# rattling noise at partial throttle?



## water_wetter (Jun 2, 2006)

ok, so i would consider myself a pretty good vw tech, considering i was trained by vw... with that said i have a little problem that i need some help with.
i have a 91 gti with an obd1 aba swap. very well maintained running on digi1, no a/c. some modifications but nothing too serious.
first, i will describe the noise to the best of my ability. it sounds like a rattling/tapping noise, kind of like, oh lets say a bic lighter in a vibrating bucket (sorry but its a very strange noise).
second, when it makes the noise. it seems to happen with certain throttle positions with certain rpms, kinda like little throttle low rpm and moderate throttle at higher rpm. but never at full throttle or idle mainly cruising at 3k in 5th at 65-70mph.
third, where the noise is coming from. ultimately this is the reason for posting but ill narrow it down. definitely the motor, belt side > tranny side. sounds like the cylinder head area or behind alt. bracket, but also sounds like its resonating through the intake manifold.
and finally, what i have checked/considered. nothing on engine is lose i have pretty much removed and reinstalled every bracket. not any accessories, detentioned belt with no avail. checked plastic cam splash guard. no pulley vibration either. basically it is not obvious, or even slightly hidden. also i can get it to make the noise by hitting the wot switch to raise the idle, but it is not as loud as when driving.
it has done this since the engine was installed running 20w50 bout a year ago. not a lot of miles on the motor either.
thanks for looking and thanks in advance for any help


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## MecE2.0 (Dec 20, 2005)

*Re: rattling noise at partial throttle? (water_wetter)*

gonna throw a couple out. 1) loose exhaust manifold shield. i know you went through everything but i had this problem despite everything seeming tight. just used some washers to act as bushings and took care of the rattle. 2) starved lifter. thats pretty thick oil and you might have a dry lifter. back in the day (i say it like i'm old) we ran 20w50 on our aircooled cars and on the engine that used to be in my mk1. on those, not too bad. on my aba's 5w40 synthetic year round.


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## water_wetter (Jun 2, 2006)

*Re: rattling noise at partial throttle? (MecE2.0)*


_Quote, originally posted by *MecE2.0* »_gonna throw a couple out. 1) loose exhaust manifold shield. i know you went through everything but i had this problem despite everything seeming tight. just used some washers to act as bushings and took care of the rattle.

no heat shield here.

_Quote, originally posted by *MecE2.0* »_2) starved lifter. thats pretty thick oil and you might have a dry lifter. back in the day (i say it like i'm old) we ran 20w50 on our aircooled cars and on the engine that used to be in my mk1. on those, not too bad. on my aba's 5w40 synthetic year round.

definitely not a lifter noise i have seen so many not really a ticking noise more like a gurgling/rattling noise. besides the obd1 motor, from my research, requires 20w50 and they switched to 5w30 on obd 2 to reduce engine friction and stress for mpg and emissions competition. in my exp. the obd1 motor is just a noisier motor than obd2 and has got larger tolerances than obd2. if i run anything less than 20w50 the oil light comes on at idle and goes off at 2k rpm, this was before i installed the oil press. gauge but i havent tested it with the gauge. the motor has a new oil pump as well.
the key factor here is its related to throttle position
2500 rpm no throttle=no noise
2500 rpm cruise throttle=most noise
2500 rpm 3/4 throttle=no noise
2500 rpm full throttle=no noise
highway version
4000 rpm no throttle=no noise
4000 rpm partial throttle=no noise
4000 rpm 3/4 throttle=most noise
4000 rpm full throttle=no noise
*ok bam! my girlfriend just nailed when it does it... imagine an up shift light, but just a rattling noise instead of a light.*

this has stumped me and everyone at every shop i know so the only way i will know for sure is to disasemble the motor, which will probably happen because its just getting annoying now so im just trying to gather any more options i can before it comes down to a rebuild/upgrade.
thanks alot for the tips, and keep em coming.


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## MecE2.0 (Dec 20, 2005)

*Re: rattling noise at partial throttle? (water_wetter)*

maybe have a look over your vacuum system, particularly the evap. sounds like it might be doing it at a particular vacuum level. maybe the canister is cracked or damaged.
oh and both my aba's are obd1's and neither have ever had an oil pressure problem running the lighter synthetic. i'd maybe look into replacing some seals if you're getting the light with lighter oils.


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## water_wetter (Jun 2, 2006)

*Re: rattling noise at partial throttle? (MecE2.0)*

* WRIST PIN RATTLE.* was apparently a problem with the earliest obd1 engines. and is not really a major problem just damb annoying.

_Modified by water_wetter at 6:04 PM 11-23-2009_


_Modified by water_wetter at 11:53 PM 11-23-2009_


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## MecE2.0 (Dec 20, 2005)

*Re: rattling noise at partial throttle? (water_wetter)*

crazy. did not know that. maybe not a bad idea to post the fix and any info you can find on it, let the mods know so it can go in the DIY.


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## water_wetter (Jun 2, 2006)

*Re: rattling noise at partial throttle? (MecE2.0)*

the easiest fix is some new pistons, basically this happens on engines that have higher mileage, or engines that have been over heated... which is probably my scenario. big thanks to Mike and Barry Palmer for the solution. http://****************.com/smile/emthup.gif http://****************.com/smile/emthup.gif http://****************.com/smile/emthup.gif 
and what actually happens is when just the right amount of load is put on the motor i causes the piston to "float", either on the wrist pin, or the pin "float" in the connecting rod.
just what some further research has turned up
Piston-Pin 
Knock Piston-pin knock is identified more as a metallic double-knock rather than a regular clicking sound like that heard in valve and tappet noise. In addition, it is most noticeable during idle with the spark advanced. A check can be made by idling the engine with the spark advanced and then shorting out the spark plugs. Piston-pin noise coming from a cylinder will be reduced somewhat when the spark plug for that cylinder is shorted out. Causes of this noise are a worn or loose piston-pin, a worn bushing, and a lack of oil. 
Piston-Ring Noise 
Piston-ring noise is also similar to valve and tappet noise since it is identified by a clicking, snapping, or rattling sound. This noise is most noticeable on acceleration. Low-ring tension, broken or worn rings, or worn cylinder walls will produce this sound. To avoid confusing this sound with other engine noise, make the following test: remove the spark plugs and add an ounce or two of heavy engine oil to each cylinder. Crank the engine for several revolutions to work the oil down past the rings. Replace the spark plugs and start the engine, If the noise has decreased, it is probable that the rings are at fault. 
Piston Slap
Piston slap may be detected by a hollow, bell- like knock and is due to the rocking back and forth of the piston in the cylinder. If the slap occurs only when the engine is cold, it is probably not serious. However, if it occurs under all operating conditions, a further examination is called for. The slap can be caused by worn cylinder walls, worn pistons, collapsed piston skirts, or misaligned connecting rods. 
Crankshaft Knock 
Crankshaft knock is a heavy, dull, metallic knock that is noticeable when the engine is under load or accelerating. When the noise is regular, it can be contributed to worn main bearings. When irregular and sharp, the noise is probably due to worn thrust bearings
Rod knocks are loudest at higher speeds (over 2500 RPM) Feathering the gas pedal may result in a distinctive back rattle between 2500 and 3500 RPMs.
Bad rod knocks may double knock if enough rod bearing material has been worn away allowing the piston to whack the cylinder head in addition to the big end of the connecting rod banging on the crankshaft rod journal. It will sound like a hard metallic knock (rod) with an alternating and somewhat muffled aluminum (piston) klock sound.

Wrist pin knock in modern engines is very rare today but is a favorite for the misdiagnosticians.

Determining which cylinder contains the noisy parts may be aided by shorting out the plug wires one by one with a common low voltage test light. Now you won't get the bulb to light up but it is a convenient way to short the cylinders without getting zapped or damaging the ignition coil.
Attach the alligator clip to a convenient ground, away from fuel system components, and pierce the wire boots at the coilpack or distributor end of the wire.
If the noise is changed when the plug wire is shorted to ground, you can figure that the problem is in the reciprocating bottom end parts. (piston, wrist pin, connecting rod or connecting rod bearing)
The reason the sound changes is that when you short the cylinder plug wire you are stopping the combustion chamber explosions that are slamming the piston downward making the inside of the big end of the connecting rod bang against it's connecting rod journal. Or in the case of piston slap, no explosion changes how the piston is shoved hard sideways against the cylinder wall.

If you get a change in the sound when you short a cylinder out it may become moot as to what the problem is because the oil pan and cylinder head must be removed to correct the problem. [Generally speaking, an engine with damage to reciprocating parts (pistons, rings, connecting rods, wrist pins or rod bearings) and more than 70 thousand miles is not cost effective or risk free enough to attempt to repair. Replacing a crankshaft, for example while the rest of the engine has 70k perfectly maintained miles on it is risky enough but whatever killed the crank has scored the rings and packed the lifters with debris and smoked the piston pin bosses etc.]

If the sound doesn't change, look at parts other than the reciprocating ones. In many cases of rod-knock or piston slap, more than one is banging so even if you eliminate the noise from one rod the other one will still be a-banging away with a different, more singular tone.
http://****************.com/smile/emthup.gif










_Modified by water_wetter at 1:26 AM 11-24-2009_


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