Accuracy of obd2 readings vs gauges?

[the fat bastid]

I'm planning on getting a triple gauge A-pillar as well as a obd2 scangauge like thing (long story but this (http://www.mercurymarauder.net/forums/showthread.php?t=102608)).

Like everything on the internet there are people on both sides of the issue.
Some say the obd2 isn't as accurate, polls kind of slowly, and is really only for checking for trouble. Gauges are better.
Other people say obd2 is more responsive than any gauge and it is hard to say what PIDs we even have.

I don't want to duplicate function so I'm not sure what to put in the pillar anymore (original idea was fuel pressure and trans temp). The 3rd gauge is a boost/vac gauge..which i assume the obd can't read since the blower is not stock.

What do YOU think?

[EMAS]

If you want to know the real numbers then reading it from the computer is the way to go but not with you basic OBDII reader as that data is often "filtered" to tell you what they think you want to know. On Ford products the biggest difference is in engine temp. When Ford developed fail safe cooling which is on many of their vehicles in the last 10-15 years they knew that once the coolant no longer fully surrounds an immersed sensor it stops working properly. So they switched to a Cylinder Head Temp sensor which actually reads the temp of the head not the coolant. However OBDII protocol requires a coolant temp reading. So Ford filters the CHT reading to get an aproximate coolant temp and sends that IF you are looking at the OBDII data stream. Look at the PCM data stream and you'll find a different number.

I recently picked up a Bluetooth OBD II dongle and the FORscan software. With it you have the ability to read the OBD II stream as well as the PCM stream like the Ford IDS system. I've toggled between the two streams and there is a definite difference in the CHT PID directly from the PCM vs the data sent for OBD II purposes.

The data obtained via the OBD II port will be refreshed much quicker than an aftermarket gauge. However with that you have to realize that it generates a lot of noise that a regular gauge filters out by averaging the inputs. The fuel gauge readings are the best example of this. When you are driving around accelerating, decelerating, going around corners and just a bumpy road cause the fuel to slosh around quite a bit. It would drive most people nuts if their fuel gauge would fluctuate between full and 1/2 when you really have ~3/4 of a tank. So that reading is averaged by the gauge so you see a steady reading even if you aren't sitting still.

TL;DR the data obtained from a OBD II port is much more instantaneous than you'll get from any gauge but depending on which data stream you are looking at you may be getting data that has been filtered.

I highly recommend a ELM dongle that reads MS-CAN and the FORscan software. Not only does it read all the OBD II data it also gives you access to every module in the car. So you can see codes in the LCM and RAS/VAPS module and initiate the self tests as well. With the extended licesnse that I still need to get you can actually do things change tire sizes and axle ratios as well as program new transponder keys when you have a single key or none at all.

[the fat bastid]

Great insight there. I was just looking at FORscan as well. My plan was to get an elm bluetooth, link it up to a raspberry pi sitting in my trunk running FORscan then send the data to the overhead console.

Hum, now what automete ultra lite gauges are not read from the comp. Maybe a temp gauge hooked up to the s/c coolant...oh, they have a nitrous gauge too. Guess i need a nitrous kit now lol.

[Lowndex]

Aeroforce Interceptor gauges with sensors

[Zack]

The Marauder does not have a cylinder head temp sensor

[Lowndex]

The Marauder does not have a cylinder head temp sensor

Using Aeroforce Interceptor gauges, I am measuring EngTemp at the rear head and OilTemp on the oil cooler return.

[Zack]

Using Aeroforce Interceptor gauges, I am measuring EngTemp at the rear head and OilTemp on the oil cooler return.

Did you install a sensor in the rear of the head?

[Lowndex]

If I did, the car would explode. :)

Yes, KC installed two sensors. I purchased two from Aeroforce. I assume they were the ones used.

So, anyone could do the same with their stock Marauder. Certainly highly skilled 'wrenchers' like you, sir.

[95chickn]

Did you install a sensor in the rear of the head?

Is that necessary, i heard it wasnt needed so I left off. Mine broke and i was gone replace but a poster said that it isnt needed

[Zack]

Is that necessary, i heard it wasnt needed so I left off. Mine broke and i was gone replace but a poster said that it isnt needed

The Marauder never came with a cylinder head temp sensor. Only 2V cars have them

[Vostok]

The Marauder never came with a cylinder head temp sensor. Only 2V cars have them

I get CHT readings on my scanner. Where are they coming from? :confused:

[Zack]

I get CHT readings on my scanner. Where are they coming from? :confused:

It is the reading from one of the 2 sensors in the COT

[RF Overlord]

What Zack said...one of those sensors does nothing but run the dash gauge, the other is read by the PCM. I forget which is which, but I understand they are not interchangeable.

[justbob]

Drivers side


Sent from my iThrone using Tapatalk