Temperature gauge VT V8 without BCM

[Drew_au]

Along the same theme as my other thread regarding the automatic transmission shift mode switch - I have stumbled on to another snag with my proposal of running my VT V8 without a BCM or OEM instruments.

The temperature sensor goes direct to the PCM. The temperature gauge in the instrument cluster runs on serial data from the BCM. I want to run a basic AutoMeter temperature gauge. So I tried wiring the gauge in parallel with the PCM on the line from the temperature sender. The PCM doesn't like this and throws a code and displays "HOT" and fires up both fans. Interestingly, the OEM temperature gauge didn't falter (still read accurate) and the autometer gauge appeared to be accurate although I didn't test it too long.

Does anyone know what a solution might be? I already have the AutoMeter gauges and I plan on using them. I don't want to run the OEM BCM and Instrument Cluster. I wonder if there is anywhere else on the engine I can mount a second temperature sender dedicated just to the gauge?

I have a similar problem with oil pressure, but I can get around it using a tee piece on the oil pump and run two senders (if the PCM isn't happy with the autometer gauge in parallel like the temperature gauge).

Now that I'm getting in to it I'm starting to see why most hot-rodders stay away from EFI engines.

Andrew.

[Holden202T]

surely there has to be a bung somewhere near the thermostat housing that you can mount the autometer sender in, if theres not you can always drill a hole and make one .... top of the thermostat housing might be an easy option to do it too.

[Drew_au]

surely there has to be a bung somewhere near the thermostat housing that you can mount the autometer sender in, if theres not you can always drill a hole and make one .... top of the thermostat housing might be an easy option to do it too.

I was just pouring over the engine and considered exactly that.

Now that I've spent some time away from it, it appears logical to me; the OEM temp sender and PCM form a current loop - when I place the analogue meter in parallel - it has low impedance and therefore alters the current flowing in the loop.

Thanks for the tip,

Andrew.

[Helical]

When I put a VT S1 5L V8 into my VS ute I had to install the VS coolant sensor (for the gauge) into the intake manifold. There is a flat spot on the front of the intake manifold where the earlier 5L's have the coolant gauge sender (the lump of brass with a single terminal type).

I drilled and tapped mine in the car, I just used a heap of grease in the drill bit and the tap to draw out the swath and only drilling/tapping in small increments before clearing the swath and re-greasing.

The differences I have found between the VT S1 5L intake manifold and the VS S2 5L is the absence of ports for coolant gauge sender and the intake air temperature sensor.

I haven't looked at your other thread at all, but what I'm doing is trying to go from VS S2 spec (MAP) to VS S3 spec (MAF) but I have a VT S1 engine. I will be running a VS S3 tune (same PCM as the VT) DRRR as soon as I have modified the VT S1 loom I have. The oil pressure switch is my main hold up, you may find this too, as the VT only uses a single wire to the PCM where as the VS uses another two which cut off fuel via the EFI relay if there is no oil pressure (that's if I read the diagrams right)

Troy

[Jayme]

nah, the oil pressure sender doesnt cut fuel pump, its the opposite. if the fuel pump relay fails to engage, then the oil pressure will engage the fuel pump as a backup. if you lose oil pressure you just lose the backup circuit, the fuel pump will continue to run off the relay.

[Helical]

Ah, thanks for clearing that up.

I forgot to add that one of the extra wires on the VS S2 does the oil pressure warning lamp, whereas I believe the PCM does this on the VT.

Troy

[Drew_au]

Thanks Troy. I'll have a look at my manifold and see where I can mount a second sender.

For the oil pressure, I guess I'll run a tee piece. Looking at the schematic, the PCM connects to the oil pressure switch which appears to be a simple switch to ground. I wonder if it is normally open. If so I will try to run a simple indicator LED in parallel with the PCM. If I use a LED it's high impedance shouldn't interfere with the PCM.

Might have to wait until next weekend to continue experimenting.

Thanks for the replies,

Andrew.

[Drew_au]

Spent some time up the shed after work this evening:

The oil pressure switch is a simple normally closed to ground contact, just like on older cars.

I wired a lamp to +12 V on the line to the PCM and everything worked as advertised. Cool.

Andrew.

[Helical]

I remembered I have the VS manifold down the shed (mate I sold the engine to wanted to go to a carby as he can't understand EFI )

So here's a couple of pics of the empty hole where the sensor for the gauge is located, I can't remember the stock tap size unfortunately, I think it was a BSP thread...

Troy

[Drew_au]

Thanks for posting those photos Troy. I'll have a look on my manifold and see what's there.

I'm a fair way off needing the sensor working as I am only just staring on the chassis now. I took the opportunity to test all these functions on the V6 VT I'm wrecking before I start pulling it to bits.

Thanks again everyone for your help,

Andrew.