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MegaSquirt (aka MS) is a DIY fuel injection controller designed by 2 stellar guys, Bruce and Al (B&G).  I am using it to convert my International Harvester Scout Traveller from a Carter "ThermoCrap" carbueretor to TBI FI.  Here is information to help out anyone wanting to do the same.

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Links

My MS Pages Ignition options Different MS codes Why do it the MS way MegaBaro docs List of autoparts sources Electronics primer by Neon John

Bruce, Al and Lance Official MegaSquirt MegaManual / mirrored MS-II code / manual PWC o2 controller UMSinfo Sourceforge Project MS

Yahoo! Groups MegaSquirt MS message archive 68HC programmer MegaShift GM IAC control MegaCoding

Before I start, let me offer a warning.  This project has taken up most of my spare time for the past 2 years.  It has nothing to do with the quality of the MS project.  Actually that went together painlessly in under 2 days.  It has more to do with all of the ancillary issues in the conversion from carbueretor to fuel injection and the research into appropriate parts I had to do.   I just don't want anyone to think this is something they can do in a weekend to their main wheels.  The MS kit is reliable enough to use in your daily driver after you get it installed and happy.  But it would be better to start off with a weekend car to get your feet wet.

Intake
If you want a little info on machining for port injectors, check out Eliot's site; the following is for TBI use. The Scout has a 4bbl spreadbore Quadrajet style manifold and I wanted to use a GM 2bbl TBI to keep the conversion simple and cheap. I needed an adapter and it turns out few companies make these, I used Painless Wiring. It is part number PRF-60118 available through Summit Racing for $50. CFM and TD performance make adapters. I am concerned about using 51MM bore adapters with 43MM bore TBIs because it unshrouds the base passageways, but others have done it and says it works fine.

Why not use a Holley TBI? Because they are expensive, somewhat rare birds, and some say are of less than desireable quality. The GM TBI on the otherhand is as cheap, reliable and common as dirt in your local boneyard. GM made them by the millions for most 1987-95 4.3-5.7 liter engines. The 7.5L GM TBI has 51MM bores like Holley but they are even more rare and expensive. 2.8L GM engines use a TBI that is the same as the others except for smaller bores. 1982-86 2.5L GM engines used a 1bbl version of the 4.3L GM TBI. The Cadillac TBIs were of a little different design and I am not sure how much of this info is relevant.

Chart of GM TBI injector flow rates from DIY-EFI list

Color code on inj	Engine	Flow lbs/hr @ 13psi	TBI bore	GM part #
Black/White	2.8L	33	35mm	5235430
Yellow/Blue	4.3L	45	43mm	5235203
Green/White	5.0L	40	43mm	5235279
Orange/Black	5.7L PU	55	43mm	5235206
Yellow/Brown	5.7L CopCar	65	43mm	17084327
Blue/Black	Late BB PU	80	51mm	1708430
D Red/D Blue	Early BB PU	90	51mm	5235231

Fuel delivery
The first problem is getting fuel in and out of the TBI. The inlet is a 16mm o-ringed Saginaw power steering fitting, and the outlet is 14mm. There are 2 options to connect to it. Aeroquip and Earls Performance Fittings make adapters to -6AN male outlets. That is fine and dandy, but then you are locked into using several of their pretty but expensive and massively overkill adapters and hoses. I chose to go with fuel line repair kits you can get at your local parts store. They will likely not know what you are talking about so take the following information - Dorman 800-153 16mm TBI to 3/8" steel fuel line and 800-151 14mm TBI to 5/16" steel fuel line $13 each. You can slip standard 5/16" EFI fuel hose over the steel lines and use EFI hose clamps to secure the hose. Just cut the steel line and bend it how you want the inlet and outlet to face.

Any EFI fuel pump will work, the TBI's integrated regulator will just bleed off extra pressure. Master/Airtex E8228 is especially convenient with 5/16" or 8mm ports, a mounting bracket and good to 90psi. RockAuto supposedly sells it for $84. Stock GM TBIs run 9 to 14psi. You can safely bump them up to 35 psi max by fitting an Aeromotive 13301 regulator in the TBI fuel return line. Its usually suggested to put a surge tank or swirl pot in the system to prevent stalls due to fuel hiccups. I am going to try not doing it, but I will have to keep the tank over 1/4 full and be careful of my surroundings. Finally, put a return port into your gas tank if it does not already have one. Do not just dump the hot fuel back into the fuel pump inlet. And do not dump it down a vapor return line, they often have restrictions in the line and could cause fuel to spray out the gas cap if you ever opened it with the engine running.

Your injectors need to be clean to provide the best spray pattern and performance. Cruzin has a very reasonable service several have used and approved of. It would be even better to get matched output injectors. RC Engineering has a great injector calculator page and they also provide some fancy services. While we are talking about refurbishing, there are some outrageous that can be done to the GM TBI. You can get the throttleshaft bronze bushed if you have slop or binding in the throttle. Slop can also lead to too high idle speed if air is leaking past it. You can get the bore air horns shaved off. Or you can put a velocity stack on the TBI. All of this is not really necessary, but cool.

Bosch has an online fuel injector catalog. If you are looking for a really small TBI, Injectors4U shows some options. Synerject also may have some pricey options for exceptionally small equipment.

Wiring
For reasonable prices on sensors and pigtails, try Mototron. They also carry a cheap 0-100psi fuel pressure sender. If you want to work with top quality wire, I suggest Tefzel. It is available from Aircraft Spruce, Wicks or Wagaero in small or AE Petsche in large quantities. SXL wire is used in most modern cars and its half the price of Tefzel. You can check Waytek, Delcity or Spectro for it. Ira from the MS list gave me this info, and he has also been selling the GM CLT and MAT sensor pigtails as well as a nice regulated power supply for testing.

Another good option would be marine grade wire, like AncorWire. It is nice stuff... soft, flexible, finely stranded, tinned for corrosion resistance and based on the AWG American Wire Gauge standard which is bigger. I do not suggest generic auto wire. It is a pain because it is generally stiffer with coarser strands and based on the SAE Society of Automotive Engineers smaller standard. 20ga wire is overkill for all circuits except injector wires and power wires from the relays to the fuel pump and fast idle solenoid. DB connectors will take a maximum of 18ga wire. This is sufficient for 1 TBI or 2 port injectors on each channel. If have more, you will need to step up to 14-16ga and split the strands into 2 DB pins. The relay kit is nice but totally unnecessary to install your MS satisfactorily.

Other Wiring Resources
o2 sensor wire color matrix

Testing
You can power the MS with any old regulated power supply from 9 to 22VDC limited by D15. Be careful about using generic wall wart power supplies. Often they are unregulated and will feed MUCH higher than rated voltage when they do not have a large enough load. A word of advice, buy the stimulator with the MS. Its too cheap to be worth futzing around bodging a substitute. The stim's R9 100 ohm resistor will cook in 10 seconds or less if you are using above 9 volts.  Try a 330 ohm 1/2 watt resistor if you are going to be using up to 20 volts. And in the original assembly guide, it tells you to put the LEDs in backward. Here is a revised MegaStim assembly guide.

Colin's Tech Documents

Assy Guides and Tuning MegaView - assembly guide MegaStim - revised assembly guide Part numbers - alternates for MegaStuff, mostly Digi-Key nums MSTweak3000 - additional tuning instructions Tuning info - for my application and general instructions MS memory map - tweak hidden settings in MegaTune memory editor

Heavy Duty Modding Using GM 3Bar - MAP sensor for turbo above 21psig MS firmware code mods - lots of stuff, table of contents at top Assembly programming - tips and information C programming for MS - tips and code snippets Calcing MPG - to be able to add this feature to MS

<To be continued...  This page will be under construction for a while>



Ordering
You need the following to make a standard MS -

1. Partial Mega-Squirt/Stim/Relay/View kits from B&G
2. Lance's automatic parts purchasing baskets for Digi-Key
            MS ECU      |      Stim      |      Relay      |      MegaView
3. LMB Heeger case from them or  HDB Electronics
           You need a whole EAS-300 for the MS or one half of an EAS-200 for the relay kit
4. Straight thru DB-9 serial cable for configuring the MS (not null modem)
           And if you don't have a serial port, you could try a USB adapter 1 or adapter 2 or adapter 3

These parts are optional but cool...

5. Those blue end things are MegaPanels
6. MAP bulkhead fitting from your local RC store or Tower Hobbies or this place
7. Other part numbers and descriptions, mostly Digi-Key, some McMaster

You can cheat and buy MS preassembled from Robert on the MS list.

Troubleshooting
!?! I failed my smog test !?!
Use the failing report you receive and this graph to figure out what area of the VE table to tweak and in which direction to tweak it. If you need more help, here is some information from Toyota. Then, take a stab at the sniffer again.

Here are some "cheats" to help you pass a marginal car...

• Take the car on a good drive before the test to get it nice and hot (like 15 highway miles)
• Let it run/idle until the test, but minimize the time between (the cat and o2 sensor need to be 800dF for best results)
• As a last resort, try dumping some Iso-Dry gas antifreeze in the tank. This is simply pure isopropyl alcohol to act as an oxygenate for complete combustion. Be careful to not get methanol or ethanol antifreeze which is much more common.

Tach false triggers
Did you use shielded wire as stated above and attach the shield to engine ground?
Before you start, first be sure your rotor/cap/plugs/wires/coil are all in good condition. Marginal can create all kinds of havoc.
Ed capacitor can be increased from 0.001 > 0.1, it can inhibit high RPM operation.
Install an extra capacitor .22>.47uf 600V Polypropylene at junction of D5/R10 to GND at XG2, this negates Ed capacitor.
390ohm resistor can be increased in steps to 1kohm.
If there are processor resets too, run the opto led cathode (pin 2) back to the engine ground on a separate wire.
If all else fails, put a MSD box on your ignition and use the tach out to trigger the MS.  This is pretty much foolproof.

270 ohm 1/4watt resistor cooking?
Try a 1/2 watt or switch to 330ohm 1/2 watt.  Or lower the zener breakdown to 30 volts.

These things will take out a V1 MS by Bruce himself

1. Reverse voltage applied for any length of time to the +12V input. This burns the FETs, FET driver and PCB trace, if long enough D16, then D14 when voltage is corrected
2. Flyback diode backwards or bad solder joint - this takes out the FET and then the FET driver (which shorts the +12V power) - this short fries D13 because it is flowing lots of current thru low resistance
3. Injectors wired up incorrectly or there is a free wire strand at the connector shorting out the drive bank. The FET shorts out and you then get all of the stuff in step #2. For a fuse, I would use a 1 amp unit for the +12V line going into the MS box.

Others related sites

Eric's Not2Fast Engine Tools Perry's DataAcquisition page and sensor info for down DIY-EFI server Scott's Dizzy / MS / Coil interface page and archive of the MS Y! messages

Why batch and not sequential? Dave's GM IAC control page MS was SlashDotted UltraMegaSquirt is getting closer Get a MegaSquirt emblem!

MS Hardware Stuff

Add to MS MegaView - digital display for MS by B&G MegaIgnite - Ignition options Eric's Daughter Board for MS Colin's Daughter Board from ExpressPCB Boris's knock sensing

WBo2 options B&G's PWC Wideband O2 is coming! TechEdge PLX InnovateMotorsports Perry's emerging MegaWideBand

Revised MS MegaPetrol MegaSquirtAVR Sensor Data

MS Software (There are tons of other embedded and tuning programs listed on the compatibility chart)

Clientware Eric's MegaTune is the gold standard Firmware Official B&G current release is v2.986b

Other's Tools Lance's VE / VEX estimator Perry's advanced VE / VEX generator

Colin's QuickTools EFITools - spreadsheet of inj and FET current charts, plus fuel pressure and VE/AFR(done by MSTweak2.15) Coming soon! Program slows 68HC programmer

Free counters provided by Andale
No I'm not vein, I was just curious how many people were using this after I worked so hard on it