Megasquirt owners thread

[david_syd_au]

A question for the megasquirt brains trust.
I have a MS2PNP in my race car which has been tuned to run the stock engine very well.
Two weeks ago, myself and a bunch of forum regulars put a 2nd-hand built race engine in that car. This new-to-me engine has big cams, high compression (11.5:1), a bigger throttle body (Skunk2) & some head work, so of course I expect to need to do some significant retuning of the ECU.
The global fuel constant had been set from the capacity (1840cc) and injector flow (250cc/min) of the original engine, so I changed that to suit the new engine at 1950cc and 265cc/min (SE) injectors.
With no other changes the result is that the engine runs hugely rich, and requires a large amount of throttle to get it started and to get it to idle. If I reduce the global fuel constant from the calculated 12.3 to around 9.5 I can get it to idle enough to check the timing and start the tuning process.
Finally my question.
With and engine having slightly bigger injectors but which should flow a lot more air than the original I expected it would run lean not rich.
What am I missing here?

[beavis]

The global fuel constant had been set from the capacity (1840cc) and injector flow (250cc/min) of the original engine, so I changed that to suit the new engine at 1950cc and 265cc/min (SE) injectors.

Out of curiosity, did you change these values back at all just to see how it ran?

[zossy1]

Hi David,

You have some tuning to do, my friend!

AFRs are dependant on a huge variety of factors. The additional air flow you mention will be non existent at idle and will only become apparent at high RPMs and under load. Furthermore, TPS values will impact this as you now have a bigger TB than you had before, and completely different value lift and duration which will impact values such as sidewall fuel retention, etc.

If you are set up for MAP tuning, that will also impact your values as your MAP will be completely different from your stocker at all RPM values. Finally, I'm not sure what fuel pressure Lou was running, and I'm guessing you also inherited his fuel rail and FPR as well as the injectors?

Timing values will also need attention. Ignition timing with big cams is low hanging fruit (potentially) but dangerous to do without good knock detection gear.

You need Tunerstudio, and either some dyno time or some track time (or a deserted country road with understanding neighbours - not recommended) to get her dialled in.

Good luck mate, looking forward to seeing this thing go at the end of November!

A question for the megasquirt brains trust.
I have a MS2PNP in my race car which has been tuned to run the stock engine very well.
Two weeks ago, myself and a bunch of forum regulars put a 2nd-hand built race engine in that car. This new-to-me engine has big cams, high compression (11.5:1), a bigger throttle body (Skunk2) & some head work, so of course I expect to need to do some significant retuning of the ECU.
The global fuel constant had been set from the capacity (1840cc) and injector flow (250cc/min) of the original engine, so I changed that to suit the new engine at 1950cc and 265cc/min (SE) injectors.
With no other changes the result is that the engine runs hugely rich, and requires a large amount of throttle to get it started and to get it to idle. If I reduce the global fuel constant from the calculated 12.3 to around 9.5 I can get it to idle enough to check the timing and start the tuning process.
Finally my question.
With and engine having slightly bigger injectors but which should flow a lot more air than the original I expected it would run lean not rich.
What am I missing here?

[sailaholic]

Big cams and headwork likely mean the engine is less efficient (runs rich) at low rpm but runs lean at high rpm.

Injector dead time also needs to change. This has a decent effect on idle mixture.


Sent from my iPhone using Tapatalk

[gslender]

...also.... there is no rule that says the original engine and tune was based off a require fuel value that was correct, so just adjusting it now doesn't actually mean anything. It is only used as a baseline reference so that 100% VE is essentially correct for peak efficiency on the VE fuel tables. You could set the required fuel higher or lower and still tune the car fine from start, idle through to max HP... the required fuel is just a good way to baseline the VE tables.

G

[david_syd_au]

Wow, thanks all for your responses. As always, tuning this engine will be more complicated than I expected!

Out of curiosity, did you change these values back at all just to see how it ran?

It was 13.15 with original engine. The calculated value for new engine was 12.3, and I had to reduce it to under 10 to get the engine to start. Given 12.3 seemed too rich, I didn't try 13.15 :-)

You have some tuning to do, my friend!
AFRs are dependant on a huge variety of factors. The additional air flow you mention will be non existent at idle and will only become apparent at high RPMs and under load. Furthermore, TPS values will impact this as you now have a bigger TB than you had before, and completely different value lift and duration which will impact values such as sidewall fuel retention, etc.
If you are set up for MAP tuning, that will also impact your values as your MAP will be completely different from your stocker at all RPM values. Finally, I'm not sure what fuel pressure Lou was running, and I'm guessing you also inherited his fuel rail and FPR as well as the injectors?

Currently set for MAP tuning, although some reading has suggested that with large cams that can be unreliable and it might be necessary to shift to TPS tuning.
We had to switch from using Lou's NB8B fuel rail to my NB8A rail due to differences between the fuel supply and return linesl in my NB8A compared to an NB8B. I believe we used Lou's FPR.

Timing values will also need attention. Ignition timing with big cams is low hanging fruit (potentially) but dangerous to do without good knock detection gear.
You need Tunerstudio, and either some dyno time or some track time (or a deserted country road with understanding neighbours - not recommended) to get her dialled in.

Booked in at Deckspeed on Friday. I just want to get the timing set and have a stable hot idle before I take the car there.

Good luck mate, looking forward to seeing this thing go at the end of November!

Me too!

Big cams and headwork likely mean the engine is less efficient (runs rich) at low rpm but runs lean at high rpm.

Good to know.

Injector dead time also needs to change. This has a decent effect on idle mixture.

Is this due to some difference between the std and SE injectors?

...also.... there is no rule that says the original engine and tune was based off a require fuel value that was correct, so just adjusting it now doesn't actually mean anything. It is only used as a baseline reference so that 100% VE is essentially correct for peak efficiency on the VE fuel tables. You could set the required fuel higher or lower and still tune the car fine from start, idle through to max HP... the required fuel is just a good way to baseline the VE tables.

Ahh, I thought it was more critical than that. So, it is not critical, so long as long as it is not set to a such a high or low value that it is hard to find suitable VE values to compensate?

[zossy1]

Currently set for MAP tuning, although some reading has suggested that with large cams that can be unreliable and it might be necessary to shift to TPS tuning....

Ahh, I thought it was more critical than that. So, it is not critical, so long as long as it is not set to a such a high or low value that it is hard to find suitable VE values to compensate?

I'd be tuning with TPS. Are you running an IAT sensor in the intake? Are you running TPS accel enrichment?

And yeah, the global fuel constant just scales the whole table by that amount. In the end, it is just a multiplier for your fuel table so what really matters is tuning each cell to deliver the desired AFR at that load/rpm level. If the constant is lower, the figure in your fuel cell will just be higher for the same AFR.

[david_syd_au]

Currently set for MAP tuning, although some reading has suggested that with large cams that can be unreliable and it might be necessary to shift to TPS tuning....

Ahh, I thought it was more critical than that. So, it is not critical, so long as long as it is not set to a such a high or low value that it is hard to find suitable VE values to compensate?

I'd be tuning with TPS. Are you running an IAT sensor in the intake? Are you running TPS accel enrichment?

Yes, I am using the original IAT sensor.

From TunerStudio
Wall-wetting AE (EAE) = Off
TPSdot uses %WOT = Off

And yeah, the global fuel constant just scales the whole table by that amount. In the end, it is just a multiplier for your fuel table so what really matters is tuning each cell to deliver the desired AFR at that load/rpm level. If the constant is lower, the figure in your fuel cell will just be higher for the same AFR.

OK, thanks.

[zossy1]

Ahh that's right, the later model cars had one. Mine didn't and I was using the GM IAT.

Good luck David, looking forward to seeing how you go! Will Daniel be tuning it, or will you auto tune / tune yourself? I didn't know he was working with Megasquirt, if so he'd be one of the few in Sydney who will touch them - not that they are hard to tune.

[david_syd_au]

Will Daniel be tuning it, or will you auto tune / tune yourself? I didn't know he was working with Megasquirt, if so he'd be one of the few in Sydney who will touch them - not that they are hard to tune.

Daniel did some fine tuning on his dyno a few months ago He is not familiar with TunerStudio/Megasquirt, but between the 2 of us we managed some fuel and timing tuning on power runs. The basic setup, cold/warm start and idle tuning I had already done myself.
I plan to again be involved in the tuning process on Friday, and maybe he will be a convert by the end of the day :-)

[wade]

I've decided to go with a MS for my supercharged na6

I wanted to build it myself and was wondering if anyone has experience with the DIYPNP kit

Specifically what do else I need to get other than the kit below ?

http://www.diyautotune.com/catalog/diyp ... p-384.html

Do I need the sequential add on ??

Anything else?

[wade]

^^^^ anyone ??

[bartmanftw]

Just follow this guide. http://www.diyautotune.com/diypnp/apps/ ... b6-mt.html

You don't need sequential injection but no harm in getting it if you want to wire it up for that.
You'll want the tuning cable, serial to USB adapter and a GM IAT sensor.

http://www.diyautotune.com/catalog/mega ... -p-35.html
http://www.diyautotune.com/catalog/usb- ... -p-67.html
http://www.diyautotune.com/catalog/mspn ... p-155.html

Alex.

[wade]

Legend, thanks

[Ruffian147]

Installed a AEM UEGO Gauge with a PNP MS2 plugged in to factory harness and nothing on the DB37 side.

Getting AFRs on the gauge but no signal on the Tunerstudio AFR