Revdoc

iTrader: (2)

I have just completed a 165 to 730 ECM swap on my 89 GTA. Once I finally got it running on all 8 cylinders (I have a thread in the DIY PROM section about that) I took it for a test drive and everything is great. Once I started looking at the datalogs I noticed the Speed was all over the place. It seemed to be stuck at 0 for quite a while, then once it started reading it would jump from 0 to 255 and anywhere in between seemingly at random. My speedometer works fine, it's just the VSS signal to the ECM that seems crazy. Of course this is playing all kinds of havoc with my TCC lockup, and sets a Code 24 in the ECM.

I have double checked my wiring, I have pin A10 (brown wire) from the 165 harness going to BC6 on the 730 ECM, just as directed here: http://www.eecis.udel.edu/~davis/z28/ECMs/86to92.txt. I have also changed the .bin file VSS flag, it was originally checked in the stock AUJP 8D.bin so I unchecked it. No help. I tried driving with it both ways, with the box checked it seems to peg at 255 a lot more than with it unchecked. I tried to edit the VSS constant that was set at 4006 ppm, but whenever you save it resets to 3614 which is apparently a limit of the ECM.

I have searched and read every thread about VSS I could find. I am going to try this procedure VSS Test when I get a chance, but it seems strange the VSS would just go bad coincidentally when I swap from 165 to 730. Then again, everyone who has done a 165-730 swap seems to just flip the bit in the .bin for VSS and everything is hunky dory. Has anyone else ran into this much trouble with their VSS? If it tests out okay I'm thinking of rewiring it to not use the 4 output buffer to see if that fixes the problem.

The only other cause I can think of is I had recently installed a trans temp gauge and the sender has been leaking quite a bit, all over the transmission. I suppose it could have shorted the sending unit on the tailshaft housing. I will disconnect it and clean it up next time I get a chance to get the car in the air. Any other suggestions or troubleshooting ideas?

BigBadLou

iTrader: (3)

Am I wrong or does the VSS on the '730 come in on B9 (gnd) and B10 (VSS)?
It seems that his code was modified to accept signals on different pins (different from stock) so unless you're running his code, you might have trouble.

Hope you haven't fried the AIC driver (C6 is an AIC output on the '730).

Lou

Revdoc

iTrader: (2)

Hmm... most things I have found say to connect A10 to BC6 and not use the normal 730's VSS wires: https://www.thirdgen.org/forums/diy-...ed-sensor.html. Then just change the VSS bit in the bin file. Doesn't seem to work for me though.

BigBadLou

iTrader: (3)

Strange, the '730 takes a 2-wire VSS input, not 4-wire.
It appears we might be talking about the same ECM but the pinouts sound weird.
You could PM Grim Reaper to shed some light on this.

Lou

Revdoc

iTrader: (2)

Attached are copies of my current .bin file so that anyone can verify that I changed the correct VSS bit, and a datalog so that you can witness the crazy speed signal. When I get home today assuming the weather is decent I am going to try wiring the VSS without the buffer box, so that the wires go directly to the 730.

BigBadLou

iTrader: (3)

Normally, the stock $8D code reads the VSS input from pin B10. If you route the signal there and enable the VSS bit in the BIN, you should see speed readout in the datalogger. Hope that works for you.
However, the '730 ECM requires the full 4000pps signal directly from the VSS. You can try splicing into it before it reaches the Speed Buffer box (the simpler way) or you can remove the buffer completely and wire it up the way the '730 is wired up from factory.

Diagrams here: http://www.austinthirdgen.org/index.php?pid=19

Hope this helps.
Lou

Revdoc

iTrader: (2)

Well I tested the VSS today with a voltmeter and it shows +12v on the brown wire A10 when the ignition is on. Jacked up the car so the rear wheels were off the ground and started the car, put it in gear. Now the voltmeter fluctuates between 1 and 6. Exactly what it's supposed to show if the VSS is working properly. So, frustrated and not knowing what else to try, I swapped the ECM out with a spare. Repeated the test, this time the Speed readout on TunerPro RT immediately started reading 2, 5, 6, 7 mph. It was apparently a bad ECM the whole time. I haven't driven it on the road but I'm pretty sure this will solve the TCC problem. Phantom problems, don't you love them.