Noise on acceleration--RPM driven rumble

[DAKOTAKIDD]

Hey guys, I have a weird noise happening to my 91 ecodiesel.  At idle, all is well, then I accelerate either hard or soft and I am hearing this rumbling under the hood that is RPM driven.  If I am coasting along, and push the clutch in, it goes away and as soon as I hit the gas again, it comes back.  I checked the inside of the turbo today and its seems tight.

I am going to check the A/C compressor and power steering pump later in the week to eliminate them.  The alternator and idler pulley are OK.

Any ideas there guys?

Thx

[DAKOTAKIDD]

I will try and get a sound clip or video tomorrow for you to hear.

[Doug]

1. loose exhaust system contacting part of the chassis
2. leaking exhaust system due to perforation or broken manifold spring clamp
2. wheel bearings are beginning to make noise due to wear.
3. worn lower ball joints changing alignment when on and off the throttle
4. worn CV joints

[jtanguay]

does it happen at low and high speed? or just low speed?  is it a soft growl or a louder growl?  its probably one of the things Doug posted  :wink: those are the usual suspects.  there are other things that can cause the noises you're hearing, but you don't want it to be them...



GREMLINS!!!!!!!  :lol:

[DAKOTAKIDD]

1. loose exhaust system contacting part of the chassis
2. leaking exhaust system due to perforation or broken manifold spring clamp
2. wheel bearings are beginning to make noise due to wear.
3. worn lower ball joints changing alignment when on and off the throttle
4. worn CV joints

I don't think its any of the above because its strictly engine rpm related.  I can rev the engine and hear it.  It does change pitch as the rpm increases

[Jettage1]

You want to logically eliminate various systems:

To be clear:  Do you have to be in motion for the noise to occur?  If not, you can cross out CV's, axles, etc.  If yes, then there are lots of possible candidates.

If it happens in neutral while parked, then you can play with other options - clutch depressed, not depressed, etc.  Pinpoint the rpm where it happens.  Have someone hold it at that rpm while you (carefully) look around.  Is it a harmonic resonance (something loose that only vibrates at that rpm)?  Are all the accessories tight?  Is the IP tight (that creates really funky stuff if even one bolt is loose...)  Anyway, you get the drift.

[DAKOTAKIDD]

I can duplicate it with the car stopped in neutral, hood open and moving the accelerator.  It is COMPLETELY RPM driven from idle up.  Doesn't matter on clutch position,  If you rev the car (while stopped--no movement), it happens.  It get worse (louder) with the higher rpm.

It has nothing to do with any drive train component or static component like exhaust pipes etc.

What about the turbo?  Could it be causing this?

Thx for all you help guys!!!  

[jtanguay]

I can duplicate it with the car stopped in neutral, hood open and moving the accelerator.  It is COMPLETELY RPM driven from idle up.  Doesn't matter on clutch position,  If you rev the car (while stopped--no movement), it happens.  It get worse (louder) with the higher rpm.

It has nothing to do with any drive train component or static component like exhaust pipes etc.

What about the turbo?  Could it be causing this?

Thx for all you help guys!!!  

turbo doesn't really make too much noise in neutral unless you really rev it.  hard to hear over the loudness of the engine...

[Jettage1]

In terms of the type of noise, you did say a "rumble" - so I'm thinking low pitched (bass), as opposed to sharp, staccato like valvetrain, or injectors...

If you have the hood open, and you rev the engine at the IP, where does the sound seem to come from?  You can (again, carefully) put a screwdriver tip on various parts and the handle to your ear to help isolate the noise.  Some mechanics also make use of a short length of hose as a "listening tube", again to isolate noises.

Also, does it matter if the engine is fully warm, or stone cold?

[Dakotakid]

Seeing as how this has an interference engine in it, I think I would really think about getting my tools out and pulling the plastic cam belt cover and looking at your belt tightness (or lack thereof) and really determine what shape the belt tensioner is in. Or....do ya feel lucky??

[theman53]

I would take the timing belt cover off as suggested already by Dakotakid and start it. Don't run down the road just watch the TB and all the stuff. My old 81 had and Intermediate shaft that had worn away and would move in and out about to the fender without taking the retainer off :shock: . That was making a hell of a noise and tearing up my timing belts too. Could be the Bearing in the v belt tentioner too if it is the one with a/c. My Jetta growled there too. Too many options??? Throwout bearing? The list goes on. I would start with the easy non expensive stuff

[DAKOTAKIDD]

I said rumble before but being more specific its like a bad bearing sound that gets louder as rpm's increase.  I will pull the cover off on the weekend and investigate.

I just had it at a shop for a water pump change and they changed a intermediate shaft seal. They retimed the engine, IP, etc.  I also believe he said they replaced the intermediate pulley?? or tensioner as well.

Does this help any!!

Thx so much guys

[jtanguay]

I said rumble before but being more specific its like a bad bearing sound that gets louder as rpm's increase.  I will pull the cover off on the weekend and investigate.

I just had it at a shop for a water pump change and they changed a intermediate shaft seal. They retimed the engine, IP, etc.  I also believe he said they replaced the intermediate pulley?? or tensioner as well.

Does this help any!!

Thx so much guys

i doubt they would replace the intermediate pulley.  but wonder why they would replace the tensioner?  might as well change the belt too at that point.  if they tightened the tensioner too much, that might be the cause of the noise you're hearing.  if you could take video's for a sound clip of the noise that might help diagnose.  because if the belt is in fact too tight, it won't take long before permanent damage occurs.

[Rabbit TD]

I said rumble before but being more specific its like a bad bearing sound that gets louder as rpm's increase.  I will pull the cover off on the weekend and investigate.

I just had it at a shop for a water pump change and they changed a intermediate shaft seal. They retimed the engine, IP, etc.  I also believe he said they replaced the intermediate pulley?? or tensioner as well.

Does this help any!!

Thx so much guys

i doubt they would replace the intermediate pulley.  but wonder why they would replace the tensioner?  might as well change the belt too at that point.  if they tightened the tensioner too much, that might be the cause of the noise you're hearing.  if you could take video's for a sound clip of the noise that might help diagnose.  because if the belt is in fact too tight, it won't take long before permanent damage occurs.

When you say a bearing sound are you talking bout a sound a rod bearing would make {knock} or alternator {squeal}?   Are you sure it's not just the timing belt being too tight, it makes kind of a turbo like whine sound and if it's too tight it can wear out the pump bushings if let go like that and then the front seal starts leaking.

[Dakotakid]

Ya, an overly tight cam belt really tends to "roar' with increasing rpms.

And you can check the V-belt tensioner really easy when it is hot.  
Make sure the engine is off.
Just lick your fingers and touch the center of the tensioner where the little bearing lives (behind the nut and washer).

If the moisture on your fingers and the first two layers of epidermis "vaporizes,".......then you need a new bearing in the adjuster!!!!!

The little bearing in the adjuster is replaceable for about $6.00