2G Electrical Gremlin lol

[Tyler Davis]

Hey Guys! Set a new PB at the track of 11.2 @118 on the setup but of course not without issue . I still have absolutely no top end it feels like, it went 100mph to the 1/8th and finished at 118 and to me that seems wrong. IDK if that's a voltage issue, small cams, bad tune, etc. any pointers there would be helpful. I attached a log, but what would be some things to look at why my datalog shows I never go over 6400rpm, and hovers around the 6000 mark for the back part of the pull?

In the car I definitely was over that rpm but towards the back half of the pass my wideband did start to read funky like I was running out of fuel. I see my voltage appears to be very low, I just replaced my alternator and battery that same day as well as have went through about 4-5 alternators in general trying to see whats going on with that voltage issue.

Idling it never sees more than 13.5v and normally is around 12.8-13.0v while driving. Ultimately just very confused on what would be causing this. Thanks!

Update: I have tested and at idle with a meter the battery is seeing 14.4v but link still only reads 13.5v

 

[Tyler Davis]

not too familiar with what the board is supposed to look like but there does seem to be some sort of residue around some of the board as well as above the “observe eprom orientation” there is some kind of material as well, I’ve never seen it but I was just reading the forums on some people having similar issues and it ending up being the ecu

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[steve]

I don't see anything wrong with it that would cause it to read the battery voltage low. Have you tried measuring it at the ECU connector?

You'll see many threads here explaining what conformal coating is.

 

[Tyler Davis]

I don't see anything wrong with it that would cause it to read the battery voltage low. Have you tried measuring it at the ECU connector?

You'll see many threads here explaining what conformal coating is.

Which pins would you suggest testing, I got 7.8v on pin 12 and 25 labeled power supply with battery power and 4.6v on battery power for pin 33 labeled generator g terminal, can’t seem to get a reading for pin 41

Pin 82 for ignition switch is getting 12.0 while battery voltage is 12.4

Mfi relay pin 38 is getting 12.3v

And link is currently reading 12.0v for battery

I tested all the fuse box connections at the fuse box and those were all reading the same as battery as well

My apologies if it seems silly, I just really don’t understand this at all and it’s such an odd issue because it really doesn’t affect anything until I’m past 5500 rpm doing pulls and then my voltage is dropping down to 11.7v and I’ve been through several alternators and a battery trying to solve it

 

[steve]

First issue was the difference between what you measured at the battery and what DSMLink logged. Because there can be resistance in the wire and connections there will be differences in the measured voltages at different points. The resistance should be very small normally and a large drop is an problem. It's also possible that the circuit in the ECU isn't calibrated anymore do to aging or damage.

So that's why I asked to to check at the interface to the ECU to see if it was a wiring or an ECU issue. At the ECU pins 12 and 25 are the positive power inputs where pins 13 and 26 are the power ground.

Getting 7.8v on pins 12 and 25 would be really low with the key on. It should be very close to the battery voltage.

12.0v at ECU pin 82 with the key on is fine but shows that there is some voltage drop between it and the battery.

12.3v at ECU pin 38 shows that there is less voltage drop through the MFI relay coil path.

So the 7.8v measurement needs investigating since that's the power feed the ECU will use to run and where DSMLinks measurement comes from.

Second issue, the voltage dropping past 5500 rpm would seem a problem but there are a few complexities of the 2G charging system that can confuse the results. On the 2G the ECU Pins 33 and 41 are used to control the output current of the alternator. Refer to the FSM and 2G DTM for details.

 

[Tyler Davis]

Thank you, I will check the power supply wires first and see if I can find issues in those

 

[dwb]

Clean and retorque your grounds.