So the saga of the 1987 924S continues as things get sorted......I keep reminding myself to enjoy the journey.
The other day I turn the key and get a click, no starter spinning. OK, jumped the car (thought I killed the batter with a new 12v USB with an LED etc.) car fires right up, drove it and ran a couple errands, started fine during those start/stops but on the way home my tach is bouncing all over the place which is one of many symptoms of a weak battery. Battery was from previous owner replaced in 2022 and the car say for a while so I got a new battery yesterday.
Installed new battery yesterday and it fired right up, took it for a spin, tach is back to normal, cranked fine a couple times yesterday. Go out today and back to turning the key and getting the click but no starter engagement.
Battery tests out at 12.54V and when I ground it on the block it is the same 12.54V. So I suspected the starter.
On a lark I jumped it again with one of our other cars......fired right up strong as ever.
So THAT suggests to me the full voltage or amperage isn't reaching the starter......
My questions:
- Am I thinking about this correctly?
- Could it be the alternator not topping off the battery and thus causing enough of a weakness to only click?
- I believe the next step would be to get it up on ramps (after jumping it to move it), and putting a multimeter on the positive line to the starter and then the negative and have someone crank it and it "should" be 12.54V........right? If it isn't 12.54V then how much of a drop would indicate a problem enough to cause a "click"?
Thanks !!!
924S Starting Issue
I spoke with my P-car guy who is familiar with the car as his team did the previous work for me and he confirmed I was going about it in a logical way. He urged me to really clean the battery ground, the battery terminals and the new battery terminals as well.
I grabbed some course steel wool and a wire brush and went at it and reassembled and it fired right up.....BUT, the real test will be tomorrow morning after sitting but perhaps it was as simple as corrosion or film on the terminals (they weren't visibly corroded etc). The ground certainly had 40 years or rust on it, but nothing WD-40 and a wire brush couldn't handle. I also hit all of it with contact cleaner if for no other reason to give me a contact high (see what I did there?)..........
Since the starter cranked fine when being jumped we didn't really feel the problem was at the starter or in the wiring TO the starter otherwise jumping it wouldn't necessarily work as it did.
Old cars.......always something to challenge you.
We will see tomorrow.
I grabbed some course steel wool and a wire brush and went at it and reassembled and it fired right up.....BUT, the real test will be tomorrow morning after sitting but perhaps it was as simple as corrosion or film on the terminals (they weren't visibly corroded etc). The ground certainly had 40 years or rust on it, but nothing WD-40 and a wire brush couldn't handle. I also hit all of it with contact cleaner if for no other reason to give me a contact high (see what I did there?)..........
Since the starter cranked fine when being jumped we didn't really feel the problem was at the starter or in the wiring TO the starter otherwise jumping it wouldn't necessarily work as it did.
Old cars.......always something to challenge you.
We will see tomorrow.
Know a little about a lot and a lot about a little.......
2006 911 4S
1987 924S
2006 911 4S
1987 924S
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Tom
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I’d separate the symptoms and do some testing.
The bouncing tach is not really a “bad battery” indicator in my experience. A weak battery can cause click/no-crank or weirdness during cranking, but a tach bouncing while driving points more toward an RPM/ignition signal, ground, charging/regulator noise, or cluster connection issue. I'd treat that as a separate issue, at least to start.
Here's what I'd do.... First check charging voltage with the engine running. Measure across the battery posts. You should generally see about 13.8–14.4V. If it stays near 12.5V, the alternator is not charging properly and your battery is just being drained until it can't start the car any more.
Next, I'd check for parasitic drain. Since it started fine with a new battery and then clicked the next day, something may be drawing the battery down while parked. Old cars and old wiring are notorious for that. Lots of videos on how to test on YouTube. Or --more shade tree-- if tomorrow morning the car won't start again, charge it up and leave it disconnected overnight and see if it fires right up the next day. Might take a few days, but if the car is always dead after leaving the charged battery connected overnight, and always fires up when leaving a charged battery disconnected overnight, that's a very strong indication that something is draining the battery (e.g., radios, alarms, unnoticed light bulbs, etc.) I once tore my hair out with a parasitic drain on my old Mercedes. It was the light in the trunk. The switch had failed in the oddest way -- when the trunk was closed the light was on, and when I opened the trunk the light would go out! That was fun.
Next, test the starter circuit under load. Do a voltage-drop test while someone is turning the key. For the positive side, put one meter probe on the battery positive post itself and the other on the large positive post at the starter. The volt meter is showing voltage lost through the positive cable/connections. It should be a fraction of a volt, not 2 or 3 volts... Then do the same on the ground side.
And, of course, you can always pull the starter off and take it to an auto parts store for testing (though I'm cynical enough to think some of those tests are designed to sell starters, alternators, and batteries...).
The bouncing tach is not really a “bad battery” indicator in my experience. A weak battery can cause click/no-crank or weirdness during cranking, but a tach bouncing while driving points more toward an RPM/ignition signal, ground, charging/regulator noise, or cluster connection issue. I'd treat that as a separate issue, at least to start.
Here's what I'd do.... First check charging voltage with the engine running. Measure across the battery posts. You should generally see about 13.8–14.4V. If it stays near 12.5V, the alternator is not charging properly and your battery is just being drained until it can't start the car any more.
Next, I'd check for parasitic drain. Since it started fine with a new battery and then clicked the next day, something may be drawing the battery down while parked. Old cars and old wiring are notorious for that. Lots of videos on how to test on YouTube. Or --more shade tree-- if tomorrow morning the car won't start again, charge it up and leave it disconnected overnight and see if it fires right up the next day. Might take a few days, but if the car is always dead after leaving the charged battery connected overnight, and always fires up when leaving a charged battery disconnected overnight, that's a very strong indication that something is draining the battery (e.g., radios, alarms, unnoticed light bulbs, etc.) I once tore my hair out with a parasitic drain on my old Mercedes. It was the light in the trunk. The switch had failed in the oddest way -- when the trunk was closed the light was on, and when I opened the trunk the light would go out! That was fun.
Next, test the starter circuit under load. Do a voltage-drop test while someone is turning the key. For the positive side, put one meter probe on the battery positive post itself and the other on the large positive post at the starter. The volt meter is showing voltage lost through the positive cable/connections. It should be a fraction of a volt, not 2 or 3 volts... Then do the same on the ground side.
And, of course, you can always pull the starter off and take it to an auto parts store for testing (though I'm cynical enough to think some of those tests are designed to sell starters, alternators, and batteries...).
As part of this effort, it would make sense to assess your battery to starter and alternator harness. When I 1st got my 951, it was visually obvious (corrosion, flaking insulation) that it needed to go even though I didn’t have any starting or running issues.
1986 951 - Silicon Valley
That was the point of my suggesting the measuring the battery voltage while cranking. It is easy to do, and doesn't require lifting the car. If the battery voltage drops considerably while cranking, it is the battery, and given that he has a new battery, it means that something is draining it while the car is not in use. If it doesn't drop more than a couple of volts, it means that the wiring is suspect. One ridiculously simple measurement divides the problem, and helps focus on the actual issue.whalenlg wrote: Wed May 20, 2026 8:36 pm As part of this effort, it would make sense to assess your battery to starter and alternator harness. When I 1st got my 951, it was visually obvious (corrosion, flaking insulation) that it needed to go even though I didn’t have any starting or running issues.
it does rather sound like an intermittent issue doesn't it. Might be worth testing the Ignition switch as well as the other tests suggested.
Have you cleaned the M9 & M10 ground strap points from the back of the engine block to the firewall ?
Have you cleaned the M9 & M10 ground strap points from the back of the engine block to the firewall ?
All great suggestions, and I appreciate the responses and guidance here, it is great to have a resource of knowledgable folks.
Quick Morning Update:
Car sat all night, temps in the high 40s low 50s Fahrenheit, car fired right up strongly with no issues.
As some of you may have seen in one of my original threads on this car working through a cooling issue, I was having gauge cluster issues/anomalies since I got the car with the most noticeable one being the temp gauge until the Tach did a dance the other day (which has not been repeated). All signs point to ground interference.
By cleaning up the battery ground really well yesterday along with the battery terminals/connections not only has the starting been on point, but that temp gauge is acting on its best behavior, no more reading higher than it really should, no more bouncing around or flip/flopping when I put on the blinker to turn etc. So IMHO that suggests the battery ground location was one source of the interference.
I do have to locate and inspect the main ground strap, I have looked but have yet to find it through the sea of wires and hoses back there.
One day and one good 24hr period of starting doesn't prove things are 100% fixed but it sure is heading in the right direction.
All that said, I LOVE driving this car. I drive it 3-4 times per week to the golf course (pre-work 9holes to keep me sane-ish) which is a 25 mile trip each way on curvy 40-50mph roads that are absolutely perfect for this little red car. Such a joy.
Quick Morning Update:
Car sat all night, temps in the high 40s low 50s Fahrenheit, car fired right up strongly with no issues.
As some of you may have seen in one of my original threads on this car working through a cooling issue, I was having gauge cluster issues/anomalies since I got the car with the most noticeable one being the temp gauge until the Tach did a dance the other day (which has not been repeated). All signs point to ground interference.
By cleaning up the battery ground really well yesterday along with the battery terminals/connections not only has the starting been on point, but that temp gauge is acting on its best behavior, no more reading higher than it really should, no more bouncing around or flip/flopping when I put on the blinker to turn etc. So IMHO that suggests the battery ground location was one source of the interference.
I do have to locate and inspect the main ground strap, I have looked but have yet to find it through the sea of wires and hoses back there.
One day and one good 24hr period of starting doesn't prove things are 100% fixed but it sure is heading in the right direction.
All that said, I LOVE driving this car. I drive it 3-4 times per week to the golf course (pre-work 9holes to keep me sane-ish) which is a 25 mile trip each way on curvy 40-50mph roads that are absolutely perfect for this little red car. Such a joy.
Know a little about a lot and a lot about a little.......
2006 911 4S
1987 924S
2006 911 4S
1987 924S