Crazy voltage reading with a digital meter

[junkyardjeff]

Hooked up a digital meter to my 55 Ford that has a 351-w and electronic ignition and getting readings of over a hundred volts but normal with a analog meter,thought it could be something with the alternator so I took off the fan belt and still getting the crazy readings. I am going to be heading to Florida next week and need to figure out what is going on,no plug wires are arching and the only part that was changed on the motor lately is the pick up coil in the distributor.

[kb426]

Where are you testing at? Alternator, battery? etc?

[junkyardjeff]

I have the meter hooked to the battery and getting readings up over 100 volts,I have found that the farther I move the meter away from the motor the lower the voltage goes so I am thinking it could be the cheap pick up coil I installed this summer to get it home.

[kb426]

I would go check the meter on another source to see if it left the building with Elvis. Either another vehicle or if it has ac voltage, a house receptacle. Try shutting the vehicle off and check static voltage at the battery.

[junkyardjeff]

It works fine on other vehicles and as soon as the motor is shut off the reading goes down to 12.7.

[wayne petty]

i have a crazy question.

is that the alternator and wiring harness out of your Crown vic with the gold heated windshield..

there is a relay in that harness that cuts out the alternators connection to the battery and also full fields the alternator while switching the out put to heat the windshield at around 100 or so volts..


just for fun... i got tired of typing it out..

the voltage drop test with 7 steps... percentage of battery charge at the top..

and six additional steps..   test 5 on most fords would go to the positive side of the starter relay stud threads...

http://i.imgur.com/Mo57rdb.jpg

linked so it will open full screen..

test 6 checks the continuity of the alternator output to the battery ..

less than 3/10ths of a volt on most with the test 1 voltage over 13.8.. is accepted..  less is better..

post results by number..

1 thru 6..

[junkyardjeff]

Its not the charging system from the crown vic with the heated windshield,I hooked a analog meter to the battery and it showed 14.5 so I figured its not the charging system. To try to figure out why the meter has a crazy reading I first took off the fan belt and it still has the crazy reading so I moved the digital meter away from the motor and the reading got lower when it was moved away from the motor,from what I can tell its something with the electronic ignition causing the crazy meter readings and the only part replaced on the motor was the pick up coil in the distributor.

[wayne petty]

lack of RF shielding in the meter...  or the meter battery going dead..  spark plug wires put out one heck of a corona...


had a crazy expensive fluke 8060A meter read 25 volts on a fresh alternator install.  turned out that the battery was going dead..  as the meter used the stable 9 volt battery as a reference voltage..  my brother who was an recording studio chief engineer and i were looking at it..  going that cannot happen.. the battery would have been boiling..

on monday... both of my meters and my hand held digital scope were acting crazy. could not get a steady reading...   and i was checking dwell on an autolite V8 distributor.. being spun by a drill... all hooked up..  turned out the crimp on ring terminals that are screwed to the JS potter piercing telco clips were loose..  both of them.. i thought i was going insane..   i have had wires fatigue... wires break... meters die.. i never got readings.. you should have seen the CHOP pattern on the scope...  it was a true WTF..

nothing worse than after hours of work chasing down shorts to ground in continuity beep.. putting tools away to go home and both sides of the harness are disconnected...  its still beeping.. i left the leads hooked up to the harness.. but unplugged them from my meter... and the meter was still beeping in my hand..

[junkyardjeff]

I could only hook one lead to the battery to get the meter to start showing some voltage,it was not the battery as I replaced it and since it works fine on other vehicles I have no idea on what is going on.