Volt meter gives wrong reading

robertj · 07-24-2005, 07:37 PM

So while trying to troubleshoot my 914 probs, I tested the battery voltage while it was running and found it to be at 13.5, yet my center console voltage mater was reading in between 10 and 12 volts. Can I not trust the center console meter? Is this telling of yet another problem in the car that I need to track down? Do these gauges need calibrating? etc, etc. :-)

Lyle · 07-25-2005, 06:49 AM

You might expect a slightly lower reading since the gauge picks up its signal up under the dash but not that much lower!. Check the condition of you grounding points under the dash and where your grounding wire on the tranny connects to the body. Also use a good digital voltmeter to measure the voltage using the same connections that your console voltmeter uses. This will help determine if the console voltmeter is good.

Dave at Pelican Parts · Dave at Pelican Parts's Garage

The console voltmeter is never good. It's mostly there for entertainment value; it is very nearly worthless as an indicator of the health of the charging system. Mine reads 12V at best, less when any lights are on. (Headlights, turn signals, brake lights, etc.) The voltage across the battery terminals, however, is 14V.

When you get used to how the voltmeter behaves, you can use it to tell when a light bulb has burned out. "Hey, the gauge only drops to 11.5V when I put the brakes on--I must have one bad brake light bulb!" And when it starts dropping even lower than you've seen before, then you know your charging system is bad. But that's only a very gross indication; you generally only notice that when the charging system has completely failed and you are running off of an almost completely-discharged battery. (Don't ask how I know that...

)

--DD

914GT · 07-25-2005, 08:52 AM

When I did my V8 conversion I wired the voltmeter to a terminal strip mounted next to the battery. Now it normally reads about 13.5 when the engine is running. The voltmeter itself is good, it's just the stock wiring location that sucks. I think it was originally wired off the brake light switch.

velomann · 07-25-2005, 06:54 PM

robert,
does this mean your battery is holding a charge and you got it running?

robertj · 07-26-2005, 08:15 AM

Not yet--- I charged it, ran it around the block, and about halfway it started running really rough again, including at idle and felt like it was going to die. Te battery still read 13.5 ish though. I had planned on replacing fuel lines and the fuel filter in hopes of maybe curing some of this. Upon doing so I found that one of the injectors had a cracked plastic cap (the green part at the end of the injector) and so I will be replacing that this weekend. Maybe that will fix the running rough problem. I have a feeling that I will still have some electirical issues though- the heater blower doesn't work for one. Not sure if it's the motor itself, or the wiring. I wonder if I can hook it up directly to the battery just to see if it works?
Will keep you posted- thanks for asking! :-) It would be really nice to have this thing up and running before summer is over!!

Dave at Pelican Parts · Dave at Pelican Parts's Garage

That is one way to test the blower, hooking it up directly to the battery.

You can also test the connections to it--check for 12V across the two wires when the heater handle is all the way up and back. The typical failure mode of this system is that the switch under the handle gets unplugged or corrodes to where it won't close any more. I'd check that first. Ground the wire going to the switch, and with the ignition on, see if you can hear the fan run.

--DD

velomann · 07-26-2005, 01:39 PM

hey robert,
i know this may seem very basic, but double check your fuses and relays on your relay board for the blower fan as well to maker sure they are working. like we talked about on saturday at the jw meet, the relay board can have some gremlins all its own!!! let me know when you get it home.

robertj · 07-26-2005, 04:10 PM

Thanks velomann- I will be doing some electrical checking this weekend (along with hopefully installing a new injector). I don't have the Hanes manual in front of me at the moment, but for some reason I was thinking that the fuse for the blower motor was shared by another component, and that componenet (whatever it is, I forgot) was working, so I had ruled out a fuse as the culprit. But I might have all of that wrong...
I'll let you know when I get it home, and thanks again for all of your help.

On an aside- do you know how to get in touch with 'Bill'? Not sure if you know him, but he was the guy with a minivan just outside of the fence where the vendors were. He was selling a few parts that he hadn't brought with him, and I forgot to get his phone #. I believe he lives up in bellingham.

Thanks!

robertj · 07-26-2005, 04:12 PM

BTW will the heater blower fan run with just the ignition set to on and the engine NOT running? :-) The questions never end....

Dave at Pelican Parts · Dave at Pelican Parts's Garage

The blower fan doesn't care about the engine running, just the ignition being on.

--DD

velomann · 07-26-2005, 09:27 PM

it is funny that you ask that about bill....there is a thread on 914club right now with the same question and he pops up on there. i do not know him by car or name, maybe by face! how did it go today with the repairs??

robertj · 07-27-2005, 12:42 AM

Heh, that post is from me too :-) I should have stuck with the same name, and not confused everyone!

I haven't been able to work on the car since last weekend, I'll hopefull have the new injector and get everything hooked up again to test it out on Sunday, and with any luck will be able to drive it home. Will keep you posted. It's killing me not to have it here at my house to work on, and being too busy this week to get over to west seattle to work on it.
(Although having a girlfriend who's willing to bring beer out to me while I work on it might be incentive enough to leave it there to work on!)

robertj · 08-02-2005, 10:24 AM

Hmmm i discovered that the volt meter reads ZERO with the lights on, I know it's inaccurate, but can it be that off??

914GT · 08-02-2005, 10:34 AM

Quote:

Originally posted by robertj
Hmmm i discovered that the volt meter reads ZERO with the lights on, I know it's inaccurate, but can it be that off??

With the lights on, do your brake lights work?

Dave at Pelican Parts · Dave at Pelican Parts's Garage

That is sometimes caused by a blown fuse, either #8 or #9 in the fuse box.

--DD

robertj · 08-03-2005, 08:23 AM

Brake lights still work with headlights on, I'll check the fuses though. Thanks!

914GT · 08-03-2005, 12:13 PM

That's interesting, because the voltmeter picks up 12V at the brake light switch. Maybe it's miswired

robertj · 08-03-2005, 12:44 PM

Wouldn't surprise me at this point....

robertj · 08-04-2005, 07:28 AM

I noticed that when I turn on the lights my engine drops by about 150 rpm. Not normal, right?