Data Logging computer wires to tap?

RichM

RichM

Registered User
I have a datalogger that I need to tap into the EEC on my 91 SC. I wanted to check to see if I have the correct wires to splice into.
So is this right?

RPM tap should be
pin 4, Dark Green/Yellow wire​
The speed sensor should be
Pin 3, Dark Green/White​
MAF tap should be
Pin 50, Dark Blue/Orange​
TPS tap should be
pin 47, Dark Green/Light Green​
ACT tap should be
pin 25, Light Green/Pink​
Ground taken from
Pin 20, Black​
 
Do I read this right?
91SCEECpinout.jpg
 
XR7 Dave said:
Ground should be taken from circuit 359 sensor return.
Click to expand...

Dave, is there any specific pin that is best tap for the ground.

Blown 91, it all came down to price. Also, PLX seemed a little more user friendly considering that LM-1 seems to require their AuxBox to do data logging. The LM-1 web page still has my head swimming with it's lack of clear information.
 
XR7 Dave said:
Ground should be taken from circuit 359 sensor return.
Click to expand...

359???

I have hooked into my wiring for my PLX as well, and the sensors all appeared to be doing OK, but the "signal taps" were all noisy.

I then used some aluminum foil as a shiled for my "tap harness", and ran a bare ground wire agaisnt the "aluminum foil shield" and did my best to solder the wire to the foil...

I still got noise on VSS, and the RPM (taken from injector 1, as per the PLX tech help)

When I pulled the motor, the grounds all seemed good in the engine bay, but I was thinking that perhaps my noise suppression cap was dried out or someting...

I used the chasis ground to the best I remember, Might have to look again.

Now if I used the wrong return, the voltage levels could be affected, but that should have no ipact on the signal noise should it?

I see several 359's on that list, and a 359j, how do I know which one to use?
 
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sizemoremk said:
359???

I have hooked into my wiring for my PLX as well, and the sensors all appeared to be doing OK, but the "signal taps" were all noisy.

I then used some aluminum foil as a shiled for my "tap harness", and ran a bare ground wire agaisnt the "aluminum foil shield" and did my best to solder the wire to the foil...

I still got noise on VSS, and the RPM (taken from injector 1, as per the PLX tech help)

When I pulled the motor, the grounds all seemed good in the engine bay, but I was thinking that perhaps my noise suppression cap was dried out or someting...

I used the chasis ground to the best I remember, Might have to look again.

Now if I used the wrong return, the voltage levels could be affected, but that should have no ipact on the signal noise should it?

I see several 359's on that list, and a 359j, how do I know which one to use?
Click to expand...

I combed though the PLX forum and as much of the web as I could and the "recomendation" is to use a chassis ground as close to the ECU as possible. There is a ground stud located just forward of where the ECU bolts in so I think I will try that first. I'm a little uncomfortable in pushing all that current into the 359 circuit right now, afterall the O2 sensor is powered though/into that ground connection.

sizemoremk, did you try to take the RPM signal off circuit 11 (pin 4)? If so was that too noisie a signal? I have checked that ciruit with a multi-meter and I get a readable singnal (about 26 Hz at 750 rpm idle). At least readable with my meter.
 
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RichM said:
I combed though the PLX forum and as much of the web as I could and the "recomendation" is to use a chassis ground as close to the ECU as possible. There is a ground stud located just forward of where the ECU bolts in so I think I will try that first. I'm a little uncomfortable in pushing all that current into the 359 circuit right now, afterall the O2 sensor is powered though/into that ground connection.

sizemoremk, did you try to take the RPM signal off circuit 11 (pin 4)? If so was that too noisie a signal? I have checked that ciruit with a multi-meter and I get a readable singnal (about 26 Hz at 750 rpm idle). At least readable with my meter.
Click to expand...


I'm sure I used the closest chasis ground, or created one...

I was told by the PLX folks and also our own fastsc92, that an injector wire was a better source for RPM... So I never tried the RPM signal.

It appears that the last time this was brought up, it was left off where we are now....
http://www.sccoa.com/forums/showthread.php?t=50342&highlight=ground

It looks to me though, that you can use the offset voltage feature to correct any of the "displayed voltages" through the PLX software...

And there is only one ground for the whole unit as far as I recall, so I don't see how it would do any good to use only one of the sensor returns, unless they are all tied together....

Whatever happened to gound is ground the world around:confused:
 
Just thought I should chime in here......

There is a power and a ground being supplied dirrectly to the computer. Off the top of my head I dont really remember which pin it is located at. I did however use that pin for my set-up and its been 3 years without any trouble. My rpm signal is really clean but the speed signal is noisy and I just never got around to fixing it since its really just a novelty and not used for tuning. I'm assuming the output frequency is just too random for he PLX.

I did however have to change some of the offset voltage values in the program. If you probe the actual sensor, and then take a reading from the digital dash there might be a slight difference in the signal. I'm assuming this is due to resistance in the wires from the computer to the sensor itself. Mine voltage values were all off slightly, but once I adjusted things, I get an accurate reading. This is important if you plan on logging ACT so that your numbers are dead on.

Also as a side note, I fed the wideband singal (brown wire) into on of the wires in the tap harness so that I can log that as well.

To sum it up....all the wires being connected at the PLX, including power ground and signal are all being supplied by the ECU harness in my application. I got some nice quick disconects for the power and ground to the unit is easily transferable even though its tucked far into the dash. In fact, it has already traveled to a bunch of my buddy's cars.:cool:

I'm really happy with the set-up and it has paid for itself 4 times over. I got this tuning down to an art.:p
 
Hmm, I think my power source comes from my switch panel source, which is in the ashtray, which is probably comming from the cigarette lighter, not sure right off hand...

Maybe I'll get in there and rew-re it with the EEC power source then...

Mine is permanant though, I soldered mine in, cuz I don't trust wire taps...

Man I hate getting upside down and backwards, in that little corner. I'm what we call in our parts a "good sized ole boy" and don't fit in there very well. :eek:
 
Well all I can say for Ford now is.... they don't even follow their own wiring diagrams. At least in regards to the color coding. Not one wire color was correct, the pin positions where right. I had to verify every conection with the multimeter... well except the vehicle speed sensor since I didn't want to tear the dash apart or climb under the car.

I'll try to post when everything is hooked up and running.

Once again, don't trust the color codes in either of the top two posts. Go by pin position and double check with a multimeter.

RichM said:
I have a datalogger that I need to tap into the EEC on my 91 SC. I wanted to check to see if I have the correct wires to splice into.
So is this right?

RPM tap should be
pin 4, Dark Green/Yellow wire​
The speed sensor should be
Pin 3, Dark Green/White​
MAF tap should be
Pin 50, Dark Blue/Orange​
TPS tap should be
pin 47, Dark Green/Light Green​
ACT tap should be
pin 25, Light Green/Pink​
Ground taken from
Pin 20, Black​
Click to expand...
 
sizemoremk said:
I was told by the PLX folks and also our own fastsc92, that an injector wire was a better source for RPM... So I never tried the RPM signal.
Click to expand...

I finished up the install tonight. It runs, but I should have taken your advice. The signal for RPM off of pin 4 seems far too weak to be used. Once I connected the PLX up my dash tach began reading erratic and almost half what it should have been reading at low RPM, at high RPM it seemed to work ok. I also got a solid CEL but didn't have time tonight to scan the computer. I'm going to have to pull that tap tomorrow and try wiring it up to the #1 injector as well as pull that code to see if I didn't mess something else up.

I pulled the vehicle speed sensor from Pin 3 and it seems to be working for me, 0.5 Units/Hz gives me only a 10 percent optomistic reading on the laptop.

AFR, the wideband says I'm spiking way lean (over 19:1) after I let off from a few seconds at full throttle.

More after I get some sleep and can look at the graphs some more.
 
You should use the voltages at the EEC and the reference ground that the EEC uses. Why? Because that is what the EEC uses for data processing. If you calibrate your datalogging to some other source, accurate or not, you will never know what your EEC is seeing and therefore will be unable to properly calibrate your EEC. It can also be a way to verify a bad sensor or bad sensor wiring. If you get #'s that don't seem right, then you can acually fix a problem based on what the EEC is seeing rather than what another less important device is seeing. I've verified my readings many times against things like fan turn on temp and it's accurate to the EEC.

As for dirty tach signals, I don't know. I've datalogged about 100 SC's and some of them have bad tach signals whereas most are rock steady. I use pin 4 for tach because I tune all EEC IV cars and I have a plug in adapter. There are only so many pins that are the same for all EEC IV cars and pin 4 is one of them.

For anyone looking at the above diagram, keep in mind that this is a 91-2- or 3 diagram (not sure which). Wires will vary some if yours happens to be a slightly different year than the one in the picture. Just by looking at the wires and codes listed, they all look right to me but I didn't go out and verify anything. Yes Ford has some variations but they are consistent. Sometimes the wires discolor with age too so it can be hard to identify for that reason too.

Sorry guys, don't remember which signal return wire I used. I went through the OE wiring diagrams and used the one which the EEC uses for the sensors in question. As was pointed out above the device uses the your power source for ground also so the sensor ground is just that, a sensor ground.

Sorry, I've never tried to tap the VSS, I didnt' have any need for it.

Your car should go lean on decell (well not all years) because the EEC has a parameter to shut off fuel. If it is just spiking lean then it is most likely sensor overheat, and it will likely require a heat sink to work properly.
 
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Dave is right, the car should go lean for a very brief second after you let off the gas from a WOT run, or between shifts. What you really want to look at is your tip-in. When you smash the gas the AFR should go right down to 12.2-ish. If it spikes then you have to adjust your accel fuel table and other various things that go along with it.

I'm not sure which signal i used for the speed but i know my signal is very noisy. I dont recall using pin 4 though, I'll have to try that once my car gets back on the road again.

If you need help comparing data please feel free to contact me. I've been using that software and set-up for almost 3 years now.
 
I changed from pin 4 to pin 36 for the tach signal and I have the tach in my dash back and no check engine light. After checking the logs it seems the signal is a bit noisy. I'll log some more data and double check in a few days. I've also posted at the PLX web site to see what they have to say.

The MAF signals seem realistic as well as the TPS.
Although with the O2 sensor being independent of the rest of this I am fairly sure that I have a boost leak. Now I just need to figure out why I'm blowing grey/black smoke out the tail pipe at WOT but not reading rich on the wideband.

More time will tell.
 
RichM said:
Now I just need to figure out why I'm blowing grey/black smoke out the tail pipe at WOT but not reading rich on the wideband.

More time will tell.
Click to expand...

Remember the 02 sensor only reads oxygen, not fuel. If you have a cylinder misfire it will read lean and dump fuel on that bank. However, it is more likely that you are running very lean.
 
make sure your calibrate your voltage readings otherwise you'll be logging slightly off numbers
 
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