Piggyback ECU installation write-up - PeachParts Mercedes-Benz Forum

Blown_M104 · #1 10-27-2005, 01:01 PM

Over the first year of my supercharger install I have looked for better ways to manage fuel control . I’ve tried a Boost proportion fuel pressure regulator and also played around with switching in different resistor values for the Inlet Air Temperature sensor IAT. In the end I was still running lean under boost and leaving a lot of HP on the table due to the wrong A/F ratio. For cost reasons I did not want to go with a new stand alone ECU unit; even most of the Piggyback units out there are rather expensive. After a lot of looking I found the Apexi S-AFC II for just $220 that would work with the stock ECU. (I have the Mercedes 1993 Hot Film Mass Air Flow system on a 3.2L M104).

Basically the Apexi unit wires in series with the Mass Air Flow Sensor input into the stock ECU. Since the ECU uses the output voltage from the MAFS as one of the primary factors in determining injector firing time this is an ideal lever to increase fuel flow. Apexi gives you the ability to multiply the signal from the MAFS at 12 different RPM points by +/- 50% . It has two different multiplier maps that are switched between depending on throttle position. I’ve got map #1 set to all zeros for stock driving, but above 33% throttle open I switch in MAP #2. The numbers for this second Map are based on my math calculations for how much more fuel I need at different levels of boost. It’s also worth noting that I’m using the stock Bosch 0280 155 209 injectors which are rated at 3199cc. My math says these injectors are good for around 325 HP at 6 psi of boost.

After driving the car for a few days I’ve realized I never should have done the blower installation without the Piggyback… the increase in performance is so much greater with the A/F ratio corrected. Also for a normally aspirated car this might be the trick for you; you could change you’re A/F ratio down from the stock 14.7 to a richer mix under heavy acceleration.

The Apexi wires in very easily, one connection to 12V (off the over voltage relay) , ground connection , rpm input wire (I tapped into the Cam position sensor), and then two wires to change the Mass Signal (one to the MAFS and one to the ECU). The wire to the throttle position sensor was tricky to find but I got it (with the help of 300EVIL here on the Forum). Attached is a quick diagram of what the wiring looks like.

Have fun with it.

MDMB69 · #2 11-01-2005, 08:28 AM

Thanks for the info. Because of what you've said I'll get the Apexi too. My installation is very similar to yours except on a 2.8.
Is there any further help you can give me on exactly where the wires are to tap into and also how you calculated your math on the fuelling increase.

You e-mailed me part of your Powerpoint slideshow on your installation back on 9th Sept which was very helpful.
You can e-mail me if its easier.

Blown_M104 · #3 11-01-2005, 09:05 AM

Best of luck with your Apexi install, I think you'll be very pleased with the results. Below is a summary of the wiring connection points.

For the MAFS I spliced into the 4-conductor cable going to the MAFS from the ECU. The yellow wire with white strip is the output signal.

For the RPM signal I tied into the Cam position sensor wire in the wire duct on top the fuel rail. This is a shielded cable with a pink center conductor. Just connect to the pink wire.

For the throttle position signal I went directly to the cable connector at the throttle body. The Factory wiring diagram list the actual-position-sensor wire as being red/yellow for my model. The wiring diagram is wrong! Red/yellow is for the set point potentiometer; the red/white wire is the actual position sensor which is what you want.

+12V power I got off pin 7 on the over-voltage relay. You might have different style relay, just find a pin that is switched with the key position II.

The Apexi has two ground wires, follow the instructions that come with the unit for connecting them to the ground wire going to the ECU (solid brown).

I ran the wiring harness for the piggyback though the pass side firewall and then mounted unit under the dash. I high recommend soldering all wire splice connections and using wire rated for engine bay temperatures.

Math:
I’ll email you two spreadsheets I used; one is for injector sizing and the other calculates increased airflow (as weight) at different levels of boost and for two different desired A/F ratios. The air density calculations are all based on equations I got from this very cool link :

http://webpages.charter.net/chrisstephens/EEC%20Help%20files/Files/Air-Fuel%20Flow%20Calculators.htm

Jim Villers · #4 11-02-2005, 09:47 PM

Have you put your car on a dyno with wide band monitoring? Until you have gotten some accurate air-fuel monitoring under maximum load conditions, you are flying blind. At best, it will work as hoped; at worse, it will run lean on fuel and burn pistons.

Blown_M104 · #5 11-03-2005, 10:04 AM

Well said Jim; a dyno run with wide band monitoring is the only way to properly adjust the fuel MAP. I've been shopping around for a dyno shop that doesn't want an arm and a leg for a couple hours with monitoring. I'd really like to check/adjust the A/F ratio across a wide range of RPM values.

MDMB69 · #6 11-09-2005, 04:38 AM

A big thanks to Blown_M104 for all his groundwork on this.
I can now report that even on a standard non-supercharged or non-modified engine this makes hell of difference to the performance at low revs.
One problem with the M104 engine is the lack of low down power before the variable valve timing kicks in.
Now with the Apexi fuel controller installed I've increased fuelling by about 15% at low revs when I push the throttle and now that lathargic pull away when switched to economy mode on the gearbox (no kickdown) has all but gone, even at low revs the exhaust growls a lot more and the car takes off as I think it always should have done.
My initial results were dissapointing as fitting the Apexi with standard settings slowed my car a lot, but since increasing fuelling...Wow!

Definately worthwhile fitting but bear in mind its not easy to fit if your not competant and tracing wires in the engine wiring loom, (or trying to understand the instructions).

wbain5280 · #7 11-14-2005, 01:29 PM

You need a Rising Rate Fuel Pressure Regulator to increase fuel pressure in proportion to the boost. Go to the junkyard and find a Volvo 740 Turbo, 760 Turbo or 940 Turbo, 240 Turbos will also work, and get the (RR)FPR. The cars must be the turbo models. Check the trunk lid or check the exhaust manifold if it's there. There should be a flat mount for the turbo.

Hit Man X · #8 12-02-2005, 04:20 AM

Hrm... I've been curious about this for a while on other MAF vehicles. Would this setup easily be adapted to a 400E? I know most of these W124s (even 300Es) run VERY lean at WOT for some reason...

Blown_M104 · #9 12-02-2005, 11:43 AM

Hit Man:

Installation on a 400E should be the same as long as you have the Hot Film Mass Air Flow system.

I think you'll be amazed at the results even on a NA engine. Gaining back control of A/F mapping, for the couple hundred bucks you'll spend on the Apexi unit, is a good spend.

Hit Man X · #10 12-02-2005, 04:31 PM

Ah excellent news!

I've been reading about the 400/500E fueling at WOT and running stoich at those speeds is far, far too lean. 12.3-12.7:1 is what I'd hope for to max power.

Thanks for the info.

ke6dcj · #11 12-05-2005, 01:36 PM

For the price, this is wonderful.

Can it be integrated into a data-logger ?

BTW: Has anyone considered the Apexi AFC2, aka as the "Euro" version of the S-AFC II or the V-TEC version ?

S-AFC II:
http://hpautoworks.com/apafeucarmo.html

S-VTEC AFC II
http://hpautoworks.com/vtecafc1.html

The V-TEC version allows you to set a map for our variable valve timing, which would be great for our M104 and M119 engines, plus the newer version has a knock sensor input, and the resolution is every 200-RPM.

:-) neil

http://www.racingworks.com/apexi_vtec_controller.htm

The A'pexi V-AFC 2 Vtec controller is the easiest way to modify the Fuel Maps and Control Vtec from one handheld unit. The On-Screen Display is easy to navigate and modify. Apexi has redesigned the Face Plate of the Vafc2 Vtec Controller and added a Knock Sensor monitor into the features. The Apex V-AFC 2 Vtec Controller allows the user to modify the fuel curve at 24 adjustable increments as well as change the VTEC Engagement Point. Most cars will see a 10-20 increase in horsepower. Installs in 1 Hour. The US Version of the Apexi VAFC2 Vtec Controller is BLACK with Plum Display Panel, like the GT-500 Limited Edition Apex S-AFC Simple Air Fuel Controller.

Features of the Apex VAFC 2 Vtec Controller Include:

Fuel Control
Adjust Fuel Delivery Range of +50% to -50% up to 1% Step Increments in 100 RPM Increments
Unmatched Fuel Control, Richen or Lean out the Fuel Mixture when Vtec Engages

Vtec Control
Adjustable Vtec Control for RPMs, Throttle Angle, Upshift / Downshift, Engine Speed
Vtec is Adjustable in Increments of 100 Rpm for a Total of 24 Throttle Based Points
VTC Vtec Monitoring for i-Vtec Equipped Engines
For Vehicles with Vtec Engine Swaps, The VAFC-2 Can be used to Activate V-TEC for a Non-Vtec ECU.

Monitoring Functions / Apex VAFC 2 Updates
Digital Real Time Display of RPM Gauge and Knock Sensor Monitor
LED Lights up Green / Red when Lo / Hi Vtec Cam Engages
The VAFC-2 has password Lockout and Retains Memory of Settings if the Battery is Disconnected

Blown_M104 · #12 12-06-2005, 12:50 PM

Don't waste your money on the Apexi SAC II 'select' or Euro version. From all my research it is the same thing as the base unit; it simply includes the wiring diagrams for Euro cars, functionallity is the same. It cost $50-100 more based on where you buy it.

The unit I have has the knock sencor inputs and some simple graphic data logging capablities. There are certainly piggybacks out there that will do a lot more but then the cost are considerably higher also.

ke6dcj · #13 12-06-2005, 01:30 PM

What about the VTEC version ? This would allow us to turn-on the "fast cams" sooner or later on our M104 and M119 engines that have variable cams.

:-) neil

rainmaker · #14 12-07-2005, 09:35 PM

Neil,

aren't the engagement of the "hot cams" mechanically controlled in our cars?

ke6dcj · #15 12-08-2005, 12:50 AM

Quote:

Originally Posted by rainmaker

Neil,

aren't the engagement of the "hot cams" mechanically controlled in our cars?

While the mechanism uses hydraullic/mechanical means to retard/advance the intake camshafts, it is electro-magnetically controlled by the ECU.

In fact, if you look at the front of our engine's heads, you will see a 2-pole connector on the two INTAKE camshafts. Remove the connector and apply 12VDC (observe polarity) and you will make make the camshafts go into advance (aka, "hot") mode.

BTW, here's the current pattern for retarded vs. advance intake camshaft timing:

0-to between 1000 & 2000 RPM: retarded, for improved idle, cylinder scavenging, and reduced valve overlap;

Between 1000-2000 RPM and upto 4700 RPM (depending on load): advanced, for increase torque, reduced waste of intake charge;

Above 4700 RPM: retarded, so intake valves open & close later, improved volumetric efficiency

Engine shut off: retarded, for easier starting

One could probably lengthen the amount of advance to about 5500-5800 RPM for more performance, at the expense of fuel-economy.

Most likely, this pattern was chosen for balance between emissions friendly and fuel-economy at the higher RPMs.

Also, the 500E was meant to cruise the autobahn all day at above 140 MPH. If you're just steady state at 4700+ RPM on the autobahn, you most likely want the best fuel-economy!

The beauty of the Apexi product, might be the same stock map for easy driving, and a more aggressive map, (more advance) when WOT.

Also, with the inclusion of interfacing with the factory knock sensor, one can safely add longer amounts of advance without fear of detonation.

:-) neil