# Sound Identification - Bearings, Piston Slap or ?? - BGP at 152k miles



## Vwspen3310 (Oct 25, 2010)

I have a 2007 vw rabbit 2.5l with a manual transmission with 152k miles on it. Recently I have noticed a bupbupbupbup-like sound only when the engine is under load (usually on the freeway with cruise control on going up a hill) after the car has had some time to warm up. Usually likes to occur between 2k and 3k rpm. It feels like the engine is missing under load on a cylinder but I don't get any corresponding check engine codes. If I give it WOT when the sound is present, the engine noise evens out but the sound could be drowned out by the magnitude of all other engine noise at that moment. If the noise is present and I let off of the gas pedal and leave the car in gear to lightly engine break, the noise goes away immediately. I'm noting that this noise is that at 2k rpm (equal to 33.33 hz), and the bup-bup noise is much less frequently occurring. Only 1 out of 2 revolutions does each cylinder fire, so if the noise is related to a single cylinder firing, then it will fire at 16.66 hz and this would be the frequency of the sound which might be about right. Hard for me to count to ~16 in one second while I'm driving however... Also note that the noise seems to be growing in intensity as time goes on. The engine runs great and has great power. I get okayish gas mileage, usually 23-26ish mpg for mixed city and highway.

I scanned the car (vag com) and initially got a cylinder 5 misfire due to a bad coilpack, but after replacement the bupbupbup noise continued as did the misfire-like feel under load, but I get no trouble codes. I tried an "Italian tuneup" one day to see if it was carbon buildup in the cylinders and got another trouble code to pop which was intake camshaft over advance (P0011), prompting me to change the VVT, but the code never reappeared after clearing with the old VVT valve or the new one.

*Things I have done to the car in the very recent past (within 10k miles):*
-Timing chains (upper and lower) and all guides, clutch pressure plate, flywheel and throwout bearing (single mass flywheel conversion). The noise wasn't present before this maintenance. I didn't notice if it was present after doing this maintenance. I believe I would have noticed it at that time as it is quite noticeable now. Rechecking timing is one of the things on my todo list, but I painstakingly verified my timing when performing the timing chain procedure so I'm about 90% certain the timing is good.

*Things I have done to attempt to diagnose and mitigate this noise and issue:*
-tried premium gas (91) for a tankful vs regular which I usually run (87). No change in the noise as it was still present. I don't believe the noise to be pre-detonation as it isn't pinging sounding. 
-swapped a known good coil pack in and moved it from cylinder to cylinder through all 5 cylinders but the noise persists.
-Pulled all fuel injectors, ran them through an ultrasonic cleaner and reinstalled them. They weren't coked up or overly dirty looking. I also listened for each injector to be clicking using the screwdriver stethoscope method and they are all clicking at about the same volume.
-Changed the oil (as I do regularly every 5k miles) with rotella T6 5w-40 full synthetic (yea I know, not OEM approved). The noise was still present after. Previously this had quieted the noise, but I couldn't be certain if it fixed it or not due to the seasons of when the oil changes were and the fact that it could be temperature dependent (very cold winter in MN vs hot summer). Note: I have not found any metallic flakes in the oil or the oil filter which I cut open and spread out to inspect.
-Put in new spark plugs. Old plugs (not sure how old) didn't look bad when they came out. With new plugs the engine still made the same noise.
-Put in a new VVT solenoid valve as I thought it could be the culprit but the noise was still the same after replacement.
-Monitored the cam phasing command and the cam feedback via vagcom to ensure that the (intake?) cam is operating as it should be and tracking the command signal. I would assume if this valve was truly bad that I would see a trouble code.
-Replaced the driver's side transmission mount (not the dogbone) as I was concerned the noise may be normal to the engine and that it was being abnormally transmitted into the vehicle body through a worn out mount. The noise still persisted after changing the mount. The passenger's side mount is relatively healthy, as is the dogbone mount.
-Thought that the A/C could be causing issues as I believe it is directly coupled to the engine via a belt, and that the A/C compressor internals never stop rotating (although the swashplate mechanism internally adjusts to stop pumping). I turned the A/C on and let it run for a bit with the noise present on the freeway and then turned it back off. I didn't notice any change in the noise with the A/C on vs off.
-Thought the transmission could be causing a noise somehow, so I set the ebrake, put the car in 1st and let out on the clutch (just great for my new clutch... I know) and I get a slow frequency low thudding sound which I interpret as being the bup-bup-bup noise that shows up at increased engine rpm. This leads me to rule out any transmission related issue and that it is an engine issue when the engine is loaded.


*Things I plan on doing next:*
-Get an audio clip of the sound for better identification (or video w/ audio)
-Compression test on all 5 cylinders
-Depending on compression test results, leak down test
-VAG COM diagnostics for fuel trim at idle and off idle to see if an injector is dying
-VAC COM diagnostics for cam phasing to ensure intake is 
-disconnecting the A/C belt (thereby removing all accessories to the engine) and driving it around the block to see if the noise persists
-verify timing at the crankshaft and camshafts
-pull the oil pan and shake the connecting rods to look for wear. Probably pull bearing caps and inspect bearings visually as long as I would be down there. Don't want to do this just yet as I just did an oil change.

Possible diagnoses at this point:
1. Rod bearings
2. Main bearings
3. Piston slap
4. Piston blowby
4. sticky lifters or broken intake or exhaust valve or springs
5. Engine accessory is having issues (AC compressor, water pump, alternator
6. Exhaust manifold could have a hole in it causing one cylinder to sound funny (not sure how this would directly impact the feel of the engine being rough at a certain RPM)
7. Engine cover banging around under the hood due to some weird engine resonance?

Anybody have any experience with something similar to this on a 2.5? I'm starting to lose my mind a little bit. If anyone has suggestions on what to monitor through vagcom to better diagnose this, I'd love to hear them. I'm a new vagcom user and don't quite know what is what yet.


----------



## Ichabod0525 (Feb 11, 2018)

Thinking you are on the right track with the compression / leak-down test to sniff out piston slap as this should affect compression seal. Do both at the same time, you're at it anyway so go. If you go as far as pulling rod caps get yourself a *plastigauge* kit and measure along with your visual inspection. Other than that sounds like you have a comprehensive plan to follow. Post updates so we can see where it leads.


----------



## Vwspen3310 (Oct 25, 2010)

Did the compression check right after work today when I got home. To my surprise, all 5 cylinders were in the 185 to 195 psi range. From other posts (my Bentley is loaned out to my dad) these pressures are well within tolerance. I didn't have time to do leak down so that will have to wait for the weekend, or there may be no reason to do a leak down test at this point seeing as compression was good.

I pulled the accessory belt off that couples the crank to all accessories and still got the deep bupbupbupbup in the driveway with the e-brake on when letting the clutch out in first.

Sound clip here:





I took a good look at the exhaust manifold from underneath and don't see any holes or black soot at any joints. I'm ruling that out for now. I have had gnarly exhaust leaks before and know what it sounds like at idle and the rabbit doesn't sound like that. 

Don't think the engine cover is banging around that much as I can get this to happen with the car stopped and the hood up (ebrake on in first gear).

If it was piston slap, I would think compression would be down and its not. It could be the early early stages of piston slap so it hasn't affected compression yet, but I'm not quite buying that. 

Since compression is good, my list of possible causes is now:
1. Rod bearings
2. Main bearings
3. Injector clogging and misfiring a cylinder and somehow not throwing a code

My roommate suggested that I have the oil analyzed for bearing material (something like $20). The oil from my last oil change is dark, but clean with no chunks or metallic sheen. I don't want to throw money away on an oil analysis that says "you might have a bearing out and you might not". I'm thinking that I will wait for the next oil change interval and drop the pan then inspect the bearing situation by the grab and shake method and with plastigage as mentioned.

Any other random thoughts on this one? It's shaping up to be bottom end bearings of some sort it appears.

I'll post up an autoscan when I get a chance if there are any random ideas.


----------



## Ronny Bensys (Apr 17, 2014)

Do you get the noise at high speeds only? Is the noise speed or rpm dependent?

If it was piston slap, it would show up at idle and the compression would go down. The car drives nice, shifts nice and the fuel economy is good. No misfires, no CEL or fault codes. I checked the video but couldn't hear bupbupbup like you described. Did you check axles / CV joints?

*If the noise is present and I let off of the gas pedal and leave the car in gear to lightly engine break, the noise goes away immediately.*

This is an indication of axles, CV joints, transmission.


----------



## WtErKeWlEdUbbEr (Jun 20, 2005)

Ronny Bensys said:


> Do you get the noise at high speeds only? Is the noise speed or rpm dependent?
> 
> If it was piston slap, it would show up at idle and the compression would go down. The car drives nice, shifts nice and the fuel economy is good. No misfires, no CEL or fault codes. I checked the video but couldn't hear bupbupbup like you described. Did you check axles / CV joints?
> 
> ...


I agree with this poster. CV axle or trans. 

Was this ever diagnosed?


Sent from my iPhone using Tapatalk


----------



## Ronny Bensys (Apr 17, 2014)

Vwspen3310 said:


> I have a 2007 vw rabbit 2.5l with a manual transmission.....


Hey Vwspen3310! Are you done with the noise?


----------



## Vwspen3310 (Oct 25, 2010)

Hello Gents,

No, I never got to the bottom of this. I'm still dealing with it and I'm not sure if I will ever solve it. The car now has ~168,000 miles on it and the noise is still there sometimes but has *not *gotten progressively worse. I can get it to happen as well when I pull the parking brake and put it in first and let out lightly on the clutch (eliminates drive train such as CV axle or trans as they aren't rotating at that point). Something weird with how the engine is firing under load being not quite balanced.

Honestly, I'm just going to ignore it at this point and keep driving the beast until something more major gives up. The rear brakes on these things like to seize (or the bleeders corrode so the whole calipers need to be redone) and I need to deal with that next. Rockers and back hatch are starting to rot and front end is in need of ball joints, tie rods and control arm bushings (aka a whole new front end refresh kit). These are more pertinent to me at the moment asides from this noise. So long as the noise doesn't get worse and its not burning oil and there is no metal in the oil filter, I'm just going to keep driving it.

Since my old posts I have done the following:

Junkyard (cleaned) injectors swapped in
fixed coil electrical connectors
Resealed the vacuum pump (need to do it again and will get the proper kit instead of just RTV'ing up the gaskets)
Put new brushes in the alternator (need to put in a new alternator as the commutator bars on the alternator were very worn when I put the brushes in)
Oil changes every 5k (cut the filters open to look for shiny metal or any particulate but everything looks good)
Oil cooler filter housing replaced due to oil leak
Valve cover gasket
PCV valve replacement (in valve cover)
Brake booster hose replaced (old one cracked)
Probably some other stuff I'm forgetting

Its a daily and its not going to win any beauty contests with the rust in the rockers. As long as it scoots down the road and lets me save the extra cash to put towards a new vehicle (TDI maybe?) I'm all good. Sorry I don't have answers. I wish I did.


----------



## cylinder head o7k (Feb 13, 2021)

wow man you sure did put alot into hunting this noise down. you are dedicated


----------



## Vwspen3310 (Oct 25, 2010)

cylinder head o7k said:


> wow man you sure did put alot into hunting this noise down. you are dedicated


Its either dedication or stupidity... I'd guess maybe a healthy mixture of both


----------



## WtErKeWlEdUbbEr (Jun 20, 2005)

Vwspen3310 said:


> Hello Gents,
> 
> No, I never got to the bottom of this. I'm still dealing with it and I'm not sure if I will ever solve it. The car now has ~168,000 miles on it and the noise is still there sometimes but has *not *gotten progressively worse. I can get it to happen as well when I pull the parking brake and put it in first and let out lightly on the clutch (eliminates drive train such as CV axle or trans as they aren't rotating at that point). Something weird with how the engine is firing under load being not quite balanced.
> 
> ...


Thrust bearing?


Sent from my iPhone using Tapatalk


----------



## cylinder head o7k (Feb 13, 2021)

the engine gods dont allow bearings inside the engine to make noise for very long


----------

