Mystery Noise in 96 STS

[LindaSpencer]

Can someone please help me. I have a 1996 STS with 59,000 miles on it, I have a noice that sounds like a tapping noice or a broken belt. I've been to 4 mechanics whom have ruled out that it is the water pump, fuel pump, broken belt, power steering pump etc. Would anyone have somewhat of an idea?

[BodybyFisher]

Can someone please help me. I have a 1996 STS with 59,000 miles on it, I have a noice that sounds like a tapping noice or a broken belt. I've been to 4 mechanics whom have ruled out that it is the water pump, fuel pump, broken belt, power steering pump etc. Would anyone have somewhat of an idea?

Noises are the most difficult thing to diagnose in this medium. If you had a digital recorder you could record it..and email it to me, that would help.

That said, I have a 96 Deville pretty much the same setup with the exception of horsepower (cams). Now I want you to be safe here and careful. But go buy a 3/4" heater hose about 3 feet long. Carefully and I mean carefully (no long sleeves, scarfs, chains, pony tails hanging, ), put the hose by your ear and put it next to all the turning components. Components to listen to are the Serp tensioner wheel, Idler wheel, AC hub, Alternator (generator in picture) and harmonic balancer. DO NOT put your self at risk and keep your hands and arms and the hose away from the turned belts and wheels. For the HELL of it you could remove the serp belt and start the engine BRIEFLY and see if the noise is gone...BRIEFLY... that will give you and indication that its an accessory turning noise or internal engine noise. While the belt is off, you could turn each accessory and wheel by hand (while the car is OFF) and see if the bearings are rough, dry, loose, wobbly or noisy....

Here is a diagram of the front of the engine, let me know what you find out, Mike

[LINDAL]

Some of you may laugh at me but, I had a noise on my 95 sts and I was sure it was the front driver wheel. It was a popping noise, I pulled over more than once thinking it was the wheel. It turned out to be my stupid speaker in the door on the drivers side.

Go ahead and laugh. But, I thought it might help someone else with a mystery noise. Especially, if the mechanic's don't find it, maybe it is something really simple.

[BodybyFisher]

na I'm not going to laugh!

I understand whole heartedly

For a year I was hearing noise on my roof, I looked at it and could find nothing

Then one day I was driving about 65 and my fake convertible top EXPLODED off the car and hit the car behind me. The noise I was hearing was the fiberglass shell, that had broken loose (adheasive broke loose) and it rattled for a year...

[Cadillac Jim]

You need someone who is familiar with later model cars and the on-board diagnostic (OBD) computers. You car has the second generation, called OBD-II. There is a connector under the dashboard, above and to the left of the brake pedal that they can hook a cable to and read the codes. On your car, there is a way you can do this yourself. Click here for instructions on how to do it for your car. Write them down and post them in a reply to this thread. That will tell us what to look for. Without the codes we can only guess.

On your car, I belive that you can read the codes as follows. If these directions don't make sense, follow the link above to get the OBD-II codes from your car.

Turn the key on and start the engine, and let it idle in Park. On the A/C controls below the radio, press OFF and the cooler (down) side of the rocker switch for the passenger side temperature at the far right of the A/C buttons, both together, for about 5 seconds. When all the lights on the radio and dashboard come on at once, release and start watching the driver information display below the speedometer.

You will see a series of messages such as "NO RFC CODES," E010 HISTORY," and "E011." The OBD codes are the parts of each message with single letters followed by three numbers. If one doesn't have "HISTORY" after it, mark it as "current" when you post it here. There will always be some history codes because the OBD-II is always taking notes for any mechanic who might check them, and it keeps them for months. When you finally see "PCM?" then press the "Info reset" button above the radio to turn off the OBD II scan. You are done, and have accomplished what some shops charge $65.00 to do.

59,000 miles is very low mileage for a 1996 model. You might look at when the car was last serviced, and what grade of oil they put in it. If it has been over six months, or they put the wrong oil in it, then it could be just a valve lifter sticking -- something that would probably clear up with new 10W-30 oil and a filter, followed by a 30-mile drive without a lot of stoplights. If there are no codes of any consequence on the OBD-II readout, then that's what I would look at first.

[LindaSpencer]

Thanks Mike! We've done those checks, it is definitely an internal engine noise. Unfortunately, these mechanics seem to be shying away from the car because it takes so much work to go into the engine? Is that true?

Thanks LindaL, but it's definitely not a speaker, lol.....

[BodybyFisher]

Thanks Mike! We've done those checks, it is definitely an internal engine noise. Unfortunately, these mechanics seem to be shying away from the car because it takes so much work to go into the engine? Is that true?

Thanks LindaL, but it's definitely not a speaker, lol.....

You might be suffering from the COLD CARBON RAP. Do a search in the archives under cold carbon rap... (it happens when the engine is warm also)

Here is something that Ranger posted it describes it nicely... Change your oil, make sure its not low (on stick) before you do any WOT procedures. Here is the rap or knock desciption is this what you are getting?:

***************************************************************************

Occasional Full-Throttle Acceleration Is Good For Your Engine

There are many advantages to occasional full throttle accelerations with a Northstar and any engine.

It keeps the carbon cleaned out of the combustion chamber. This is maybe a little more important with the Northstar than some other engines due to the tight squish volumes between the piston and the cylinder head. It's designed this way to promote good in-cylinder mixture motion (good combustion) but it has the down side of providing a ready place for carbon build-up to touch the piston - causing noise. Ever heard of the Northstar "cold carbon rap" problem?? Simply put you'll hear a rythmic, piston slap-like noise when the engine is cold. Very prominent and very annoying. Cause: excessive carbon build up causing the the piston to contact the carbon on the head - causing it to rock in the bore and "slap" Much more evident when the engine is cold and the pistons haven't expanded to full diameter yet. Simplest and easiest "fix" for this: A few good WOT (wide open throttle) accelerations to clear the carbon out. That is all it takes to eliminate the problem and prevent it from re-occurring.

Occasional WOT accelerations also help seat the rings to the ring lands and exercise the rings and keep them mobile and from becoming stuck in carbon in the ring lands. At high RPM and WOT the rings move around on the piston - they actually rotate on the piston and will polish away any carbon and seat themselves to the sides of the ring grooves. This is especially important on the 2000 and later Northstars which had hard anodized top ring lands on the pistons. Very hard and wear resistant - also harder to break-in and seat the rings to the sides of the ring-lands to promote the best possible seal. Many oil consumption complaints on the 2000 and later engines are related, to some extent, with the rings never seating to the sides of the ring-grooves due to lack of load as the engine was babied around forever. Even engines with rings stuck in the ring-grooves due to carbon build up can eventually be freed up with enough high RPM operation.

WOTs warm up the engine thoroughly and clean out the exhaust due to temperature in the exhaust and high flow rates blasting particles, rust and such out of the system.

Frequent WOT operation will not hurt the engine or the transmission. They're designed for that. The healthiest engines that I have seen at high miles are always the ones that are run the hardest. Rings are free on the pistons and sealing; no carbon buildup.

The exercise that I think works best for many things is to select manual 2nd gear on an isolated stretch of expressway. This takes the transmission shifting out of the question if you are worried about hurting it. Start at 55 MPH or so and go to WOT in 2nd gear and hold it until the RPM reaches near the normal shift point - i.e. 6500 for an L37 and 6000 for an LD8. Hold the throttle wide open until the engine reaches, say, 6200 for an STS and then just let completely off the throttle. Leave the transmission in 2nd so that the engine brakes the car and creates some pretty heavy over-run conditions at high vacuum levels. Let it slow until it is about 55 or so and then go to WOT again and repeat. This exercise really loads the rings, allows variable RPM operation at WOT for several seconds continuously, creates heavy over-run which tends to unload the rings and make them move and thus exercise them in the ring grooves and it will blow-out carbon and the exhaust - all without creating a spectical of yourself and attracting the attention of cops. You can do it on most any freeway and stay within the 70-75 MPH range allowable. Once a week like this will keep the engine cleaned out and healthy and is DEFINITELY recommended for the Northstar in particular.

The Northstar engine was designed/developed/validated to be run hard. It was expected that people would use the performance of the engine - which few people seem to do. The biggest single problem that many issues stem from is lack of use at full throttle by the owners. It just doesn't like to be babied around. The rings are low-tension by design for good high RPM operating characteristics and low friction/good power. They work best if "used" and kept free.

In every conversation with owners I have had, once the owner started doing the WOTs and using the power of the engine they report no more carbon rap, better oil economy, no "smoke" when they do light it up (keep the exhaust cleaned out. If you notice a "cloud" at WOT then you are not doing enough WOTs...) etc... A bit of judicious use of the other end of the throttle travel is a GOOD thing...

[LindaSpencer]

MIKE, I am so impressed with your knowledge of these cars! I just want to also tell you that I do drive around town and not without much WOT. The noise started actually started after gunning it several times on a highway trip to do just what you said, do you know what that would be? And should I take it to the dealer? I really want to get the car fixed. I'm just afraid they're gonna rob me.

[BodybyFisher]

How loud is the noise?

I would change the oil put a high quality 10W30 in her, new filter and see what happens. Sometimes the oil can become diluited and noises become apparent.. You have a 96 like me, there was a discussion yesterday about Delvac 15W40, you might try using that once and see how you like it.... You can buy it in my neighborhood at Costco...

Good Luck and thanks for the nice comment... its just from spending so much time here and loving cadillacs and mechanics since I was a tot...

[The Fred]

I don't know a fourth of what these guys know about this but check your oil pressure.. my stupid ex wifes little chinese car was tapping at me once when the oil pump was going out

[Ranger]

Linda,

Does this "tapping" noise go way after a few seconds or is it constant? Does it increase with RPM? A stethescope can be had relatively cheaply from any parts store and would be a great help in locating it. Mike's hose trick also works very well.

Maybe your STS knows that you are looking for a Deville and is just acting out.

[JohnnyG]

I'm with BodybyFisher on his first post, but he seemed to be backing off of his original diagnosis on his second post. A 1996 with 56,000 miles seems to be a prime candidate for carbon buildup of any kind. We all really need to know more about the noise, like when it occurs, when it is most noticeable, how loud it is relative to something else, etc.

I'm not sure where the "change the oil first" stuff came from, but I'd take it out and run the heck out of it a couple of times. Doing the WOT, or just take some highway on-ramps with the throttle to the floor. As to oil grade or weight, at 56,000 miles, your engine is barely broken in. It was validated to 300,000 miles with the oil that is called for in the owners manual, so the 15W-40 oil recomendation is totally unwarranted.

I am not an aggressive driver, and do as much (W)ide (O)pen (T)hrottle stuff as I feel my wife can stand, but sometimes it is just NOT enough. I was comming back from Pgh. the other day, engine warm (more like hot) after about the first 100 miles........I had to pass one of those Ford Fusions to get off at my exit. I floored it at 70 (he was being a goof) and kicked it down into 3rd gear. I was amazed to see the amount of dust, carbon and crap that came out of my exhaust!

That was a notable trip in fact. I had filled up with Speedway gas in Marietta Ohio, and made the round trip to PGH. using 1/3 of a tankful LESS than I normally do. I think they have recently started putting more detergents in their gasolines to meet STP recommended levels.

[LindaSpencer]

Thanks to all of you guys and your information! To try and answer all of your questions. I did give it a complete oil change and several Wide Open Throttles. The noise sounds like a tapping and it is continuous whether i take it on a long ride or short. Last night I met up with a Brogan Caddy service tech that does work on the side. He said it might be a chain in the engine? He's not sure, he'll have to take it apart and said it would be a big job! My boyfriend "as a last ditch effort" put an additive in my oil last night, in the hopes that something is just sticking somewhere, if that dosen't work I geuss I;ll have to go for the big bucks!

[BodybyFisher]

We didnt mean long or short drive, we meant does it change by increasing the RPM, meaning stepping on the pedal, does the noise get faster as you press the gas pedal down in neutral...

By the way, someone clarify this, but the timing chains RARELY are a problem on the NS..

[LindaSpencer]

Hello again Mike,

Yes it gets quicker with the RPM, and the Caddy guy says that rarely happens with these engines which makes it even more confusing!

[Regis]

I'm with the others on what appears to be carbon buildup. While doing the initial series of WOTs you probably dislodged chunks of carbon. It's going to take WOTs in frequency to expell much of it. And 59,000 miles on a 96 STS.... it's still in diapers. I've developed the carbon rap myself due to very short drives to work and not enough WOTs. The house projects are taking up the WOT procedure times but they're almost done so the caddy will get my full attention soon.

I've heard the NS timing chain referred to as "the million mile timing chain".

[MAC]

By the way, someone clarify this, but the timing chains RARELY are a problem on the NS..

I've been surfing Cadillac forum websites for over 3 years and I have yet to come across a situation where someone verified a problem with a Northstar timing chain. I would try everything else before jumping to conclusions about the timing chain.

[epricedright]

Mike, maybe you need to explain to Linda how to do the WOT's correctly. It's not just heavy accelerating.

[BodybyFisher]

Ok it is posted above but here it is again as outlined by the guru:

Frequent WOT operation will not hurt the engine or the transmission. They're designed for that. The healthiest engines that I have seen at high miles are always the ones that are run the hardest. Rings are free on the pistons and sealing; no carbon buildup.

The exercise that I think works best for many things is to select manual 2nd gear on an isolated stretch of expressway. This takes the transmission shifting out of the question if you are worried about hurting it. Start at 55 MPH or so and go to WOT in 2nd gear and hold it until the RPM reaches near the normal shift point - i.e. 6500 for an L37 and 6000 for an LD8. Hold the throttle wide open until the engine reaches, say, 6200 for an STS and then just let completely off the throttle. Leave the transmission in 2nd so that the engine brakes the car and creates some pretty heavy over-run conditions at high vacuum levels. Let it slow until it is about 55 or so and then go to WOT again and repeat. This exercise really loads the rings, allows variable RPM operation at WOT for several seconds continuously, creates heavy over-run which tends to unload the rings and make them move and thus exercise them in the ring grooves and it will blow-out carbon and the exhaust - all without creating a spectical of yourself and attracting the attention of cops. You can do it on most any freeway and stay within the 70-75 MPH range allowable. Once a week like this will keep the engine cleaned out and healthy and is DEFINITELY recommended for the Northstar in particular.

The Northstar engine was designed/developed/validated to be run hard. It was expected that people would use the performance of the engine - which few people seem to do. The biggest single problem that many issues stem from is lack of use at full throttle by the owners. It just doesn't like to be babied around. The rings are low-tension by design for good high RPM operating characteristics and low friction/good power. They work best if "used" and kept free.

In every conversation with owners I have had, once the owner started doing the WOTs and using the power of the engine they report no more carbon rap, better oil economy, no "smoke" when they do light it up (keep the exhaust cleaned out. If you notice a "cloud" at WOT then you are not doing enough WOTs...) etc... A bit of judicious use of the other end of the throttle travel is a GOOD thing...

[Ranger]

By the way, someone clarify this, but the timing chains RARELY are a problem on the NS..

I've been surfing Cadillac forum websites for over 3 years and I have yet to come across a situation where someone verified a problem with a Northstar timing chain. I would try everything else before jumping to conclusions about the timing chain.

I agree. The Guru always said that the chaines would last forever and I cannot recall of ever hearing about a problem.

The thing that bothers me is that if it were "cold carbon rap", it would go away after 30-60 seconds when the cylinders warm up. If I am reading Linda correctly, this is continuous.

[JohnnyG]

BUT, Aren't the chain tensioners operated by oil pressure? I seem to remember that from a couple years ago during the timing chain discussions. It seems to me that it may not be the actual chain, but the tensioning mechanism. If I furthe recall correctly, the tensioner is supposed to "ratchet" out so that the next time the engine is started, there is not a significant amount of play in the chains prior to the engine oil pressure building up.

So, in essence, any one of those minor items can be "simplified" into the timing chain description by the tech.

Once again 59,000 miles on this year of car...it's done a lot of sitting OR a lot of short trips, couple this with a slightly inferior oil (possibly?) (was this pre-OLM?) and you may end up with a stuck tensioner.

I might give an engine oil type flush a whirl before I tore the fron covers off, maybe something like Marvel Mystery Oil, Top Engine Lube, or even Auto RX. These are all thin additives.

I remember years ago seeing a mechanic pour Top Engine Lube (to unstick hydraulic lifters) into a running engine, and listen in amazement as ALL valve clatter dissapeared in a matter of seconds!

They probably don't sell it anymore, but I think it was a CD2 product.

[Ranger]

Johnny,

You are correct about the ratcheting tensioner. It will tighten but not loosen. Not sure about hydraulicly operated though. I don't remember that. I would think a stethescope should be able to pin point the location.

[LindaSpencer]

I can't thank all of you enough for your knowledge and input. We put the oil additive in 2 days ago, and I'm supposed to run it 100 miles to see if the noise is still there. I'm on 25 miles and it's still there, but I'm praying that It will subsede! I've been told to sell it and just buy a Buick, but as a Cadillac lover I'd rather try everything possible to perserve the car. I'll try and get a picture of it on this site. It's in excellent condition and a pretty Pearl White. Just one more thing, the Caddy tech said that if the additive dosen't work he will have to take the valve cover off and check the Hydrolic Chain Tensioner and the Chain guide, would any of you know how much time and labor would go into that? Would I be spending thousands?

[Ranger]

Well, I guess that answers the question about hydraulics. I think the chain tensioner is under the front cover, not the cam cover, making it a little harder to get at. Not sure if it can be done with the engine in the car or not. Someone with more expirience will have to answer that one.

[JimD]

There are three hydraulic chain tensioners. One on the chain between the crankshaft and the intermediate sprocket and one on each of the chains that drive the cams from the intermediate sprocket.

You can see the small actuators in the picture. The red colored pieces are synthetic material chain guides.

http://i70.photobucket.com/albums/i101/Jim...t/camchains.jpg