PCM Voltage lower then Battery
10-10-2014, 01:44 AM
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PCM Voltage lower then Battery Well I've been doing some upgrading.
I put a truck (kg3) alternator in the car as well as the big 4 (alt to battery (+), chassis to battery (-), engine to battery (-), and Battery to fuse junction box (+). All lines are 0/1 gauge except the battery to fuse junction box which is 4 gauge.
Here's my issue. At cold start with a voltmeter I see 14.7v at the battery. At the fuse box I see 14.4v. At the PCM the dash gauge reads over 13 but pcm shows voltage at 13.3v per my scan gauge as well as HPT.
After a good long drive the dash gauge is hitting the red, the pcm shows voltage at 12.0v. My battery reads 13.4v and the fuse box shows 13.1v. This is with lights, stereo, and ac on. If ac and lights are turned off the pcm read 12.4v, the battery reads 13.8v and the fuse box reads 13.4v.
Why is the PCM showing such a low output?
Only thing I can think of is the stock wiring coming from the fuse box is worn. My understanding is the two orange cables on PCM wire harness are constant power through a 10amp fuse. Should I cut this and wire directly to the battery with new cable and have a 10amp fuse inline?
Looking forward to suggestions and info.
Thanks!
I put a truck (kg3) alternator in the car as well as the big 4 (alt to battery (+), chassis to battery (-), engine to battery (-), and Battery to fuse junction box (+). All lines are 0/1 gauge except the battery to fuse junction box which is 4 gauge.
Here's my issue. At cold start with a voltmeter I see 14.7v at the battery. At the fuse box I see 14.4v. At the PCM the dash gauge reads over 13 but pcm shows voltage at 13.3v per my scan gauge as well as HPT.
After a good long drive the dash gauge is hitting the red, the pcm shows voltage at 12.0v. My battery reads 13.4v and the fuse box shows 13.1v. This is with lights, stereo, and ac on. If ac and lights are turned off the pcm read 12.4v, the battery reads 13.8v and the fuse box reads 13.4v.
Why is the PCM showing such a low output?
Only thing I can think of is the stock wiring coming from the fuse box is worn. My understanding is the two orange cables on PCM wire harness are constant power through a 10amp fuse. Should I cut this and wire directly to the battery with new cable and have a 10amp fuse inline?
Looking forward to suggestions and info.
Thanks!
