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Lambda Fluctuating !!! Is that normal...?

MoTeC M1 Software Tutorial

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Anyone can help to find what cause my Air Fuel Ratio too much fluctuating and changing... Is it normal or there is something wrong...!?

Model: Nissan Patrol

Engine: TB48

Transmission: Manual

Modified: Piston 100mm low pressure + Injector dynamics 1000cc>


2 Times I tuned the VE table after one day when I go to revisit the cell and check all sites, it shows sometime lean and sometime rich in

Lambda Target and AFR too much fluctuating.

Check the attachment for i2 data logging...

Attached Files


The Engine Efficiency table looks nothing like any other TB48 Package that I have. You have a big ridge in the table at 2250 rpm, but 200 rpm either side the cells are delivering ~25% less fuel. There is a further ridge at 5000 rpm that isn't as aggressive. Having a ridge there will effect the fueling as the engine transitions through that range.


Now I am just start learning the tuning and this was my fist engine tuned. And I am still learning.

Like this I sent data logging to show you what I did to correct the mistakes that made during the tuning. I saw all these ridges and I was wondering why these cells have a huge number compering to other cells…!?

So now, in your opinion, what is the problem….?

And what you suggesting..?

I agree, the ridge Stephen mentioned in the VE table does appear extreme.

Is that the area you're concerned about?

Are you finding you're needing high VE values to achieve the desired result lambda value?

Please be more specific about which RPM/load areas you are focused on so we can better review and offer more specific advice.

In the meantime, I suggest adding fuel closed loop control to your datalog list to aid in review.

Also, the fuel film system can have a large impact on fueling. I suggest checking this out and adjusting accordingly:

110 | Fuel Film Quick Set up - MoTeC M1 (hpacademy.com)

Anyone can help and find what’s cause this ridge..!

Note that the rest of the table it’s fine.

Ridges like that are caused by either the intake or exhaust system. When pressure pulses at a certain frequency (i.e. engine RPM) coincide with valve timing events putting either extra air (which needs extra fuel), or stopping airflow (so less fuel is needed).

You can also fall into this trap when using a load-controlled dyno, if controlled speed is not exactly in the center of the cell. You end up compensating in an exaggerated way with the next cell over. You might try interpolating the values on either side of the ridge (bascially take any ridge/dip out), and then going back to steady-state tuning, with the neighboring cells closer to the ball park.

So far I haven't found a convincing answer and what exactly is the problem !

So what did you try?

Looking at your log, it looks like you have tuned the fuel to give the engine what it wants. But, I notice your Fuel Timing Primary Main looks more like what we see for an injector mounted well away from the intake.

Perhaps you should try using a constant fuel timing (say 375-400 deg at all RPMs) and see what that does. Or you could vary the timing while the engine was running at constant speed to see what values give you the lowest Lambda value, (ie. richest meaning it's combusting more of the fuel you inject). After finding the optimum timing, then you re-tune the fuel map to get back on target.

I wonder if that ridge at 2000 RPM isn't because timing of your very short pulses (large injectors) are just not mixing well before the valve event changes the airflow at that RPM. Looks like you have the tools to give that a try.

Have a look at this webinar to review how to find the best injection timing (a great demo starts about 20:00 in) :


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