Battery/starting problem

[zajo]

So occasionally my '90 C2 ended up with rather low battery charge and wouldn't start but I always assumed that I forgot a light on or something, because when I jump start it it would go without problems for months (I do drive the car it never sits for a long time.)

One evening, 40 minutes *after* a short drive without problems, the car didn't start. After a few attempts the battery died completely, and since jump starting didn't help I towed the car home.

Then, assuming the battery was bad, I got a new battery. The new battery got the engine cranking like crazy but in 5-6 attempts it still wouldn't start, so I gave up.

That was two days ago.

Tonight, after reading some related posts here, I decided to check the DME relay. And what did I find? The brand new battery that was happily cranking the engine two days ago is *completely* drained! In two days!

Someone please help!

Thanks,
Zajo

[Newsboy]

Is it possible that you have a trunk or engine compartment or glove box light that is not going off and draining your battery. You need a multimeter to find where the drain is coming from. You can start pulling fuses, and see when the drain decreases or stops. Strange that you cannot jump start though. Did you put in a new DME relay?

[rgreeny]

Have your alternator checked. I ran into the same problem and had to replace the alternator. That fixed it. It's worth a try.

[jpachard]

Somewhat similar situation and my problem ended up being the voltage regulator. THat was an easy fix and less costly than an alternator.

[zajo]

Battery is now charged. Replaced the DME relay with a spare I have from the previous owner, it was in the glove box in a box that had "new" written on top. I hope that means that it's a new DME relay! Anyway, the car didn't start with either of the two DMEs I have. :|

jpachard: can you give me more info? How do I go about checking if it is the voltage regulator?

rgreeny: similar question, is there a way for me to check the alternator myself?

Thanks a bunch guys I wouldn't know what to do without you!

--Zajo

[jpachard]

Zajo, My voltage regulator failed in an odd way which might be your problem too. What you will need to do is get a voltmeter and check the battery when the car is off. Then start it up and see what the reading is, it should be approx 13.5VDC. After that drive the car around for a bit and check again. My failure was intermittent which made it difficult to diagnose. I figured it out when I stopped one time to check and the voltage was ~6.5VDC.

Cheers, James

[zajo]

Ah. But my car doesn't start. :|

[jpachard]

OK, So I assume it turns over now. Have you checked that you are getting spark to the plugs?

James

[Traveller]

Originally Posted by zajo

The brand new battery that was happily cranking the engine two days ago is *completely* drained! In two days!

You need to do some simple tests that require a Digital Multi Meter (DMM) with a DC current capability of 10A. They're available for under $50.

To find out if anything is draining the battery...

Set the DMM to DCA 10A.

Disconnect the negative terminal of the battery and insert the DMM leads in series with the negative ground cable and the negative post of the battery.

You should see all zeros. If so, set the DMM to DCA 200 mA. You should see maybe 20 mA; not much more (make sure all your interior and hood compartment lights are OFF).

If you see larger numbers such as 100 mA for example, you then start removing fuses one at a time till you see the reading go to near zero. That fuse is the circuit that is drawing current.

Once you start the car...

Set the DMM to DCV 20V.

Measure the voltage across the battery with teh engine running and the headlights on and the engine reving at about 2000 RPM. You should see your voltage at about the low 13V up to 14.4V maximum...or at least increasing if the voltage is lower.


Thats why installing a voltmeter in the car is such a good idea. It tells you what your charging system is doing. An ammeter is far less useful.

[zajo]

Traveller: thanks for your help, I will do that as soon as I get the car starting again.

Update: I used an inductive light to rule out electrical problems with the ignition (unless someone tells me that despite the light firing there might be a problem.)

So what's next? Is the fuel pump easy to reach? How can I make sure that fuel is reaching the sparks? It's still cranking like crazy but not starting :|

Thanks,
Zajo

[Traveller]

Originally Posted by zajo

So what's next? Is the fuel pump easy to reach? How can I make sure that fuel is reaching the sparks?

As on some cars, the fuel pump can be heard operating. I haven't had my Porsche long enough to know if you can on these cars.

Have you tried by-passing the fuel pump relay so that it is on all the time (for testing purposes)?

Next, take a fuel pressure reading. On the 993 there is a test port on the driver's side fuel rail; you might have an identical port on your model. You'll need a new cap.

Are the injectors getting a signal?

[zajo]

Alex, how do I check if the injectors are getting a signal? Also, I suppose I need a special tool to take fuel pressure reading right? Is there a way to check this easier? Like, unplug a hose, see if it sprays gas or something?

[Traveller]

Originally Posted by zajo

I suppose I need a special tool to take fuel pressure reading right?

A fuel pressure gage. I bought mine at Harbor Freight and modified an OEM fitting to connect to the gage kit (it comes with fittings as well).

HF Fuel Injection Pump Tester - #92699-3VGA - $19.99

For example, you could use the OEM cap as a fitting and connect the fuel gage to it after you modify it.

Originally Posted by zajo

Is there a way to check this easier? Like, unplug a hose, see if it sprays gas or something?

Before buying the pressure tester, sure. I loosened a banjo fitting on the fuel filter of my Honda and gas sprayed out. I had some kind of pressure, but do not know if I had enough or too much.

As for a signal to the injectors, I never had to do that check but I would assume you need a scope for that.

Do the easy no-cost checks first.

[zajo]

Thanks to some excellent threads on this message board, I think I need a new fuel pump but I hope someone confirms this.

I already had figured out that I get spark and since the engine is cranking fine, there seems to be a problem with fuel delivery. I read that with turning the key to the ON position, the DME relay turns on the DME, and then after the DME detects that the engine is cranking, it sends a signal to the DME relay to send juice to the fuel pump through fuse 34.

So... since at fuse 34 I get zero volts before the engine starts cranking, then 12 volts when it starts cranking, this means that the fuel pump should be getting juice yet the car doesn't start. (I was thinking to connect the fuel pump directly to the battery as a test, but it's so tight under there that I can't get with a wire to the + port of the pump at all.)

I should probably take a fuel pressure reading just in case but I don't know how. I have a pressure gauge kit but I don't know where to connect it. Can someone tell me how to use this thing, or should I not bother and just buy a new fuel pump (90 something K miles on the car)? Also, is there a good step-by-step description for changing a fuel pump?

Thanks a bunch, I would be completely lost without this forum!!

--Zajo

[bazar01]

Originally Posted by zajo

So... since at fuse 34 I get zero volts before the engine starts cranking, then 12 volts when it starts cranking, this means that the fuel pump should be getting juice yet the car doesn't start. (I was thinking to connect the fuel pump directly to the battery as a test, but it's so tight under there that I can't get with a wire to the + port of the pump at all.)


Thanks a bunch, I would be completely lost without this forum!!

--Zajo

There is another way to power up the fuel pump and injectors for test purposes only. You will need a triple jumper wire.
The DME relay has two sets of contacts to supply 12V to injectors and fuel pump.
Terminal 30 is the battery voltage
Terminal 87 for injectors
Terminal 87b for fuel pump.
So if you pull out the DME relay, and looking at the socket side,
If you put a jumper across 30 and 87b, it will turn on the fuel pump.
If you put a jumper across 30 and 87, it will power up the injectors.

[zajo]

It was the fuel pump indeed. I changed the fuel filter as well. The only thing that caught me off-guard was that since the fuel lines were empty, it took 3 good solid cranks to get her going but it's all good now. Thanks everyone for the help!