HELP!! Random no start

[offwhiteghost]

UPDATE:

[I don’t know if this is related but if I turn on my lights my radio will lose sound.

Any ideas?] + PO had an aftermarket alarm that was disabled.


So heres the deal,

I have an 89 325i auto with a random no start. It will start fine for 3 days then just wont but if i hook it up to a charger or jump it starts fine. Battery is fine and measures 12.4 volts even when it wont start. Both battery connectors replaced.

Could it be the starter relay and where is the relay located?

Please advise

[jlevie]

A battery at 12.4v is only at 75% charge. And if the battery is old it may not be able to deliver sufficient peak current to start engine.

Have the battery tested, of if more than 4 years old replace it. Also check to see if the alternator is working properly.

[offwhiteghost]

A battery at 12.4v is only at 75% charge. And if the battery is old it may not be able to deliver sufficient peak current to start engine.

Have the battery tested, of if more than 4 years old replace it. Also check to see if the alternator is working properly.

The battery is 2 yrs old and the autoparts store tested it ok, the alt gives 13.6 volts

[BrassDrummer]

A battery at 12.4v is only at 75% charge. And if the battery is old it may not be able to deliver sufficient peak current to start engine.

Have the battery tested, of if more than 4 years old replace it. Also check to see if the alternator is working properly.

I'm sorry, but a battery at 12.4V is not 75% charge. Each battery Cell has 2.1V, and 6 Cells. That adds up to 12.6V. 75% charge would be 9.45V. At 12.4V, your battery is still very good if it can hold that charge over an extended period of time.

[BrassDrummer]

Does it crank and not start? Or just nothing?

If it cranks and does not start, first off, check all your basics. Fuel pressure, Spark, and compression. If it has all three of these, check the Connector underneath the intake manifold. It is a round connector. This can often times become corroded or even loosen itself up over time. It is hard to diagnose no starts over the internet. But the more info you give us the better.

[offwhiteghost]

Does it crank and not start? Or just nothing?

No crank, lights work but no sound.

[jlevie]

I'm sorry, but a battery at 12.4V is not 75% charge. Each battery Cell has 2.1V, and 6 Cells. That adds up to 12.6V. 75% charge would be 9.45V. At 12.4V, your battery is still very good if it can hold that charge over an extended period of time.

That would only be true if you had a dead cell.

Extracted from a battery manufacturer's site:

%chg Voltage S/G
100 12.7 1.265
75 12.4 1.225
50 12.2 1.190
25 12.0 1.155
0 11.9 1.120

Sulfation of batteries starts when specific gravity falls below 1.225 or
voltage measures less than 12.4. Sulfation hardens the battery plates reducing
and eventually destroying the ability of the battery to take and hold a
charge.

Only 30% of batteries sold today reach the 48-month mark. In fact 80% of
all battery failure is related to sulfation build-up. This build up
occurs when the sulfur molecules in the electrolyte (battery acid)
become so deeply discharged that they begin to coat the battery's lead
plates. Before long the plates become so coated that the battery dies.

[dnguyen1963]

Theoretical (BrassDrummer) versus Practical (jlevie) argument on battery charge state...I'll go with Practical any day.

[offwhiteghost]

Im about to pull my hair out, any e30 master out there wanna take a look at my wiring and make some $$$?

[Gregs///M]

Pull the relay out from the steering column and clean its contacts. Check the Engine to Chassis ground cable that runs from the oil pan to the frame rail on the drivers side. If this cable is dirty, corroded or has a poor connection, you will have many electrical problems including the starter circuit. Check my signature for more info on that cable, I sell replacement cables all the time.

If your starter has never been replaced, I would consider it. Better to replace it on your own time, than be stuck on a trip needing one. Most often the problem lies in the starter solenoid but replacing the starter and solenoid is just as much money, so I recommend both.

[offwhiteghost]

I cleaned the contact points and replaced grounding wire from the block to the engine.....

No start again today.

[Gregs///M]

For the no start problem, I would suggest you bite the bullet and replace your starter and solenoid. I had no start when engine was hot. I finally decided to just replace the starter and solenoid and it no longer fails to start.

During your no start period, try probing the smaller terminal on the starter solenoid. If it gets 12 volts during cranking but it does not crank, your solenoid has failed. Cost of the solenoid is just as much as a new starter so might as well replace both.

For your radio problem, it is not related.
Since you have after market head unit, someone wired it wrong. Your illumination wire is wired up to your head unit's ground. Common mistake for amateur installations because the illumination wire will show "ground" with the lights off and key off. Once the lights are turn on, the state will turn from ground to 12 volts. This is why your head unit shuts off when the lights turn on. Disconnect your ground wire and run a new one to chassis ground.

[offwhiteghost]

No Start again today.

Took voltage at the starter facing the car, Diagram below. Car jumped started no problem and battery is at 12.35V

No Start by offwhiteghost, on Flickr

[jlevie]

That being the end of the starter solenoid, the lug on the left side is the connection from the solenoid to the starter, the lug on the right side is the connection from the battery to the solenoid (starter power) and the small lug at the top is the START signal from the ignition switch. The START signal must go to 12v when the key is turned to start to engage the solenoid.

[offwhiteghost]

The START signal must go to 12v when the key is turned to start to engage the solenoid.

The switch terminal stays like 0.5V when the key is turned, i think the aftermarket alarm that was "disabled" is at fault.

It now needs to be jumped almost everytime