Understanding Wideband AFR

[blaze_away]

Primarily to those with wideband AFR lambdas, but others views welcome

I have fitted a dynojet to my Chim and have a few (what I think anyway) odd observations.

The car is running perfectly well (though average mpg is still only around 15mpg).

What I am seeing is.....

1. At idle the engine runs stable around 950rpm and afr is 14 to 15

2. Whilst driving under moderate load its around 13

3. Hard acceleration, not much change still around 13

4. Motorway cruise at 60mph its around 12.5 to 13

5. Coming off the throttle it AFR drops to 11, which seems odd to me.

Background info.

MAF is good, drops to 0.34v sharpish on switching ignition on.

TPS is a new Genvey version all setup correctly.

Compression is good across all cylinders, all cylinders running same exhaust temps. Long term trim is 0% short term around -40% both sides. No induction leaks

What do you think ?

[Belle427]

These are some values i found to aim for when tuning an aftermarket ecu, may help you see where things are running a bit rich.
Someone more knowledgeable on the 14 cux will be along soon.

Low/idle rpm 0.92 Lambda 13.5 A/F
Full throttle 0.88 Lambda 13.0 A/F
Acceleration, rising to 0.85 Lambda 12.5 A/F
Cruise 1.05 Lambda 15.4 A/F

[blaze_away]

Belle427 said:

These are some values i found to aim for when tuning an aftermarket ecu, may help you see where things are running a bit rich.
Someone more knowledgeable on the 14 cux will be along soon.

Low/idle rpm 0.92 Lambda 13.5 A/F
Full throttle 0.88 Lambda 13.0 A/F
Acceleration, rising to 0.85 Lambda 12.5 A/F
Cruise 1.05 Lambda 15.4 A/F

Interesting, thanks. My cruise AFR appears way too rich, I noticed it often sitting at around 11

[Belle427]

Just wondered what tune resistor your using?
I would expect to see things closer to 14.7 general driving around.
The first section of this information explains things well.
http://www.g33.co.uk/pages/technical-fuel-injectio...

[spitfire4v8]

Assuming you are on white tune / map 5 then you have no lambda control going on at all.

90 percent of the deriving on the lucas is under lambda control, it only goes open loop for full throttle or over 3500rpm (or thereabouts)

Everything else should be clamped to 14.7afr (transient fuelling notwithstanding)

Investigate why you have no lambda control and fix that.

[blaze_away]

Belle427 said:

Just wondered what tune resistor your using?
I would expect to see things closer to 14.7 general driving around.
The first section of this information explains things well.
http://www.g33.co.uk/pages/technical-fuel-injectio...

Its on white tune map 5 with lambda control.

[blaze_away]

spitfire4v8 said:

Assuming you are on white tune / map 5 then you have no lambda control going on at all.

90 percent of the deriving on the lucas is under lambda control, it only goes open loop for full throttle or over 3500rpm (or thereabouts)

Everything else should be clamped to 14.7afr (transient fuelling notwithstanding)

Investigate why you have no lambda control and fix that.

Oh dear, thanks Joolz, I made a test rig to plug inline and watch the actually volts going on whilst the engine was running and rovergauge was logging data. At that time they were switching fine, and then it was still only doing 16mpg so at that time I concluded the problem was elsewhere.

I will pay another visit to that area and see what I find.

[QBee]

You might just save yourself a lot of stress, fuel and worry, Frank, if you just do what I would do in this situation.

I would pick up the phone and go and spend a happy hour or two in Chesterfield, paying for the wonderful knowledge that Jools has in his head,. drinking his coffee, and watching him using the rolling road that enables him to perform his magic, even with the 14 CUX.

He last mapped my car about 4 years ago and it has been brilliant ever since.
And I get 23.5 mpg day in day out (apart from on track days), from a 4.6 turbo.

[blaze_away]

QBee said:

You might just save yourself a lot of stress, fuel and worry, Frank, if you just do what I would do in this situation.

I would pick up the phone and go and spend a happy hour or two in Chesterfield, paying for the wonderful knowledge that Jools has in his head,. drinking his coffee, and watching him using the rolling road that enables him to perform his magic, even with the 14 CUX.

He last mapped my car about 4 years ago and it has been brilliant ever since.
And I get 23.5 mpg day in day out (apart from on track days), from a 4.6 turbo.

Thanks Anthony, this has been my intention all along but wanted to get the car there with no known faults to avoid the worst case situation of Joolz says "its got a duff xyz" and then having to order one and wait for it to arrive and repeat the round trip. But having said that I think I will do as you've suggested.

[QBee]

It's quite likely, given that he does engine management system installations, that he will have a spare xyz or two if he divines that you have a duff one.

[blaze_away]

I gave Joolz a call to book in and we talked through the symptoms. Conclusion was he was equally baffled.

We talked about merits of replacing the 5AM MAF with the 20AM I have on the shelf, he agreed it was worth a try.

I have given it a try and glad I did, the AFR is now doing what it should.

At idle it sits at 14.5 to 15.5
At any driving condition if I come off the throttle it blips to 14.0 ish and then right over to 18+

The unfortunate thing is now its running well enough to go to Joolz he isn't taking any work on for a while so the remap will have to wait.

[QBee]

A new 5AM AFR was about £100 ish from Rimmers last time I had to buy one, and while a 20 AM may require a remap a 5AM shouldn’t. Just a thought.

[steveo3002]

blaze_away said:

At any driving condition if I come off the throttle it blips to 14.0 ish and then right over to 18+

a blip on overrun isnt a massive concern

you want sensible numbers for cruise /fuel econ and a decent number for wot

[Zener]

Closed throttle / deceleration will enable Over-Run Fuel Cut so your AFR will go super lean (big numbers) this is normal ECU behaviour inc after-market ECU's if its been enabled anyway

[blaze_away]

QBee said:

A new 5AM AFR was about £100 ish from Rimmers last time I had to buy one, and while a 20 AM may require a remap a 5AM shouldn’t. Just a thought.

And a good thought it is too, just worried it's one of the cheap chinese at double price. How is your one going ?

[blaze_away]

steveo3002 said:

a blip on overrun isnt a massive concern

you want sensible numbers for cruise /fuel econ and a decent number for wot

That's next on my list to evaluate, thanks.

[blaze_away]

Zener said:

Closed throttle / deceleration will enable Over-Run Fuel Cut so your AFR will go super lean (big numbers) this is normal ECU behaviour inc after-market ECU's if its been enabled anyway

Brilliant thanks, and which it wasn't doing and it is doing now

[QBee]

blaze_away said:

QBee said:

A new 5AM AFR was about £100 ish from Rimmers last time I had to buy one, and while a 20 AM may require a remap a 5AM shouldn’t. Just a thought.

And a good thought it is too, just worried it's one of the cheap chinese at double price. How is your one going ?

Thinking back, I am not sure. And I don't have any AFM these days.

Working backwards, I am now on an Emerald ECU which uses the wideband lambda rather than an AFM.
Before that I was on a 20 AM, and as far as I remember that was from 2013 onwards.
I bought the car in 2012 with the standard 5 AM AFM, but that was before I decided I needed more power and went to the 5 litre.

So I think the truth is that it was a 20 AM I bought from Rimmers - I needed it in a hurry because my car wouldn't run, Mat didn't have a spare 20AM, and I needed the car running.

Rimmers are LR specialists and I would be extremely surprised if they were selling chinese junk. Suggest you phone them to discuss. 01522 568000

[blaze_away]

QBee said:

Thinking back, I am not sure. And I don't have any AFM these days.

Working backwards, I am now on an Emerald ECU which uses the wideband lambda rather than an AFM.
Before that I was on a 20 AM, and as far as I remember that was from 2013 onwards.
I bought the car in 2012 with the standard 5 AM AFM, but that was before I decided I needed more power and went to the 5 litre.

So I think the truth is that it was a 20 AM I bought from Rimmers - I needed it in a hurry because my car wouldn't run, Mat didn't have a spare 20AM, and I needed the car running.

Rimmers are LR specialists and I would be extremely surprised if they were selling chinese junk. Suggest you phone them to discuss. 01522 568000

Thanks Anthony, the 20AM appears to be working well on the 450 cat map I have, long term trim has settled at -11/-15 short term bouncing around mid point zero and AFR is behaving normally. 14.7 at idle, 14.5 ish on light acceleration, 13 under hard load, 20+ throttle off, and it drives strongly from 900 and up past 5500rpm, can't fault it, maybe revs just holding a bit too long approaching junctions, will keep an eye on that.

[QBee]

blaze_away said:

Thanks Anthony, the 20AM appears to be working well on the 450 cat map I have, long term trim has settled at -11/-15 short term bouncing around mid point zero and AFR is behaving normally. 14.7 at idle, 14.5 ish on light acceleration, 13 under hard load, 20+ throttle off, and it drives strongly from 900 and up past 5500rpm, can't fault it, maybe revs just holding a bit too long approaching junctions, will keep an eye on that.

Sounds like you are sorted pro tem