Suzuki Wagon R+ 1.2 - Vibration under load/misfire

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Sun 16 Jan 2011 21:58
Suzuki Wagon R+ 1.2 - Vibration under load/misfire - stunorthants26

'98 car, 35k.

Im getting vibration, felt through the steering when the engine is under load, esp at higher speeds, uphill for example, ( between 2800-3200 rpm ) and at low speeds from idle to about 1400 rpm. Its not gear specific although is most noticable in 3rd at low speed and 4th/5th 45-60 mph. It smooths out above 60.

The important bit is that the vibration completely goes away under engine braking and it disappears progressively as you decrease the load on the engine.

Ive also noticed that the engine note sounds a bit off, like its misfiring abit. It doesnt seem down on power but it sometimes doesnt fire up quickly, although other times it does.

Ive put some injection cleaner through which makes a temporary improvement ( but not a fix ), but im unsure if its the cleaning effect or the octane boost the stuff sometimes gives.

Its had new plugs and leads in the last month and the EGR has been cleaned out.

It does have a pattern part exhaust section which sounds a bit throaty, not sure if that would cause such an issue.

My instinct was its either a fuel delivery issue or a sensor, but I may be way off and I dont know enough about modern engines to be any more specific.

Any good clues appreciated :-)

Edited by stunorthants26 on 16/01/2011 at 21:59

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Sun 16 Jan 2011 23:39
Suzuki Wagon R+ 1.2 - Vibration under load/misfire - bathtub tom

What happens at harmonics of this (5600 RPM) ?;>)

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Mon 17 Jan 2011 00:27
Suzuki Wagon R+ 1.2 - Vibration under load/misfire - stunorthants26

Nothing, smooth as you like at those revs.

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Mon 17 Jan 2011 10:41
Suzuki Wagon R+ 1.2 - Vibration under load/misfire - unthrottled

Misfiring under heavy load at low/medium revs is a good indicator that the coil packs are breaking down.

Don't waste your time taking readings with a multimeter, you'll only get a false negative. At high load/low RPM the spark timing is very retarded and the cylinder pressure at the point of spark timing very high, so it takes a very large voltage for the spark to jump the gap. This can be more than the insulation can cope with. The problem tends to become more acute on longer journeys and might not be present ata cold start. As you back off the throttle or increase the revs, either the cylinder pressure drops, or the spark timing is advanced which has the same effect. Either way, stress on the ignition system is reduced.

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Mon 17 Jan 2011 14:08
Suzuki Wagon R+ 1.2 - Vibration under load/misfire - stunorthants26

Ah funny you say that. I booked it in at Suzuki dealer today and the workshop manager was there. First thing he said was after id described the symptoms was ' If its something like the coil...'.

Seems he had the same thought which makes me think it could be a good direction to go in.

Problem is present right from cold. It idles pretty unevenly aswell, tends to hunt between 800 and 1000 rpm, esp when hot.

Thanks for the very good explanation, makes sense to me.

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