SH Megasquirt questions

Related to the Bowling & Grippo Fuel Injection system.
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scott.venables
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SH Megasquirt questions

Post by scott.venables » Thu Jul 12, 2007 3:22 am

Hi guys I am looking at a second hand MS setup. Most of you have probably seen the ad but here it is again:

I have a fully built and functional MegaSquirt. It is mounted in a Bosch L-Jetronic case which makes it perfect for L-Jet cars. It also has the flyback board installed in the case for L-Jet low impedance injectors. Because its in an L-Jet case it will bolt into your orginal EFI computer position and will just plug right into the wiring harness. It has also had the necessary fuel pump circuit modification done to it.

Simon's
(Hollywell) Alfa 75 3.0 V6 ran perfectly with this MegaSquirt and he got it somewhat tuned through the rev range.Simon had it running with MAPdot but it will come with a Vishay TPS (from FarnellOne group buy) so you could run TPSdot.

What your getting:

* Complete and functional MS in L-Jet case with FlyBack board installed and functional
* Air/Water temperature sensor.
* Variable Resistance TPS with mounting plate for Alfa throttle body
* Stewart/Aussie stimulator which is functional and complete
* Serial/null modem cable for PC or PDA connection


I have a few questions that I am hoping you might be able to help me with. This will be going into my stock daily driven Alfa 75 2.5.

As a newbie to programmable EFI, how suitable is this setup given that I haven't built it or experienced troubleshooting it?

It seems to be setup for MAP(with partial MAP tune) but also comes with a "Vishay" (brand?) TPS with adaptor plate to fit TB. Would it be best to try and make the TPS thing work or just setup up a MAPsensor and use the MAP tune?

I am looking at this conversion for a few reasons. Simplicity, reliability, easy starting, and improved economy(about 12-14 l/100km in my 2.5 L-jet car :( ) Will this conversion give me what I'm looking for?

How "plug and play" is this? I understand I'd have to wire up an air temp sensor, and maybe a MAP sensor, much else?

How intuitive is MS in self tuning (if at all)? It runs in closed loop I presume but the mixture has to be set pretty much spot on doesn't it?

Any help is much appreciated.
Thanks, Scott
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Re: SH Megasquirt questions

Post by P.Webb » Fri Jul 13, 2007 8:51 am

scott.venables wrote:Hi guys I am looking at a second hand MS setup. Most of you have probably seen the ad but here it is again:

I have a fully built and functional MegaSquirt. It is mounted in a Bosch L-Jetronic case which makes it perfect for L-Jet cars. It also has the flyback board installed in the case for L-Jet low impedance injectors. Because its in an L-Jet case it will bolt into your orginal EFI computer position and will just plug right into the wiring harness. It has also had the necessary fuel pump circuit modification done to it.

Simon's
(Hollywell) Alfa 75 3.0 V6 ran perfectly with this MegaSquirt and he got it somewhat tuned through the rev range.Simon had it running with MAPdot but it will come with a Vishay TPS (from FarnellOne group buy) so you could run TPSdot.

What your getting:

* Complete and functional MS in L-Jet case with FlyBack board installed and functional
* Air/Water temperature sensor.
* Variable Resistance TPS with mounting plate for Alfa throttle body
* Stewart/Aussie stimulator which is functional and complete
* Serial/null modem cable for PC or PDA connection


I have a few questions that I am hoping you might be able to help me with. This will be going into my stock daily driven Alfa 75 2.5.

As a newbie to programmable EFI, how suitable is this setup given that I haven't built it or experienced troubleshooting it?

It seems to be setup for MAP(with partial MAP tune) but also comes with a "Vishay" (brand?) TPS with adaptor plate to fit TB. Would it be best to try and make the TPS thing work or just setup up a MAPsensor and use the MAP tune?

I am looking at this conversion for a few reasons. Simplicity, reliability, easy starting, and improved economy(about 12-14 l/100km in my 2.5 L-jet car :( ) Will this conversion give me what I'm looking for?

How "plug and play" is this? I understand I'd have to wire up an air temp sensor, and maybe a MAP sensor, much else?

How intuitive is MS in self tuning (if at all)? It runs in closed loop I presume but the mixture has to be set pretty much spot on doesn't it?

Any help is much appreciated.
Thanks, Scott
That's a lot of questions but here goes.

MapDot is just fine. You don't really need the TPS except for flood-clear mode. If it comes with a TPS, super but don't worry if you don't want to install it. The switch type TPS will show max for flood clear mode and MAPDot will do the accel enrichment just fine.

Many of us here helped Simon when he build that setup (I know I personally put a lot of time into his build). It should be just fine to run as is. Get a stim if you can.

As far as installation, it should be mostly plug and play. If it's in a Bosch box with connector, it already uses the existing sensors on the car with the compensation resistors. CLT is taken from the front of the thermostat, IAT is inside the AFM and it already wires in. TPS should already be wired in too but as above, don't worry about it. F-Idle isn't an issue with the AAV that runs independent of engine management. The MAP sensor is onboard on the MS that plugs into the passenger footwell. You need to run a MAP hose from the plenum inside the car to the nipple installed on the box. Where the wiring harness comes through on the passenger side there is a convenient hole on the grommet you can enlarge for a 1/4" OD vacuum line. Thats about the only modification you'll need once it's wired into the L-Jet connector. You can install it in literally half an hour.

Self-tuning only works with UEGO. It's actually called TargetAFR. Don't worry about it too much. If the box already comes with a VE table that runs well, stay with it. Chances are the REQ_FUEL will be a little high for the 3.0 so just play with that. The VE is going to be pretty similar, as are the AE and WUE settings.

Plug in your laptop and get an idea of what sets what on there and make sure you download and save the MSQ file from the box as it sits. And keep backups when you change things so you can put it back to running in case you mess something up.

My rule of thumb is simply this. No matter how tempting, once you get it running well leave it alone. Resist the tempation to tweak.

-Peter
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Post by scott.venables » Mon Jul 16, 2007 3:38 am

Thanks Peter I really appreciate it. The installation doesn't sound too painful, and tuning shouldn't be too bad once I get the hang of it. It comes with a stim so that's good, and an IAT sensor(to do without the AFM I guess)

It's probably a stupid question, but what does VE stand for? I think I know what it is but I can't think what VE stands for.

Thanks again,
Scott
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Post by P.Webb » Mon Jul 16, 2007 11:37 am

scott.venables wrote:Thanks Peter I really appreciate it. The installation doesn't sound too painful, and tuning shouldn't be too bad once I get the hang of it. It comes with a stim so that's good, and an IAT sensor(to do without the AFM I guess)

It's probably a stupid question, but what does VE stand for? I think I know what it is but I can't think what VE stands for.

Thanks again,
Scott
Volumetric efficiency. The tuning strategy is simply this:

The REQ_FUEL is the total injector open time at maximum revs at 100 VE. The table is a interpolated percentage of that number minus corrections.

In other words (and we'll use simple numbers here).

A REQ_FUEL of 20 is 20ms of fuel per revolution at full VE and RPM. If you change to 2/squirts per cycle, the REQ_FUEL number cuts in half.

An abbreviated VE table might look like this:

KPA VE

100 80 90 100
90 70 80 90
80 60 70 80
70 50 60 70
60 40 50 60

RPM 4000 5000 6000

Where the numer is the percentage of that REQ_FUEL number. So at 100kpa (atmospheric) and 6000 RPM you would squirt 20ms. At 70kpa and 5000 rpm you'd be squirting 12ms or 60% of 20ms.

Assuming under the ideal gas law that the volumetric efficiency of the engine decreases at a linear rate (which it doesn't so your numbers won't be this simple). As the piston goes down, it creates a theoretical 100% vacuum. Air attempts to fill that vacuum but as the throttle plate restricts the amount of air that can rush in to fill it, therefore creating a partial vacuum measured in KiloPascals. The volumetric efficiency of the engine is how much air is actually in the cylinder to burn and how much fuel it requires to create a ratio of air to fuel to create an explosion.

Do some reading on the ideal gas law and the Helmholz principal of volumetric efficiency.

Once you've got that down we'll talk about brake specific fuel consumption or BSFC which deals with the energy of fuel and loss in the motor. You can actually calculate the power output of the engine based on its VE, fuel consumption and loss.

-Peter
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Post by scott.venables » Thu Jul 19, 2007 4:59 am

Thanks Peter you're a great help.

I remember reading about VE in David Vizards BMC tuning books. I did a little reading on Helmholtz and a little on Ideal Gas Law, but I need to go over them again. It's interesting stuff. Thanks for the insight on tuning as well. How many load and rpm points are there?

Scott
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Post by P.Webb » Thu Jul 19, 2007 11:48 am

scott.venables wrote:Thanks Peter you're a great help.

How many load and rpm points are there?

Scott
Depends which chip and code you're running.

Base MS-I is 8x8, MS-I with Extra is 12x12. MS-II is 12x12. More than you need. There's also interpolation between points. That means that it calculates the VE per the closes 4 points on the table, not the closest cell. But table/top bottom is still in effect so if you hit anything over 100kpa or 6000 rpm in the above example it will use the top value. The table top is where you set it. For example in a forced induction setup where the intake would be above atmospheric and create pressure.

Also keep in mind the table top is going to vary by where you live and drive. 100kpa is atmospheric at sea level so you'll have to go to the beach to tune :)

Where I live, 97kpa is atmospheric (don't know the actual elevation).

-Peter
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