Blue Wire Mod

[OverboostXS]

What is it and how would i go about doing it? Thanks

 

[kpt4321]

The blue wire mod allows you to plug the O2 Sensor output wire into a spare input on the SAFC, so that you can read the O2 volatge through the SAFC's diagnostics screen.

The answer of how to do it, would be "don't." This mod changes the O2 signal that reaches the ECU, and makes fuel trims all whacky. There is no reason you need to view the O2 voltage anyway.


....Kyle T.

 

[OverboostXS]

Thanks I was told to do this before i sent it to get tuned. He said it would make it a lot easier.

 

[kpt4321]

Then I suggest you get your car tuned elsewhere. In fact, I would very strongly suggest this. If I knew you, I would probably threaten to never be your friend again if you sent it to wherever you were thinking about sending it.

But I'm just some jerk on the internet, so you probably won't listen to me.

DON'T DO IT!!!


......Kyle T.

 

[brads]

I measured the before and after effect of the blue wire mod, when I had an AFC, using a digital multimeter. The difference in reading at the ECU was negligible, if I recall correctly, I couldn't see a difference down to the 0.001V range. That should be more than sufficient for most people. It worked well enough to read O2 voltages.

Of course, if you do a poor job of wiring the blue wire mod, you will mess things up. I unplugged the O2 sensor, then soldered the blue wire into the O2 sensor wire at the ECU. Lots of people do stupid crap like using those vampire clips to wire it in, and those are very unreliable, and can mess the sensor and readings up.

I also pulled apart the AFC, and looked at the circuit for the blue wire in it. It was somewhat low impedance. I was really surprised that it didnt affect the results. But it didnt.

Either way, if you want to tune, get a logger. O2 voltage doesnt tell you enough to tune. And with a logger, it will tell you O2 voltage, so there would be no need to do the blue wire mod. Save yourself the hassle by doing it the right way(logger) the first time.

Brad

 

[pneumo]

On my first DSM I noticed about 0.05 volt difference between the blue wire mod reading and the logger reading.

I didn't do the blue wire mod when I switched the SAFC over to my next DSM.

 

[1LE]

One nice thing about seeing O2 voltage is that you can tell when to replace the O2 sensor... You'll notice when it's starting to have problems, then you can replace it before it dies.

 

[brads]

Originally posted by pneumo
On my first DSM I noticed about 0.05 volt difference between the blue wire mod reading and the logger reading.

That most likely means the grounding is off slightly between the two or the calibration is a little off on one, hence the different readings on the two different things. Also the loggers have only a .02 volt resolution(8bit AD, 5 V range, thats expected). If you were seeing different readings on the logger when you installed/removed the logger, then you could say there could be a difference. But what you saw only proved you didnt have the things referenced at the exact same point

When I tested them, I measured the values with a digital multimeter, in addition to the AFC, as I added/removed it from the circuit several times back to back for repeatable results. The difference in the DMM readings was negligible, around 0.001V give or take. The difference between the AFC reading, and the DMM reading was much larger than that, but it was constant, and repeatable, which shows it was just an error either due to ground location, or calibration of the AFC A to D converter itself. Nothing to worry about. Its the testing with it in the circuit, vs. out of the circuit, that would show there is a difference.



Brad

 

[pneumo]

Yeah, I didn't see it as a problem, I just wanted to use whichever reading was more "normal" since I never felt comfortable seeing 0.82 volts at WOT (this was on a '90). Using the logger made me feel better since it showed 0.87 v.

I agree that the blue wire mod is repeatable and consistant, which will allow pretty good tuning (as far as O2 sensor tuning goes) But a logger is better.

 

[kpt4321]

It is my opinion that the blue wire mod is just too "sketchy" to do. However, if you do take out a digital multimeter and check to make sure it is working ok, and it is, then by all means use it.

However, I still stand by the conviction, that if a shop wants you to do that so that they can tune, that they are not the place you want to be going.


....Kyle T.

 

[OverboostXS]

Thanks i was told to do it as well with the data logger and then to check it to see its reliability so it easier to work with only the Safc-2 i dont know if there is a difference from the first blue wire modin the Safc 1 and the blue wire mod in the Safc-2 I will keep you updated on my situation kyle. Thanks for caring and thanks for your guys help i love your the people that make me love owning a DSM Zach

 

[tlnpwr]

Originally posted by kpt4321
However, I still stand by the conviction, that if a shop wants you to do that so that they can tune, that they are not the place you want to be going.

i have to agree with kyle. if the shop is going to use that to tune it, why dont u just do it urself. im not sure of the conversion, but i believe that as long as the O2 voltage reading is around .9 volts then your are running pretty good, not too rich and not too lean. if they are telling u to hook it up to "make it easier to tune" then they are just going to get the reading off of the safc. i was told how to get to the screen, but i forget what menu it's under now.

if using the search on this "mod" u'll also read a lot of ppl saying that they didnt use it b/c the O2 will send a "signal" to the safc resulting in a fasle reading....and i also read one person saying that it could send a "signal" back to the safc causing damage to the safc.