Question for you EFI / AFR / Wideband users & experts:

What are good target values for lambda as an Olds 455 is cold starting?

With my current qjet cold start (choke) adjustments, I’m seeing lambda values as low .85 or .90, then as the car warms up it approaches 1.00 depending on how good my tune is.

It makes sense that the lambda values are low (aka rich) for cold start, but I’m wondering if .85 or .90 is too rich.

Since this is tunable, where do you all aim for easy cold starting?

In case it matters I live in a moderate climate near San Francisco - it never snows here, but we get 2 weeks a year of 100F+.

Looking forward to your views & experiences.
Chris

 

What ECU do you have?

 

These cars have no ECU — I’ve just added a wideband O2 sensor to help me tune an 800 CFM qjet on my 455. It is HEI equipped but no CCC at all.

The qjet is an M4MC (?) aka a ‘77 Olds pre-computer controlled one with electric choke. It has and APT (adjustable part throttle) and the idle screws have been revealed. I just redid the carb gaskets and set up the idle screws with both high vacuum grease and some little O rings to eliminate vacuum leaks out the idle screw passages.

I think I’ve got idle dialed in at .98-1.00 lambda, but at cold start the lambda is more like .85 or .90. Part throttle cruise ranges from .97 to 1.02 depending on hills, demand and so on.

While we’re at it, do you have a view on lambda at WOT?

Thanks for any insight you’d like to offer up. It’s been really fun to read your EFI posts for me.

Chris

 

Being able to control cold start via a choke is a difficult task at best. .85-.90 lambda is probably ok. If it runs fine don’t touch it.
WOT is normally .88-.90 or so. But remember stoich for todays E10 pump gas is 14.1, not 14.65.

 

Mark (right?),
Many thanks for keeping me from chasing my tail. Both cars start up easily and on demand. I’ll probably leave it alone. Chokes are pretty crude in comparison EFI for cold starts, but mine work o.k.

I’m reminded of the comparison between digital fuel injection using nanosecond based microprocessor controlled metering and a carb which is “like covering your intake with a gasoline soaked rag”.

Still, it all gets to metering the right amount of fuel for RPM, demand and the other variables. Digital is great, but I’m staying analog for now. I’m getting 10-11 mpg around town and around 14-14.5 on the highway having tuned the spring/analog components with the wideband. But there aren’t many of us out there going to those lengths, so it’s hard to find information on what I shoudl be shooting for.

Gotcha on the stoich differences. This is the exact reason I switched to lambda from AFR. I never know quite what the alcohol component in CA gas will be so it made sense to me to use the lambda values which are fuel-agnostic. Plus AFR’s are scaled lambda anyway in my Innovative O2 sensor, so I feel better about using unsealed values too.

And many thanks for the WOT value.

Cheers
Chris

 

You’re welcome. Glad you were able to get decent values with the Innovate, not my favorite.

 

Is everything skewed by a value of 0.55 with E10?

Hypothetically, if my car was dyno tuned for max power at say 12.6-1 on non ethanol gas and then had to run E10, would the WOT value move to 12.05 or is it not that cut n dry?

 

The short answer from what I’ve read is bump the AFR values down by .5 AFR. I’m sure there’s a more complex answer.

But instead of playing the “how much alcohol?” game, you might check out using the lambda scale instead. For some reason when EFI came in, AFR took off as the popular measure here in the US, but in other parts of the world, lambda seems more popular.

It’s pretty easy to get used to, but the big deal is that it is a fuel independent scale. Whatever your fuel consists of, it just tells you whether you burned the mixture correctly, or how far off you are on the rich or lean side.

More or less I shoot for lambda values with a target of 1.00 (perfect combustion). Below that and you’re a bit rich (which you may want sometimes, like when accelerating). Above 1.00 and you’re a bit lean which I find happens off the throttle when you’re going down hill.

With a bit of tuning I can get my idle to be right about .98-1.00 lambda, then part throttle is say .95 or so, WOT maybe .80 fully open.

The other good thing is when you have a vacuum leak, you’ll see it right away since the lambda values will be leaner than they should be. Sometimes by a lot. For example this week I regasketed my qjet and didn’t tighten it enough, so it was vacuum leaky. Lambda values at idle of 1.05 - 1.15 and I knew I had a problem. Then once I left the PCV vacuum line unhooked and lambda values were like 1.30. Dumb me, but at least now I have a signal to tell me something is really wrong.

Anyway the wideband O2 sensor is one helluva a tuning leap for someone like me who is totally untrained as a mechanic. I have no “ear”, nor anything except hobby experience, so having a machine to tell me how close my jetting, idle and WOT are to optimal is great.

Cheers
Chris

 

Mark,
Just following up - what other O2 sensors would you recommend over the Innovative Solutions?

I like my “VW” a lot, but am open to upgrading if I knew what better choices there are. When you have a sec it would be great to get schooled up.

It’s probably important to say these are big Olds street cars, not racers. - a ‘66 Starfire and ‘66 98. With their qjets, and HEI, that’s about it for electronics. No MSD or crank triggers or EFI. I enjoy these cars driving my kids around & running errands, not a 1/4 mile at a time.

No rush, just curious
Chris

 

"AFR" is just one of those acronyms that are so popular now. "Air to fuel ratio" has been around for many, many years in the US.
"In the old days", most people had their cars tuned up by shops and dealers, so they were unaware of the numbers.

 

It’s not the sensor that’s the issue, it’s the controller/processor. Innovates are slower than most, making them difficult to use for EFI. However for carbs they’re ok.
The best and fastest is the AEM X series. I have two on my Dyno. When I tune to those I always make the most power.
Nick- I’ve found that at WOT E10 is pretty close to non ethanol, around 12.8 or so in most cases. It’s not a linear thing. That’s why I never agreed with people who say “just add 10% for E10 and 30% for E85”. Never found that to be true.

 

Thanks for the education Mark, as always.

 

Mark
X2 on the thanks. Nice to know about AEM processor & controller and that the I/O rate for Innovative wideband will work for my purposes.

If i ever decide to switch over to EFI, you’re top on my list of people to call / write. But that commute from San Francisco to Florida would take a while.

For a long while I’ve toyed with switching over one of my 455’s to sequential port injection, but I’m not there yet since it’s such a departure from a simple qjet & HEI.

Am I in the ballpark that such a switch on an existing good engine would be in the ballpark of $3500? Plus time & tuning?

Great to have your participation & guidance,
Chris