knocking - piston slap or because its runnin lean??

[ArcticCatJay]

So I have a 94 AWD TSI. Well last night I finally got the tires taken care of and reg. and insurance on it, so i could take it for a ride. When I got back, I noticed a loud knock around 2k-3K. Sounded like rod knock or piston slap. The car is 100% stock and has 156k on it. I pulled the plugs and they all appear to be running lean (they are all whiteish color). I don't have a logger or anything like that, nor do I know how to use one. I just can't figure out why all of a sudden the knock appeared and it started running lean. Even after I started it the first tim after sitting so long, it didn't do that.

There is only one o2 sensor on the 1g's right?? What else would make the car run lean??

Can someone please help?!? I'm about to give up on the car and sell it, but I really don't want to!!

 

[95blackGsTurbo]

If it is making it in the 2-3k range odds are it is knock. Easiest way to tell is start it, rev it to the range where it makes the noise and then one by one pull off the spark plug wire. This will take the load off the cylinder and cause the noise to go away on the rod that is knocking. Just do them one by one and see if it changes. Piston slap is pretty rare on a stock motor. Usually happen on rebuilds when piston to wall clearance isn't checked.

 

[ArcticCatJay]

Thanks for the response...that is a good idea! I will definitely try that. I have a video of it too, but i can't get it to upload. The knock is pretty loud, and when I put my hand on the throttle in the engine compartment to rev it up, I can feel it in my hand.

The knock however sounds like its up high in the engine, which made me think is has something to do with it running way too lean. Is it possible really bad gas would cause it to run lean and possibily knock??? I just want to rule out all possibilities before I decide if I should sell it or not. thanks

 

[95blackGsTurbo]

Bad gas will cause it to make some noise but not like you are describing. If that doesn't help pull the valve cover and check the lifters and springs.

 

[ArcticCatJay]

I let the car idle the other day for while and I still have the knock. The more I think about it and listen to it, I think its a compression knock due to it running lean. Like I stated before, the gas in the tank is about 4 years old and of course there is about 3/4 of a tank too. The o2 sensor was new when the car died on me 4 years ago.

Here is a dumb question...since my 1g only has one O2 sensor and its in the manifold, a rusted cat wouldn't contribute to it running lean.

Also, my exhaust manifold is crack and leaking, but wouldn't that make the car run rich according to the O2 sensor reading more air coming in?

I have been reading other post trying to figure this out. I read something say the FPR could make it run lean too. Is this FPR at the end of the fuel rail? How much are they? I just need a stock FPR. I need some ideas for a place to start...any ideas? PLEASE???!!???

 

[jrohner]

If it does it when you're not boosting, just in neutral, I wouldn't believe lean could cause it (unless it was lean when boosting and took out a piston). You can run about as lean as you want when not under load without issues. The bearings are probably on their way out.

 

[1g6boltAWDkilla]

damn the gas is 4 years old. why did you let it sit so long? Why didnt you drop the tank and drain that old gas? Just curious.

 

[Littlebeeper]

damn the gas is 4 years old. why did you let it sit so long? Why didnt you drop the tank and drain that old gas? Just curious.

why didn't you remove the gas tank drain bolt and drained the old ass gas.......yes the gas tanks have a drain plug on 1g's (maybe even 2g's)

 

[ArcticCatJay]

I sold the car to a friend of mine and it sat for 4 years and he never did anything with it. I just bought it back and got it running. I honestly didn't know there was a drain plug in the tank. The car is an AWD, and it is probably behind the cover on the bottom of the tank.

I didn't drop the tank cause the car is at my parents house and I don't have alot of time to work on it. I'm gonna try changing the gas and a few other things. If that doesn't work, she may be going up for sale...any interest?

 

[skylinegtr00440]

im having same issue with my dsm. except my noise started as a small tickand go progressively louder as like a week went by. it knocks hard on first start up then after engine is warm at idle its fine till it hits roughly 2k-3k rpms. Oil pressure perfect, engine starts perfect, compression perfect.

 

[ArcticCatJay]

Well I'm glad that someone else is having the same problem as me. (I would rather neither of us have the problem though! haha) Something just isn't right and I can't put my finger on it. This knock just came out of nowhere...it can't really be heard at idle. I was so close to getting it back on the road, then this happened, and I don't want to drive it till i figure out what is wrong with it. I don't want to destroy anything!

 

[skylinegtr00440]

i was told my motor was junk now because of it but if i can save my motor i would love to. does anyone got any suggestions for us as to if the motors are fine and just need to change some stuff out or what?

 

[ArcticCatJay]

How many miles do you have on your motor?? Mine has 156K on it. I changed the timing belt about 5K ago and when we had the head off, the head and cylinder walls looked brand new!! If my knock is a rod knock, then the motor is in trouble too, however, i'm not completely convinced that is what it is. Like I said, the knocking just started, it ran for a few hours with nothing. I'm not giving up on it yet. I'm trying to do some more research on things that could make it run lean. A bad FPR could cause it. Let me know what you find out, and i'll do the same

 

[Patamos]

hey i think i have the same problem, i had it running on 3 cylinders without the exhaust manifold, (the flames were so cool) and as soon as i got it running on four cylinders i got this knocking noise that sounds like piston slap, however it doesnt make the noise when the gas is let off, and the rpms are going down, when under power it makes the noise again or at idle. now i had a machine shop hone and bore it with 85.5 2g pistons, and the piston to wall clearance is .0012" or twelve thousandths of an inch. Could this be a possibility of piston slap or not? I dont know about the cylinder head i got it complete from another guy who said it had 70 miles on it? any help?

 

[sho_shane]

im having same issue with my dsm. except my noise started as a small tickand go progressively louder as like a week went by. it knocks hard on first start up then after engine is warm at idle its fine till it hits roughly 2k-3k rpms. Oil pressure perfect, engine starts perfect, compression perfect.

Yours is for sure a rod knock. Im sorry to tell you that. But the knock you hear when you first fire it up is the bearings not having any oil on/in them and the knock at 2-3K is common for a rod knock.

 

[GooeyGus]

hey i think i have the same problem, i had it running on 3 cylinders without the exhaust manifold, (the flames were so cool) and as soon as i got it running on four cylinders i got this knocking noise that sounds like piston slap, however it doesnt make the noise when the gas is let off, and the rpms are going down, when under power it makes the noise again or at idle. now i had a machine shop hone and bore it with 85.5 2g pistons, and the piston to wall clearance is .0012" or twelve thousandths of an inch. Could this be a possibility of piston slap or not? I dont know about the cylinder head i got it complete from another guy who said it had 70 miles on it? any help?

twelve thousandths of an inch is .012", .0012" is 12 ten-thousandths of an inch.

I just wanted to clear that up. unfortunately I'm not sure of what the PTW clearance should actually be, so I cant comment on that

 

[Patamos]

twelve thousandths of an inch is .012", .0012" is 12 ten-thousandths of an inch.

I just wanted to clear that up. unfortunately I'm not sure of what the PTW clearance should actually be, so I cant comment on that

wow i cant believe im answering my own question. i looked in both the haynes and chiltons manual and it said that the piston to wall clearance is 12-20 thousands of an inch. so im positive that its not the problem. It must be the valvetrain cause it only makes the noise when under load. Plus i bought the cylinder head, and the guy told me that it had about seventy miles on it built to flow 500hp. i think he was lying out of his butt.

 

[GooeyGus]

Usually noise under load will be the bottom end. The valvetrain does basically the same amount of work, regardless of load. 5000rpm at WOT going 100+ and 5000rpm free revving in neutral puts basically the same amount of load on the top end.

Noise from the bottom end will definitely change with load. The knock from the bottom end is usually a rod and the crank making metal on metal contact due to a bad bearing. If there is no load on the engine, oil will fill in the cracks and prevent the surfaces from hitting, but once there is a greater load the force breaks down the oil barrier and you get knocking.

Pull the spark plug wires off one at a time and see if the noise stops when one cylinder isn't firing.

 

[Patamos]

i know for sure that as soon as i got the number four cylinder firing, that then the noise started. and from one of my previous posts i had drained the oil from my car, and accidentally ran it for about 30 seconds so then bearing damage would be most likely to cause it then.

also if i have bearing damage, would i have cam bearing damage as well?