944 S2 Suddenly Started Running Badly, Ugh!

[Latitude48]

I don't drive my 944 S2 or 951 very much (and may think about selling one or both) but I do take them out regularly to "exercise" the engine, etc. I took the S2 out the other day and after I had driven about 1.5 miles and had turned onto the main 2-lane highway it started running very badly, like it was missing and hesitating. I turned around as soon as I could and thankfully I was able to make it back up the hill to the house with a lot of hesitation, bucking and just crappy running.

I ran it again today and it feels at times like it's running on 3 cylinders as the idle is rough and it has momentary periods like it wants to die, then perks up for a bit.

The fuel pump, fuel filter and fuel pressure regulator were all changed around 11,000 miles ago, so I don't think it's a fueling issue (although it seems to react that way), so I suppose it could be a bad injector.

When it's running normally the engine just purrs and pulls very strong to redline. Now, not so much!

Any thoughts on where to begin the diagnosis? Thanks.

[Tom]

I don't drive my 944 S2 or 951 very much (and may think about selling one or both) but I do take them out regularly to "exercise" the engine, etc. I took the S2 out the other day and after I had driven about 1.5 miles and had turned onto the main 2-lane highway it started running very badly, like it was missing and hesitating. I turned around as soon as I could and thankfully I was able to make it back up the hill to the house with a lot of hesitation, bucking and just crappy running.

I ran it again today and it feels at times like it's running on 3 cylinders as the idle is rough and it has momentary periods like it wants to die, then perks up for a bit.

The fuel pump, fuel filter and fuel pressure regulator were all changed around 11,000 miles ago, so I don't think it's a fueling issue (although it seems to react that way), so I suppose it could be a bad injector.

When it's running normally the engine just purrs and pulls very strong to redline. Now, not so much!

Any thoughts on where to begin the diagnosis? Thanks.

Sorry about that. Does it run poorly just idling in the garage, or does it need to be under load? It will be easier to pin down if it happens in the garage. You can pull injector leads one at a time to see if it really is running on 3 cylinders -- if it is, nothing will happen when you pull the lead off the dead cylinder.

[Latitude48]

I don't drive my 944 S2 or 951 very much (and may think about selling one or both) but I do take them out regularly to "exercise" the engine, etc. I took the S2 out the other day and after I had driven about 1.5 miles and had turned onto the main 2-lane highway it started running very badly, like it was missing and hesitating. I turned around as soon as I could and thankfully I was able to make it back up the hill to the house with a lot of hesitation, bucking and just crappy running.

I ran it again today and it feels at times like it's running on 3 cylinders as the idle is rough and it has momentary periods like it wants to die, then perks up for a bit.

The fuel pump, fuel filter and fuel pressure regulator were all changed around 11,000 miles ago, so I don't think it's a fueling issue (although it seems to react that way), so I suppose it could be a bad injector.

When it's running normally the engine just purrs and pulls very strong to redline. Now, not so much!

Any thoughts on where to begin the diagnosis? Thanks.

Sorry about that. Does it run poorly just idling in the garage, or does it need to be under load? It will be easier to pin down if it happens in the garage. You can pull injector leads one at a time to see if it really is running on 3 cylinders -- if it is, nothing will happen when you pull the lead off the dead cylinder.

It runs poorly all the time, but it's also intermittent as it will be idling poorly and will then act like it's going to quit, then come back to life but still running poorly. When this first happened, it was like flipping a switch when it changed from its normal great running to barely able to accelerate.

Could one of the traces in the AFM be giving up the ghost? DME on its way out? I mean, it's only 35 years old

[TooManyWrenches]

Sounds like either a vacuum leak, or broken wire electrical failure.
That failure mode is classically a brittle hose that popped off.

[Tom]

I don't drive my 944 S2 or 951 very much (and may think about selling one or both) but I do take them out regularly to "exercise" the engine, etc. I took the S2 out the other day and after I had driven about 1.5 miles and had turned onto the main 2-lane highway it started running very badly, like it was missing and hesitating. I turned around as soon as I could and thankfully I was able to make it back up the hill to the house with a lot of hesitation, bucking and just crappy running.

I ran it again today and it feels at times like it's running on 3 cylinders as the idle is rough and it has momentary periods like it wants to die, then perks up for a bit.

The fuel pump, fuel filter and fuel pressure regulator were all changed around 11,000 miles ago, so I don't think it's a fueling issue (although it seems to react that way), so I suppose it could be a bad injector.

When it's running normally the engine just purrs and pulls very strong to redline. Now, not so much!

Any thoughts on where to begin the diagnosis? Thanks.

Sorry about that. Does it run poorly just idling in the garage, or does it need to be under load? It will be easier to pin down if it happens in the garage. You can pull injector leads one at a time to see if it really is running on 3 cylinders -- if it is, nothing will happen when you pull the lead off the dead cylinder.

It runs poorly all the time, but it's also intermittent as it will be idling poorly and will then act like it's going to quit, then come back to life but still running poorly. When this first happened, it was like flipping a switch when it changed from its normal great running to barely able to accelerate.

Could one of the traces in the AFM be giving up the ghost? DME on its way out? I mean, it's only 35 years old

If it were the AFM, you should be able to find some throttle positions where it runs ok, and others where it's bad. Have you checked how much vacuum it has a (poor) idle? Could be so many different things - you'll need to collect a little data to start honing in on it...

[gb951]

If you think that it is a hard miss on one cylinder, use an infrared thermo gun and point it at each of the exhaust manifolds. The one that is missing will show a lower temperature than the others.

[Latitude48]

If you think that it is a hard miss on one cylinder, use an infrared thermo gun and point it at each of the exhaust manifolds. The one that is missing will show a lower temperature than the others.

That's a good tip! However, with the help of a former S2 owner, Terry Thomas, we fixed it using the brute force method; we just changed the spark plugs and plug wires. The car currently has 155,571 miles.

The plugs were Denso Iridium, last changed in January 2016 at 144,837 mi (so not that long in mileage); #3 & 4 looked wet with fuel, #1 & 2 looked pretty good, but not perfect. The plug wires were Kingsborne 8mm, last changed in January 2003 at 90,867 mi, so roughly 65K miles and 22 years ago (ugh).

We installed a new set of Denso Iridium (5307) spark plugs and Clewatt Engineering High Performance 8mm Plug & Coil Wires I happened to have on hand. Yureka, the S2 runs as good as ever!

S2 owners should be familiar with the two plastic plug wire holddown clips that attach to the cam cover. As it turned out those holddowns are a wee bit too small in diameter so when installed using 8mm wires they put too much pressure on the wire cover. Looking at the #3 plug wire at this location the cover was severely cracked through. I should be able to snap the clips together and drill the holes oversize to fit the new wires, but in the meantime, I'm sure glad this has been resolved.

Oh, and we also fixed what I originally thought was an ABS pump that was making some clanking noises. That turned out to be the washer fluid reservoir that was rattling against the body and after things warmed up the noise would go away. Dodged another bullet, ha, ha. Edit: nope. That wasn't the cause. I ran the S2 today and the noise is definitely coming from the bellhousing area, like a rhythmic knock, knock, knock, knock, knock. It does away after a few minutes, OR if you step on the brake pedal (?). Weird.

Now I need to decide if I want to sell this car I've owned for 28 years (or the 951) to Terry Thomas, as he's looking for a new project.

Cheers, Tom

[zooklm1]

Tom,
On your knock noise, have you considered exhaust manifold gasket going bad or crack in the exhaust manifold? I had a 2002 Volvo turbo with a cracked manifold. When cold, it would have knock like sound but once it warmed up, it went away as the manifold expanded.
Lee

[Latitude48]

Tom,
On your knock noise, have you considered exhaust manifold gasket going bad or crack in the exhaust manifold? I had a 2002 Volvo turbo with a cracked manifold. When cold, it would have knock like sound but once it warmed up, it went away as the manifold expanded.
Lee

Thanks, but I don't think that's the issue. I thought it was "fixed" the last time I had the S2 in the shop as they couldn't reproduce it after doing a brake fluid flush. But as soon as I got it home it started acting up again. The knocking happens without the engine running, just turn the key on, then put your foot on the brake and it goes away. I haven't investigated further as it's in the 30s - low 40s here now and I don't feel like fooling with it.