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loud underhood noise


re037

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hey guys, with the "cold weather" and rain finally hitting socal, my 260z has been making a really loud noise in the morning and also at night time when i leave work. the car was running fine throughout all of summer until it began raining. its sounds like a high pitch gritty rusty old wheel. when its happens, the engine also experiences low to medium vibration. I double checked the belt tension and everything looks good but the noise is still present. It will only make a loud noise when i rev it up to turn on the alternator. I have a improperly wired 280zx alternator, so the alt turns on only when i rev past 3500~ rpm (the wiring on this car has been butchered by previous owners so the voltage regulator rewire causes a weird battery drain when the car is off). anyway, the noise and vibration eventually goes away once the car has been driving for atleast 10 minutes. the noise appears to be coming from the fan clutch/water pump or the alternator. its so loud i really cant discern the exact source. any suggestions on how to further diagnose this?

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do you have a cat?

 

Cat converter? Probably neutered by now.

 

 

An internal regulated zx alternator can work on a pre '77 car if the external regulator is disconnected and two pairs of wires connected. I don't know if the 510 re-wire is the same for the Z car... likely, is all I can say. Here's the schematic

 

510iraltswap.jpg

 

Poor output until 3,500 plus drain when off suggests to me that the alternator is pooched. Then there is the possibility of mis-wiring.....

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Spin the radiator fan. That'll tell you what shape the fan clutch is in. I had one self destruct a few months back; at least Z-car ones can be replaced independent of the water pump unlike mine. If that's not it, or just check anyway, see if you have water pump wobble by trying to move the pump pulley up/down/side-side. . Could be on its way out.

 

To check the alternator bearings you'd need to pull the belt. If this car has any idler pulleys I'd check those too. A/C'd cars usually have one.

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  • 2 weeks later...
its the crankshaft pulley!  confused.gif

its a 2 piece design (wtf nissan engineers) and the alt/waterpump pulley has about 7 mm of play and rubs the front of the engine... fml. the front pulley for the ac compressor has no play at all. can i switch to 1 piece designs? are there 1 piece designs?
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