DBJoe996

Hope you remembered to remove the rags from the intakes. I was hot and tired, did several test fits of the intake plenum and rear crossover plenum to get it just right, was about to start putting in the manifold bolts and remembered, very fortunately, that I had not removed the shop towels stuffed in the intakes. Whew!

996Fever

That rear crossover plenum is a real bear to try to work out with the manifolds in place following Pelican's instructions. I found it's easier to leave it in there until you unbolt the left intake manifold. Then you can move the manifold a little to the left, making it much easier to remove the rear crossover plenum. Using this method on install makes it much easier also.

996Fever

I may have bigger problems than I thought. I'm fairly sure my AOS was bad because there was so much vacuum that is was almost impossible to pull the oil filler cap off. After I got it spinning yesterday and turned it by hand 50 times, I pulled the fuel pump fuse and spun it over with the starter 50 more times. Sounded great. I now do not think there was anything solid stuck inside the engine. Put the fuse back in and started it. Started right up, but it's still smoking. But just from the right exhaust tip. It is also misfiring, probably from a bad plug at the minimum. There is still vacuum at the filler cap when removed, but the cap comes off easy now. If the new AOS was pouring oil into the plenum, I'd think it would blow smoke from both sides, plus I just removed the throttle body and the first plenum looks dry inside. I tasted the inside of the right hand exhaust tip and it was sweet, not oily. I'm thinking my AOS was going, but real failure here is a head gasket or worse. I think when it hydro locked the other day trying to start it, it was on coolant, not oil. It probably made it easier to leak enough into the cylinder to hydro lock when I had all the coolant hoses off and the coolant tank out for a week during the AOS change. It's back up on stands now, mufflers off. In the morning I'm going to pull the drivers side plugs out, see how they look and what's in there, and do a pressure test on the cooling system. Any other ideas?

Ahsai

A little more history of the engine symptoms would help. It sounds like the exhuast was smoking before the AOS change? Was it always on just the right tailpipe (bank 1 cylinders)? Any oil/coolant intermix?

Definitely read this thread. You can see the crack with the spark plug removed.

https://rennlist.com/forums/996-forum/503269-intermix-cracked-head-repair.html

996Fever

Ran like new for 3 years. We went out to eat, when we got there the CE light came on, no smoke still. Drove it home 5 miles. Still not smoking bad. Read up about AOS failures. Went out started it up, now it was smoking good (can't remember if it was one side or both at that time), and you needed to be a strongman to pull the oil filler cap off against the vacuum. So I replaced the AOS. Standard operating procedure. Old AOS does not hold vacuum at the diaphragm and I did have oil in the plenums and manifolds, so I'm figuring it was at least in a slow fail mode. I don't have any foaming in the oil and the AF looks clean. Maybe a head gasket since it only appears to be coolant leaking in the cylinder (maybe). I should have a better idea when I look in the cylinders and do a pressure test on the cooling system in the morning.

Ahsai

If you are sure you got coolant in the cylinders, it's likely you have a cracked head. The head gaskets don't fail on these engines. The fastest way to check for crack is looking into the cyl #1 spark plug tube (photos in the link I posted above. Very common for 3.4 m96.

996Fever

I looked at your link very closely (it's a long one), I will be looking for that as I remove the plugs. That entailed an intermix which I don't seem to have yet, so we will see. Thank you for your input. I value it dearly even if I try to not hope you are right. Cylinder #1 is drivers side front (or rear?) on the 3.4 being a rear engine car? I'm assuming it's the one below the alternator? No bother, I can google it. Thank you again very much.

996Fever

I'm not sure of anything yet. Once again, we will see when I do a coolant pressure test and remove the plugs.

Ahsai

I truly hope you don't have coolant in your cylinders but if you do, a cracked head is the number one culprit.

Cyl#1 is on the left rearmost one. #4 is the right rearmost one.

JohnCA58

I would check your oil for coolant, possibly the coolant passages in your AOS failed along with coolant getting sucked in your intake.

Macster

When the AOS fails it tends to favor one cylnder bank with oil. This is an artifact of the intake system. It is meant to evenly distribute air not liquid.

Thus after replacing the AOS there can be smoke from one exhaust outlet but not the other one when the engine is first started and this can be repeated more than once if the engine is not run very long before being shut off again.

(Even a new and "perfectly" functioning AOS allows some oil vapor through and this impacts the intake wall opposite where the AOS hose connects. This vapor becomes liquid again and tends to flow towards the cylinders one bank.)

If the engine locked on coolant and then you cranked the engine with the plugs out coolant would have spewed out one or more spark plug holes.

Did any coolant spew out?

If you want collect an oil sample and have it analyzed for among other things the presence of antifreeze compounds.

996Fever

Sorry guys, I got called out of town by work for 4 days. Never got a chance to look at it yet. I'm really hoping I don't have a cracked head. Residual oil would be nice, even if it's a wishful thought. I know what you say about the flow favoring one side as the AOS interface at the throttle body is on the left side, meaning any vapor is most likely to flow to the 1-3-5 side. It was misfiring after replacing the AOS and starting it, so either way I need to pull the plugs, pressure test the cooling system, and install new plugs. If the system holds pressure should that mean the head is OK, and how long should it hold pressure? My thought would be a long time since it is a sealed system?

JohnCA58

The manual says to test system to 18.8 psi, but not how long..... I would look for about 15 mins. with no loss, cap check at 20.3 psi open and close at 14.5 psi

996Fever

Hi Guys,
Update time.
So, I pulled the plugs. They all looked fairly good actually (pics below), at the worst 1 and 3 were more damp than the rest, and no cracks can be seen in the spark plug holes. They are also very clean inside.
Pulled fuse "C4" and had the wife crank it over while I watched the bank one plug holes. No liquid, no vapor, nothing visible came out of the holes.
Next I pressure tested the cooling system and it held 19 psi of pressure for 30 minutes without any drop. And, as I said earlier, I don't have any intermix going on, so I think we can dismiss the cracked head thoughts. Hopefully.
The bank one muffler and pipe still had dampness inside, so I'm beginning to think when I started it last weekend that the smoke was just residual oil/AF (not sure which now) from the failed AOS. I put new plugs in and am going to start it again tomorrow. My issue now is to figure out why it was running so bad when I started it last weekend. Whether it was just a fouled plug and will run good now, or if I have something not on right from the AOS change. Going to look at the bellows again before I take it back down to the ground. Fingers crossed. I have a local Porsche event to go to in the morning, so I won't get a chance to get to it until the afternoon.

1-3-5


2-4-6



Randy
2001 996 Cab 6 spd
1986.5 928 Auto
Various other not as cool cars

996Fever

No smoke now, but still running bad. Rough. Idle fluctuates between 1700 and 400, backfiring when it gets low. Only let it run about three of these idle cycles and shut her down. I must have something not right from the AOS change. I'm going to make sure the bellows is on correctly, but what else could it be? Intake leak? Some sensor I disturbed? Thanks in advance.
Randy