I have a '92 LT1. Just got me a laptop, ALDL cable (from ALDLcable.com) and TTSDatamaster software. Hooks up to PCM ok (default settings) but at least half the records have data errors although the results from my road run seem pretty accurate (speeds / RPMs etc).

The ALDL cable ( 12 pin to serial connector) comes with a built-in 12vdc jack plug - I wonder if this is needed and may be adding noise to the signal? It's raining today so will not be doing another run until the weekend - I'll try connecting to the PCM without the 12v jack connected.

Thanks for any help, Andy.

 

A 12 volt power supply shouldn't be needed.

I would just make sure the aldl is connected firmly in the dataport.

 

So I went out for another run at the weekend and started getting data errors in Datamaster immediately. Then it lost sync with the PCM and intermittently (like every 2 seconds or so) reconnected, grabbed some records, lost contact etc.

I have tried everything they recommend in the datamaster manual including handshake, dash refresh, PCM sync timeout, display refresh, fewer records per second blah blah yada yada. Even tried a different laptop, same problem.

I have a couple of questions, I wonder if someone can help:

1. I heard 1992 vettes supply the info at 160 baud. The ALDL connector under the dash on my '92 has a contact in pin M (8192 baud) but pin E is empty. Does this seem right?

2. The 12v supply feeds a small circuit board on the Serial connector at the laptop end - it has a few capacitors on it so is probably for noise reduction. Without connecting to 12v I cannot connect to the PCM at all. Anyway, is it possible that noise from the cigar lighter is causing electrical noise on the data stream?

3. Will it work if I run a straight piece of wire from pin M to a pin on the serial port on the PC?

4. Anyone know of any problems where the ALDL output is 'unclean' and what do do about it?

Thanks guys.

 

You can not run a peice of wire. The laptop rs232 signals are not the same as the aldl signal. You may cause damage if you do that.
The aldlcable.com cable looks like it needs the lighter adapter pluged in for power. You would need a schematic of their interface to know if it has other ways to get power.

 

I just thought of the answer.

Make sure the IR port is disabled on your laptop.

 

Check all the ground points in the harness.

 

On the cable end spread the connector blades a little bit to ensure they're making good contact with ALDL chassis plug. Mine started to error during WOT runs and this "adjustment" resolved the problem immediately.

 

Sorry guys, still got loads of errors. I've made sure I have a good ground connection via the cigar lighter, and 'cleaned up' the supply with a capacitor. The IR sensor is disabled on the laptops.

Plan 'B'. Having talked to the previous owner, and given the heavy level of mods in the car, he said it is very possible that the ECM was modified (i.e. later year). Is it possibly upgraded? How can I tell what version number ECM/PCM is installed? Would a mismatch with the software cause datamaster to give checksum errors?

Running out of ideas now.

 

I didn't mean the aldl ground. Was talking about the PCM grounds. Check the PCM connectors to verify the power and grounds are connected propperly.

ground-
D1/blue 1
C32/grey 32
A18/red 18
A2/red 2
--------------------
12v-
B15/black 15
B31/black 31
B30/black 30
D3/blue 3

One more thing to check, the back of the heads for a grond strap. There needs to be one from the heads to chassis. Make sure you have one going to the firewall and that it's tight. The ignition fires the plugs, they ground to the heads. If the ground strap is not connected the voltage will seep through the ECM grounds and into the PCM, possibly causing EMI interference. This is just a theory of mine at this point, but worth checking out. Please report back with any results...

-Tim

 

Thanks Tim I'll check over the weekend.

 

Also, I had the same probably when I wan't getting a good ground connection with my MSD unit.

I hooked it up to the battery's ground terminal and it fixed all the data errors.

If you have an aftermarket ignition box, check into this.

Good luck

 

Try playing with the FIFO settings on your COM port. Turn FIFO off and try it. Try setting FIFO level as low as possible. To get there open the Device Manager, go to Ports, select properties of your COM port, then Advanced settings.

It sounds like it might be a timing issue to me, but it could also be noise. The ECM outputs the datastream at 8192 bps. The UART in a PC can't match that data rate exactly due to it's clock frequency, but it can get close enough. The logging software sets the UART as close as it can get it. Maybe the UART in your laptop(s) is not capable of setting the data rate to a non-standard rate?

BTW, FIFO setting has nothing to do with the data rate, it just controls how much data will be cached by the UART before notifing the logging program that data is available.

 

update?

 

I've tried adjusting the FIFO settings but at low settings I can't even connect to the PCM.

I have checked some of the grounding - using the 12v on the battery it is a clean connect to the heads (zero ohms). Next on my list is checking the grounding on the PCM connectors, which will be tonight.

This is frustrating now because I know I have problems at WOT above 5k RPM and I want to do some diagnosis on it..

 

I have been tuning on an S10 with the exact same problem. The owner has not found the problem yet, but I told him to do the same thing(ck all grounds). If we find the problem before you then I'll be sure to post the source. If you find it then LMK. It is a frustrating problem! You have a ground strap from the back of head to the firewall, right?

-Tim

 

I haven't found a ground strap but will look again tonight. Where abouts on the firewall should I look? (Drivers side, passenger side etc.).

If I find the problem I'll post straight away.

Thanks!

 

What kind of computer are you using? Most cables don't convert the TTL level PCM/ECM output to the RS232 levels. Most computers are happy with 0 - 5v for RS232 but some are not and require signals closer to the RS232 standard (-12 to +12 I think). Maybe that's your problem? Try a different computer.

 

I have tried two different laptops - both Dell. Both have IR disabled, both are running Windows XP. Maybe that's my problem. Who knows..

 

Hey Scott94C4 - do you mean that you hooked up the body of the MSD unit to the battery ground?

Thanks,
Andy.

 

Have you made sure you set up Datamaster for Corvette and not F-car? Just a thought...