New Member with engine noises..

[BmXRacR96]

Hello all. This is my first post here on this forum. I have a 1993 Formula A4. Vehicle is very well kept. Been a mechanic for the past 9 years. but having a problem with an annoying noise at 2200-2400rpm, which i cannot figure out. I run an auto shop, and have unlimited access to all diagnostic tools except a scope. Now to the problem.

It makes this noise regardless driving down the road or sitting still and reving. Sounds like a harmonic noise, something how a worn out wheel bearing sounds at 60mph. Its not wheel bearings cause it also does this at a stand still with reving to 2200-2400rpm. Previous to this noise i had the motor mounts collapse, front of the motor nose dived into the sway bar, but not hard. After finding out I cannot buy them aftermarket and the dealer wanted $85 (wholesale) each, i installed energy suspension inserts and new ES trans mount. At that point i noticed this noise. At that point I found out that the 94 Impala used a similer center piece in their mount(aftermarket by Pioneer). Tried that. Same noise. Finally bought an OEM mount... Installed.. and SAME noise with slight variations between each. At the same time installing the mounts I removed the front half of the echaust and welded a new converter on(original was hollowed out by previous owner). Converter was exact size replacement, just a weld on unit.

Each time changing the mounts i checked around the engine looking for any contact with the body. All areas had atleast 1/2" to 3/4" minimum in between engine/trans and body. Also no signs of shiny metal from something hitting it.

Things checked today:

Checked with snap-on scanner found:
No Codes.(OBD1)
both O2's slow, the right side was worse(02's only 3 months old),
TPS read 0-100%, .8volts to 5volts. Should be OK.
Blocklearn was 113 on left bank and 111 on right bank. Which would show computer compensated lean for an overly rich condition..
Ignition wires are Taylor with MSD Sleeving. (12mo old) no arcing found.
Opti is Delco, replaced a few months ago. Roughly 8k on it.
NGK Dbl Plat plugs replaced with opti.

Known Mods:
Lingenfelter 58mm throttle body
Port matched intake
Flow master muffler with stock pipes
I was told motor was stock, but i beleive there is a cam installed, but mild.
Not sure if PCM was tuned. Prom chip has a Small yellow smiley face sticker on it. Not something i that GM would put on, but im not sure. Also i found knock sensor is not working. all wires are good. but does not respond.

All these mods have been on for about 2 years and never had a noise problem. Fuel mileage is roughly 17/25 on midgrade fuel.

Tomorrow i will be doing a power balance test, rechecking fuel pressure, and installing new delco dbl plat plugs. Also new replacement O2 sensors.

Sorry for the long post. Im just trying to get everything out at once. Has anyone had a similar problem? What else is left to check? Any offers to trade your prestine 98+ T/A or SS for my broken car will be accepted...

Thanks guys. Please help if you can.

Doug

[TraceZ]

remove the serp belt and rev it to 2200

see if it still makes the noise.

[BmXRacR96]

Yes it does, Tryied that too. forgot to put that in there.

Doug

[fastTa]

It's not uncommon for the harmonic damper on the LT1's to separate from the rubber damper ring. If it has been separated for a while, it could be wreaking havoc on the #1 main bearing and "squeeling."

Another thought could be any part of the water pump drive assembly. Since the water pump is cam driven, there are several places internally and on the back of the pump that are subject to bearing failure. Is the water pump weep hole dripping?

[BmXRacR96]

Balancer was replaced 3 months ago
Waterpump was replaced with the opti, No leaks right now, also used a stethescope and its not making any noise that i can hear.


This noise has been going on for 3 months now with only slight variations. It hasnt gotten any louder or changed drastically like normal wear and tear noises do..

So confused.... Thanks for all your help guys.

Doug

[fastTa]

Since you say it sounds like a wheel bearing type noise and still makes the noise even with the serpentine belt off, the only other thing I can think of off the top of my head is the thrust bearing. I see the car is an auto. It is not very common, but sometimes a malfunctioning torque converter can prematurely wear the thrust bearing.

Could be a walked cam bearing as well. Is the oil pressure good?

Do you have any way of posting a sound clip of the noise?

[BmXRacR96]

Torque converter seal and bearing replaced last year. It was replaced due to leaky seal. but no probs since then. By thrust bearing, do you mean the main bearings? If so wouldnt it be noisy all the time? Also it has been doing this for atleast 3 months. Wouldnt the bearing burn up by then? It had not gotten louder since it first happened. and Oil is clean when being changed(its not shiny with metal)

Oil pressure is good, has not changed in the past year or so. does not sound like a cam bearing noise. Maybe the word noise does not describe it correctly. Its more like a humming resonance sound like a very loud exhaust coming from the front passenger side(i think, it somewhat drowns out everything and with an exhaust it doesnt help either) and only at 2200-2400rpm.

Doug

[BmXRacR96]

No new information yet. Will get down to the shop tomorrow to run more tests..

Thanks
Doug

[fastTa]

Torque converter seal and bearing replaced last year. It was replaced due to leaky seal. but no probs since then. By thrust bearing, do you mean the main bearings? If so wouldnt it be noisy all the time? Also it has been doing this for atleast 3 months. Wouldnt the bearing burn up by then? It had not gotten louder since it first happened. and Oil is clean when being changed(its not shiny with metal)

Oil pressure is good, has not changed in the past year or so. does not sound like a cam bearing noise. Maybe the word noise does not describe it correctly. Its more like a humming resonance sound like a very loud exhaust coming from the front passenger side(i think, it somewhat drowns out everything and with an exhaust it doesnt help either) and only at 2200-2400rpm.

Doug

The fact that the seal had to be replaced could be a sign that the TC's stator/stator support was worn and was allowing the TC to place abnormal forward pressure on the crank. If the stator assembly has as little as .030"-.040" of end play, it can prematurely wear the thrust bearing. On a small block Chevy, the thrust bearing is the #3 or middle main bearing.

A badly worn thrust bearing will usually wipe out the other 4 main bearing but not always. And when the thrust bearing gets abnormally worn, it will cause a weird harmonic vibration type noise.

But, obviously I am just completely guessing and tossing out ideas since I cannot hear the noise in person.

[BmXRacR96]

Does anyone have a part breakdown of where the front subframe meets the body? Is there bushings in between or spacers? Has anyone had these go bad? I have never taked the subframe down so i am unsure. Once again Thanks

Doug

[fastTa]

Does anyone have a part breakdown of where the front subframe meets the body? Is there bushings in between or spacers? Has anyone had these go bad? I have never taked the subframe down so i am unsure. Once again Thanks

Doug

No, there are no rubber isolators between the k-member and the frame rail like the Dodges. The k-member bolts directly to the frame rail with 3 large bolts on each side.

When the motor mounts were replaced, was the whole clamshell replaced or just the rubber isolator inside?

Have you checked to see if the k-member stand on the driver's side of the k-member has come loose? The k-member stand is what bolts between the driver's side clamshell motor mount and the k-member.

[BmXRacR96]

FastTA,

Passenger side entire mount was replaced, the cage and the insert with a GM unit. I will check the driver side stand even though i hear it mostly on the passenger side. it wont hurt to check. im beginning to think its exhaust related, but theres no contact with the body anywhere.. will look more into it.. thanks. this will get fixed one day..

doug

[Injuneer]

Was there any evidence of damage to the front of the engine when "front of the motor nose dived into the sway bar"? Have you checked the timing cover for damage?

[BmXRacR96]

There is no damage to the front of the engine. The engine did not hit hard, the balancer was just skimming it while under a load. There was no damage done to the balancer from this, I replaced it cause it was questionable.

BTW also just picked up a T56 from a bud at a junk yard. The 95 T/A came in totaled after a tree jumped infront of it. Other than that was in good shape. They claim if the vehicle comes in unable to drive, the transmissions are questionable and automatically receive the name CORE so their not liable to offer any warranty..So i got it for $75. So i got a 50/50 chance. Ever gear shifts smoothly and easily on the bench, no grinding or harsh gear lash. Transmission fluid came out nice a nice red color and clean.

Even if needs a minor rebuild, I got a friend in a tranny shop that will do it on the side.. The benifits of working at a private auto shop

Now i just need to fix that noise from the motor..

Oh yea if anyones got:
pedals
clutch slave/master/hose
aftermarket shifter
t56 wiring pigtails
New clutch
bell housing with cover
Clutch fork
Center console from 98+ bird, for a M6 and lower shift boot
t56 crossmember (isnt this the same as A4?)
torque arm bracket (isnt this the same also?)


let me know they are needed.

Thanks Doug

[Jeff_in_Atl]

Here's a really good write up on the conversion. http://www.afrashteh.com/tranny_pics/T56.htm

I got my conversion parts from http://www.tennesseeauto.com/