Sounding (really) rough at idle.. need help with a diagnosis!

ojobson

ojobson

Hi,

The mrs came home form work the other day with her micra ('96 1.0 16v, just under 100k miles) sounding like a transit van. The oil was low so I gave it a full service (sparks, oil + filter, fuel filter, air filter - it was about due for it) - I gave it a 5 minute run round the block and to be honest it sounded really sweet - you could hardly hear the engine running from inside the car! The old spark plugs did have some pretty heavy carbon deposits, but were not oily and theres never any smoke when started cold or otherwise from the exhaust.

She set off for work the next morning and 3 miles down the road (in traffic) she phoned to say it was sounding awful again. She came home and I had a look and it sounded somewhere between an exhaust 'puffing' noise and a tapping noise. However it still seems to run ok and doesn't seem to be down on power (we live on a big hill). I parked it on the drive and after work I started it and it still sounded rough (from cold this time) I took the belts off and felt the oil/water pulleys and they felt smooth. I replaced the belts anyway (again, they were about due) but it still sounded rough when I started it. I then pulled the ht leads off of the plugs one at a time to see if it was miss firing, but it is definitely firing fine on all cylinders.

The next morning when I started it once more the noise had gone and it was sounding ok again - confused!

Sound clips: running smooth.
and running rough. (at the end of this second recording I placed my phone very close to the chain inspection cover as it's this end of the engine that the noise seems to be coming from.

I also took the cam cover off and looked at the chain, it seems fairly tight, teeth were a little worn, but looked ok. The cams also seem to be in the right positions so I don't think the chain has jumped.

pics & vid of exhaust gasket and chain/sprockets (with cylinder 1 at 5 degrees before tdc):
http://www.flickr.com/photos/oliverjobson/sets/72157630270433386/with/7435111150/

I don't think the chain needs replacing (can't really see the bottom one, but there is minimal chain noise at the moment and it seems to be properly tensioned) - however having said this, I have no idea what the chain should look like having not done this before!

Do you think it could be the exhaust manifold or its gasket seal? - I'm starting to lean on the side of it being compressed air escaping that is making the sound. Perhaps when the engine gets hot the seal around the exhaust manifold is being compromised...

In light of the carbon deposits on the plugs could it also be the MAF sensor which apparently can go (making it run rich) - I don't know much about this one though?

If it wasn't for the fact that the engine was still idling ok I would be thinking a compression test might be required in order to determine if the head or block is cracked - but if it was something this serious then surely it wouldn't be an intermittent issue and it would screw up the idling of the engine too.

Sorry for the massive post! Hope someone can help me out - there seems to be quite a few good people on here who are keeping these cars on the road! The car has done us proud so far, so I would like to get it healthy before I sell it on (plus I like getting my hands dirty and don't need much of an excuse!) :)
 
the noise is very high frequency eh ojobson, like every link of the chain is catching something, i would run it with the cam cover off
 
ojobson said:
Yeah, I suppose it could be. Is running it like that ok for short periods? I've got no oil in it at the moment...
Click to expand...
it,ll just spatter a bit (with oil in) but you might see/hear the chains jitter, if there is a chain or tensioner fault
 
maybe lay down some sheets of cloth around the exposed head and not wear ur best clothes when running without the cam cover?

it sounds like a dieselo_O my upgraded 370cc injectors kinda makes that tappy diesel noise abit, but not on a stock fuel rail.

the upper and lower chain tensioners have a spring that exerts a constant small preload during low oil pressure.

the upper chain tensioner has a ratchet stopper to prevent the upper chain from getting too loose during startup with low oil pressure IF the chain isn't stretched beyond spec. you normally hear the chain chatter abit during cold start with low pressure then 5secs later the pressure rises, pushing the tensioner and silences the chain.

the lower chain doesn't have this ratchet stopper so relies on the small preload during startup and then oil pressure when running.

the oil passage to the tensioners are a tiny pinhole. if abit of sludge had loosened during oil change and blocked the pinhole, the tensioner won't have any hydraulic pressure to push against the chain so it'll simply be trying to tension a rapidly spinning jittering chain with a tiny spring which could cause a rough rattly loose chain noise.
 
OK, so managed to run it with the cam cover off (also had the inspection plate off the side, out of which poured quite a bit of oil on to the drive belts :/ Thankfully not too much though! The chains looks fine and as you say the small amount of chain noise that there is does disappear a few seconds after start up. I took it for another run and it runs fine until after about 10 minutes of driving (quite hard) and then it turns in to, as you say, a diesel and starts to sounds awful.

It isn't down on power - in fact it runs great, it just sounds really bad. I left the car for a while after this test run and then started her up - the noise comes back for a minute or so and then goes away until you take it for a drive. Seems like the noise is only happening when the engine is very hot. There are no warning lights on the dash, but do you think it could be over heating?

I'm stumped. Unless anyone here has a good idea of what it could be I think I may have to put her up for sale for spares/repair or scrap her. I just won a new contract and won't have a lot of time to fix anything too complicated - which is a shame as I'll never get to know what the problem is!

Cheers for the help so far!
 
Sounds like the noise is only there at idle / coming off throttle...originally i was thinking it might be a vibration (e.g.exhaust heat shield), though you'd have thought it'd be there from the start.

And after listening a few times to them both at the same time, its very hard to say...but at a punt possibly exhaust manifold related?. It does have a slightly similar sound (in places) to when i ran the car with the lambda out of the exhaust (leaving the port open).

If the bolts will come out easily maybe remove the exhaust manifold heatshield and check over the manifold incase theres a crack or something and incase the sprung bolts have broken (you'll see those just by looking at the exhaust before you remove anything). Tissue paper held around the manifold / engine block, will flutter if theres any gasket issues (as you probably know).

Theres the engine breather pipe (big black rubber pipe at the front of the engine) that can get full of crud and block up...cant say it'd cause the noise you've got...but just running through the possibles that are around that area. :D

Tbh i'd start at the top and assume everythings broken, then work your way through the engine checking everything :)
 
ojobson, this sounds exactly like the same sort of issue i have with mine. i was going to start looking at the chains tomorrow but now ive seen your experiences im having second thoughts. As with you all the issues have arisen after a low oil issue. I topped mine up and the noises went only for them to return a few weeks later. Oil level is still good, but the source of my noise definately seems to come from the oil pump or behind.
 
Ian i tried running her without any belts on for a short period but the noise persisted so I don't think it was the pumps. If I was you I would buy a cheap compression testing kit (about £15) which would provide vital insight into the issue. Think I'll be sending her to the scrap heap as I just don't have the time to fix her right now and we don't have the room to keep her - I've got more valuable freelance work to be getting on with. I think its either an exhaust gasket issue or maybe an issue with the crank (big ends etc). Bugs me that I will never know!
 
before scrapping anything its probably worth putting in some cleaning products. i had a similar noise, but as i'm a big believer in injector cleaner, i put some in for 2 full tanks nd the noise disappeared. i've had other engine noises cured as well, using a full fuel system cleaner, and a miniature birds nest in my mid cat (after it'd been off for a week. that was just the hose got that out, and no birds disrupted!)
 

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