Need some help from the experts once again
928 S4 5 speed 1989

I haven't driven my 928 for a few weeks and when I tried to start it this morning it was totally dead.
I measured the Battery voltage and got zero. I also check resistance between the two Battery posts and got 7 Ohms, so I think it was shorted.
Since it was a fairly new Bosch Battery, I took it to Pep Boys and they replaced it under warranty.

The problem is that when I tried to install it, I got quite some sparks on the new battery and some weird noise underneath the car.
I suspected of maybe some short somewhere (alternator wiring or starter?)

I lifted the car over ramps and inspected the harness / cables and cannot see anything obviously incorrect. Besides the car worked fine a few weeks ago.

Any insight about what it can be and recommendations about testing something?

Thanks in advance

 

That doesn't sound good, under the car the pos cable runs to the starter and then to the Alternator and then splits to the Anti-lock brake system and to the Jump post.

With the battery disconnected, you could disconnect (isolate) the 14 pin and pos cable going into the CE, and troubleshoot to see if any of three items I listed above have an issue, place an Amp gauge in-line and re connect the battery, see what the draw is.

Like any problem, break it down to smaller bits and go from there, someone here may have a better suggestion, be careful as the three above mentioned items are not fused!

Dave

 

The critical question will be around whether the new battery was installed with terminals reversed. Battery positive terminal goes towards the front of the car.

Meanwhile, something drained your old battery. The possibilities are many, the diagnostic steps are systematic, isolating all the possible causes and reconnecting them one by one as you watch current draw on your voltage source. When I suspect a serious short-circuit as you seem to have, I'd have a smaller battery for testing so available current is limited, and/or a fuse in series with a connection to protect the wiring.

Noises under the car while reconnecting could be almost anything especially if the battery was backwards. First candidate in that case is the alternator, where a matrix of diodes is used to convert the alternating current from the alternator windings into direct current to run the car. With the battery backwards, those same diodes route all the battery current backwards through the stator windings to ground, essentially making the stator windings a heating coil. The diodes are rated for, lets say, 150 amps. The new battery supplies 650 or more cold-cranking amps, so the diodes and windings wouldn't last long at all before being damaged.

On your car, the alternator sits, electrically, between the positive terminal on the starter and the engine-side connector at the jump post. There's another lead to the ABS power connector on the front left, under and immediately forward of the power steering fluid reservoir. Lift all those connections. Then, with a maybe 5 or 10 amp fuse in series with the ground connection at the battery, reconnect the wires at the starter end. Then reconnect the battery through the fuse, and see if the fuse survives. Roasted/shorted diodes will pop the fuse. If the fuse is intact, plug your current meter into the fuse holder and reconnect the disconnected cables one by one. ABS seldom causes trouble, so that one first. Then the fuel pump line and each cooling fan wire one by one to the positive battery post. There should be no current flowing through any of those. Finally, the engine-side terminal to the jump post will power up the central-electrics panel. If there's a serious draw as you do that, you have the option of mapping all the fuses, and restoring them one by one to see where the power is passing through.

 

I think so far everything sounds completely normal... But I don't know what the sound was...

When you connect the battery - usually the hatch is open and the interior lights are on - on an '89 thats about 50W of interior lights (so about 40A instantaneous current when the filaments are cold).

Sparks are normal under these conditions if you aren't careful in connecting quickly to the posts.

When you test for ohms you will always have cold filaments so 7 ohms is actually a quite high value (too high - you may have measured it wrongly).

[edit] If you mean you tested across the battery posts on the battery itself - then 7 ohms is also way to high - orders of magnitude too high in fact - it was basically OC (for a battery anyway).

I have no idea why the first battery died - probably bears some inventigation to protect this one from the same fate - however I think everything on reconnect was probably OK. I fail to see any concern from a few sparks... quite normal to me.

Alan

 

More:

http://www.harborfreight.com/30-amp-...ter-67724.html This circuit tester is a perfect accessory of chasing current drains. I have an in-line fuse holder that this will plug into, with alligator clips on the fuse-holder wires. The clips then go to ground on one side, and the battery grround strap (isolated from ground). With the tester plugged in, it's effectively a small 30-amp capable ammeter. With the 14ga fuseholder wiring I have, I won't put anything bigger than a 20 Amp fuse in the tester socket.

 

Wow 12 bucks! That's a must have, thanks dr bob !

 

Thanks for the input so far folks.

The Battery (posts) are placed correctly, so I will try to follow the instructions to check for issues as indicated. I will have to read this a few more times as I am electrically impaired.

This car had a bad battery when I bought it and it had over 100 mA drain. I replaced the battery a while back and ran the drain tests described on some Rennlist threads. I isolated the issue to an aftermarket Audio Amplifier.
Since then I disconnect it (amplifier) from power, but left it there in case I ever wanted to use it again or to use on trips, until I have it replaced.
The drain went down from over 100 mA to about 36 mA, not quite what I read on the threads (20-30) but quite good, I think?

I am very puzzled that this happened with the car sitting, i.e., I used the car normally a few weeks ago.

Thanks

 

Ah, one more thing. Last item I messed up with was I installed a pair of Fiamm horns. I used the car original horn wiring to connect one of the horns and then spliced the + to the other one. As the horns were also working fine (at least apparently) and only when intended, I would think this would not cause issues, right?
Thanks

 

The horn connections were fine - didn't cause this based on how you described doing it.

alan

 

Update

I think I might have found the issue, but almost had a heart attack in the process...

When I replaced the Motor Mounts a while back, I believe I routed the Positive Cable incorrectly. Please see picture below. It stayed in between the Mount and the Exhaust. So I believe it got in contact with the Exhaust and after melting a bit after my last ride, it might have made contact between the Positive and the Ground (Exhaust) and shorted. This would explain why it worked fine last time, but did not this morning.

So, I moved the Cable away from the Exhaust and tried to connect the Battery again. Everything seemed fine. No significant sparks or weird sounds. I was happy.

But....as I entered the car and placed the key into the contact to check the gauges, the car started to crank to start. I removed the key and - what the heck !!@@#- it continued to crank, so I rushed to the Battery to disconnect the cables and obviously they did not come out right away. Holy cow!

Now, please stop laughing and tell me if this Cable has more than one lead , so it melted and made contact internally and triggered the cranking by itself

Thanks for the help again, guys.

 

No its just a battery to starter cable - this sounds like another gremlin altogether - where is the starter solenoid cable run...?

Alan

 

The wirng inside that red sleeve includes the battery positive between the starter post and the alternator, on to ABS and jump post. It also includes the #50 circuit wire to the starter relay contact in the relay panel (not used in your 5-speed car, jumper instead), and on to the ignition switch. The routing of that cable is under a heat shield as it passes over the crossmember, and it's also secured to the crossmember with a clamp, and tied to the steering rack pinion area with tie-wraps on my car to protect it from heat and abrasion. Meanwhile, the heat shields don't seem to be in place in your picture. Did that one (or both...) get left out when refitting the new motor mounts? It's really tempting, 'cuz they are a real b!tch (chore) to get fitted right when you finally notice they are the only parts left on the bench at the end of the job.

 

Ahh I guess I didn't know what I was looking at there... how bad is the burned up area?

Alan

 

Update and new questions:

This is how the Engine Wiring Harness looks like, where it touched the Exhaust over the Front Suspension / Cross Member on the Driver's Side.
Once I removed a bit of the Sleeve, you can see that the Black Wire insulation melted and it allowed contact between it and the Red Wire.

I have disconnected the Wires from the Starter and the Alternator to allow some room to cut the Sleeve and noticed that there were NO clamps securing the Harness to the Cross Member. This Wiring is fairly new as it was replaced recently by the PO. I suspect, if it is supposed to have Clamp(s) securing the Harness, that the PO did not install them back. I am attaching below a picture from Dwayne's MM DIY showing the Clamp on his car.

I obviously routed the Harness incorrectly after I replaced the Motor Mounts.

Now I need some help with the following, please:
1. Is my car (1989) supposed to have this Clamp(s) and if so, how many and which part number?

2. Any suggestions or tips to repair this Black Wire?

3. What do I use to isolate the Harness where I had to cut the Sleeve?

4. Finally, how do I route the Wiring from the Starter over the Cross Member? I am thinking it should be between the Mounts and the Fender, but am not sure. If anyone has a picture, I'd appreciate it.

I know I am stretching my luck with so many questions...

Thanks again for the help

 

It's just a regular line mounting clamp that you can find locally or online. They usually come in small sizes so you'd need to measure out how big of a clamp you'll need.

To repair the sleeve, buy the self-adhering electrical tape sold by 928 MotorSports. Works really nice for this application and also comes in orange. I used it to repair tears to the line going to my alternator.