General 1G Diagnostic Port/MMCD Issue

[MyBlack94GST]

Hi all,
I have a Palm M100 that I've been using to run MMCD on my 1994 GST quite uneventfully. I just bought a 1990 GSX, however, and I get an "ECU comm error" message when I try to hook it up to this car. Just to check that I didn't mess the cable up, I plugged it back in to the 94 and everything was fine. Is there anything I have to change due to the fact that the car is a 90, or is it some random electrical gremlin that requires hunting down? What are some good fuses to check, etc?

TIA!

 

[MyBlack94GST]

Still no progress on this front, I'd appreciate the help if anyone has had this problem before.

 

[steve]

is it some random electrical gremlin that requires hunting down?

Nothing unique about a '90 in this regard, nor are there any fuses involved. There are just the two wires running from the DLC back to the ECU for data and mode. Are you sure the ECU is working? Have you tried looking for it's heartbeat with a regular meter?

Steve

 

[Mindslayer]

I'm hav'n the same problem with my DSMLINK and my 93

 

[MyBlack94GST]

The car runs great, so the ECU better be working. Is there a check I can do with a multimeter?

 

[steve]

When the ECU doesn't have any error codes it outputs an on off on off pattern on the diag terminal, it is its "heartbeat".

Just measure between pin 1 (positive) and pin 12 (ground).

Steve

 

[Mindslayer]

Good info steve I'll check mine today. I just got my ecu Socketed So I hope its sumthing stupid.

 

[cybertrip]

im having same prob checked heart beat and nothing just site there at zero so im assuming that i have a short some where in the wiring between the diagnostics port and the ecu is this correct in assuming?

 

[steve]

Normally, the next thing you would do is check at the ECU and then test the wires between the ECU and DLC.

The first thing you would do is make sure the ECU is getting power.

Steve

 

[Mindslayer]

I fixed my problem. I need to connect the cable to my laptop before i turn it on. And I can pull the info of my ecu.

 

[MyBlack94GST]

Back from the dead!

Steve, the car has a healthy heartbeat. However, still get the "ECU Comm Error" when I try to plug in the logger. Not the Palm or the cable, because it works like a charm on my 94.

Is my ECU scrooged?

I also have a weird cold start problem where it'll idle like an injector is not working for like 10 seconds... and finally come up to normal. More signs of a messed up ECU? It's a 1990 EPROM with the caps replaced.

THANKS!

 

[HighPSI TSi Guy]

Friend of mine had that happen when he tried a JDM ECU..

You have a strange problem indeed though, i'd definitely check the wiring. FYI the engine starts in batch fire mode during cold start, and switches over to normal soon after it starts making heat.... if i'm not mistaken... i would rewire the connector

 

[MyBlack94GST]

Is this "batch fire" a feature on 90's? My 94 starts right up, strong. The 90 always has a weak cold start due to that problem.

And what connector should I rewire?

 

[Talesin]

Check if you have an 'auto-on' logger cable. Short version, I was told that auto-on cables will never turn on when used in a 90.

When I was purchasing mine, the seller had to send me a one-off... from what I was told, the 90 ECU doesn't produce enough of whatever signal to trigger the auto-on. Which is apparently only there to avoid having the ABS computer shut itself off (diagnostic mode).

 

[green_bread]

Check if you have an 'auto-on' logger cable. Short version, I was told that auto-on cables will never turn on when used in a 90.

When I was purchasing mine, the seller had to send me a one-off... from what I was told, the 90 ECU doesn't produce enough of whatever signal to trigger the auto-on. Which is apparently only there to avoid having the ABS computer shut itself off (diagnostic mode).

i think you are talking about the difference between active and passive cables. from what i understand, a passive cable is the same thing as what you are calling 'auto on'. this means that it will work by being powered off the car. an active cable requires an extra power source to boost the output signal so that it can be read.

here is a pic of what i believe someone has done to make a passive cable an active cable by running a wire from the data cable to the fuse panel:

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To be honest, I am not completely sure how this works or needs to be wired up since my system works fine with a passive cable. if i am wrong, please correct me about this stuff... if anyone else has anything to add here, please chime in!

The only other thing I can think of is that my data cable only has 2 wires it uses. one connects to pin 1 and the other connects to pin 10. there is, however, a wire that comes out of the back of the connector for pin 10 that goes to another connector for pin 12. not sure if it matters, but you might want to make sure pin 10 and 12 are spliced like that or try it if they arent.

Hope this helps you out at least some!

ADAM

 

[steve]

i think you are talking about the difference between active and passive cables. from what i understand, a passive cable is the same thing as what you are calling 'auto on'. this means that it will work by being powered off the car. an active cable requires an extra power source to boost the output signal so that it can be read.

Nope, there are both active and passive versions of auto on.

Auto On refers to the circuit that grounds pin 10 on the DLC. An Auto On cable doesn't ground pin 10 until the datalogger begins to talk to the ECU. That way the cable can always be plugged in but it won't cause the ABS system to go into diagnostic mode because it sees the mode pin (10) pulled low when it powers up.

here is a pic of what i believe someone has done to make a passive cable an active cable by running a wire from the data cable to the fuse panel:

Nope, only active cables use a power connection, therefore this is an active cable.

To be honest, I am not completely sure how this works or needs to be wired up since my system works fine with a passive cable. if i am wrong, please correct me about this stuff... if anyone else has anything to add here, please chime in!

The only other thing I can think of is that my data cable only has 2 wires it uses. one connects to pin 1 and the other connects to pin 10. there is, however, a wire that comes out of the back of the connector for pin 10 that goes to another connector for pin 12. not sure if it matters, but you might want to make sure pin 10 and 12 are spliced like that or try it if they arent.

If pin 10 and 12 are connected in the way you describe or connected back at the circuitry, it's not an auto on cable.

Steve

 

[green_bread]

thanks for setting the record completely straight Steve!

like i said, i wasnt completely sure. especially because i had never heard of 'auto on' before.

If pin 10 and 12 are connected in the way you describe or connected back at the circuitry, it's not an auto on cable.Steve

this is why i had to do the ABS switch mod.

so how does one make an auto on cable? it cant be any different than a normal, non-auto on cable.

An Auto On cable doesn't ground pin 10 until the datalogger begins to talk to the ECU.

how is this achieved?

ADAM

 

[steve]

it cant be any different than a normal, non-auto on cable.

A non-Auto On cable doesn't have any circutry on the wire going to pin 10 of the DLC. A Auto On cable has a circuit that doesn't ground pin 10 until the PDA/Computer is connected or starts transmitting. Implementation of that circuit is left as an exercise for the student.

Steve

 

[EDT007]

Normally, the next thing you would do is check at the ECU and then test the wires between the ECU and DLC.

Steve

Steve, I'm having similiar problems. I know the ecu is working fine but I am not able to log anything either. I have tried the cable in my friends car and it works fine. Do you know what pins I would check on the ecu. Also, I noticed that neither my ABS or Check engine light come on when I turn the key to the "ON" position. Any thoughts? Thank you.

 

[steve]

Also, I noticed that neither my ABS or Check engine light come on when I turn the key to the "ON" position.

Sounds more like your MPI relay is never turning on. Does the car run?

Steve

 

[steve]

Back from the dead!

Steve, the car has a healthy heartbeat. However, still get the "ECU Comm Error" when I try to plug in the logger. Not the Palm or the cable, because it works like a charm on my 94.

Is my ECU scrooged?

Perhaps. I've got a bad ECU right now on the bench that won't talk to the outside world but it does put out a heartbeat on pin 1.

Does the heartbeat go away when you ground pin 10?
Have you checked the wires from the DLC to the ECU and made sure pin 12 is a good ground?

Sorry with all the other people jumping into this thread I missed your question.

Steve

 

[EDT007]

Sounds more like your MPI relay is never turning on. Does the car run?

Steve

Yeah, the car runs fine. No problems. Where would I find the MPI relay? Do you know what lines I would be checking by the ecu? BTW: Thanks for your help.

 

[EDT007]

Also, I noticed that neither my ABS or Check engine light come on when I turn the key to the "ON" position. Any thoughts? Thank you.

I just noticed what I wrote. What I meant to say was that my ABS or check engine light DO NOT light up even when I put the key to the "ON" position. Please guys, any help would be appreciated. Need to get my logger working ASAP Any pins I can check on the ecu?

 

[MyBlack94GST]

Check if you have an 'auto-on' logger cable. Short version, I was told that auto-on cables will never turn on when used in a 90.

When I was purchasing mine, the seller had to send me a one-off... from what I was told, the 90 ECU doesn't produce enough of whatever signal to trigger the auto-on. Which is apparently only there to avoid having the ABS computer shut itself off (diagnostic mode).

Bingo to you and green bread! I tried a friend's cable (with the extra wire you plug into the fusebox) and wouldn't you know it, the logger came to life. My logger cable is only good for 91+ I guess, as it doesn't have the extra power wire.

PROBLEM SOLVED!

 

[Boost95]

Bringing it back from the dead. I have the same problem in my 90. I have a serial comm error and that's it. Sometimes my CEL comes on and sometimes it wont..

Does the cable you use still have 3 wires? 2 ground and 1 to power in the fuse box?