Scanmaster and Datamaster read low 12s or high 11s on the voltage but taking the reading at the battery and at the rear of the alt reads 13.0, as well as the distribution block. Why is this and what can cause this?

I am diagnosing a miss at 5600+ and this one peice that I need to clear up before attacking the fuel pump or opti.

I do run an MSD 6AL, connected and disconnected, same results. I have a few other small items that are one but I should still see 13+ volts. Where is the descrepancy coming in at?

 

That reading seem alittle low if the car is running.... It should read close to 14.2 volts.. Your alt may be going out???


93Z Will

 

Anyone else have ideas?

 

The ScanMaster is reading the voltage at the PCM. I've noticed the same problem. My ScanMaster is reading in the high "12's", and the voltage seen by my MoTeC computer is logging at 13.5-13.8. I asked the same question a long time ago and nobody ever came up with the answer. Would appear to be either a significant voltage loss in the wire to the PCM, internal voltage regulation at the PCM, or an interface problem in the programming of the ScanMaster. And neither the ScanMaster or the MoTeC reading agrees with the voltmeter on the dash....

 

Injuneer: what are your dash readings?

What should the voltage be a the battery at idle and the tap off the alt?

I am leaning towards a bad alternator and possibly a battery that is for junk...