voltage ?


boost is better!!
I am currently using direct scan on my TR. At a idle my DS reads 12.5 volts and if i check at the back of the alt. it is 14.3. Is this normal or do I have problem? Also on a run the voltage will drop to 11.6 on the DS. Any information would be very helpful , thanks.. I Am using a inverter to run my DS if that helps anything..


Staff member
TurboBuick.Com Supporter!
Remember, DS reports only what the ECM "sees". This is the voltage being read and converted internally, not the battery or alternator.

Steve Wood

Active Member
check the voltage in the orange ecm (battery) wire after the fusible link to see if it has dropped at that point.

also check the the fuse block at a few points to see if the voltage has dropped there.

It is not uncommon to have corrosion in the orange wire and/or some of the splices coming off the fusible links in the wiring harness that causes a high resistance connection.

Another possibility is in the firewall connector.

disco stu

Active Member
I have this same problem. Posted a thread about the same problem. About two volts less inside the car. Not Just what the ecm sees, but everything at the fuse box. At WOT it drops to 10.5 as seen on DS. Right when TPS goes high voltage drops. Checked voltage at alternator with a voltmeter, rock steady 14.2 WOT. I replaced my fusible links, checked for corrosion at fuse box bulkhead (none), and checked for corrosion at splices in engine harness(none).
:confused: :confused: :confused:
The resistance in mine is in the fuse box maybe? Wonder how much of pain it would be to be replaced.

I hope you find your problem, still looking for mine.
Sorry I couldn't be of any help.

Steve Hill

New Member
What you might do is take a digital volt meter...
...one lead to the alternator post, the other lead to the positive battery terminal.
You are looking for voltage discrepancy, or 'voltage drop'.
Normally, you would not see any significant voltage. If you do see something like 1.0 volt or more, you may have a bad connection between the alternator and battery.
Keep working your way through other electrical components.

You should also do this test between the negative battery terminal and engine or chassis ground.
Once again, normally you would not see more than a few hundredths, or, couple tenths of a volt. Uh, unless there is a high resistance connection somewhere, that is.

disco stu

Active Member
Hey Steve, is there any body grounds we need to be checking? Other than the five grounds on the back of the head?

Steve Hill

New Member
I really don't know where all the grounds attach, but there is the one primary battery ground cable that attaches to the front of the engine block somewhere below the turbo.
There is also another, smaller gauge ground wire that goes, um, uh er, somewhere..... sorry, I've never chased it out.
However, I can tell you I've seen a situation where this one, small wire was carrying the entire electrical load because the much larger, primary battery cable was disconnected!
This particular car (mine, I'm embarrassed to say) even cranked normally....don't ask me how!


Daily Driver
I had the same problem as Steve H. with the GN when I bought it.

Ran off the aux. grounds for a week until I checked it over and found no bolt in the turbo bracket where the big main ground wire goes. :eek:

Thankfully the engines are low compression. ;)

disco stu

Active Member
This is a bump to the top. I am still having the same problem. Did you find oyur problem Salvage?
Here is what I have done......

Voltage drops on charge back wire a, Batt + and - wire. All are very fresh anyway. Nothing changed when the old ones were replaced.

Ground stretcher kit, and checked grounds. Almost no resistance.

New fuse links.

Alt. has been replaced with 140A.

Checked splice in main wiring harness. My manual is at work, and have forgotten #. No voltage drop there from fuse links to fuse box bulkhead.

With a Fluke in my lap with leads going to the alt. at WOT voltage is rock solid 14.2.