My 3.2 is randomly dying. It's irritating.

[old man neri]

This winter I dropped the engine on my 3.2 and replaced a bunch of components.

A few months ago when I started driving it daily I noticed that every once in a while I would get very faint momentary loss in power. Barely perceptible.

It has not progressed. My car randomly dies now. Unfortunately all I have to do is coast to a stop and it starts right up again. I wish it would die and stay dead so I could properly diagnose this.

-The car dies instantly, there is no cough or sputter. It's like someone killed it with a key.
-Starts right up after I have come to a stop.
-If I leave it in gear while I am coasting the tach still reads (I think this has some sensor and DME implications)
- It's random. It might do it three times in a row in a minute and then not do it again for a few hours.
-This feels like an electrical issue.
-It never did this before it went under the knife.

Thoughts? I really don't want to randomly replace parts. I want to diagnose.

The only thing I can think of is a bad DME connection (I had an issue when I first put it back together) or maybe the coil (I never replaced it)

[sugarwood]

I bet people will tell you to check your grounds.

[911obgyn]

Did a bunch of components include the reference and TDC senders?

[Tippy]

The ol 3.2 intermittent gremlin.

Good luck, very common.

You’ll get a bazillion answers.

BTDT, lost.

[Targa Me]

My 3.2 did the same thing, it turned out to be the fuel regulator. My fuel pressure was up to 116 psi.
Check your fuel pressure.

[ischmitz]

The common culprits are the DME relay and the FW sensors. Both have a tendency to fail. However, rather than replacing parts by probabilities I'd do some systematic tests.

The fact that the tachometer still registers when the engine doesn't make power and you coast with the car in gear does mean the DME is still powered (it's not an alarm or ignition switch issue) and the sensors are still reading the flywheel. This would indicate you either loose fuel (e.g. DME relay is intermittent and fuel pump shuts down, fuel pressure goes low), have too much fuel (O2 sensor is intermittently disconnecting) or you loose spark (damage inside the DME itself).

A DME relay is a cheap first investment. After that you'll need some diagnostics tools if you want to systematically track the issue down. And the fact that it is intermittent doesn't make it even harder.

Ingo

[proporsche]

Just an idea..is it heat related? Do you have an aftermarket alarm?If yes there is a possibility that there is a relay in the system and that goes bad after warming up...
Ivan

[Joe Bob]

A DME relay is a cheap first investment.

^^^^

This....if it isn't bad now it will be, don't buy a URO product.

[GaryR]

Listen to Ingo, and if it isn't the DME relay (or the connection you mentioned) ship him your ECU for a rebuild as cracked traces and other 30+ YO components in there can cause nightmares and a ton of grief trying to figure out the issue if it's not a simple fuel supply problem... which I doubt from the way you say it dies like someone pulled a kill switch. Obviously check battery ground and the transmission to body ground too..

[DanielDudley]

Everybody should have a spare DME relay in the glove box. Mine is a solid state device that runs the fuel pump for three seconds after you turn the key to ON. I always know if the fuel pump is working.

Check all grounds, check all connections where they plug in, check all vacuum lines. Why not ? Check all the fuses for hairline cracks or corrosion.

Does it happen at throttle ? At the same RPMs ? At coast ?

[mikedsilva]

Originally Posted by DanielDudley

Everybody should have a spare DME relay in the glove box. Mine is a solid state device that runs the fuel pump for three seconds after you turn the key to ON. I always know if the fuel pump is working.

Check all grounds, check all connections where they plug in, check all vacuum lines. Why not ? Check all the fuses for hairline cracks or corrosion.

Does it happen at throttle ? At the same RPMs ? At coast ?

solid state?

[old man neri]

Originally Posted by ischmitz

The common culprits are the DME relay and the FW sensors. Both have a tendency to fail. However, rather than replacing parts by probabilities I'd do some systematic tests.

The fact that the tachometer still registers when the engine doesn't make power and you coast with the car in gear does mean the DME is still powered (it's not an alarm or ignition switch issue) and the sensors are still reading the flywheel. This would indicate you either loose fuel (e.g. DME relay is intermittent and fuel pump shuts down, fuel pressure goes low), have too much fuel (O2 sensor is intermittently disconnecting) or you loose spark (damage inside the DME itself).

A DME relay is a cheap first investment. After that you'll need some diagnostics tools if you want to systematically track the issue down. And the fact that it is intermittent doesn't make it even harder.

Ingo

Thanks for the reply. Tried a different DME relay. No joy.

The O2 sensor is new but it could be the connection. However, I am having a hard time believing a disconnected O2 sensor would cause the car to suddenly die. I mean, it can run without an O2 sensor right?

Today I think I am going to open up the DME again and have a closer look at the solder joints.

[old man neri]

Originally Posted by proporsche

Just an idea..is it heat related? Do you have an aftermarket alarm?If yes there is a possibility that there is a relay in the system and that goes bad after warming up...
Ivan

No aftermarket alarm, only the factory one that has been bypassed for at least 10 years.
It's happened to me on a cool crisp +10C morning just after pulling onto my street to yesterday when it was +30C and I had been drving it for an hour. There seems to be no relation to temperature.

[old man neri]

Originally Posted by 911obgyn

Did a bunch of components include the reference and TDC senders?

Yes, the speed and reference sensors were replaced.

[old man neri]

Originally Posted by Targa Me

My 3.2 did the same thing, it turned out to be the fuel regulator. My fuel pressure was up to 116 psi.
Check your fuel pressure.

I measured the fuel pressure after she was put back together. It was perfect. I suppose I could do it again however.

[spoke]

I had the same problem with my '86 930. Would die, then start up again. A couple of times it wouldn't start. Traced it to a relay near the engine. This is the relay which runs the fuel pump when airflow is detected. Maybe this is what folks call the DME?

It turns out the relay has a circuit board and a relay inside it. Taking the internal relay apart I found the contacts were oxidized and not making robust contact. I cleaned the contacts and adjusted the contact pressure. Haven't had an issue since then.

[sugarwood]

"FW sensor" means cam/crank ref sensors?
Flywheel?

[Jesse16]

Sounds like you've eliminated (mostly) the various sensors and Fuel relay. I suggest you try a friends ECU or ECM whatever is the correct term. Box under your seat with the chip. Not a huge cost to get one rebuilt or repaired if you find that helps and pretty easy to do if you have access to someone who trusts you. Gotta be electrical issue and not much left. And the O2 sensor should not shut the engine off. GaryR said it best above, 30 year old electrical for sure.

[old man neri]

Well, this morning I jiggled as many things as I could to get it to stall and only stalled once when I really shook the FW speed sensor. I think I actually unplugged it by accident because I was shaking too hard.

I opened up the DME brain and noticed this.




I resoldered the three. We shall see what happens.

[mysocal911]

Open the DME ECU and check for bad solder connections as indicated. This is the most common intermittent problem
with that unit.