MS I to MS II conversion lessons learned

[Zmanco]

I've recently finished upgrading megasquirt from the early MS I processor to the more powerful MS II and thought I'd share some lessons learned for those who have yet to go down this path.

 

First, a little background on my application:

 

L28 N/A

N42 head

Reground cam 284/284 .480"

Header

Stock EFI intake and fuel rail

280ZX turbo injectors

Bosch 3 wire IAC valve

280ZX turbo distributor (installed when I upgraded to MSII)

 

In the beginning I wanted to get the megasquirt installed without spending a lot (sound familiar?) so I went with the MS I processor. I wanted to be able to control idle so ran the MSnS (MS I extra) code.

 

Lesson 1: The MS I Extra idle code is pretty crude.

They say this up front, and they are correct. I spent a lot of time experimenting to be able to get it to hold a steady idle and to deal with the e-fan kicking in without having the engine stall. And even then it didn't work all that well.

 

Lesson 2: The algorithms that determine fuel from the VE tables are quite different between MSI and MSII.

I had expected that I would just import my VE tables and be on my way. In fact, I had to start over from scratch. All the time I spent tuning on MS I was thrown out, with the exception that I'm more experienced and hence better at it the second time around.

 

Lesson 3: The MS II Extra idle code is pretty good.

If you plan to use MS to control idle or think you will in the future, go directly to MS II Extra.

 

Lesson 4: If you can swing adding spark control into your plan, do it.

I am quite pleased with how MS handles spark. It's so easy to create custom spark curves that vary not only with rpm, but also with MAP - think of MAP as the opposite of vacuum if you haven't crossed over to MS yet If you hear any detonation, you can dial the timing back from the driver's seat (parked of course!) by as little as 1 degree. And unlike with a mechanical distributor, you can pick a narrow range of RPM and/or MAP to reduce the timing and then let it go back to normal for the rest.

 

Lesson 5: When you begin tuning, follow the advice in the MS documentation and start off with no accel enrichment, O2 correction, over run cutoff, etc. All those add-ons make it hard to tune the VE table properly. The first time around I didn't listen. This time I did, and was pleasantly surprised how well the tuning software, MegaLog Viewer, works without all those other systems running. And with a good VE tune, those other systems, especially Accel Enrichment, will require much smaller values. Too often, people try to fix poor VE tables with excessive Accel Enrich values.

 

At this point the driveability is excellent, nearly as good as an OEM system. It starts cold just by turning the key - no pedal pumping or holding a high idle for a few minutes is required. Power is good, but in fairness was good with MS I and even the triple webers I had on originally. Mileage is great - if I keep my foot out of it, I see mid to upper 20's. The best I EVER saw with my triples was 19, and that was on a long highway cruise. I do have a huge issue of detonation in the 3.5k - 5.5k rpm range that no amount of richening will solve. But I'm in the process of prepping a shaved P90 head and I'm expecting that will allow me to run full advance.

 

So if you're thinking of going with MS, I'd strongly recommend you start with MS II. The extra cost (~$70) is really quite small in the overall scheme of what you'll spend, especially if you include the price of gas consumed while tuning.

 

I'm attaching my msq file for anyone who may find it helpful.

megasquirt200807080859.zip

[cygnusx1]

MSII was my choice from the getgo so I have no experience with MSI. All I can say is that it runs as well as the factory EFI with the benefits of being able to extract more power and tune to optimal performance in the critical areas.

 

My only tune area that needs improvement is the cranking startup settings. I have yet to get it as perfect as the factory was. It's only a matter of tuning time.

 

Right now, from cold, it cranks a few times over and sputters a bit before taking a nice idle. I need to tweak my ign timing and pulsewidth during cranking.

[proxlamus©]

hmm..

 

i like my MS I !! lol

[Zmanco]

I know you're kidding Ryan, but I hope I didn't come across as suggesting there was something wrong with MS I. I don't think there is. If I wasn't controlling idle, I think I could have stayed on MS I and been quite happy

 

My point was that if I was starting from scratch today, I'd go straight to MS II.

[mobythevan]

Lesson 2: The algorithms that determine fuel from the VE tables are quite different between MSI and MSII.

I had expected that I would just import my VE tables and be on my way. In fact, I had to start over from scratch. All the time I spent tuning on MS I was thrown out, with the exception that I'm more experienced and hence better at it the second time around.

 

I bet the majority of this problem is caused by the low res injector control in MSI. You also have to re-tune if switch to hi-res MSI code. MSII has much much finer resolution than the MSI hi-res code.

[Zmanco]

I bet the majority of this problem is caused by the low res injector control in MSI. You also have to re-tune if switch to hi-res MSI code. MSII has much much finer resolution than the MSI hi-res code.

I think you're right. Overall the engine runs so much smoother and is more consistent in its behavior, even when I don't have a particular portion of the map fully tuned yet. I think the MS1 processor running the MS I Extra code didn't have enough power to keep up.