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Let's talk MEFI


justgary

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So I had a few spare hours this weekend and decided that I just had to know more about the MEFI OBD data protocol. So far I have confirmed that it is definitely OBD 1, 8192 Baud and my old cable that I made for our old GM vehicles will work. I have not gotten the boat out so I could run it and watch the data, but I popped it off dry for a few seconds to see what I could find. Throttle position is simple to find, as is battery voltage. When I run the engine I expect to find RPM, coolant and air temperatures, and maybe a few others like oil pressure and engine hours fairly quickly. I already have several candidate positions for a few data fields by simply comparing the engine off data to the car data.

Since this is not exactly a car engine (and mine does not have O2 sensors), I'm curious about the differences in available data. Do any of you have a MEFI reader, and if so, are you willing to give me a list of data items it will read? Just knowing what to look for (and not look for) can help tremendously.

I don't need links to commercial readers that I can buy. If you have useful MEFI data links, I would like to see them, but I have done a fair amount of research and have come up dry on big, juicy details. Thanks in advance for any help!

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So I had a few spare hours this weekend and decided that I just had to know more about the MEFI OBD data protocol. So far I have confirmed that it is definitely OBD 1, 8192 Baud and my old cable that

Update: I made a USB converter cable a few months ago that works great on my boat. It turns out that Indmar didn't use MEFI 3, and that mine is MEFI 2. I still don't have definition for trouble code

Here's a free ski 14 turn (you can count them) slalom pass this morning with the Zbox turned on.  It's about 11 GPH burn rate in my glide, and up to 13 GPH in my wake crossings, but usually around 12.

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And then if you get really bored https://www.m2omarine.com/resources/Indmar_MEFI5-5Amanual.pdf

5-22 looks like the complete list of parameters that you can get from the MEFI 5

These guys have a crapload of manuals posted

http://www.m2omarine.com/resource-center

Edited by oldjeep
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And then if you get really bored https://www.m2omarine.com/resources/Indmar_MEFI5-5Amanual.pdf5-22 looks like the complete list of parameters that you can get from the MEFI 5These guys have a crapload of manuals postedhttp://www.m2omarine.com/resource-center

Thanks, oldjeep. I fished around and found the MEFI 3 manual, so I'll try to log some data and continue the puzzle work. My buddy has MEFI 4 on his Response, so it will be next.

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Where did you get the connector for MEFI? Thanks!

I made it on a 2"x3" copper breadboard using a MAX232-type level converter, a 5V regulator, and a few extra parts. I used T-style finish nails from a nailer to make the connector pins. That was for a real GM ALDL connector, and the one of the boat has much smaller sockets. I need to change the pins to something that will fit properly.

8192schm.gif

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  • 4 months later...

Update: I made a USB converter cable a few months ago that works great on my boat. It turns out that Indmar didn't use MEFI 3, and that mine is MEFI 2. I still don't have definition for trouble codes, but I know enough about the data stream to diagnose problems as they might arise.

I sent a cable to someone else on the crew to try on his MEFI 4 boat, but I don't think he has tried it yet.

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Update: I made a USB converter cable a few months ago that works great on my boat. It turns out that Indmar didn't use MEFI 3, and that mine is MEFI 2. I still don't have definition for trouble codes, but I know enough about the data stream to diagnose problems as they might arise.

I sent a cable to someone else on the crew to try on his MEFI 4 boat, but I don't think he has tried it yet.

JustGary was AWESOME and sent me the cable. The cable came out VERY professional looking and JustGary knows his electronics.

It can read most data from my MEFI4b ECM. I am having an odd issues of weird corrupt data but I am 99% sure its the driver needs updating (I used the default windows driver vs the one for the chip JustGary used).

Thanks again for all your help! I have been meaning/wanting to post on it but I wanted to get the driver issue fixed first which I have not had the chance to yet. Hope to soon!

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Stingreye -

Are you sure that the corrupt data isn't just the chatter going on? Are you using your program, or the probe.exe that I sent you? Your program should turn off chatter, but probe will not.

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Stingreye -

Are you sure that the corrupt data isn't just the chatter going on? Are you using your program, or the probe.exe that I sent you? Your program should turn off chatter, but probe will not.

I was using the program I have, I did not use the probe yet and I have only spent less than 5 minutes with it. My other cable that came with my program has a "glitch" every 20-30 data points (almost like a lost communication with ECM error I think). The one we hooked up has it about 75% of the time. So for example, hours will read the correct number then a crazy number like 32,523. Same with all the sensors. My other cable acts up too but just less often. That's what made me think it was the driver.

The program has a "raw data stream" view which is where I see an error message related to losing the connection or something like that. I will try to get it hooked up and verify what the message was.

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If you are getting data at all, it is probably not the driver. I wonder if the USB cable is loaded too much. Both of them seemed to work fine on my boat, but maybe I got lucky. I plan to try it on my friend's '04 Response later this spring when he gets it out again.

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Sounds like someone might be able to make a few bucks selling these cables. I would buy one for the right price.

I'm sure I can't make a few bucks selling them at the right price. The parts alone are about $25 buying them onesey-twosey. I enjoy the work, but it won't pay enough for the time I would have in it. If you can solder a few wires, you can build your own.

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Gary,

Would you consider doing a DIY write up? I'm very curious about the program and cable to accomplish this.

I would consider it, but it will take me some time (read: maybe never) to get to it. In the meantime, search for various combinations of "ALDL", "8192 baud" and "OBD1 cable".

It's all pretty simple anyway, at least getting data. Figuring out what you got is the fun part.

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  • 2 weeks later...

Parameters that I'm sure (or nearly sure) of:

- Fuel Pump on

- Desired Idle

- MAP

- Battery Voltage

- Barometric Pressure (MAP at startup)

- Coolant Temperature

- Throttle Position

- Engine Load %

- RPM

- Runtime this startup (increments in seconds)

- Engine Hours (which actually increments in minutes)

- Wide Open Throttle flag

Parameters that I may know, but are hard to nail down with much confidence:

- Crank flag

- No Reference Pulses flag (Engine not turning)

- Throttle Closed flag

- Idle RPM Control flag?

- IAC Minimum Keepalive

- IAC Position

- IAC Throttle Follower

- Total Spark Advance

- Base Spark Advance

- Injector Pulse Width

- Engine Running flag

- Enrichment flag

Parameters I pretty much don't know:

- Fault Codes, except MAP Open Circuit was easy to spot when I unplugged the MAP sensor.

I easily know enough to diagnose most issues with the engine, and the unknowns are either hard to set up a test for (or I don't care enough to) or the related parameters are similar enough to each other to not be able to figure out exactly which one is which. For example, the three IAC parameters are clearly related, but I'm not declaring names until I can compare the plots to a known set of plots.

I got most of the parameter names and scale factors from studying other GM ECM definitions. Some of the scale factors are different from ones for cars, though, so the fun is convincing myself that the "suggested" scale is wrong and I have it right. That's one thing keeping me from nailing down Spark Advance and Pulse Width.

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Gary, you are using a MAX232 which is an RS232 transceiver. I'm pretty sure that MEFI uses the CAN protocol. Can you explain in detail which IC's you are using for interfacing from USB to CAN?

Another question how did you receive the data from the ECM? Do you have to enter some read command to achieve the data. Or do you just listen on the USB port and gather all data what is coming out. Can you maybe post the raw data that you read from the ECM. I'm just wondering in what format it is coming out.

BTW: I'm also investigating a few things to make a DIY MEFI reader.

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MEFI 5 uses CAN as far as I know (but have never tried to read it). All of the previous versions use 8192 baud serial, exactly the same as GM ALDL (OBD1). ALDL is very well documented on the web, so check that out. You probably have MEFI 4, and can verify it by checking the part number.

I have now moved from a MAX232 circuit to a USB TTL-232 converter that is much simpler to make. When I get some time, I'm going to see if it can be even simpler (and also solve stingreye's issue). It is very likely that you can simply tie transmit and receive together at the data pin on the connector. Simple enough if it works.

You do have to poll the system to get useful data. I'm not sure how best to post data here, but it is just a stream of bytes with a checksum on the end.

Getting data from the ECM is the simple part. Figuring out what it means is the trick, and the main reason for this thread. I'm willing to work with anyone who has a genuine interest. I enjoy data mining, but I need help interpreting some of the data items. Figuring out the spark advance values, for example, has been tough.

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Sort of off topic, does the gauge computers pull data from the ALDL port? I have seen a few of the bu's of my generation have a gauge that shows various parameters that sounds like it is.

I know the gauge pc uses a bus communication but haven't looked into it to much.

I wonder if there is a way to get the scanners like the Edge insight or Scangauge to work.

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I think the Medallion unit does pull engine data, but I haven't looked into it further. I think the Mode 2 data would cover it, no need to pull the longer Mode 1 message.

Most any OBD1 scanner will work with the proper definition, which is essentially what I'm trying to figure out.

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