Why not use existing sensors for gauges?

[Dave C]

I want to add gauges (boost, pryo, tranny temp, etc.). These engines have sensors everywhere so that the PCM/ECM can do their thing. Why can't I tap into the engine's existiong sensors for my gauges instead of having to install additional sensors? :rolleyes: Just something I've been wondering about. smile.gif

[slagona]

You can tap into the existing sensors for info.

Tools like autotap, car code, any OBD-II code reader, the GM Tech 2, and many others do this.

There are several problems:

1) There is no EGT sensor - so you would need a pyrometer.

2) The boost guage is relative to the barometer, so the current barometric pressure needs to be subtracted from the sensor's reading - you will get a reading about 14 psi too high, IIRC.

3) You either need to purchase a product to tap into the GM Computer Connection (where you read your codes from) or write your own code to convert the electrical signals from each sensor to an understandable value. If you purchase a product, you have to use a laptop and carry it in the vehicle whenever you want to monitor anything - or some handheld divice. It's hard to view the monitor and drive at the same time......

Several people have stated that they will write their own programs - not a simple or quick task. There are some available out there - I lost my links but would be more than happy to find them again if anyone is interested. Biggest problem is that the protocol for GM OBD-II enhanced parameters is not really public knowledge - the generic parameters are well know, but the GM specific (those not required to be public) are somewhat elusive. They can be found - but may not be reliable. Once found - they need to be converted. I haven't checked in a while, but at last check, no one has successfully (other than "commerical" applications like autotap, car code, ....) deciphered all of the enhanced GM parameters.

Not to say it can't be done - but you're in for a long project. For my purposes, guages were easier to read and I had to have a EGT guage anyway, so I just went with a triple A pillar for boost, EGT, and Trans temp. The only other info I would like to regularly see is Intake Air Temp. If I every get around to that, I'll switch out the Trans temp since I don't tow often. I did tow once - a GVWR of over 17K pounds from NY to FL and only had one climb where the trans temp started to get a little high - so I'm not worried about the trans temp......

I think that using the existing sensors is a good way to go - but there are some compromising that needs to be done....

--Scott

[Dave C]

I figured there were some good reasons. I currently have a OBD II interface device that I plug into a laptop. The interface was $88 and the software was free http//obddiagnostics.com/ (http://obddiagnostics.com/) if you already have a laptop, or a desk top within 10 feet of the truck, it's great. But your right it's not practical for use while driving.
Thanks for the reply.
Dave