through to flat out for me

lm 1 ...so old , but its had very little use , figures are steady on a run or wot but fluctuate on idle

not much chance of me having a 4 gas tester , and no garages i know that would set it up /diagnose it rather than throw parts at it

 

[dannyp]

what Ecu is it running ?

Garage gas analysers are slow compared to wideband. If it runs and drives all right I wouldn’t over worry. I bet if I pulled the golf out now and ideled it the wideband trace would be bouncy as hell until it had been for a drive then it would settle. The oem Ecu with lambda should once warm sort themselves out aftermarket Ecu all depends how it setup. I run quite long cams an I’ve never set the warmup curve properly I find if shunt it about a lot without actually driveing it it cokes itself up and runs like a dog as with throttle bidys and cams when it’s cold it just wants to be run stupidly rich. If I leave it at garage for mot and they idel it warm no way in hell will it pas mot emissions test take it for a quick blast down the road I mean it only needs 30 seconds up and down the lane and it’s purring like a kitten and straight through emissions

 

[steveo3002]

stock ecu

drives okay ...certainly an issue around idle still