[jaap]

Hi,



I have an annoying problem with the car which is difficult to diagnose

When accelerating / decelerating through or even cruising at around 2300 rpm the car makes a different sound (exhaust note?) which sounds like some sort of resonance.

With the car in neutral, clutch in or out or car in gear with the clutch in and slowly increasing the revs, around 2300 rpm it feels/sounds less smooth. At lower or higher RPM it feel definitely better/smoother. It is difficult to say whether it actually is misfiring or just vibrating /shaking. It does not seem to have an influence on performance, it will run straight to the rev limit (7100, promax chip)

I remember reading that 2300 is also the RPM range where a single mass flywheel introduces noises in the transaxle. I have also noticed there is a slight shudder when letting the clutch out when taking off. Could this be an indication of a bad DMF?



Jaap

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[flash]

that is possible - if the dmf is stuck, you would essentially have a single mass flywheel



there could be other things though that are causing this



exactly what is the sound like?

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[jaap]

[quote name='flash' date='May 22 2006, 05:03 PM']exactly what is the sound like?

[right][post="21367"]<{POST_SNAPBACK}>[/post][/right][/quote]



The sound is difficult to describe (especially for a non native english person) but it sounds a bit more hollow than the normal exhaust note and seems to come from the forward half of the exhaust/car area. May be like the exhaust is causing a resonance noise. When the balance belt broke a while ago that gave a sort of similar sound but over a wider RPM range. The thing that worries me more than the sound change is the fact that if I rev the car up in neutral and gently going through the range it feels like the engine stumbles a bit but only in this RMP range. It runs nicely through the rest of the range. On the move it is less obvious. I know what the car feel/sounds like when the balance belt is of but that gave a vibrations through a large RPM range. I checked the belt and alignment anyway and it was ok. Do bad engine mounts show up in the 2300 RPM range (probably only at idle?) I might try to make a recording, but it is subtle, but the change in engine behavior is obvious

Jaap

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[flash]

doesn't sound like a dmf thing - actually sounds more like a jumped tooth thing on the balance belt

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[jaap]

Thanks Flash for the suggestions, however I just verified the balance belt alignment and it is correct. It had skipped a tooth after the OPC installed it, but they corrected that. The only thing I don't know for sure is whether the sprocket could be 180 degrees out of sync, but the O marks show up at the right locations. Would a skipped balance belt only show up at the 2200-2400 RPM range. The engine is smooth otherwise.



Jaap

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[flash]

yup - that is EXACTLY what was going on with ron's car - sounded like it was struggling - lower balance pulley was off about 180

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[jaap]

Ok, will verify again if the lower sprocket is installed correctly. I assume there should not be any roughness/stumble when the engine runs at around 2300 RPM and the car stationary with the clutch in or out. Flash you have a lightweight flywheel; do you (or others) notice any of these symptoms when doing this rev test?



Jaap

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[flash]

nope - quite the contrary - all i have is the rattle in the G44

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[Renalicious]

I too get a rattle, but it's only with a cold engine at around 1800 - 2000 rpm. It sounds like it's coming from the right side of the car. Sounds heat-shieldish. I only really hear it when shifting gears and the engine passes that RPM range. Once everything is at temp, the rattle is gone. I'll try recording this sometime this week.



Another thing I hear after driving for a while, while the car is idling, is this squeaking type sound coming from the back. It seems like it's more insync with cam rpm's than crank rpms. Worn tranny or exhaust mounts perhaps? I'll get a recording of this too <img src="/forum/images/smilies/968/wink.gif" class="smilie" alt="" />



Finally, anyone else have a squealing engine (sounds like belts) durring low rpm accelerations or engine loads? Checking the maintenance records, it looks like it's something that previous owners have experienced as well. I actually made a recording of this previously. Engine squeak recording This was recorded from the little plastic cubby inside the engine bay, hood closed, after I had new belts and rollers put in. But I was hearing it with old belts and rollers as well. Everything except the alternator belt was replaced.

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[flash]

that rattle is probably the small shield on the right side down near the bottom - they tend to break and then rattle



i heard the squeak - sounds like a belt - check the tension on your alternator belt - it should not deflect more than a half inch with a good push on it - make sure yo uloosen the mounting bolts before adjusting the turnbuckle



if the belt is more than 5 years old, replace it anyway

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