e30 m3 tach converter

[Rev Engineer]

A lot of guys are really interested in correcting the mpg reading. Must be those high gas prices… Has anyone calculated the error? I’m wondering if it will be consistence within an engine model and car. I can probably adapt the same board to correct a fixed percentage, or maybe 4 different percentages with the dipswitches. A better solution might be to have a variable knob where you could dial-in a certain percentage. This will be slightly harder to do and will take more time. If we can come up with a fixed percent to correct, I might be able to get something going faster. Here’s another idea – you tell me what percentage your mpg reading is off, then I can program the board to correct that same percent - might work. Keep in mind that I haven’t experimented or tested anything in regards to the mpg readings, just getting some ideas together.

[Jason89i]

..... I’m wondering if it will be consistence within an engine model and car. .......A better solution might be to have a variable knob where you could dial-in a certain percentage. .

great work. nice to have a techie here.

your best solution (to make everyone happy) is to install a variable knob. the obc uses only two inputs. speed. duty cycle (how long and fast the injectors are open.) problem is, it assumes a specific injector and a specific fuel pressure. if you increase/reduce the fuel pressure, you mpg will be off. if you add different injectors, your mpg will be off. i personally have larger injectors, my buddy opted for larger injectors and adjusted the fuel pressure. if it was maped for the stock configuration, it wouldnt be accurate for us. cheers, jason

[NickP]

A lot of guys are really interested in correcting the mpg reading. Must be those high gas prices… Has anyone calculated the error? I’m wondering if it will be consistence within an engine model and car. I can probably adapt the same board to correct a fixed percentage, or maybe 4 different percentages with the dipswitches. A better solution might be to have a variable knob where you could dial-in a certain percentage. This will be slightly harder to do and will take more time. If we can come up with a fixed percent to correct, I might be able to get something going faster. Here’s another idea – you tell me what percentage your mpg reading is off, then I can program the board to correct that same percent - might work. Keep in mind that I haven’t experimented or tested anything in regards to the mpg readings, just getting some ideas together.

I'll buy two WHEN you build them!
You'll have to intercept the fuel duty signal (white/black not to be confused with the black/white wire I believe) and manipulate it accordingly.

Another way of doing it is to try and reverse engineer the information stored on the coding plug on the back of the OBC. There's conflicting info as to how the information is stored on the chip - some say there's an injector value; others say its a coded map table that is used for lookups - the latter one seems to make more sense.

[Rev Engineer]

I'll buy two WHEN you build them!
You'll have to intercept the fuel duty signal (white/black not to be confused with the black/white wire I believe) and manipulate it accordingly.

Another way of doing it is to try and reverse engineer the information stored on the coding plug on the back of the OBC. There's conflicting info as to how the information is stored on the chip - some say there's an injector value; others say its a coded map table that is used for lookups - the latter one seems to make more sense.

I'm surprised more people are interested in correcting the obc mpg reading! I'm getting further on this and I'll be adding a potentiometer which should let people dial-in the right correction factor. Any idea what range I might need to accomodate? My obc has been reading around 30mpg and I suspect I'm only getting around 20. It will help if people can let me know how far off their readings are.

As for the coding plug, I looked into this. There's some data going between the plug and the cluster when power is applied. It's feesible to decode the data, but it might be more work than it's worth. I suspect it's an injector value as I never saw any data being transmitted after power-up - unless the whole map is transmitted in that blurb of data.

[equate975]

I really want my obc to work again too :)

[NickP]

I'm surprised more people are interested in correcting the obc mpg reading! I'm getting further on this and I'll be adding a potentiometer which should let people dial-in the right correction factor. Any idea what range I might need to accomodate? My obc has been reading around 30mpg and I suspect I'm only getting around 20. It will help if people can let me know how far off their readings are.

As for the coding plug, I looked into this. There's some data going between the plug and the cluster when power is applied. It's feesible to decode the data, but it might be more work than it's worth. I suspect it's an injector value as I never saw any data being transmitted after power-up - unless the whole map is transmitted in that blurb of data.

I told you back on page one; you'll sell tons of these if you get the correction factor thingy working!

Actually several people in the e36 world may be interested as well - I believe they have the same problem when they upgrade their injectors - its not a huge market but I'm sure its somewhere in the hundreds to thousands range.

I would say you'll have to affect the signal by up to 2.5 times to cover all bases. I'm just going by lowest to highest injector values out there. 17,19 stock whatever it is, 24 pounds for s50 upgrades and 42 pounds for the forced induction crowd.

[BeirBrennerE30]

ill take a mpg thingy too when you get it working

[tjhartge]

ill take a mpg thingy too when you get it working

Mr REv Engineer,

any updates on the mpg unit?
i may have 3 orders in hand.......

[Rev Engineer]

Progress on the mpg correction thing is on hold for awhile. After thinking about it for awhile I determined that it's going to be harder to code than my tach coverter software. The tach converter software is always processing a signal and the signal it needs to process is well defined (500-8000rpms, fixed duty cycle, always present). The obc mpg signal is much different. Sometime the signal goes away (under deceleration) and the range of duty cycles is much different. I need to study and understand the mpg signal before I can go much further. If anyone knows more details about this signal, please chime in.

It's about time to put my e30 m3 away for the winter, so I'll lose my ability to test. I'll be picking this idea back up in the spring. My goal is to have this board accomodate tach conversion, obc mpg correction, and speed signal correction.

[dude8383]

can this work for an m42 motor?

my car will be revving to about 7500-8000 when im done with it.

[Rev Engineer]

can this work for an m42 motor?

my car will be revving to about 7500-8000 when im done with it.

So you're using a m42 tachometer with a m50/s50 conversion? If so, yes. This converter board should work fine and make your tach accurate again.

[kroberts]

Mr. Rev Engineer,

Do you still sell these converters? I need one...please.

Thanks

kroberts

[Jason89i]

I emailed you a while ago. When you get more made, I'll take two.

cheers, jason

[AlexFunction2ND]

I'll take 1

[Rev Engineer]

Everyone - Thanks for being patient. I got some more built and tested and I am now ready to ship some out. Please PM me if you are interested. I only have a limited quantity available - exactly5 with the ability to make 5 more. Cost will be $40 shipped standard USPS mail. Let me know if you are outside of the US and we can figure out shipping.

Thanks.