Overrun tuning help

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Overrun tuning help

Postby 16vboost » Thu Feb 02, 2012 2:26 pm

I'm having trouble tuning the overrun portion of my VE map. Mostly the AFR reads lean under overrun conditions from 6000 rpm down to about 2000. I say mostly because it tends to oscillate between lean and extremely lean. If I run VE analyse, it bumps some of these cells up to 140 where the next cells up are all between 70-80. These hugely rich VE values seem to help, but the AFR still jumps up from time to time.

The engine is burping and backfiring during this overrun so I don't really trust the AFR numbers. I've tried different ignition timing values in this area from 30 degrees to 60 degrees. It doesn't seem to matter. It seems as if the mixture just isn't combusting under these conditions. I really want to get all of the table dialed in so I can run EAE. I'll eventually switch to overrun fuel cut.

Any thoughts? What should I do?

I can post msq's and logs if anyone is interested.

-Alex
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Re: Overrun tuning help

Postby muythaibxr » Thu Feb 02, 2012 2:48 pm

If you're fighting with those kinds of problems, you're most likely running into the area of injector operation where the injectors are non-linear, and/or your dead-time is wrong.

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Re: Overrun tuning help

Postby 16vboost » Thu Feb 02, 2012 4:12 pm

I think you're right. I think the injector opening time is too small. It gets down to 1.43 ms during over run.

I've done my best to tune the opening time by switching from 2 squirts/cycle to 4 and back and fourth. I shoot for the same idle AFR with EGO correction off of course. So I'm pretty confident in my opening time.

It sounds like I should just make those cells look right and move on.

Thanks for the advise.

-Alex
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Re: Overrun tuning help

Postby jsmcortina » Thu Feb 02, 2012 4:36 pm

16vboost wrote: I'll eventually switch to overrun fuel cut.

Why not turn it on now?

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Re: Overrun tuning help

Postby 16vboost » Thu Feb 02, 2012 5:01 pm

Just because I was tuning that portion of the table. Also, I've had it on before, but had problems entering idle way too lean. I think this will not be an issue once I tune and enable EAE since MS will know that the fuel puddle has evaporated during the fuel cut / overrun event.

-Alex
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Re: Overrun tuning help

Postby jsmcortina » Thu Feb 02, 2012 5:09 pm

The idle problem could also be if you are trying to run fuel cut until too low an rpm ? But yes, EAE could help with that too.

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Re: Overrun tuning help

Postby Perkele » Wed May 09, 2012 1:42 am

I have also run in to the same problem as "16vboost" that the AFR jumps lean when in overrun area even when overrun cut turned off. As I too now started to tune my EAE curves.
As you can see in the log capture the AFR behaves as the overrun fuel cut would be on even when it's not.
It might be because PW gets too low to 1.2ms and at idling it is 1.7ms. Injector dead time is 0.55ms calculated with flow testing "Deka 630cc"
log_ve_table.bmp

But will this affect my EAE tuning?
I will use overruncut anyway when I'm done with the EAE curves.

And another question to the EAE tuning, perhaps a silly one.
There are instruction on how to tune the EAE. Keeping the rpm steady and chaning the kpa example from 40 to 80 and change the curve EAE curves depending on the result. But whitch point of the curve, the 40 kpa point or the 80 kpa or something else?

Thank you.
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Re: Overrun tuning help

Postby HidRo » Wed May 09, 2012 2:08 am

I also have the Deka 630, and I also have a not-steady idle when warm, and a pig rich idle when cold.
From a topic jsmcortina created
Megasquirt-3 MS3 Injector Dead Time Measurement :
http://www.msextra.com/doc/ms3/injdeadtime.html

the Deka 630s will have a 0.4ms deadtime @13.2
That is what I use. But when idling, it will show a 1.2, 1.3ms PW, which is the non-linear region.
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Re: Overrun tuning help

Postby Perkele » Wed May 09, 2012 5:02 am

I'm using Jean's P&H-board to controll the injectors so my testings gave me a bit different value for the dead time.
But I don't have any problems with the idle AFR because my normal idle has PW of 1.7 and it's on the linear zone.

Just over run seems to go to the non-linear zone.
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Overrun tuning help

Postby Paul_VR6 » Wed May 09, 2012 12:54 pm

.4ms seems awfully small for the 630s, the set I had were calc at .85ms @ 4bar.
-Paul
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Re: Overrun tuning help

Postby HidRo » Thu May 10, 2012 3:30 am

This was tested by jmscortina, and I've seen information that is similar in: http://siemensdeka.com/specsheets/FI114961cs.jpg
So, I would say that it should be correct.
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