Friday, April 10, 2009

What to do with the PCM?

Things are still moving slowly with my conversion. Gas tank and gas lines have been removed, but not much progress beyond that. I've been very busy with other commitments lately - I'm hoping things will calm down after next week.

No huge surprises in removing the gas tank, except that the air wrench (600 ftlbs of torque!) was not able to break the bolts holding the gas tank straps. They didn't look that bad, not too rusty, but the wrench wouldn't touch them. So I ended up prying the strap hinges out of the frame instead.

While under the back of the car, I did notice that one of the suspension components (stabilizer link for the sway bar) on the driver's side had snapped. Shouldn't be difficult to replace, but I'm wondering about the added stress of 800 lbs extra weight back there. May have to do some engineering calculations and see if a beefier component is warranted.

At some point I know I'm going to be bringing the engine and exhaust pieces somewhere for recycling (scrap metal yard?) but I don't know what to do with the gas tank. I've heard rumors that it is a very difficult thing to get rid of. May be worth an EVDL (Electric Vehicle Discussion Group) search on the topic.

Another aspect of the conversion weighing on my mind is what to do with the PCM. In my mind, there are 4 options with the PCM:

1. Leave it untouched. Simplest approach, but then I either have to look at the MIL all the time or cover it up. Question: Will the PCM work at all without receiving signals from a non-existent engine (for instance, vacuum sensors, temperature sensors, crankshaft sensors), or will it assume that the engine is off all the time?
2. Leave the PCM but create a magic box which will fool it to believe that the engine is running, and running properly. The magic box will no doubt be very complicated, especially if more than a couple of signals will be required to keep the PCM happy.
3. Reprogram the PCM so it ignores inputs which are no longer pertinent. Complicated, and I believe will require a special interface and software.
4. Remove the PCM. My preference, since it is the most elegant (remember, I'm really out to save the world by getting everyone to convert!). Questions: What other systems rely on outputs from the PCM (ABS, SRS, instrument panel, etc.)? Will the car pass annual inspections without a PCM? (According to the Mass RMV website, the OBDII check is done only for emissions purposes and thus would not apply to an electric vehicle. But how do I confirm that?)

I've started to ask other EVers (and done an EVDL search) on the PCM topic, but thus far I haven't gotten a consensus. Some go with Option 1 without any obvious issue, but I wonder if it is car-dependent. Some decide not to convert anything with an OBDII connector to avoid the problem.

In the meantime, I'm hoping to get some time Sunday to get rid of the last straps for the exhaust and gas tank, start gutting the interior, and take a few measurements for the motor adapter. Until then...


  1. You should get the Saturn PCM data to check, but my Civic's PCM does the Automatic Transmission, Dash systems, VSS, Air Conditioning Clutch, Brake light systems, blinkers and who knows what else.

  2. Gas tank: yikes! PCM: Hmmm. Rear suspension: good thought, batteries sure are heavy.

    Sorry, I couldn't be more helpful today. Gettin' late.