21 Turbo Renault 21 Turbo and Alpine A610 Fuel Computer issue/solution!

[r5gordini]

A bit of background. I have had three fuel computers fail on me in about a year! The problem seems to be the LCD. I suppose it's just unrealistic to expect a 20 year old LCD, let alone one engineered by Renault, to work perfectly!

I got my thinking cap on and came up with the idea of using an Arduino single board computer to replace the Renault computer. After a weekend's work, I have come up with the following. So far I have just got the fuel gauge working. Next bit (mpg, trip, etc.) is a bit harder.

There are several advantages to this method of solving the problem:

1. Modern electronics: easily upgraded and replaced
2: Modern display technology: my solution uses lovely OLED. No backlight required!
3. Flexible: we can program and calibrate it to our needs. Different injectors? No problem. Different wheel diameters? No problem!

For me, a working fuel gauge is a must, which I have got working today. It still needs a bit of calibration. After that, I intend to add (in complexity order):

1. Temperature in degrees celcius!
2. Speed in mph. Average speed
3. Trip distance
4. Mpg
5. Miles left in tank

So how did I do it? Took an old 21 computer, desoldered the connection block:



Soldered it onto some veroboard:



Did some wiring on the verobard to connect up to the Arduino:



Wrote a bit of software to interpret the fuel sender's output. Graphed its resistance, working out an interpolated fuel reading. Used the software I use every day at work. Needs to be calibrated a but better but this is a rough start:



Um... Wired up the power pins and plugged it in!



I am very happy about the result and am excited about the project. It's going to take me a while to get where I want, but I will keep going!



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[r5gordini]

Hahaha! Your soldering is as bad as my welding! But soldering is easier than welding! Good stuff, Sibley! Keep going! I'll post an update on the project tomorrow. Did some work on it this morning but haven't had time to test it.

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[DaveL485]

Your soldering is as bad as my welding!

 

[r5gordini]

@DaveL485 - do you have any more info on the OE injector flow? It doesn't appear to be pulsing. I have checked it and I can't read anything from it. On the wiring diagram for the 21, I see it shown as a flowmeter - a separate box to the OE ECU.
Maybe I have blown mine up - I'll try putting the original fuel computer back in...
The A610 pinout lists pin 5 as flowmeter signal, pin 8 as trip computer lighting and pin 9 as flowmeter lighting. Why would it have two separate pins for lighting?
Is is a bit confuzzled.
On the plus side, fuel gauge readings are ok, speed, trip mileage and average speed all working.
I think I'm going to have to get testing with an oscilloscope. Time to dust mine off!

 

[DaveL485]

The two lighting pins i think could be the two different lighting settings...it gets brighter or darker when you turn your lights on and off right?
The fuel flow thing was as I said earlier in the thread, one pulse per 160 cubic mm of fuel used so it wouldn't pulse that often at idle I guess. Thats why I asked if you were using the ECU flow feed or the injector pulse itself. They are vastly different.

 

[r5gordini]

Yep. Understand. Thanks for explaining again. I am using the OE feed to the computer, which I presume is the ECU flow feed. I have checked my electronics and they work fine, so when I generate a manual pulse the computer sees it. It's just not seeing the ECU pulses. Is it a +ve pulse? I presume so.

One thing. I haven't got any of the rest of the dashboard instruments plugged in. I am wondering if that is causing a problem?

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[DaveL485]

I am wondering if that is causing a problem?

A number of them, I would imagine. Your alternator won't be charging for starters, and i'd imagine there may well be earth issues?
The info on the trip fuel use came from @Red21 so he may be able to furnish us with more info, however as a general rule I think the ecu triggering bits work on switched earths (The injectors for example are an ign live 12v one side and are triggered by the ECU switched earth). I don't know if it would be 12v or 5v though so be careful if you test for it. Maybe wait till Rich (red21) weighs in

 

[r5gordini]

OK so I have done a tiny bit more investigation. With the ignition on the injection output is floating. As soon as I crank the starter, it goes low (earth), or hovers around earth anyway.
It varies by a few millivolts around the earth point - on an oscilloscope I can see it just looks like a noisy signal.
Any thoughts on that?

 

[DaveL485]

Any thoughts on that?

No....lol! I still think average-level is your best bet. That solution will work for everyone regardless of ECU with no alterations. The Renault fuel feed is obviously a bespoke engineered-for-application solution and as soon as you alter anything, even injector size it needs recalibrating.

 

[r5gordini]

I may well end up doing that. It will be a bit crude. Here's the trace from the injection output relative to ground (earth). I was going to measure it relative to +VE too but I managed to accidentally short out a pin on the Arduino, blowing it up, so I gave up for a bit!
There might be a slightly higher voltage when I am driving and the peaks might be slightly closer together but it's very difficult to decipher and interpret! And I don't understand why it's so low in the millivolt range.

 

[r5gordini]

By the way, I am using a Picoscope currently, like this one:

PICO TECHNOLOGY - PICOSCOPE 2104 - OSCILLOSCOPE, PEN TYPE

Pretty impressive bit of kit. Not very portable with the need for the laptop, hence why I am building the kit one too. It has yet to arrive.

 

[DaveL485]

Thats one weird log. Makes no sense at all!

 

[Red21]

That trace seems to have a lot of interference in it.
Can you apply a filter to the trace which I know you can with the more advanced kits.
Also what is the trace like over 60s at idle, 2k 2.5k & 3k to see if a pattern emerges