Shift Mode switch VT V8 auto without BCM

[Drew_au]

G'day all,

I'm planning building a street rod with a VT V8, as mentioned in a previous post. The build hasn't progressed much due to life getting in the way.

I have come across another difficulty I need help with. I have purchased a complete VT V6 as a donor car for many other parts and after looking closely I have realised there is a snag with what I plan to do with the auto transmission shift mode switch.

Basically, I want to run the VT V8 without the BCM, thanks to some kind help from this forum I have got around the security (VATS) issue but I want to be able to swich shift modes and see what mode the computer is in.

Looking at the wiring diagrams I assumed the shift mode switch was a toggle, so I was planning on running a double pole double throw switch, one half switching the PCM input to ground, the other half of the switch for a mode indicator. But now I have a complete running car I see that the switch is momentary and that sort of throws my idea out the window.

I could have a momentary switch but I can't see how I will be able to tell what mode the PCM is in as the original shift mode indicator is run via SDI to the instrument cluster from the BCM. I don't want to use the original VT instrument cluster in my vehicle and I don't really want to run the BCM either.

My other option is to tie the switch input to ground permanently so the PCM always puts the transmission into power mode.

So I'm wondering if my PCM can be re-programmed to give me this functionality. Either to make the shift mode switch input not momentary, i.e. floating = Normal, ground = Power mode - or program a spare output (is there such a thing?) to run an indicator to show when power mode is engaged.

Sorry if the above seem incoherent ramble, I'm not sure how else to say it. Also I'm not set up to program memcals so I might need some nice person to burn a chip for me. (I don't want much do I?!)

Thanks,

Andrew.

[kojab]

Having never actually looked or examining one of these switches I did not think they were a momentary type switch. My understanding is when F12 (Power/economy input to PCM) is not grounded economy mode is selected. When F12 is grounded power mode is selected. Have you put a meter on one of these switches?

[Drew_au]

Thanks for the reply mate. I haven't got around to testing the switch yet but I'm almost 100% certain it is momentary. I feels momentary (not that that means anything I guess) and I've discovered that if I hold the switch down and cycle the ignition, it toggles between power and normal. So my idea of just tying it to ground is no good because every time I switch the ignition on I will get a different mode.

Just went for a quick drive and it's quite noticeable the change in shift pattern in the different modes, so I guess I could just wing it and just wire a momentary switch with no indication of what mode it is in. This isn't ideal though.

I've stumbled on to another snag with my temperature gauge - see my separate thread in this section.

Andrew.

[charlay86]

Yeah it is a momentary, the PCM reads the status of the switch input and if it is closed it exclusively ORs (effectively toggling) the bit in memory that controls the shift mode.

[Drew_au]

With many thanks to VL400 - I have a solution to the shift mode indicator issue. BCM Sim to the rescue - and it gives me the much needed Check Engine Light.

Andrew.

[yoda69]

I may need to update yor memcal, as the BCM Sim I think can also support the low speed fan request.
When you get closer to getting everything going let me know and I'll see if any updates are required.

yoda69

[VL400]

Yep can do low speed fan if you want to use that function.

[Drew_au]

Yeah I'll need the fan control. Thanks yoda.

BTW, while reading through my service manual PDFs I noticed there was a Holden technline on memcals that refered to my memcal version (CJDN) and that there was an issue with the engine not restarting and there was a new memcal released to replace CJDN.

Does this ring any bells? Did you modify my code along these lines or was it only a minor issue affecting a small batch of vehicles.

I can't find the actual document anymore, no matter how hard I look. I'll keep looking!

Andrew.

[Drew_au]

I knew I'd find it eventually!

99techlines - CJDN memcal.pdf

(65.32 KiB) Downloaded 295 times

Andrew.

[Holden202T]

where was the bcm sim when i put the ecotec in the torana