Cascade Crew

fiveoformula

Well me to. Rolling Eyes

Working on an '87 Firebird with a 305 4bbl.
Car started and ran fine about a week ago but all the sudden wouldn't start one morning, I then jump started it and let it run for a bit, while doing so I noticed the volt gauge needle half way between the 8 & 13 volt marks. I ending up charging the battery up and checking voltage at the power post on the alternator while running the car (with the freshly charged battery). it was getting 9 or 10 volts there at the time so I thought this was a text book bad alternator so I got a new one with no change. soon after I noticed the battery leaking so I had it charged and tested and it tested bad.

So now I have a new alt. and battery, and the really interesting thing now is my battery voltage reads 12.6 at the posts right now but it will not crank without jumper cables hooked up to another battery. Any thoughts?

aaron_sK

QwkTrip · Posted: Mon Feb 06, 2012 7:16 pm Post subject:

What do you mean by doesn't crank? Solenoid doesn't throw, or solenoid throws and starter won't turn engine?

fiveoformula · Posted: Mon Feb 06, 2012 7:18 pm Post subject:

Starter does not turn engine, I also checked voltage between battery ground and the post at the starter, and its the same 13v.

QwkTrip · Posted: Mon Feb 06, 2012 7:21 pm Post subject:

You might have damaged the starter when the battery voltage was low. Low voltage causes solenoid chatter and that can wreck the starter contact disc in a hurry. Opening solenoid contacts at slow starter speed (or stalled) is really damaging because the starter current is so high and spark energy is very intense. Might take a look at the starter solenoid high current contacts.

It's basically another form of high resistance somewhere in the circuit, like what Aaron is pointing you to look at.

chevymad · Posted: Mon Feb 06, 2012 7:26 pm Post subject:

Hook your voltmeter from the positive terminal to the battery cable lug at the starter. Now try to crank the car while watching the meter. Do the same for the negative side.. one lead on the negative post, the other on the engine itself.

These readings should both be less then a volt. Optimally they should be near 0. This is called a voltage drop test. If either reading is higher then 1v then you have a bad connection or a bad cable.

fiveoformula · Posted: Mon Feb 06, 2012 7:41 pm Post subject:

Ok I'll have to rig up a way to do that with my meter.
Another thing that may be worth noting is that my battery voltage with the key off is 13v, if I just turn the key to the on position, voltage rapidly goes down. Its like counting down the new year.... 10, 9, 8, 7, 6 etc. but then I turn the key off and voltage goes back up slowly to where it was.

QwkTrip · Posted: Mon Feb 06, 2012 7:57 pm Post subject:

I would take the battery back and have it load tested to make sure it meets spec. If the battery does pass, then buy a clamp-on ammeter on the way home and use it to find the short in your electrical system.

fiveoformula · Posted: Mon Feb 06, 2012 9:21 pm Post subject:

Well I did have them charge and load test it, Tested good. Put back into car, starts, runs with 14v. 13.8v with headlights on. For how long I don't know... I think I'll limp it to work tomorrow to see if I can do more testing there. The last time it ran it started just fine and eventually the radio and heater stopped, lights got dim and it wouldn't start back up after I shut it off.

fiveoformula · Posted: Wed Feb 08, 2012 7:22 am Post subject:

As for an update, ever since I had the battery fully charged up the car has been starting fine. I discovered my craftsman multimeter reads roughly 1.5v high when compared to a VAT40 machine at work Rolling Eyes

. So when it was reading 12.7v, it was really 11.2-ish.
Im thinking maybe the battery wasn't fully charged when I bought it and the alternator couldn't keep up running the heater full blast and headlights?

fiveoformula · Posted: Wed Feb 15, 2012 4:52 pm Post subject:

Well I drove the Car to autozone after I had to charge the battery again... The guy there put his tester on it and goes "Whoa, you need a new alternator buddy." Rolling Eyes

I then told him that it's a brand new unit I just bought from his store, so he gave me another one to try. Love these guys that think they know everything... It would be nice if thats the problem but im not betting on it. I'll put it on and see what happens though.

iansane · Posted: Wed Feb 15, 2012 11:46 pm Post subject:

Did he say why you needed a new one? Low voltage output? Bad diodes? Too much bacon grease?

fiveoformula · Posted: Thu Feb 16, 2012 8:04 am Post subject:

Yeah he said it wasn't putting out any voltage, went really low when I turned the headlights on. But I already knew all of this... Back to checking wiring, New "good" battery and good alternator, something isn't connected right.

QwkTrip · Posted: Thu Feb 16, 2012 7:28 pm Post subject:

Did he measure charging current? If battery is discharged then voltage will be below specification. The battery drags down the whole system.

If you keep getting alternators that "don't work"... then why don't you think you just have incorrect or bad wiring in the car for the alternator?

fiveoformula · Posted: Thu Feb 16, 2012 8:57 pm Post subject:

I figured it out, the car had a check engine light on that I assumed was unrelated to the charging problem... When I tried to retrieve the flash codes nothing happened, checked for power to the OB1 connector and had nothing. Checked the wiring diagram, it showed power comes from the 10A ECM fuse... which was blown. (didn't look blown but no power could go thru it). Embarassed

Thought I checked over those fuses well. This will teach me to be more thorogh.

QwkTrip · Posted: Thu Feb 16, 2012 9:01 pm Post subject:

Gotta wonder why the fuse is open?

fiveoformula · Posted: Thu Feb 16, 2012 9:09 pm Post subject:

I have been doing alot of work to this car, could have easilly bumped something that arc'd, not sure why it blew but I will keep an eye on it. If it blows again I'll check for shorts on that circuit.

fiveoformula · Posted: Thu Feb 16, 2012 9:12 pm Post subject:

Alphius · Posted: Thu Feb 16, 2012 9:47 pm Post subject:

I am confused. Won't the car not run at all if the ECM fuse is blown? Regardless, glad it's fixed now.

aaron_sK · Posted: Fri Feb 17, 2012 6:24 am Post subject:

The ECM gets it's power on more than one pin and from more than one fuse. I have found most of it to actually be fed by the fuel pump fuse (the one in it's own holder next to the battery).

If you're curious: