924Board.org

[rixxertii]

Alright guys, I am having some serous issues with my 931.
Originally I recieved the car and it wasnt running well, not good power, idled rough, the works. I got the car after it had been sitting for at least 2 years and not run during that time.
I changed the air filter, oil, fuel filter, plugs, plug wires, cap and rotor, and nothing seemed to help the hesitation and bucking I got under load. Therefore I took my injectors to be flow tested, and 3 were clogged so bad I couldnt even use them, 1 was fine and almost brand new, so I replaced all 4 of them with brand new Bosch injectors.
Now for the lousy part....the car still doesnt run for crap, it bucks, hesitates, feels like I have some massive ignition problem, but I know that I have good spark!! The coil is the only part I havent repalced yet and I intend to do that tomorrow.
To add yet another layer to this lovely problem, I pulled off my upper intake, and found a nice layer of oil right after the turbo, I cleaned it, ran the car for a few minutes, opened it back up and there the oil was again.
Now, one final thing, (I promise:)), I have some massive amount of oil/vapor coming out the breather hose off of the puralator filter that empties into the air box, I know a small amount of oil vapor is normal, but this is smoking so much that it rolls out from under the hood at idle.
If anyone can help with any of these problems I would be most appreciative, thanks
Joel
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1980 931 - just bought it
1996 Ford T-bird - system car.
Other things, but we dont talk about them for fear that it may incarcerate me.......I had hoped that I had grown up and gotten the speed out of my system but its to damn addictive.

[Lizard]

Joel

replace the WUR on the car, and the frequency valve if the car is a O2 sensor equiped car, this should help the bucking, but you MAY need a new fuel pump,

as for the oil in intake the turbo seals are shot and you will have to pull the turbo and have it rebuilt, you can do this with the engine in the car, but it is not easy by any stretch of the imagination,

as for the smoke coming out of the crank breather, it is time to do a compression check and a leakage test as you probably have cooked rings, if you do, pull the engine and rebuild it and the turbo and then reinstall, if your exhaust manifold has cracks dont bother repairing as it will just recrack again, if you wish to spend the money you could have one made out of stainless,

a couple of notes,
the exhaust housing on the turbo will HAVE to be replaced as will the heat shield just inside that housing!.
also the 931 is an interference engine and the timing belt should be replaced every 45kmiles, however most of these cars odometers dont work, so just change it about once a year,

and welcome aboard
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3 928s,

[numbbers]

Well, if it has been sitting for two years, I would guess that the rings are just stuck. Once you get it running OK, just take it for a good long hard run, and they might free up. The same may happen with the turbo seals, as they are just rings just like your piston rings. My guess is they are all a little rusty.
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1980 924 Turbo

[rixxertii]

Lizard:
Wow, that is really not at all what I was hoping to hear, but I had feared that that was what it was...alright, lemme tackle these one at a time then.

When I said bucking, I mean serious power loss, as in, one second I will be pushed into my seat and the next the car isnt moving at all. Is that what is caused by the pressure regulator and frequency valve? (forgive my ignorance, I am new to this engine)

My question about the oil seals being shot in the turbo is that I have never seen a turbo act this way and blow oil into the intake, every turbo thats gone bad on me has smoked like a mother whenever it was revved up. Again, is this a characteristic of this car, or should I be looking for smoke out the tailpipe to 100% conifirm leaking seals inside the turbo? Also, is it recomended to buy a professionally rebuilt unit, or are the rebuild kits such as available from turbo city and the like a decent alternative?

I did a compression check on the engine about 15 minutes ago and it came up as follows from front to back:
#1: 100PSI
#2: 130PSI
#3: 110PSI
#4: 110PSI
Are these acceptable numbers for this engine? (and to perhaps help out a possible stuck ring on #1 I poured some marvel mystery oil into the cylinders and turned it over a few times, letting it sit until tomorrow.)

About the exhaust manifold...where do they generally crack, I have some crack sensing dye I use for weld testing, so I can check it out on a near molecular level , I just need to know where to look.

The timing belt is on order right now and should be changed by next week. Thanks very much for your help, and I am glad to be here, you guys seem to know just what is going on with these cars and I am sure will provide an invaluable resource in the trials that await me
Joel
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1980 931 - just bought it
1996 Ford T-bird - system car.
Other things, but we dont talk about them for fear that it may incarcerate me.......I had hoped that I had grown up and gotten the speed out of my system but its to damn addictive.

[Smoothie]

Excessive piston ring blowby would account for both the large amount of oil vapor from the breather and less than wonderful running. A compression test will reveal what's going on there. Most likely the rings need replacing, but there are quick-easy-cheap things to try first such as Techron fuel injector cleaner and a top cylinder cleaner such as Marvel Mystery Oil (sorry, I didn't name the stuff, but it's good (kinda smells nice too)) Both of these can help break down and rid the valves, cylinders and rings of carbon and other assorted gunk. It's possible for rings to be gunked up and not floating freely in the piston grooves thereby not sealing and allowing excessive blowby - just quick-easy stuff that makes sense to try before tearing down the engine. A cleaner like Marvel Mystery Oil can be squirted into each cylinder through the plug holes, spin the engine with the starter to distribute the stuff around the rings, then let it sit a while to do its' work. This could be done in conjunction with the compression test - (1)- dry compression test (2)- wet compression test (with oil injected into cylinders) (3)- clean cylinders-rings with MMO or whatever (4)- compression test again. If this doesn't cause a marked improvement, then the ring job and whatever else should be done.

I get a light coating of oil in the plumbing between turbo and intake manifold with my good turbo and engine that burns so little oil it's not noticable. With that and since you're not getting a lot of smoke out the exhaust I'm not convinced you even have a problem there.

Any other symptoms with the hesitation? For instance - does it occur only at low rpm, high rpm, at a specific rpm, only when starting out, under load, etc.?
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"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[Smoothie]

Ok, so I type slow... 3 replies since I started.
Glad to hear you already know about MMO - I'm always pretty sure people think I've fallen off my rocker when I mention that name.

With your updated description of the bucking, it's possible that what you have is a malfunctioning wastegate (torn WG diaphragm). With that, you get unlimited boost (presses you back in your seat) followed by an abrupt halt as the overboost cutoff switch kicks in and shuts down the fuel pumps. When it happens, it feels like you're going to be thrown through the windsheild.
If what you're experiencing is less severe than that, there's something else to look at - The lower pressure pipe (the small section that's mated to the outlet of the turbo with an o-ring joint)... this pipe should be connected to the front of the block via a small bracket. It's not unusual for one of the bolts on that bracket to fail - constant vibrations tend to cause the bolt to be sheared in half. So, check that bracket. If it's not secure, you'll have good running at lower rpms, but then at higher rpms and as boost builds, the boost pressure will push open that joint between the turbo and pipe, releasing air there which in turn also screws up the air:fuel mix resulting in hesitation, bucking, etc.
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"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[Khal]

rixxertii, I'm definitely no expert in these matters But your compression seems low compared to mine -and I thought mine was low, I had been told that about 160psi should be about right Can anyone confirm what the compression should be?

Mine was;

1 = 152psi
2 = 142psi
3 = 146psi
4 = 132psi

Mine was done "dry" (I think I didn't add any oil to the cylinders before testing -just pulled the spark plug and started cranking, after the car had been sitting for some time)

If it's the case that you're losing compression, it could lend weight to the theory that your rings are buggered, no?

Does a cracked exhaust manifold or blown turbo seal affect compression?
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'80 924 Turbo

[Smoothie]

Last time I checked mine, I was getting 135-140 psi dry and around 160 psi oiled.

Cracked manifold and bad turbo seals don't affect compression. Things that affect compression are worn rings, cylinder wall wear (out-of-round, scratches, etc.), valves (burnt, out of adjustment), leaky/blown head gasket, incorrect valve timing.

The usual place for the exhaust manifold to crack is on the bottom of runner 2.
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"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[rixxertii]

Khal - yeah, that would lead me to believe that my rings are indeed "buggered" (I like that word )....however I am not sure at all what acceptable compression reading are for this car, if anyone can lend me a hand with some solid info on that I would be appreciative. And no, I dont think that a cracked manifold or blown turbo seal would affect compression, since a the manifold has no direct affect on compression and a turbo seal being blown wouldnt be noticeable to pressure variations inside the chamber until higher RPM's where a boost increase should be present...someone please correct me if I am wrong on that one though.

Smoothie - I am going to have to check out that bracket tomorrow and see if maybe one of those bolts is truly sheered off..heres hoping that that will be a part of the problem as it is a relatively simple fix. Also, when you say light coating, how light are we talking here? I have a visible film, but not enough so that it beads and runs down the lower plenum there, but a definite noticeable amount.
Joel
_________________
1980 931 - just bought it
1996 Ford T-bird - system car.
Other things, but we dont talk about them for fear that it may incarcerate me.......I had hoped that I had grown up and gotten the speed out of my system but its to damn addictive.

[Smoothie]

[Khal]

Well, mine ran just fine with the compression reading stated above. And with Smoothies response, I think you can safely assume that your compression is at best only about 80% of what it should be.

I always thought that once the rings were shot, it's rebuild time. Could be wrong. numbbers seems to think a good thrashing might fix it (I like that idea... anyone seen Fawlty Towers )

Of course, there's always the chance it's a blown head gasket or your timing's out. Here's hoping. At least you won't require a rebuild.
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'80 924 Turbo

[CMXXXI]

I too get a coating of oil inside the pressure duct running from the compressor to the throttle body, so I'm with Smoothie on that, that I don't think it's an issue. Actually, I think he has pretty well covered the bases. Do be aware though, that several of us who have rebuilt our engines have discovered broken rings, so it is not that uncommon of an occurance. Running with broken rings opens you up to all sorts of bigger potential problems, like damaging pistons or scoring the cylinder walls.
Click for more photos

The bolt holding that duct on mine has not sheared, but it has pretty well messed up the threads in the aluminum duct. I put in a slightly longer bolt than original in order to hold things, but I suspect I'll have to put in some sort of insert the next time I have to make a fix on it.

I'd hold off on replacing the control pressure regulator until I exhausted all other avenues. It's an expensive part, and unless you have a CIS test gauge to validate it, you may be just throwing money away. It is possible, perhaps even likely it is contributing to your problem (cars that sit for years un-used frequently have many fuel system issues), but normally it will affect cold engine vs. warmed up engine performance, both at idle and/or under load moreso than cause sudden changes under constant conditions.

The exhaust manifolds come in a couple/three varieties depending on the manufacture date, but normally when they do crack, the cracks appear underneath the #2 runner like Smoothie said. Not huge gaping seams, but cracks none-the-less. Here's a photo of the two styles, you can see the newer one has a reinforcement "web" added. The old style one in the photo has a crack (circled) that you can just make out if you look closely. As you can see/imagine, actually seeing the cracks while the manifold is in the car is not a simple matter.
Click for larger image
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'79 Eurospec 931