LeadFoot

While my 91 is at idle in drive the battery and oil pressure gauges read really low. The oil pressure gauge reads about 10-15 psi and the battery gauge reads about 10 volts, but with a volt meter I am seeing 12.7 volts. I am also seeing a flicker in the LED display when accessories turn on. On the road, everything seems to read normal. This has just started within the past few weeks. What do you think?

jackdaroofer

:cheers:

Not sure where or how you are getting your voltage reading, but at idle, volts should be 13 +

How long has this been going on?

How old is the battery?

robtx

What's the voltage on the battery with the car off?

Rick Williams

my uneducated experience with simular symptons was to replace the battery,which I did, but that was not the problem..I replaced the alternator..corrected the problem..

LeadFoot

The battery is a three year old DieHard and reads about 12V with the car off. I have been suspecting the alternater, but it has only been 8 month's since I replaced it. The 84-91 C4's seem to eat them but that just seems really quick. The heat really makes the difference in the readings, that is what makes me suspect the alternater. All readings are normal when the car is cold and when the car gets in traffic I notice the problem. What do you think?

jfb

Engine idling and a/c on , or a heavy electrical load can tax the alternator because it cannot deliver it rated current at such low rpm and the battery will assume most of the load causing low voltage. The big difference between your measurement (12.7) and the dash (10) may be due to ignition switch resistance, or marginal voltmeter performance with low operating voltage. Also, low operating voltage will make the dash flicker. Raise the rpm to 1500 or higher, and the battery voltage (your voltmeter) should be 14.3-14.7 cold, 13.3-13.7 hot. If the alternator is not charging, then the red battery light will light on the dash. If you measure 13.3 to 14.7 across the battery at 1500 or higher rpm, then your alternator is ok. If you are running a 5W** engine oil, in the summer you could see low oil pressure at idle.

jackdaroofer

I too had an alt go out in about 8 months

The first time I went with what I could get right away, a second class rebuild

This last time, 18 months ago, I got the NAPA first class rebuild...only costs $20 more and they put all new parts in it, not just replace the parts that sem worn out

You are right, heat kills thses things and the cooling vanes are set up to suck hot air in from over the exhaust manifolds.

Stuck in stopped traffic one day I had my voltage drop to below 13..I Opened the hood and within minutes it climbed back to 13.5

Jack