• doormat posted an update 4 months, 4 weeks ago

    Hi
    Ive got a 1999 V70 2.5 petrol.
    I’ve had problems starting when hot or cold, and in any weather. Battery is sound. It doesn’t appear to ignite unless you put your foot hard on the accelerator when it’s playing up.

    Ive started today twice in -2 first time. I’ve driven motorways for 60 miles.

    I got home for an hour and it started first time. I drove for a mile and didn’t stop the engine. On the return trip the car started to shudder. When I accelerated in any gear. There is a slight petrol smell. I drove it at 70 for 3 miles but it hasn’t cleared. It shudders at idle.

    Could this be a spark plug problem? I don’t know when they were last changed . 165 k on the clock.

    Any ideas gratefully received. Thanks.

    ps oil and fuel filters haven’t been changed in 12 months and I’ve had new wheel bearings both sides front 5 months ago.

    • Any error codes? You can get a generic OBDII code reader for a tenner that connects to your phone etc by bluetooth/wifi. Cheaper than a garage, and will do most fault systems (usually not airbag errors though).

      • Thanks. There are no engine lights on at present.

        • Always bear in mind that the dashboard lights can be fail too, so maybe the engine light does not light! you could perhaps try and force it to light by creating an engine fault situation

          Getting a code reader is a good double check if all else fails.

    • I’d check the plugs and the rest of the ignition system.

      Poor starting and petrol smell both suggest this. Spark plugs can just give out for no good reason. If you have a look in the dark tonight with the engine running you should be able to see if you have an insulation issue.

    • Where is the petrol smell from? Exhaust or engine bay? Through the heater vents?

    • Thanks all.

      petrol smell seems like from under the bonnet. No exhaust smoke.

      I can’t get in with the mechanic I use until next week. After a chat he seems to think ignition coils.

      Im no mechanic. It just took 5 goes to start it after my walk and the judder and poor acceleration remain.

      How do the coils and plugs work? Do they ignite once on turning the ignition, or on every cycle of the cylinders?

    • Don’t know the model, but if it has an ecu have you disconnected the battery recently? Could be a coked throttle body and the computer has reset. Just saying because I’ve recently had something similar in my 05 avensis. Or a lambda sensor – They can be sporadic when it comes to throwing error codes.

    • Sounds very similar to when the coil pack went on our car!

      • Yes. If was a diesel I’d suspect a clogged fuel filter due to the cold weather, but that’s unlikely with petrol.

    • Thanks all.

      Im not going to drive it again except to the garage next week. There were no engine lights on last night.

      Do all the cylinders move in sequence due to the timing belt? If so is the one that’s possibly. It working just moving in sequence and not firing?

      Apparently all the 5 cylinders have an ignition coil. Do all need replacing or just the faulty one?

      Thanks for your time

      • OK, very simply, and probably a bit inaccurate…

        Inside the engine is a crankshaft. Initially this gets spun by the starter motor.

        The crankshaft is connected to the pistons by..er..connecting rods. As the crankshaft goes round a clever bit of mechanics means the pistons go up and down in the cylinders. The movement and position of the pistons is fixed depending on the position of the crankshaft as it goes round. The only way it can change is if something goes horribly wrong, and trust me it’d be a lot more than a judder.

        Ignoring the timing belt and valves and stuff, this happens:

        Piston pulled down by crankshaft – air goes in with a squirt of petrol.

        Piston pushed up by crankshaft – petrol and air compressed, spark plug sparks, mixture goes bang.

        Force of explosion shoves piston back down, spinning the crankshaft round, pushing another piston into position where there is another bang, spinning crankshaft round and pushing the first piton back up to blow the burnt gas out of the exhaust.

        So your five cylinder engine continually goes bang bang bang bang bang.

        One cylinder not firing you get:

        bang …. bang bang bang bang …. bang bang bang bang …. bang bang bang etc.

        It’s that missing bang that gives you the loss of power.

        • Thanks for the idiots guide to the internal combustion engine)). That has helped my understanding.

          What makes the plugs fire each time? The ignition coils on every bang?

          • Here is another guide written by an idiot.

            So the position of each piston is determined by the position of the crankshaft, ok?

            If a piston is at the top of the cylinder, in the first revolution of the crankshaft it goes down and then up (induction and compression strokes).

            The spark plug fires, igniting the fuel/air mixture, and during the next revolution of the crankshaft the piston goes down and then up again

            (ignition and exhaust strokes).

            So the spark plug in each cylinder needs to spark at a precise point every 2 revs of the crankshaft.

            The crankshaft also drives a distributor shaft, which is geared to rotate once for each 2 rotations of the crankshaft.

            At the end of the distributor shaft is an arm/lobe, which is essentially a position sensor. At 5 points during each rotation of the distributor shaft each of your 5 pistons is at point when you need a spark at the relevant spark plug.

            At that point the distributor senses the position, sends 12V from the cars electrics to the relevant ignition coil, which steps that up to a few thousand Volts, which causes the spark to arc across the spark plug electrodes.

            As the distributor senses the next firing position for another cylinder the above is repeated for the next ignition coil in the sequence.

            Obviously there is a bit of a lag between position detection and spark creation, and as engine speed increases/decreases the timing of the spark plug firing needs to change. This is all done electronically.