Can a chip read EGT?

[Ken Cunningham]

I ran a Thrasher 108 at the track this weekend with leaded fuel so I removed the O2 sensor. One drawback is I am lacking O2 readings to help tune the car. I was wondering:
If you remove the O2 sensor and put in an EGT probe;
Plug the probe into the now-unattached O2 connection;
Could a chip be programmed to read the EGT probe signal along the (former) O2 sensor wires?

I don't know beans about what I am suggesting, BTW. I don't know what type of signal an off-the-shelf EGT probe delivers, I don't know what type of signal the O2 sensor delivers. I expect that there is an incompatibility there that maybe the EGT probe needs some sort of matching circuitry. If the ECU could merely report the EGT values to a Direct Scan output, that would be great. No need for an actual EGT meter, it is already there for real time reporting or for data logging. Now if the ECU could be programmed to also use the EGT data in its fuel delivery calculations, that would be great. Any merit in this?

 

[TurboJim]

Nope

I suppose if you could plot a mixture to temp thing you could MAKE something work, BUT it wouldnt account for any problems stemming from timing, individual hole problems etc.

Why are you taking the O2 out? I believe the trasher does use O2 info, just not for idle. Unless the 108 is different

 

[Ken Cunningham]

I took the sensor out so I wouldn't have to add a $40 replacement sensor to my cost of racing for the day. The Thrasher has a feature that allows you to remove the O2 sensor. The chip, when the O2 signals stop, defaults to the existing BLM values without setting an error code. This feature was specifically added (I believe to both street and strip chips) to allow you to save on O2 sensors when leaded fuel is run.

 

[Scott231]

Originally posted by TurboJim
Nope (can't plug EGT into the ECM)

Why are you taking the O2 out? I believe the trasher does use O2 info, just not for idle. Unless the 108 is different

The Thrasher runs open loop at idle and WOT...the latter of which is the same as a stock chip. However, as Ken noted, Thrashers work at the track without an O2. I generally do not tote this feature as I don't want a bunch of people trying it

In order to plug in an EGT probe to the ECM, you would need some pretty serious code and hardware re-work that no one is going to want to invest their time.

 

[ijames]

Omega and Fluke both sell little adapter modules that take a thermocouple input and output 0-1 V, so you can use a regular digital voltmeter to read temperature. The O2 input is 0-1 V so you could plug it all together. You will just have to do your own conversion of volts to degrees, and since the a/d resolution is only 8 bits you may get pretty bad temperature resolution. The modules are $50 to $100 if fuzzy memory serves. Start at www.omega.com.

 

[Ken Cunningham]

Thanks, Carl. That's exactly what I had in mind. Step 1: the first benefit from such an arrangement would simply be a report of EGT via the ALDL. This kills two birds with one stone. If the O2 sensor is removed, something must be put in its place; either a spark plug, an old sensor, or a bung plug. Why not an EGT probe? Step 2: if that data is coming in anyway, why not put it to use by the ECM?

BUT, with the current Thrasher, if I simply replace the O2 sensor with the EGT probe (suitably adapted to 0-1 vdc), the chip will still think that the data stream comes from the O2 sensor, will not use the default BLM values (until WOT), and the EGT numbers will probably serious freak out the ECM. EGT rises reflect leanness right? As the temp rises the vdc probably rises as well. This would be the opposite of what the O2 sensor sends (rising vdc represents richness, right?)

So what would be required is a way to tell the chip NOT to use the "O2" values, but just report them out the ALDL. I would be happy to do the manual conversion of the mV O2 data into the appropriate Fdeg EGT.

 

[ijames]

Step 2 is pretty ambitious - there's a big difference between reporting egt and reprogramming the ecm to do something with it. Anyway, when you just remove your o2 sensor do you get a code 13 with the thrasher? I'm pretty sure you will get the same error with an egt since the chip wants the O2's to bounce high-low-high in closed loop and the egt value won't really move that much or in directions the ecm thinks reasonable. After some initial delay period it will give up and set the code. Without the O2 it won't use "default" blms, it will use the stored ones it got last time it was in learn mode (which you can reset to all 128's by unplugging the ecm power wire).

 

[Scott231]

Originally posted by ijames
Step 2 is pretty ambitious - there's a big difference between reporting egt and reprogramming the ecm to do something with it. Anyway, when you just remove your o2 sensor do you get a code 13 with the thrasher?

You shouldn't. Tom and I found that the lean cruise feature would trigger that fault code. Tom was to have "fixed" that

 

[ijames]

Originally posted by Scott231

You shouldn't. Tom and I found that the lean cruise feature would trigger that fault code. Tom was to have "fixed" that

Okay, so it doesn't set the code but does know to ignore the sensor if it's not responding. I think the egt input would give the same result.

 

[Ken Cunningham]

Then this may be worth a try.
IF the chip will ignore the odd data stream coming from "O2 sensor" (actually an EGT sensor),
AND IF the chip will treat it like a sensor not there (which never tripped a code for me when I drove it w/o any O2 sensor to the track, at the track, and home from the track),
AND IF the EGT values will be reported out on the ALDL in the place of the O2 mV,
AND IF the a/d resolution of 8 bits is not too limiting,
Then there may be some merit in this experiment.
Although that seems like a lot of ifs, I may just be willing to be the guinea pig on step one of this.

 

[Scott231]

Originally posted by ijames
Okay, so it doesn't set the code but does know to ignore the sensor if it's not responding. I think the egt input would give the same result.

Signal, or no signal. On or Off. For more than X amount of time.

An EGT signal is a signal...the ECM will try to do something with it.