REALLY weird problem - exhaust?!?
 

Ugh.

I went for a nice long drive today before work, and it was a really wonderful drive. The car was running great, the weather was perfect...

...until I got about 1/4 of a mile away from work. Then, all of a sudden, the exhaust note seemed to change. Not only that, but there seemed to be a lot more vibration at all RPM.

I tried to drive normally, but the car was much louder than normal, especially over 3000 RPM. It had that low, burbly "tuned-exhaust" sound, but not in a good way.

Now, the first thing that I thought was that either something came loose or separated in the exhaust assembly, or a hole opened up (all of a sudden?).

But here's the weird part: I noticed when this happened that my battery light came on and stayed on. Not only that, but the dash lights were noticeably dimmer than usual when I drove home from work tonight.

It gets weirder: I turned the 944 off so I could move some cars around in the driveway, and then went to turn it on again. No dice... it wouldn't crank over, it would turn about twice and then the battery light would dim - you know, what it's like right before you decide you need a jump start.

What is going on here?!? How would an exhaust issue affect the electrical system to the point where there is a drain on the battery while I am driving?!?

The only thing I've tampered with in the past week or so is taking off the distributor and rotor because the rotor was loose. And yes, I already check that. Everything there looked A-OK.

PLEASE HELP!

It gets weirder. After letting the car sit for about 10 mins, it starts with no problem.

Re: REALLY weird problem - exhaust?!?
 

Just a thought, but maybe its the other way around. I think an electrical issue (might) affect exhaust sound more than vice versa. If ya think about it, the exhaust is a dumb system. Only pipes with some fancy polutant removers and sound absorbers.

Thinking out loud here only... But maybe low voltage causing weak spark/misfire or bad reading from AFM or O2, etc? Would that change exhaust note any?

Looking at cause and effect I'd assume the electric issue adversely effect other systems as opposed to exhaust.

Good luck. Hopefully someone else has some more useful insight.

Hmm. Well, you might have a point if the engine was running funky... but, like you said, exhaust is only pipes and such. The computer, etc, would have very little effect on the exhaust as compared to the engine..... and the engine is running great. Seems to pull and rev fine.

Only louder...

just my$.02 but there Must be a leak Somewhere or it wouldn't be louder than before, as to the other problems, wiring going to the starter?

Yes... but why would these problems seem to occur simultaneously?

Here's to hoping for FRWilk's or SoCal's invaluable assistance.

speaking of socal - where has he been lately? or am i just blind...

if the car cranks, chances are the wiring to the starter is in fine condition... did you wash the car recently? any water under the hood that could have shorted something? how's your coolant level?

When your battery sits, it it will come back to life a little. I had my alternator die on my '85 eventualy battery went down to the point the ignition shut off turning onto the road I live on. glided, waits about 10 minutes, started, and later drove it back. If you have a volt meter, check and see that your battery is receiving and sending power. You may have already done this, but its something I would check.

After replacing my alternator and re-routing the cables, the exact same thing happened to me. I immediately shut the car off & started feeling around. My battery was HOT. Turns out... I re-routed the cables in a not so good spot and it melted the shielding & shorted out. Oh, and I had to buy a new battery the next day.

Bad alternator diode? It sounds to me like an overall low current condition.

Is the exhaust getting louder, or just changing tone? sounds like you have a cylinder cutting out. If you have weak voltage you might not get a good spark out of the coil. how old is your battery?

Totally off the wall here, but could the bearings in your AC compressor have gone out? That would explain the vibrations, and if the belt which the AC and alternator share was slipping because of the AC compressor you wouldn't be getting enough charging from the alt....just a shot in the dark here.

"After replacing my alternator and re-routing the cables, the exact same thing happened to me. "

Interesting... but I haven't messed with anything like that...

"Bad alternator diode? "

How do i check this?

"Is the exhaust getting louder, or just changing tone? sounds like you have a cylinder cutting out. If you have weak voltage you might not get a good spark out of the coil. how old is your battery?"

Battery is about 2 years old. It seems as though the exhaust is louder... I am pretty sure it is, but, of course, the vibrations might theoretically just make it seem louder.

"Totally off the wall here, but could the bearings in your AC compressor have gone out? That would explain the vibrations, and if the belt which the AC and alternator share was slipping because of the AC compressor you wouldn't be getting enough charging from the alt....just a shot in the dark here."

Interesting. I'm not sure how this would effect the exhaust sound, but interesting nonetheless.

If you have a cylinder thats not firing, you will get a low toned popping sound out of your exhaust, mixed in with your smooth exhaust sound.

I talked to my mechanic today, he seemed to echo 1-tamad's idea that there is something bad on the alternator... voltage regulator? I am going to poke around and see what i can see in there, and I will fill you guys in.

I know its random but if the exhaust cracked by the header or such then could it be pouring hot gasses directly onto the starter and heating up the enging compartment leading to inefficiency of the alternator and poor starter operation?

Yes, let us know what you find out....
I seem to agree with the Alt. area...
Good luck/skill.

Well, we're narrowing it down...

my mechanic (a very good guy) let me borrow an extra alternator brush/voltage regulator thingie to eliminate that possibility. Got it installed after the pain in the azz of removing the airbox assembly, but still no dice.

I am bringing the car down to his shop in a few mins.; he is going to voltmeter the alternator itself and troubleshoot from there. This is a big favor he is doing me, because his shop got flooded due to the excessive rain last week and they are not currently taking cars (he had to total a few cars whose owners didn't pick them up after phone calls of warning. among them were a Lotus Esprit and a pre-impact bumper 911)

Leak in the exhaust at the weld just north of the cat caused excess noise /vibration...


vibration then cause electrical connection to loosen?


Had that happen with me but different electrical symptoms

We found the culprit.

the crankshaft gear that connects to both the balance and serpentine belt had split in two! This is what caused the weird vibration and (unless there is a very unlikely scenario where there is an exhaust leak and/or a bad alternator) the electrical issue.

As long as the car is in the shop, I am also having the motor mounts done... I have been putting it off long enough.

Thanks to everyone who (tried to ;) ) help. I will let you know how everything goes.