idealcheese

My 1984 had developed a little belt squeal so I went in and tightened the V-belt and accessory belt as close to spec as I could eyeball. Started up the car, no squeal! Take her for a drive to the car wash, get her all shiny, and then take off for a sunny spring afternoon drive. Suddenly the power cuts out and the battery light comes on. Just as I'm pulling over, power comes back. A half a mile later at a stop light, the power goes out completely but I'm able to restart. Cancel the drive, come home and check the battery cables. They are slightly loose from being disconnected on and off, but they have been like that for a while because I get lazy about tightening them and so far it hasn't been an issue.
I really don't want to find myself stranded at the side of the road, so I'd love to diagnose this issue in my garage. The battery seems to have power no problem, starts up great. All belts were replaced last summer and lots of maintenance done. Is it surely the battery cables? Or could I have messed up when tightening the belts?

Jfrahm

Loose battery cables cause exactly the problem you describe. They can also cause damage to your alternator, DME, etc. from voltage spikes.

idealcheese

@Jfrahm Thanks for confirming what I suspected. It only happened twice so I hope it hasn't damaged anything. Luckily I have a solid state DME. I've tightened the cables and will keep my fingers crossed.

Jfrahm

I'm not talking about the $25 DME Relay, I am talking about the DME, the engine ECU, the "brain". The DME relay powers the DME and the fuel pump. Somewhat more expensive and they are starting to fail due to age and this kinda stuff.

bonus12

Shouldn't the car keep running even if the battery is disconnected? Is this a brand new problem after the car wash? Sounds like something major is happening to cause loss of all power while you're driving. I would start with a voltmeter at the battery with and without the engine running. You may have faulty intermittent voltage regulator at the alternator. It sounds like you have a simultaneous problem with the battery cables or connection at the battery terminals

idealcheese

@bonus12 That’s what I thought too, but my guess is that even with a dead battery that you use jumper cables to start, it’s connected and being charged by the alternator as long as the car is running. If the battery becomes completely disconnected, the alternator can’t charge it and the DME shuts the car down? Just a guess.

I took the car for a couple of local drives with no more issues since tightening the cables, so I’m pretty sure that was the issue. Now if I could only get my lower belts to stop whining! I tighten them and they stop whining for 1 day then start again. Aaaargh

bonus12

Glad to hear the problem has been gone (at least for a bit)! I am nearly certain the 944 will continue to run if the battery is disconnected while it's running. Purportedly this is bad for the car and can damage the DME ... voltage spikes?

On another note, squealing of the accessory or P/S belts is common if they are loose. Whining and damage to the bearings may occur if they are too tight.

idealcheese

@bonus12 I hope someone else can chime in about whether a battery disconnect should cause total engine power loss. Regarding the belts, maybe they are TOO tight? However the sound IS more like a squeal than a whine. Anyway, I estimated the deflexion at 5mm for the V-belt and 2mm for the accessory belt which should be OK. Maybe I will try loosening them a bit anyway.

walfreyydo

Your alternator belt sounds like its loose, hence the whine and hence the battery light coming on and hence the sudden loss in power

Why? The ignition system discharged the battery because the alternator isn't charging it and it no longer has any charge to fire the spark plugs which means the engine will no longer run...

I highly suggest you look at the tightness of the belts or the health of your alternator (hint: with the car running your multimeter should read at least 13.5 volts across the battery terminals)

idealcheese

@walfreyydo I just went out and tested the battery. With the ignition off, it's reading at 11.8 volts, and at 13.8 with the engine running. I also double checked the alternator belt, it's really tight. Just about exactly 2mm deflection, as per spec. The v-belt also feels at spec. Do I need to start suspecting the timing or balance belt for making the squeal? Both were changed last fall.

bonus12

OP said that when they pulled over, power suddenly came back. Dead/dying battery doesn't add up.

Chalt

At 11.8 volts, your alternator isn't keeping the battery charged, at least not consistently, since the battery is now discharged. Also, if the alternator bearings are giving up, it may cause some squeal-age. With the alt belt loose does the alt pulley spin smoothly?

walfreyydo

Another thing to check would be your ignition switch - but the battery light is telling you there is low voltage which usually indicates an issue with the alternator (or belt)

idealcheese

I come bearing news. Today I fired up the 944 to go to the local park to play pickleball and as I was pulling out of the driveway I realized that (a) the battery light was still on, and (b) the power steering was DEFINITELY out. I’m no weakling, but making a 90 degree turn felt like it required a black belt.
Turned around and pulled back into the garage, popped hood. Guess what? V-BELT AND ACCESSORY BELT ARE BOTH MIA. Gone.
This leads me to conclude that I definitely tightened them too much. Right? They were less than 6 months old. I’m baffled that they bit the dust in unison, but I guess I need to be reading this as a message from the gods. But what is the message? Other than replace the belts?

bonus12

As readers, it's hard to know if they were over-tightened. But I can say that if one belt comes off, it can take the other one with it! Over-tightened belts doesn't explain the issue you're describing, though. I would say loose belts are more likely to come off but you said you had yours within spec.