My car is making me lose my mind. I'm befuddled. (944 content)

So my '84 944 sat for a couple of years. It was parked because it had a leaky head gasket. I had a spare head, so I had it resurfaced and rebuilt it so it would be ready to go for when I decided to change the head gasket.

I swapped heads a couple of weeks ago and everything was working fine for about a week. Ever since then, it's had a really bad miss that happens sometimes under throttle, and every time I shift until it warms up. The really weird part it, when it starts to miss, it's losing compression. If it dies while it's missing, when I restart it it sounds like it's got a bad timing belt until it builds up compression and starts. When it's missing, it doesn't smoke or smell odd. I can smell a rich or lean exhaust from a mile away, and it doesn't do either.

I've checked all the ignition components and they're fine. I did a compression test (cold) and I got 168, 170, 174, 175, so I don't think that's the problem. When it does it, it just randomly drops a cylinder (or sometimes two). I don't think it's fuel washing the cylinder out, because once it builds up compression again it doesn't smoke at all.

The only think that makes sense to me is if a valve or lifter is sticking. And if it is, why did it wait a week to start sticking?

Any other ideas?

how do you know it is losing compression?

You can hear it. Ever hear a car with a bad timing belt? If it dies when it starts missing, it sounds just like that for the first five seconds or so,and you can hear that it's only got compression in one or two cylinders, then it starts to build compression, then it starts.

When a normal car is cranking over it sounds like (and when I start this car MOST of the time)"re-rur-re-rur-re-rur-re-rur-re-rur-re-rur-re-rur-re-rur-re-rur".

When it's missing so bad that it dies, it sounds like "reeeeeeeeeeeeeeeeeeee-rur-reeeeeeeeeeeeeeeeeeee-rur" when I restart it for probably five or so revolutions, then it will start to build compression again and start.

I hope you get the gist of my sound effects.

Have you re-checked your timing? And re-checked belt tension?

I know the 968 had some interesting multitiming abilities.. but I don't think the 944 had them.

Just a long shot.. bad lifter? I think they are hydraulic.. if one is collapsed or collapsing, it might not open the valve enough to pull air in to compress it

Yep, they're both spot on. The car ran perfectly for a week or so, and still runs perfectly once it's warmed up. This issue happens for about the first 5-10 minutes I'm driving, and it doesn't go away all at once. It gradually runs better until it runs completely normally.

I even tried the "italian tune-up" tonight. Drove home from work keeping it around 5k rpm for 10 minutes or so, then beat the snot out of it down some back roads before going home. I went out and started it an hour later and it ran like crap again.

Check the grounds and relays near the ecu and clean them.

mad_machine wrote: I know the 968 had some interesting multitiming abilities.. but I don't think the 944 had them. Just a long shot.. bad lifter? I think they are hydraulic.. if one is collapsed or collapsing, it might not open the valve enough to pull air in to compress it

That's a thought, though you usually hear some serious lifter noise in these engines when the lifters aren't pumped up all the way.

My thought was actually the opposite. Like maybe a lifter was coming apart and the button was bulging? Or maybe they're just too pumped up when it's cold and at a certain RPM? I know on a 16v VW (my namesake), if you swap cams you have to wait 30 minutes to an hour for the lifters to bleed back down, or it won't have any compression due to the lifters not letting the valves fully close. So maybe something is causing a lifter or two to over-fill with oil and not letting the valves close all the way? Seems like a long shot, but that's the only theory that makes any sense to me right now.

Also, read this:

http://www.2carpros.com/questions/porsche-944-1984-porsche-944-car-hesitates

Worst case is a cracked head that warms up and seals. Best case is lifter is bad. You need to do compression test with it to see if it is constant on one cylinder.

Just a thought, in this digital age is it possible you could make a decent quality video (or two) on your phone of the issue and upload it to the youtubes?

might help people confirm the issue or potentially identify a issue you might of not thought of.

dean1484 wrote: You need to do compression test with it to see if it is constant on one cylinder.

I've tried. It only loses compression when you give it throttle when it's cold. If it dies because of it, compression will come back within 10 revolutions (by the sound of things), so in the amount of revolutions it takes to do a compression test, it's back to normal.

Ottobon wrote: Just a thought, in this digital age is it possible you could make a decent quality video (or two) on your phone of the issue and upload it to the youtubes? might help people confirm the issue or potentially identify a issue you might of not thought of.

I actually had the same thought. I'll try to shoot a video after work tomorrow. After it cools down from the trip home, of course.

A leak down test would eliminate pistons and rings.

Just a longshot, maybe try and ask the same question here- Pelican Parts 944 board

Coolant temp sensor going open, floods it and washes the cylinder walls down, or one of the injector drivers goes to ground, or an injector sticks open, or the cold start injector sticks open (If it has one).

Not a cam timing problem. Timing can't go off, then come back again.

Hydraulic lifters could theoretically do something like that, but the odds are pretty darn long, in my experience. They are way more likely to lose oil and clatter.

Valves sticking in guides, sticking buckets?

Since it is linked to cold, I would expect coolant temp sensor, failing coil pack, nasty old oil gumming something up...could be a lifter, but they don't usually fail that way. The only thing I could see there is if dirt got into one and it lost pressure or something temporarily, but to have the symptoms you're seeing, it would have to be holding the valve open rather than closed. That's an interference engine if I remember right, so I would think you would know if that was happening...

Is your oil full of fuel? I'm going along the lines of temp sensor or sticky injectors as well.

Giant Purple Snorklewacker wrote: Is your oil full of fuel? I'm going along the lines of temp sensor or sticky injectors as well.

+2, especially on an early 944 that has sat for a few years and today's ethanol blended fuels that like to clean the fuel system right into your injectors, etc. Might be time to upgrade to the later DME so you can go Rogue MTune and the like.

Maybe try swapping injectors around and see if the miss chases an injector? That way maybe you can tell if it is an injector or the wiring.

dean1484 wrote: A leak down test would eliminate pistons and rings.

Haha, I actually posted there about the same time I posted here.

http://forums.pelicanparts.com/porsche-924-944-968-technical-forum/861583-another-weird-problem.html

gearheadE30 wrote: That's an interference engine if I remember right, so I would think you would know if that was happening...

It is an interference engine, but if something was causing a valve to stay open a 1/16" or so, it would be enough to lose compression in that cylinder and not contact a piston.

How old is the O2 sensor? Have you looked at the air flow meter for wear?

Giant Purple Snorklewacker wrote: Is your oil full of fuel? I'm going along the lines of temp sensor or sticky injectors as well.

Honestly that was my first thought. Especially because when I had the fuel rail out while I was swapping the head, the injectors had a little bit of fuel on the tips from sitting a day or two, so they were definitely leaking a TINY bit.

But the oil smells totally fine. And if it were fuel washing the cylinders out, wouldn't I get some black smoke once it finally started firing on that cylinder from being super-rich?

BTW, I took a video, and although it actually performed a little better than usual, you can still see what it's doing. I'll upload it soon.