After a 2-hour of driving during the weekend (not too hard, around 4,500 rpm for most of the time), the engine of my 1991 Nissan 200sx is vibrating while it is idling at around 850 rpm (even the exhaust pile and gear stick are shaking). The sound of the exhaust is very rough, like the engine of a small boat. The engine is no longer shaking if I increase the engine to around 1,500 rpm or above. Everything seems normal before the trip, …
I checked the following items yesterday:
- Check & clean the air filter, & everything seem normal
- Check & clean the spark plugs, & everything seem normal (with the exception of the spark plug for the number 2 cylinder, it is a bit carbonised)
- Check all the hoses & ducts for leaking electrical connections, & everything seem OK
- Self-diagnosis for the ECU (modes III, IV & V) & there is no error message
- If I increase the engine to 3,000 rpm, there is some abnormal sound (a bit “mechanical”, if you understand what I mean) around the catalyzer. The sound of the engine appeared OK.
I drove the car this morning & the engine almost stalled at 500 rpm during the cold start, …, but it was OK since then, with the exception of the vibration!
Will the engine vibration due to the collapsed catalyzer of the exhaust, i.e. how can I be sure that the problem is due to the collapsed catalyzer? (Can I undo a bit of the exhaust pile & see what happened, if I am able to undo the bolt??) What other areas should I check before spending money for an exhaust?
Many thanks,
GKY
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I?m no kind of expert but my 309 used to suffer from a serious rattling noise coming from below the engine which would stop at higher revs, or once the car was moving along and not stationary. I sourced the problem (with a garage's help) to a manifold connector that held the motor end of the exhaust in place just before it disappears into the motor. This had come lose and was causing the exhaust system to rattle at low frequencies. Moreover, it seemed to set the engine rattling too. Very bizarre but it turned out easy enough to replace.
Your problem could be the catalyst, something along the path of the exhaust system, any of the fittings that fix the exhaust to the chassis etc. You have to try and localize the sound. What about jacking it up on axel stands and looking underneath as the motor is running (be very careful of course).
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GKY,
Usually a cat that has failed enough to affect the engine will also show in low power at speed.
Forgetting the cat noise your other symptoms are in line with one cylinder not firing correctly. This can give the "pop-pop boat" noise, an uneven idle and a stalling feeling when cold.
MM
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I'd agree with MM that your car may only be running on three cylinders. I've had a couple of spark plug failures recently (both with NGK plugs although this might just be a coincidence) where one plug stopped sparking at idle, but worked OK (with occasional misfire) at higher revs. Took me ages to figure it out the first time, especially as the plugs were almost new.
Richard Hall
bangernomics.tripod.com
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Many thanks for all the help, ? I am a bit confused at the moment after I done some more checks on my own this morning!!
The engine is still vibrating at idle but it is no as severe as yesterday. I conducted another round of ECU diagnosis (Modes I & II) and everything seem OK. I then undo the two bolts which connect the catalyzer, ? the ?mechanical sound? around the catalyzer disappeared around 3,000 rpm (I can feel some of the exhaust gas coming out of the gap), the car is also driving a little bit better.
If the engine vibration is caused by one incorrect firing of one cylinder, as suggested by MM & RH, will it cause the spark plug tip carbonised? I am going to replace the spark plug tomorrow and see what may happen.
Many thanks,
GKY
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