Low Budget DIY Throttle Body EFI with Speeduino

[19-VW-74]

[David Raistrick]

so you're still not compensating for manifold temp though, even with that solution right? you're just trying to capture head temp in a meanful way that you can use to make a guess at when to stop running rich with the cold manifold?
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...david - '66 SO-44 #231

[19-VW-74]

Now that I knew the cause of the indicated temperature discrepancy in Tuner Studio, l figured my next solution would be to find a temperature sensor that was better suited to the temperature range of the cylinder head.

After only one tank of gas, the aftermarket CHT sensor was deteriorating - it was using heat shrink that couldn't take the heat. It was melting and detaching - luckily the thermistor inside never gave up.

After a lot of googling, I settled on the 049919563B oil temp sensor that came on many 90s Audis. This sensor has the same thread size/pitch as the 311906041A sensor, but it is designed for a factory oil temp gauge that indicates up to 180C or ~360F.

It was easy to install, it just fits in the same spot as before.

Since I was very concerned about accuracy, I created my own temp/resistance correlation table by measuring it's resistance at three temperatures.

1. In the freezer (-2F)
2. At stable room temperature (68F)
3. In boiling water (~203F at 5000ft elevation)

Using the Steinhart-Hart Equation (pretty neat and worth a google), I was able to calculate a smooth resistance curve based on these three points.

The voltage output from the coolant sensor voltage divider circuit ranges between 0-5V and the Speeduino firmware expects a table of 32 evenly spaced bins - evenly spaced by voltage, not resistance.

You can see that a change of millivolts across bins 0-2 can swing the indicated temperature wildly. But in the middle of the range of the 32 bins, the temperature moves gradually. This is the nature of the beast with an NTC thermistor attached to a voltage divider circuit. To improve my resolution a little at the high end, I ended up soldering in a 70 ohm resistor in series with this sensor to shift everything down by 1 bin, and give me more of a buffer before indicated temps start dropping towards 180F again.


Bin Temp F
0 180
1 349
2 250
3 205
4 177
5 157
6 142
7 130
8 119
9 111
10 103
11 96
12 89
13 83
14 77
15 72
16 67
17 61
18 57
19 52
20 47
21 42
22 37
23 31
24 26
25 20
26 13
27 6
28 -4
29 -16
30 -36
31 180
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-Austin
My 1974 Standard Beetle Build:
http://www.thesamba.com/vw/forum/viewtopic.php?t=492617

[19-VW-74]

While this solution did work for getting a more accurate cylinder head temp, and my indicated temps were no longer falling towards 180F anymore, I found that the indicated temp was regularly getting up to 350F, based on this sensors output.

My IR thermometer did not agree with that reading, and neither did I. I figured that sensor boss is too far from the combustion chamber to be getting that hot.
I chocked it up to the lack of resolution at the limit of the sensor's range. After all, 20 ohms can change the indicated temp by over 50F at the limit.

Anyways, I now had a sensor that was more accurate than the old sensor, even if it wasn't all that accurate. However, I still had the issue of the cylinder heads heating up faster than the intake manifold.

One issue I ran into with the stock Speeduino firmware is that the warmup enrichment tables have 256 bins. By default, they range from -41F to 214F. This means that warmup enrichment must indicate 100% by the time the sensor reads 214F.

I can easily hit 214F indicated in a few minutes of idling after a cold start, but the manifold is still cold. So I'll have a good cold start, but I'll drive a block away and the engine barely wants to idle because the heads are warm, the manifold is cold, and the warmup enrichment is gone. The opening of the IACV is also directly controlled by the coolant temp sensor, so the IACV starts to choke the engine at idle before the manifold is warm.

At this point I started to consider whether I should be using a different temperature source to manage my warmup enrichment and IACV opening.

I took my old pigtail temp sensor that I used with the cylinder tin screw and moved it to the stud that mounts the manifold center section to the case. I figured that this is the portion of the manifold that needs to be hot before I can shut off the warmup enrichment, and it has exhaust pulsing through it, so it should heat up relatively quickly. As it turns out, this portion of the manifold gets cold before it gets hot. I saw it drop from 80F to 60F, then slowly climb back to 80F while I drove, only hitting 120F once on the freeway. Since ambient temps will often be in that range, this is not a useful place to sense temperature from.
_________________
-Austin
My 1974 Standard Beetle Build:
http://www.thesamba.com/vw/forum/viewtopic.php?t=492617

[19-VW-74]

[mikedjames]

I would believe the 350F over an IR gun that misreads on things that are too reflective, like bare metal.. RTFM the object has to be matt black ..its OK on a rusty exhaust but shiny aluminium..

Also why not just change the resistor values in the Speeduino module to get the sensor readings back into a sensible voltage range..

And as you use Speeduino why not simply change the source code and recompile it to modify the out of range temperature table entries to 350F rather than having to try several different sensors.

I am really interested in what you have done, I want to do a similar thing with Speeduino on my 1641 using part of a Mexican FI system I have that came with a Bosch CIS inejector controller valve system.. replace injectors, add sensors and Speeduino..
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Ancient vehicles and vessels

1974 VW T2 : Devon Eurovette camper with 1641 DP T1 engine, Progressive carb, full flow oil cooler, EDIS crank timed ignition.
Engine 1: 40k miles (rocker shaft clip fell off), Engine 2: 30k miles (rebuild, dropped valve). Engine 3: a JK Preservation Parts "new" engine, aluminium case: 26k miles: new top end.
Gearbox rebuild 2021 by Bears.

1979 Westerly GK24 24 foot racer/cruiser yacht Forethought of Gosport.
1973 wooden Pacer sailing dinghy

[oprn]

This thread and your work are brilliant! Thank you for sharing!

From my experience in process control, temperature is indeed the most difficult to pin down. Especially, as you have indicated, the broad range needed to properly control fuel in our engines.

I cannot help but wonder though if temperature would have been less critical if the fuel were injected at the valves instead of at the throttle body. That could eliminate all the intake runner fuel drop out problems so inherit to our horizontally opposed engines? Is that perhaps why VW went to port injection right off the hop?

The only throttle body injection I have experienced was our '92 Chevy 350 and it ran pretty much perfect and totally maintenance free for the 400K miles I had it. But then think about the runner lengths, maybe 6" at the most and sitting on top a hot engine with hot antifreeze going through the manifold.

Just thinking out loud, ignore me and carry on please! Your research and problem solving are very valuable!
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Our cars get old, we get old but driving an old VW never gets old!

[clonebug]

[19-VW-74]

[19-VW-74]

[19-VW-74]

[19-VW-74]

Now, that we've got a good foundation for nearly all of the hard parts, we can get to wiring in the Speeduino ECU.

For this project, I went with the Speeduino UA4C board from WTMtronics. Although Speeduino is an open-source project, and you can build any of the many board configurations yourself from the PCB up, I decided it was worth the small extra cost for a pre-assembled low-profile board with surface mount components.

UA4C stands for "Under Arduino 4 Channel" - it uses an Arduino Mega microcontroller as the brain (mounted on top), with the UA4C board as an elaborate daughterboard, populated with all the circuitry needed to power injectors, coils, IACVs, relays, etc.

Since my car is using a single injector and a Subaru waste-spark coil pack, it only needs 1 injector channel and 2 coil channels. But I went with this 4-channel option to future proof the ECU whenever I decide to upgrade my EFI to ITBs.

Here's a few pics of the bare board:

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-Austin
My 1974 Standard Beetle Build:
http://www.thesamba.com/vw/forum/viewtopic.php?t=492617

[19-VW-74]

The UA4C board is designed to fit perfectly into a Hammond brand aluminum enclosure (project box). It slides into the aluminum extrusion and a cover plate slides in over the top.
Each end of the enclosure will need some sort of custom plate for mounting and to expose the connectors on the ECU. I decided to design and 3D print my own from ASA plastic.

In the above pic, you can see an Elegoo brand Arduino Mega clone. Once you de-solder and remove the 5V input jack from the Arduino board, you can mount the Arduino to the top of the UA4C board.

On the right side of the board, you can see a small purple PCB that stands above the UA4C. This is a MAX9926 VR conditioner board that is used to convert the sinewave signal from the VR crank position sensor into a digital squarewave signal that the Arduino can interpret.

The wiring pigtail runs to a generic HC-06 bluetooth module that runs off the Arduino serial pins. This module allows me to tune and monitor the ECU from my laptop without connecting to the board with a cord. It's super convenient.

To mount the bluetooth module, I designed and printed a bracket/spacer that I glued to the inside of the rear end cap of the Speeduino case. This keeps the board positively located in case so it can't shift around.

Once it was assembled, I powered it on with a variable power supply and checked all the channels for proper function. Each injector and coil driver circuit has a built in LED to indicate that the circuit is energized.
_________________
-Austin
My 1974 Standard Beetle Build:
http://www.thesamba.com/vw/forum/viewtopic.php?t=492617

[19-VW-74]

The UA4C has an onboard MAP sensor and barometric pressure sensor for reading manifold vacuum (or boost) and compensating for altitude changes.

Some folks are critical of on-board MAP sensors because they are slower to respond than sensors mounted on the manifold or in the engine bay. Long vacuum lines take longer for air to evacuate, so the MAP signal can lag a few milliseconds.

For a stock 1600, I've had no issues with drivability due to running a relatively long vacuum line from the ECU to the engine.

I found a tiny little bulkhead fitting on ebay that I could use to run a vacuum line from the MAP sensor to the end cap of the ECU case.

_________________
-Austin
My 1974 Standard Beetle Build:
http://www.thesamba.com/vw/forum/viewtopic.php?t=492617

[19-VW-74]

Because there are a few high-current functions that the ECU will control, such as the high pressure fuel pump, ignition coil, injector(s), etc., I will be needing a relay box.

I found this combo relay and fuse box on ebay in some closeout overstock store. It was poorly labeled so I had to go searching for it. Incredibly, I paid $9.90 shipped for this thing. There were only 2 or 3 and they all went quick. Never came back in stock.

It appears to be identical to this "True Mods" relay box sold on Amazon right now (for $50), but with red silicone gaskets instead of green.

Once it arrived, I was super pleased with the quality. It appears to be made of injection molded nylon, rather than cheaper ABS plastic. The terminals were all thick gauge and the wiring harness was real copper instead of copper-clad aluminum.

I really don't need it to be water-proof because it will be mounted under the back seat. But the sealed cover is a nice touch.

For $50, I would have been satisfied - under $10 for all that is unreal. I could barely ship this anywhere for that. I even broke open one of the relays that were included - it was epoxy potted and looked great inside.
_________________
-Austin
My 1974 Standard Beetle Build:
http://www.thesamba.com/vw/forum/viewtopic.php?t=492617

[19-VW-74]

Since there is a nice open space under the driver side of the rear seat, and the factory wiring harness runs along the driver side heater channel, I decided to mount the Speeduino and relay box under the rear seat on the driver side.

I picked up some flat bar from the local steel supply and got to cutting and welding to make a mounting bracket.

This is what I came up with - it mounts to the rear floorpan bolts and rests on the seat crossmember.

I designed some soft plastic feet to keep the bracket from rubbing and making noise. 3D printed in TPU.

_________________
-Austin
My 1974 Standard Beetle Build:
http://www.thesamba.com/vw/forum/viewtopic.php?t=492617

[19-VW-74]

Once the bracket was completed, I worked on building the wiring harness.

I ordered an 8ft un-terminated harness from SpeedyEFI. Basically 40+ individually colored wires, including shielded wires for the crank/cam sensors. All wires are TXL/GXL automotive grade and the kit cost me $75. It's hard to get that many different colors of automotive grade wire anywhere else for that price.

This is the standard color coding that their harnesses use - I also figured that having a preconfigured wire color scheme that I didn't have to dream up and manage also made it worth buying from them.

_________________
-Austin
My 1974 Standard Beetle Build:
http://www.thesamba.com/vw/forum/viewtopic.php?t=492617

[19-VW-74]

Since I am running waste-spark TBI, without a turbo or VVT, and with few auxiliary items, I can trim down the harness substantially.

I basically only need:

- Ignition 1
- Ignition 2
- Stepper idles A1, A2, B1, B2
- Injector 1
- Fuel pump trigger
- IAT
- CLT
- TPS
- RPM1
- Wideband
- CKP sensor w/shielding

Once I removed the excess wiring, I terminated each wire and plugged them into the header sockets. This UA4C board version (vC5) uses Molex Micro-fit 3.0 series header connectors.

I used this cheapo tool for these small pins and it worked perfectly.

Once the harness was ready, I mounted the Speeduino and relay box to the bracket and prepared for installing in the car.

On each end of the bracket, I added a terminal block for power and ground to clean up power distribution for the relays and sensors under the hood.

I wrapped the harness in this cord protector sleeve from Harbor Freight. It's safe for temps up to 300F according to the packaging. It's been working great in the engine bay thus far. Hard to beat $10 for 25 feet.

_________________
-Austin
My 1974 Standard Beetle Build:
http://www.thesamba.com/vw/forum/viewtopic.php?t=492617

[19-VW-74]

I took this opportunity to move my hard start relay and defogger relay into this box to keep things clean. Here's how it looked before:

The whole assembly bolts in under the back seat nicely - suspended above the floor to protect from any moisture.

_________________
-Austin
My 1974 Standard Beetle Build:
http://www.thesamba.com/vw/forum/viewtopic.php?t=492617

[19-VW-74]

With the ECU mounted, I could run the wiring through the rear driver side quarter panel.

Back before I painted the car, I pulled out all of the foam from the quarter panels so its very easy to run the harness through.

Then came the fun part of crimping all the different terminals for the many different connectors.

I bought nearly all of these connectors on ebay in bulk from Jorch electric. Great quality and prices. Most connectors were under a buck a piece shipped.

I used the following connectors:

Bosch EV1 3 pin - for TPS and CKP sensor
Bosch EV1 2 pin - for injector(s) and IAT sensor
GM Delphi Packard 4 pin - IAC valve
GM Delphi Packer 2 pin - Oil temp
Sumitomo 4 pin - Ignition coil

I also used some AMP waterproof male/female pairs for quick disconnect harnesses in places.

Most of the terminals are on the larger size - they seem to be able to fit up to 16 gauge wire. My harness is mostly 20 gauge, so I folded over the wire for a better crimp.

Some of these connectors require threading the wire through before crimping. Don't do it out of order or you'll waste a terminal!

_________________
-Austin
My 1974 Standard Beetle Build:
http://www.thesamba.com/vw/forum/viewtopic.php?t=492617