noise at 2500rpm and 3800rpm ish

mosguido · April 19, 2007, 02:37:54 PM

Hey

Now that my brakes are done, i finally managed to drive the car for the first time in ages, and its reminded me of a few niggling things i thought I should ask about.

Been hearing a noise coming from what sounds like the engine bay area and i cant quite figure out what it might be. Basically if im driving along in any gear, hit 2500rpm and i hear a very slight \'chook chook chook\' - (say that fairly fast and you get the kinda sound i mean - sorta metallicy) noise, which only lasts for a second then clears up, i then hear the same sound at around 3800ish rpm.

the car doesn\'t hesistate (checked up on 3800rpm problems and hesistation is the most common) so i dont think its related to those usual problems. It on;ly does it under load, so when parked up and revving to 2500 you dont hear any noise.

Also don\'t get this noise on deceleration, only on acceleration...

any ideas on what might cause this or what it might be? or anything I can check on? This noise has been there at least a few months now, before i started working on the brakes so unrelated to that also...

any help muchly appreciated!

Oh also my car is a S4 N/A... another quickie, prev to my coolant change (was rust colored before) i had no overheating issues. As it is now, its not overheating, the thermostat is working ok (top rad hose gets hot) and temp gauge sits around 1/4-1/3 most of the time. When i give it a bit of a ragging, say 4th gear WOT (about 4-5k rpm) the temp gauge rises a bit and gets fairly close to the 1/2 way mark. hasnt gone above that but wondering if thats normal or not or if i should investigate further.. worth getting an aftermarket temp gauge to see if its actually getting hot or not?

cheers
Guy

DC-TYPER · April 19, 2007, 03:53:56 PM

is it rythmic or does the sound go with the engine?

brundish24 · April 19, 2007, 04:02:44 PM

hi mate it mite be the air pump as mine does the same and i was told it was the air pump and he showed me as well by pulling the accelorator cable you see the air pump triangle thing spin then it stop then starts spining again if its normal.

brundish24 · April 19, 2007, 04:05:45 PM

sorry last post is for a 3rd gen sorry can you get someone to delete these posts

grinder · April 19, 2007, 04:21:46 PM

could be worth getting a gauge for the top hose ... you could then see what the water is doing

im sure i read somewhere that the S4\'s have a linear gauge so it might be working just fine

mosguido · April 19, 2007, 04:43:46 PM

dc-typer - not quite sure what you mean by rythmic? i would guess it kinda goes with the engine?? I did have a bit of a drive again just before, it doesn\'t seem to do it all the time, and not really in 3rd or 4th (couldnt hear it then anyway, tho much mroe wind noise to interfere..

I did re-test revving again in the driveway, and at prett ymuch exactly 3800rpm i could hear the rear section of the exhaust rattling a little bit..so it may just be that..

I didn\'t mention it before cos don\'t know how it could be related, but the noise started ( i believe) after I had changed the spark plugs a few days after buying the car. I didn\'t notice it before changint them, but then again, i only usually look fro problems after i change something..so it may have been there before.

anyway anymore suggestions would be really good, it may just be the exhaust rattling around, i\'d just like to be sure its nothing else!

grinder - any recommendations on gauges or where to get one from? I think i may get one anyway, i hear on a rotary engine if it overheats theres a good chance it\'ll die..so anything i can keep an eye on temp would be good i think!

cheers

grinder · April 19, 2007, 04:47:03 PM

i bought my gauge from ebay and the adaptor

have a look in the mods section and there is a write up and possibly prices

and yeah if the car gets hot and you continue to drive it - you are looking at potential probs

humm the 3800 problem - still not sure about this - its when the secondaries start to fire - so i wonder if its something to do with that

but then around 2500 im sure the airpump stops spinning - so again - it could be related to that

unless at 3800 its just a magic figure for the exhaust to rattle ?? ( harmonics ?? )

grinder · April 19, 2007, 04:47:52 PM

gauge write up

http://www.mazdarotaryclub.com/forums/showthread.php?p=144188

or

http://www.fc3s.co.uk/How%20To/Top%20Hose%20Water%20Temp/top%20hose.php

mosguido · April 19, 2007, 04:57:28 PM

cheers for the gauge pics and write up there, looks sweet as, shall have to get onto that i think

sorry for being a n00b but when you say secondaries you mean...? The car definately drives fine and is very very smooth and all the power seems to be there..dunno if that helps or not.. prob not

i know a fair amount of car stuff but rotaries are aaaaaall new to me and confuse me so please excuse some of my very stupid questions form time to time! :xconfused

grinder · April 19, 2007, 05:01:48 PM

sorry

there are 4 injectors in the FC

2 primaries and 2 secondaries

the secondaries come "online" at 3800 - this is why there is sometimes a hesatation

i think this is due to the primaries getting to their limit and the secondaries start firing ( imagaine when you watch a DVD film and you can see it pause at it changed layers )

still not sure why you are getting a noise though

try taking the belt off the air pump and see if it still does it - if it does then its not the airpump - if it stops - then it is !!

you will learn quick with the FC that to fix any prob - start at the cheap/free end of the scale and work upwards

mosguido · April 19, 2007, 05:08:00 PM

lol! i like that, cheap is definately the best way, hard job taking the airpump off? what does that do exactly?

thanks for the secondaries explanation too, i\'ll learn all this stuff eventually

grinder · April 19, 2007, 06:17:21 PM

the air pump pumps air in at idle to keep the emmission down

you dont have to remove it - just take the belt off so that it stops working

and then work from there

at least you can narrow it down somewhat

try that and then we can have a re-think if it doesnt work

mosguido · April 19, 2007, 07:07:48 PM

sweet as, i may have a look at that tomorrow if i get a chance, see if we can pin it down some more, will let you know how it goes! might have a closer look at my exhaust tmrw too at the rear and see if its loose too

grinder · April 19, 2007, 07:46:38 PM

sounds like a plan

mosguido · April 22, 2007, 10:53:09 AM

ok so i was lazy over the weekend :Snoring and i didnt get to look at the airpump belt..looked too much like hard work on a nice saturday afternoon!

Anyway have driven the car a few more times..and the noise is actually also present at about 2krpm and 3krpm ish too, not as loud, but its there... i really am starting to think it may be the exhaust..is it easy enough to check the manifold bolts etc? im still going to investigate the rest of the bits and pieces but for some reason my mind is set on exhaust now as it doesnt appear to be limited to two very specific revs.. (although it is definately more noticeable at those..)

any more thoughts are cool