MoTeC Global Forum

Hi all,

I am using a M800 and it ist realy great instrument.
But I have a problem when accel roc is greater than ~500. As you can see from the attachment the firings which were loeded while opening the throttle get much too lean.
I tried making it richer and leaner with accel clamp and sensitivty but the first ignition after acceleration allways fails.

I think the reason for this is that the engine intakes zu much air because of the opening throttle after the amount of fuel for this firing has been already calculated and injected. Sure - the M800 can not know when I will open the throttle in the future and can only calculate and inject on basis of the current values. But maybe there is a function to inject extra-fuel in the same moment the throttle opens?

Does such a function exist or does anybody have a solution to solve this problem?

Thanks in advance

Hi Lip

what is your Accel Sensitivty set up at? Left at default (50?) Using just X axis or included a Y axis?

The Accel Clamp setting?

Hi figgie,
thanks for assistance. I tried every thinkable adjustment but I could not solve this problem. I tried to make it very rich (high values for clamp and sensivity) also in combination with fast decay. Then I tried to make it leaner because too rich can also cause lean spikes. I tried different injection timing and different values for accel threshold. But I could not solve the problem with the first one or two firings failing while or directly after acceleration.

In the sample below you can see that high acceleration requires less than 0,1sec. and the lean spikes also. As the engine needs ~ 0,03 sec. for one cycle at 4000 rpm the problem appears only while this 2 or 3 cycles.

I think the problem is caused because the M800 calculates and injects the amount of fuel based on a throttle position of e.g. 10% for this cycle. But the real intake of air in this cycle is much higher because of opening the throttle rapidly to e.g. 60%. But I do no know if I am right.

Is there no way to open the injectors in the same moment while the value for acceleration rises? Than I could try whether this idea is right or wrong.

Thanks Lip

Do you have logged data from the same situation with no accel fuel?

If I understand you correctly the engine missfires at this point. That would cause the lean spike on the lambda trace regardless of fuel/air mixture.

I would look at what happens with no accel fuel to try and determine if the engine is going lean or simply missfiring.

Hi idp,

I logged it with a very high clamp value (~ 150) and with clamp = 0.

As you can see it is all the same: The first one or two firings fail.

Regards Lip

It is quite normal to see a lean spike following rapid throttle movement. The extent of this will depend on a number of things including injector location, injection timing etc. You should try running a rich steady state fuel mixture and see if the miss-firing improves. This will confirm wheather or not the miss-fire is caused by lean mixture. Is this a 500D engine?

Hi RossB,

I will try. I wouldn´t mind because of the lean spikes alone. But they cause a hard breakup of acceleration.
It´s a guzzi lm1000 engine.

Regards Lip

Hi Lip

What is the logging rate of the accel rate of change and accel fuelling?
How is your accel sensitivity setup ie which channels are on the axis?
Can you send some logged data for me to have a look at?

Cheers

Hi AlanB,

enlosed you find a log file.I logged with 20hz. Until 1:45 I used the following values:

fuel accel clamp:
RPM 0 2000 3000 5000 8000
41 26 20 25 22

fuel accel clamp comp:
Acc ROC 300 600 2000
0 16 30

Fuel accel decay: 25 for all

Fuel accel sens:
RPM 0 1000 3000 5000 8000
90 70 70 25 10

At 1:45 I turned all clamp- and clamp-comp-values to 0

Thanks for your help
Lip

Your accel ignition setup is retarding the timing by 10 degrees when you open the throttle, it is possible that this is contributing to your miss fire. Have you tested without accel ignition? Have you configured this for a particular reason? You have not logged accel ignition but you can see the effect it is having if you compare Ignition Base Advance and Ignition Advance channels. It would probably be a good idea to increase your logging rates to study accel fuel as this would make things clearer.