Yabo

I had that. had two studs broken off of one port.. and it doesnt maket hat bad of a knock.. i was going to mention that, until i heard it.

roco16

Accomplished tonight:

As per Jeremy's experience, I pulled the fuel pump fuse and cranked the car 3 times, each time continuing 10 sec after the oil pressure reached full 4-5 bar. This was intended to 'fill' the lifters. Also noted there was ZERO knocking whatsoever when turning the motor over with the starter.
No change.

I removed a cam housing cap to see if the noise would get any louder (ie cam follower slap).
No change.

I removed each spark plug wire, one at a time, and cranked the car on three cylinders. The result was the same for each missing plug:
No change. Equal knocking noise across the board.

I removed the intake manifold and looked in the chambers as best I could. 1 & 2 were nice and clean, but 3 & 4 had a shiny film of oil along the chamber walls. On #3, there was a visible drip (or 'run') right above where the #3 exhaust valve is. No run on #4, just a filmy reflective bore. Both had what looked like caked up oil on the piston faces. Also, all of the intake runners (where you can see in intake valve stems) were pretty free of oil, I would almost say less oil then there usually is when I pull the manifold.
Reassembled everything: No change.
======================================

Because I wasnt able to single out one cylinder as the source of this noise, I am starting to really doubt piston slap, wrist pin failure, spun rod bearings, a bad injector, a bad or 'burned' intake/exhaust valve, an exhaust leak... etc.

The only thing left to try, other than pulling the engine+head+pan, is to remove the cam housing and check for a bad lifter.

Am I missing or misinterpretting anything ? ? ?

-Robert

Dal Heger

Why don't you just let it idle for a while?

When I replaced the cam followers on the S2 it took about 15 minutes for them to properly fill up with oil and stop tapping. It was quite amazing, all of a sudden it was quiet.

If it isn't a rod bearing then nothing will get damaged.

If it is a rod bearing, it's already dead.

Dal.

Crackhead944S

Is it possible to be off a tooth on the Cam belt and have the pistons "tapping" one of the valves?

And when you say "No change" I assume that means that its still making noise. Correct?

Any noises when turning the engine over by hand?

KLR

You'd have to be off by more than 1 tooth, and the compression numbers would not be so even or nearly so good. It certainly wouldn't idle Ok, if at all, either.

roco16

Thanks for your posts...
The engine is in time -> I verified the cam position at TDC.
No change means the noise is still there and has not varied in pitch, frequency, loudness..etc

When turning the noise over by hand or with the starter, it doesnt make any unusual noises.

Swagger93

My friend paul and I had a 1991 Loyale that had a oil pressure seal fail causing cavitation. Good oil pressure, but air was filtrating into the oil causing a morbid knock in the upper end (well, side in that) of the motor. Havent investigated what kind of oil pump the 951 has so wouldnt know if it could be the same. Replaced seal and motor ran great.

The subaru is for sale!!! 100 dollars....good transport if your 951 wont run. hehehe

roco16

Ok here's the update:
I decided to run the car for ~ 20 min or so to see if the noise would change. After about 10 min, it got noticeably quieter, and another 10 min after that the noise is almost gone. I say almost, because now it just sounds like really loud lifters, and when I grab the throttle cable a bit the knocking noise becomes much more prevalent....

Is my car fixed? No.

Releasing the throttle cable back to idle, the car immediately starts to have a *hard* time maintaining idle. It sputters and shakes as if I had removed an intercooler pipe.

Bad fuel pressure? Bad fuel pump? Dirty injectors? I don't have any noticeable vacuum leaks.

Let me know what you guys think.

-Robert

roco16

UPDATE:

I pulled the cam housing, and found 1 severely gone lifter, as well as 1 so-so condition lifter. Finally to find something wrong.
I also found some light scratches in the lifter guides. Could this be allowing oil to bypass pressurizeing the lifter, thereby never allowing it to pump up?

-Robert

brad-cam

Robert, any update ? I have similar noise and am following your thread for ideas...

roco16

I am in the middle of resealing the cam tower since it is off, so I still don't know if the new lifters will fix the problem. I'll be sure to post back later (especially if it still knocks) with an update.

-R

Gerald Allgire

My 84 had two bad lifters as a result valves hitting pistons. They were damaged internally and would only pump up part of the time. When they pumped up it was quiet and idled fine. When they didn't pump up it was really, really loud and wouldn't idle hardly at all. When I replaced them the old ones could be depressed by hand. I was able to identify the noisy ones by listening with a screwdriver while the engine was running..

Bugzy

This sounds exactley like the problem I am having with my S2. I put all new lifters in at 90,000 when I had the cam sprockets fixed, I now have 145,000 and it still has the same knock. I did take it to a guy who is known to be a little shady but is knowledgable with the 944. He listened to the car and offered me $2500.00 on the spot for it because he said the motor is shot. I could almost see the dollar signs in his eyes like he knew what the problem was. He was very anxious and persistent about buying the car off of me. I am watching this thread with great interest, Good luck!

Peckster

I had to scrap an S head because of worn lifter bores that wouldn't give them enough pressure. This might be your problem, so get them checked by a machinist.

roco16

Ok guys....The fun continues...

I finished resealing the camshaft seals, and installed 2 new lifters in the bores where the old ones were. All of the lifters went back into their resepective bores. While I had the injector rail off, I resealed the injectors and flowed carb cleaner through each one until the spray was misty/even.

Installed everything, put the car in time, tensioned the belts, and fired it up. I say fired it up but it was more like: hit the starter and let it sputter at 300 rpm before pity sinks in and I kill the motor. Hmm. Check timing-> spot on. So, I tried again. This time it ran briefly at 900 rpm with about 4-5 diesel-sounding knocks, before returning to sputter mode. I tried again but this time giving it a little gas and it just kills the motor.

Brainstorming:

1. Bad Fuel. The car has been sitting since the end of July, running only 2-3 minutes a month since then.
2. Bad spark plug wires. Mine have been replaced, but they aren't Porsche spec wires or anything nice like Magnacore, etc..
3. Problem with the DME/Mass flow sensor.
4. Bad TPS.
5. Bad O2 sensor.


Things I've checked that it can't be:

1. Timing. I swear it is dead on. I've installed about 10 timing belts now.
2. Fuel pump. I installed my buddies fuel rail and measured 44 psi of fuel pressure at idle/sputter.
3. Mechanical interference. Turning the motor over by hand reveals no unusual traits, and compression tests are consistent to what the car is normally

Let me know what you guys think.
-Robert