V40 T4, 1.9 147 KW: Ignition issues, won't accelerate

[barrybritcher]

Make sure the lpg system is working. It must start on petrol.

[canis]

Watched the vid, that engine is only firing two cylinders. Could be a coil's burnt out, especially if you've been pulling live plugs. Could be leads mixed up, as someone else said, and I'd bet money that's what it is. Who did the service, and why did they leave it this way?

You can find out which cylinder isn't firing by disconnecting the injectors, each one at a time. If the engine labours even worse, or stalls, reconnect that one and restart the engine. If it makes no difference, that cylinder's plug's not working. There will be two of these, note them down thus: Cyl 1 is on the 'left (pulley end)', Cyl 4 is on the 'right' (gearbox end) (looking at the engine from lifting the bonnet).

There are two versions; Early systems have four HT wires going to two coils mounted on a metal frame at the 'back' of the engine. Later systems have the coils on plugs 1 & 2 and wires leading off to plugs 3 & 4.

Remote diagnosis depends on which type your engine has. It's difficult to imagine how the latter type can be mixed up, so it's important to know which your car has.

[vlitavsky]

Wow, THANK YOU VERY MUCH GUYS! I have just started my car like never. Leads were in incorrect order for my T4 it should be 1 and 4, 2 and 3. Then I was trying to check lead 1 and 2 while the car was running and it appeared that valve 1 was completely misfiring. I switched once more and checked if there is issue with lead. But it was coil which was bad, I bought one, replaced the one which was not working properly and then my car's problem was solved.

I owe you the beers if you ever come to Prague.

One additional issue: The rpms are OK when I accelerate, there is no problem with gaps or lack of power but when It is idling it has tendencies to go to 0 rmps, but it never shuts down and after I even slightly put my feet on gas pedal I has great response time ( no gaps ). Could this be issue with the MAF sensor? Probably the service guy bought the cheapest one I costed around 100 EUR.

[ww1dm1]

Originally Posted by vlitavsky

Wow, THANK YOU VERY MUCH GUYS! I have just started my car like never. Leads were in incorrect order for my T4 it should be 1 and 4, 2 and 3. Then I was trying to check lead 1 and 2 while the car was running and it appeared that valve 1 was completely misfiring. I switched once more and checked if there is issue with lead. But it was coil which was bad, I bought one, replaced the one which was not working properly and then my car's problem was solved.

I owe you the beers if you ever come to Prague.

One additional issue: The rpms are OK when I accelerate, there is no problem with gaps or lack of power but when It is idling it has tendencies to go to 0 rmps, but it never shuts down and after I even slightly put my feet on gas pedal I has great response time ( no gaps ). Could this be issue with the MAF sensor? Probably the service guy bought the cheapest one I costed around 100 EUR.

A bad coil and switched leads, that does make sense. Congratulations! For your other issue, does it oscillate or just keeps low RPM in general? I believe the goal RPM for a T4 is 750.

Originally Posted by canis

Could be a coil's burnt out, especially if you've been pulling live plugs.

Hey, could you please elaborate? I assume you meant pulling the leads off the plugs with the car working rather than actually pulling plugs out of a working engine. How could this damage the coils, though?

[canis]

Originally Posted by ww1dm1

Hey, could you please elaborate? I assume you meant pulling the leads off the plugs with the car working rather than actually pulling plugs out of a working engine. How could this damage the coils, though?

It was something I read in the forum. I thought it over and decided there's probably some truth to the idea. With a plug firing ten times a second, or thereabouts, I imagine whilst pulling there must come a point where the gap between the tip of the plug and the end of the HT stem becomes somewhere between close enough to jump but large enough to create massive impediment. The intermitancy, I guess, stresses components. Induction occasionally produces suprising effects, and (I suppose) if only half of the coil's discharge makes it through the plug, the other half perhaps inducts it's way back to the LT coil, perhaps catastrophically. I've no evidence for any of this, it's all conjecture based on another long forgotten post. Of course, I'm willing to be corrected.

For years I had been performing the old "hold the base of the plug against the engine block while still connected and look for a spark" trick, but since electronic ignition became commonplace I gave it up. Besides, HT electric shocks hurt very much.

These days, with fuel injection, it's much easier to identify mis-firing cylinders by temporarilly disconnecting the injectors. It saves being electricuted, and has the added advantage that it prevents unburnt fuel reaching the catalytic converter, particularly in a "just get me home" situation when limping back on two cylinders at 3am in the pouring rain, etc.

The arcane technology of electronic ignition is since my time, I was raised on rotor arms and points. Volvo electronics are very robust, but I'd prefer not to push my luck if I can avoid it.

[vlitavsky]

Originally Posted by ww1dm1

A bad coil and switched leads, that does make sense. Congratulations! For your other issue, does it oscillate or just keeps low RPM in general? I believe the goal RPM for a T4 is 750.

It is slowly jumping/oscillating from lets say 850 to close to 0. But it doesnt sound like valve is misfiring from my point of view. And it has started after those changes I mentioned.

[loely]

Why the coil is stopping firing (damaged): the greater the gap between HT wire(spark plug) and the ground the higher the necessary voltage will be.
When the gap is to big the tension is up higher then the electronic devices inside (transistor,thyristor,....)can handle and it blows.
You can plug a old sparkplug in a sparkhead and leave the original plug in the cylinder head. Lay the old plug on the motor and fire the engine up,it will turn like a potato but you can see if the old plug sparks without damaging the coil.And if you feel a bit down,take the plug into your hand and you will be motivatad by 1000% .lol

[ww1dm1]

Originally Posted by loely

Why the coil is stopping firing (damaged): the greater the gap between HT wire(spark plug) and the ground the higher the necessary voltage will be.
When the gap is to big the tension is up higher then the electronic devices inside (transistor,thyristor,....)can handle and it blows.
You can plug a old sparkplug in a sparkhead and leave the original plug in the cylinder head. Lay the old plug on the motor and fire the engine up,it will turn like a potato but you can see if the old plug sparks without damaging the coil.And if you feel a bit down,take the plug into your hand and you will be motivatad by 1000% .lol

Doesn't the coil produce a fixed voltage? As far as I know it's basically a transformer with a low voltage in the primary coil inducing a high voltage in the secondary coil. I would think if the distance to ground is too high and the voltage is insufficient to break the dielectric barrier, then the circuit is considered open and nothing happens. Am I wrong here?

Originally Posted by vlitavsky

It is slowly jumping/oscillating from lets say 850 to close to 0. But it doesnt sound like valve is misfiring from my point of view. And it has started after those changes I mentioned.

Well, this one's tougher to tell. Does it always do it, or only when it warms up?

[vlitavsky]

Originally Posted by ww1dm1

Well, this one's tougher to tell. Does it always do it, or only when it warms up?

I drove my car only twice from that time but it happened only when it warmed up as I remember

[loely]

No, becouse it is a transformer it is called inductive and the current is always later then the tension is .(weerd but a electrical law).When interrupted the current resists and flows in the other way round in the coil ( for a very short time that is why they put a diode in a ralay over the coil to protect it)this make the current very high in the secundary of the transformer and can destroy components.
You have seen that sometimes when disconecting the powerplug from a home circuit you see a spark at other times you don't. That is the same reason.
Not that easy to explain in simple words.
Hope you can understand a bit of this hokus pokus.