neilschelly

I've been having a growing problem in my 944S2 on hotter days when the engine cuts out occasionally, sometimes for several seconds. At idle, it might stall out completely, but on the highway, it might make acceleration or even keeping up speed very difficult.

When the misfires happen, I can see the voltage gauge drop from a normal 13.5V - 14V to down near 12V instead. It coincides with the radiator/condensor fans cycling to full blast, which usually happens right away if I turn on the AC.

I did replace the brushes and install a variable voltage regulator on the alternator, so I could try turning that up again, but I feel like it's keeping the voltage high enough most of the time. The battery is reasonably new (about 1y), and I've cleaned all the engine grounds. I can think of a few other reasons this is happening, but I wanted to see if folks recognize this behavior enough to give guidance.

1. The alternator is just not keeping up with the load. The voltage regulator did help keep it higher in general, but if the voltage is still dropping under periods of high current draw, maybe the alternator just cannot keep up.

2. The fans are drawing too much current. I have no idea how to test that. Do folks see their fans cause a noticeable drop in the running voltage of the car as they cycle from normal speed to high speed?

3. The ignition system needs a makeover. I don't know the last time the spark plugs, plug wires, ignition coil, or the distributor/rotor were replaced. I could just buy a bunch of parts and replace them to see if that game of whack-a-mole fixes my issue.

4. Upgrade the ignition or fan system? Are they both just really inefficient and are there more efficient options for each that are less power-hungry?
-Neil

Cross-posted to Pelican's forums: https://forums.pelicanparts.com/pors...igh-speed.html

austin944

You can buy a cheapo clamp on meter to measure the current draw of the cooling fan motors:
https://www.harborfreight.com/digita...ter-96308.html
I don't normally recommend Harbor Freight tools but if you're using the meter infrequently it might be a good option.

Try turning on all of the accessories besides the cooling fans, like headlights, wipers, radio, defroster, cigarette lighter, sunroof, whatever you can find, to see if the same problem arises under the same operating conditions. To my knowledge, the fans and alternator are not marginally built components when they are in good operating condition.

T&T Racing

The data indicates that the alternator fails when there is more heat from increase in airflow and heat rejection from a/c combo with radiator. Increase heat=higher alternator temp. Replace the alternator. I had same issue, alternator tested OK on bench test, 70 F but failed on the race track, temp very high.

orig944

This particular meter does not do DC amps.

tempest411

I'd recommend inspecting and cleaning all connections, especially the junction at the starter lug. All of your alternator's output has to make it down to the starter and up the other cable to the battery + post, where it then makes it's way to the fuse box. It's quite a convoluted path. The connection at the starter is ripe for corrosion thanks to being close to moisture from rain and snow, dirt, and salt if that applies in your area. Also...clean all your ground connections.

neilschelly

Hmmpmh, I wasn't getting email notifications from this thread, so I didn't realize how many responses I had. Thanks everyone. I do have some updates, and the problem is not yet resolved.

I cam reproduce the problem on a lift if it's hot enoguh and I turn on everything. Defroster, stereo, headlights, fog lights, and AC on full blast. Just after starting the car and idling, the alternator is putting out about ~74A and maintaining 13+V with my adjustable voltage regulator on the highest adjustment. The overall current drops to about 55-60A after ~20 minutes or so, presumably because the battery is fully charged again and no longer drawing a current to re-charge itself. Since the alternator should be good for 115A, I know I'm not maxing it out since I know it can produce ~75A at over 13V. When it's stuttering, it's putting out considerably lower current and it's not obvious if it's because it's capable of producing less or less is being asked of it. No smoking gun, unfortunately.

I already have a nice clamp meter, but I didn't try to clamp on the fan harness. I'd have to get between the belts and the fans and that feels dangerous. Also, I don't think the fan grounds to the chassis, so I'd have to find a way to clamp around only one of the leads to the fans.

Before posting, I'd already cleaned all the grounds and the positive connections at the battery, alternator, and starter. I'm confident those are all in good shape.

I got a suggestion to ensure the alternator belt was really tight, and I hadn't checked its tension in a couple thousand miles since it was replaced. It was a bit loose, and I tightened it, but that didn't improve anything.

Someone on Pelican Parts' forum suggested I look at the ICM, or ignition (not intake, typo) control module. I guess these were specific to the 16V models, and their failure mode perfectly matches the behavior I'm seeing. And they are only $50 and easy to replace. So I bought one of those and I'm waiting for it now. Due to having a coupon for a purchase over $250, I also bought a new ignition coil and distributor cap/rotor, I'll start with the ICM, see if it fixes the issue, then the distributor because it's easy to reach, and then the coil.... and if it's still mis-behaving, I'm guessing it's gonna have to be the alternator.
-Neil

Jfrahm

Ignition module, not intake. They can cause a misfire, perhaps more commonly take out half the ignition on a 32v 928. On the 928, cheap versions of this part have been problematic, however they are a common part on Saabs and Volvos as well so a good OEM quality one should be easy to obtain. On my 928S4 I have considered keeping a used OEM one on board as a cold spare. Beats waiting for a flatbed.
They integrated the function of this part into the DME on the 968 but it can be found on the 944S and S2.

neilschelly

Ooops, yeah, that was just a typo. I didn't buy an intake control module. ;-)
Now just crossing my fingers it helps me out when it gets here.
-Neil

T&T Racing

Unfortunately, the clamp on current meter does not care which way the current is flowing. The key is to measure the voltage at the alternator and + post of battery at cold start run and then repeat the readings after turning all those devices on and getting the alternator hot. Compare voltage readings at those 2 points before and after and post readings.

neilschelly

I'm not sure what you mean about current and direction - of course it cares. That's what the negative or positive symbol is for. But you can't wrap around _both_ directions of a circuit or they will cancel each other out.

As for the voltage, I included that in my first post. I know the voltage is dropping a lot, and I know it's running fine when the voltage is up. The numbers I gave are consistent with the voltage numbers measured across the battery and between the alternator output and ground. I don't see different voltages in different places at the same time.
-Neil

T&T Racing

If the voltage is dropping to 12v when the AC is on, then the charging system is the culprit, alternator and/or cable between alternator and positive battery terminal

orig944

Echoing T&T, when it does this:

What is the voltage at the battery and alternator?

Also, if you want to measure the fan current, you can make a pair of jumpers at the connector to split the cable by using .250 quick disconnects and heavy enough wire. Make one short, and the other one long to route out to where you want your meter.

neilschelly

Well, I will definitely try to go over the terminals from alternator to the starter to the battery again, just to make sure they are all still tight and clean. Failing that and the ignition refresh that is probably overdue anyway, I will seek a new alternator, or rather, a refurbished one. Seems new ones aren't available anymore... :-(
-N

neilschelly

I cleaned up the positive and negative terminals on the battery and went for a drive today. Neither looked problematic, but there was actually a bit of oxidization between the "layers" of connections on the positive side. Every other connection was tight and clean already. I'd say that made a marked improvement. It's not super hot today (about 70 degrees), but I drove around with the AC on, fan at 4, headlights, foglights, stereo, and rear defroster on. I even moved my windows up and down a few times and had a USB charger in the 12V socket.

I didn't get a real meter out, but the voltage gauge was higher than expected for all of that. There was some light stumbling when the fans came on that maybe dropped to low-mid 12V range on the gauge when idling. If I was moving it was almost always above 13V even with everything. I never had even a single ignition stumble while driving.

Again, this wasn't a high heat day, but even on a day like today, I wouldn't expect it to be so high. It was over 14V as soon as I started it up with no extra accessories turned on yet, and that's more than I've seen on the dash gauge before.
-Neil

Jfrahm

The ignition system works when the starter is cranking, causing significant voltage drop. I would not expect the ignition system to quit until 10 or 11 volts.