Stock AFR's

[ForcedFirebird]

Anyone else put a WB and watched how a completely healthy stock m20 reacts? Having tuned several different engines on several different systems, they seem to be quite lean, and happy doing so.

Thoughts?

[jlevie]

Spec E30 race cars require a stock engine and DME. The times that I've had my car on a dyno it ran stoic (14:1).

[ak-]

I don't know if this counts or not, but long time ago when I had Miller's shitty MAF conversion and tune on my turbo m20, it always idled a little leaner than stoic or 14.7 on the dot, fluctuation from 14 to 15 as it should - and I only mention that because it's still the stock Motronic and from what I know they don't touch the value of the tables for cruise/idle.

[Kershaw]

Spec E30 race cars require astock engine and DME. The times that I've had my car on a dyno it ran stoic (14:1).

It ran 14:1 at WOT?

[ForcedFirebird]

Spec E30 race cars require astock engine and DME. The times that I've had my car on a dyno it ran stoic (14:1).

I have dyno'd many local Spec cars, as well as have done many base line pulls before builds. Just kind of brushed the AFR's off as poor electronics etc, but recently a built m20 running MS was pulled out of my good friend's car, and replaced with a stock DME/engine but the gauge remained. He loaned it to me yesterday to run some shop errands and I was surprised at the AFR's. For as long as I have been putting gauges on the m20, it was always to make a new chip tune, so I never really paid much attention to how they reacted stock.

It ran 14:1 at WOT?

Yes. Even leaner at times. It's almost as if BMW went for stoich as their AE. Most makes/engines stock will be in the low 12's under AE.

Yesterday the AFR's were always in the 15's and 16's cruising, 14/15 WOT.

[sampayne]

Yesterday the AFR's were always in the 15's and 16's cruising, 14/15 WOT.

I had the same experience with my stock m20 and wb. Pretty surprised.

[redlightpete]

Is the full throttle switch working? And where is the wideband sensor located in the exhaust?

[ForcedFirebird]

Is the full throttle switch working? And where is the wideband sensor located in the exhaust?

This is a trend I am noticing, not one car in particular. To answer your question, though, the car is in excellent running shape, all sensors working correctly.

[TobyB]

Yes, I've noticed that on a 100% stock, legal Pro3 car, too- it might run just a little on the rich
side of 14.7:1 , but not much at all.

That said, the M10 seems to make best power at numbers approaching 14:1, too...

t

[digger]

Is the full throttle switch working? And where is the wideband sensor located in the exhaust?

stock ive seen 13.5-14:1 at WOT sampling up the tailpipe which is not always an accurate way to do it with a CAT.

in closed loop mine seemed to always be between 14.5 and 14.7 as expected

[AutobahNZ]

Interesting infomation. I've got an '84 E30 320i (M20) with LE-Jetronic and everything was out of whack when I bought the car so had to open up the AFM to see what had been done.

Fortunately, I've got an AEM wideband in it at the moment to help get it running right. What I do need to know is:

What is a good air/fuel ratio for WOT? I've currently got it at about 12.7:1 which seems ok (if on the rich side) but I don't know what it is supposed to be. Not much info out there on the factory numbers for a Jetronic M20, which I dont think was ever sold over in the USA.

Idle I have set to 13.5:1 but you say that stoich is factory, digger?

[digger]

mine always seemed to be 14.5 at idle when stock from memory sampling up the tailpipe

that AFR WOT is fine

[ForcedFirebird]

12.7 is fine, but I have found the m20 likes to be in the middle 13's for most power.

[AutobahNZ]

Thanks for the help everyone! Got it running much better now - seems to be about low 15s at cruise and yet still a bit rich still being just around 12 at WOT. I'll take it as good enough for the short term. Don't want to run it leaner until I get some better fuel in and double check the timing (L-jet so mechanical).

At some point I'll see if I can throw the wideband on the Miller MAF M20B25 car to see what that is doing. Curious because the miller setup just doesn't seem have the top end compared to what the old AFM with the chip did.