Introduction:Introduction:The Pinzgauer from the factory is equipped with dual Solex 2bbl carbs. They work great, and have excellent off-road capability. They do, however require regular adjustment and cleaning. It can be a trick to get them synchronized. And, like all carbs, they are at best tuned for a compromise of the current altitude and temperature, and will often be rich or lean. You also have the manual choke issue. Again, it works, but is at best a compromise.
Electronic Fuel Injection (EFI) has the advantage of being able to provide the engine with the exact fuel required for the current load. The tradeoff is electronic complexity for the existing mechanical/hydro-dynamic of carbs. I have learned much about the EFI world from playing with the Bosch L-Jetronic on my Fiat. It is actually fairly simple once you get the big picture. The "Probst" book is a very good tutorial on how EFI systems work, and what the engine actually needs.
Controller
This
one was easy. I had considered GM ECM's, which are widely available, and are
becoming fairly well documented. The downside is they are non-intuitive to tune,
require Programmers to change table values, and are a bit more complicated than
you need for fuel only.
Enter the Megasquirt! This is a very cool kit designed by Bruce Bowling and Al Grippo. I won't go into much detail here until the tuning starts, but you should check out the website! There is also a Yahoo group mailing list with lot's of activity.
The Pinz has no Volumetric Efficiency (VE) data available for it, and I will probably not do a dyno run, so I needed a way to start faking some initial VE values. This spreadsheet was the result of this exercise, and will allow me to do some what if until I can actually start tuning.
Plenum
Rather
than build a plenum I scrounged the junkyards and found a factory unit that
looks like a decent fit for the Pinz. It came from a Saab 2.0l. The neat thing
about this plenum is that it attaches to the intake runners via a silicon hose,
and is designed for an inline four cylinder engine. The angle of the runners,
and the orientation of the TB is also correct and should fit into the space
currently occupied by the factory intake and carbs.
Another one I might try is on the Saab 900's. It is a one piece unit, but I could saw off the flanges and still use the coupler tubing like the one above.
I'm also considering a smaller plenum from a 1.9l Escort. It is a bit more compact and the runner design is ideally adapted for the flexible runner approach.
Intake
Flange and RunnersI'll have to fab the lower intake runners and flange. Intake gaskets will be used to trace the flange dimensions onto 1/4" steel. I'll cut the holes with holesaws, and cut the flange out on a bandsaw. I hope to find a tubing size that will match the ports after being broached into the correct oval shape. Hopefully the steel part of the runners can be straight and perpendicular to the flange which will make welding easy. Any bends will be made in the silicon hose joining them to the plenum runners.
Lot's of investigation on the injector bosses. Though I can order steel bosses and weld them on to have the injectors shoot at an angle, there is virtually no way to get a conventional shot at the back of the valve. Lot's of discussion on the diy-efi list has indicated that aspiration is preferred to vaporization, and nearly all TPI systems just let the injector shoot at the opposite wall of the runner. So, that simplifies things significantly. It just so happens that a 5/8" compression fitting will happily hold a Bosch injector. (Leave it to the VW buggy guys to figure this out!) So 5/8" compression to 3/8 NPT brass fittings will be my initial injector mount. See the injector section below for more detail.
Throttle
Body |
The Saab plenum I sourced comes
with a 55mm throttle body, which is a bit larger than I would prefer. I
may use one from a 900 normally aspirated model which is smaller.
I would really like to find a small progressive 2bbl throttle body similar to those used on rabbits. The small primary should give finer throttle control at low throttle settings, but provide the additional airflow needed for higher speeds. I'll try to get it running on the existing TB and experiment from there! The Saab uses a standard looking Bosch Throttle Position Sensor (TPS), but it is only a switch type rather than a variable resistor (Pot). I'll be looking at later Euro cars (BMW 325, etc) to find one that should work. |
 |
Sensors
Sensor |
Description / Source |
Ambient Air Temp (IAT) |
This one is easy. Plain jane GM parts. The sensor from a '97 Suburban 350 is a cage type with a grommet mount, which is what I will use just downstream from the air cleaner. Bosch sensors will work with a MS table change, but there is really no need. The GM sensors are available in several thread types (Std and Metric) as well as grommet mount. |
Coolant Temp(Cylinder Head Temp approach) |
This seems to be the most usable approach based on
discussion. The Bosch Cylinder Head Temp (CHT) sensor used on many FI VW
and Porsche's is widely available and appears to be a NTC resistive type
which is what the Megasquirt is expecting. There are Thermocouple sensors
which go under spark plugs which are probably more accurate, but will not
work without signal conditioning. The Bosch CHT sensor is about $18.
Update:Several Air Cooled VW folks are using the Megasquirt with a stock Bosch CHT sensor with a simple resistor change. This is the approach I will start with, probably via a hole drilled in the cooling fin. Others have epoxied a raw NTC Thermistor with similar results at much reduced cost. |
Coolant Temp(Oil Temp approach) |
An Oil Temp sensor in the sump or in the cooler line seemed
like the easiest approach, but discussion with Ron Schroder has indicated
that the oil temp lags CHT by several minutes or more. Since the main
function of the temp sensor as used by the MS is to determine if an
enrichment is needed, then the CHT is probably the right way to go.
Some VW folks use an oil temp sensor and look for the oil to come up to 30 degrees centigrade to indicate the engine is warm. This might be a usable approach, but I need CHT's anyway for tuning, so I'll end up trying that first. |
Coolant Temp(Block Temp approach) |
You could also use a standard water temp sensor located on the block, but this will be the least accurate. As with the oil temp approach, the pinz is so overcooled it may not be an accurate indicator of whether the engine is warmed up. |
Throttle Position Sensor |
This part is non-critical. Any pot type that can be mounted to your throttle body will work. In fact, it's almost easier to find a throttle body you like and just use it's original TPS. |
Fuel
Pump & ReturnVW Rabbits had a nice surge tank/fuel filter/pump assembly that I plan to use as a unit. I'm currently planning on installing this behind the passenger seat. Yes, this is inside the cab, but so is the filler intake. IE: There is already fuel routed inside the cab. Yes, adding high pressure lines does increase the risk a bit, but face it, we are in a canvas topped vehicle with the carbs less than a foot from the driver. The other alternative is behind the fuel tank tucked up like the gas can holder, but you face exposure to mud, etc there. It's under the floorpan just in front of the right rear wheel on the rabbits so the unit is designed to be exposed to the elements.
This page at sdsefi explains the surge tank approach: http://www.sdsefi.com/techsurge.htm
This page at dunebuggy.com has good info on scrounging Bosch pumps and plumbing fuel systems: http://www.dune-buggy.com/turbo/fuelsystem.htm
Fuel Pump Cutoff
Idle
Air SolenoidI have not selected a particular solenoid. The Saab plenum came with a solenoid, but it appears to be a strange variant of stepper. Not a true rotation stepper, but a two solenoid approach, with no spring return. IAC is not a priority for me, so I'll probably not attempt computer controlled idle for now. The Mega-Jolt-Lite ignition controller will have a stepper idle control, so I may revisit things then.
Default will be a normal Bosch L-Jet "Aux Air Valve", as they work and are easily available. One nice aspect of the aux air valve is that it is thermo-mechanical and opens according to the temp of the engine. The down side is they stick over time, etc.
There is lot's of dialog on this item in the MS Yahoo group. My experience is that it is non-critical to get the car running, and can be addressed once other issues are worked out. (You just manually increase throttle opening until the engine warms up.) Most folks use vacuum solenoids originally used for EGR & Cruise control. Also there is one from J.C. Whitney sold to switch between fuel tanks that SDSEFI resells for this purpose.
InjectorsHave not spent too much time on this yet. Here is what I have been able to nail down to date:
Fuel
Pressure Regulator: LinksThere is a tremendous amount of info on the web that I have leveraged. These are some that I have found useful:
