Thanks for that Peter.
The timing was out because the garage had to remove the distributor when I had the noisy hydro-tappets changed less than a month ago. I probably should have said, but wanted to keep the thread short (ish). When they handed the car back, the timing was so far out it was pinking. They adjusted it, but I still thought all wasn't well, so bought a timing light and did it myself. It's spot on now, running smoother (once its started, :-D) and cooler and pulling better.
The HT leads (high quality, OEM Beru ones) are less than a year old, so I?m sure the resistances are ok. However, I?ll check they are located properly. Would this not mean there would be a consistent problem when running though?
The whole dizzy is also quite new (12,000 miles) so I?m also sure there is no fault with this. Yet again, I?ll check them over. If you don't mind me asking, what is the coil end face? Is this the flat part which connects it with the body of the car? I'll check the connections too while I?m there.
Ah, the spark plugs! I have a shiny new set of these sitting on the desk beside me. Genuine VAG parts too. I bought these as the current ones are W7DTC (covered 10,000 miles) but its supposed to have W8DTCs fitted, so because they were good value, I got them. My uncle, during the HGF you might recall happened recently, cleaned them with a wire brush. This was another reason I got new plugs.
I?m sure its noting major as once started, its running as well as it ever has, its just been rather sudden. But I?m aware that its doing neither the cat or the engine any favors.
Thanks again, much appreciated.
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A poor battery can give this symptom, as can the coil.
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Well, its totally dead now
This, we do know:
- It has fuel (the plugs are wet when you take them out)
- The plugs are fine (been replaced)
- The dizzy cap is clean, as is rotor arm.
- It has a spark on all leads
The only thing we don't know is the resistance of the leads (we don?t have a multimeter), but as is mentioned earlier, these are new, so shouldn't be a problem.
HELP!
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im confused are new plugs fitted or not?
old plugs can spark when not under strain but fail in their proper enviroment.
--
\"a little man in a big world/\"
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im confused are new plugs fitted or not?
Yes, new plugs are fitted. But this has had no effect at all.
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the system might have overfueled then.
either take the plug (power) to the injector off and crank again to purge the engine of fuel or drag it up the road to start it.
next time vehicle been stood in fact all times resist the urge to touch any pedals till car is running,single point injector cars made in the 90"s were always a pain.
--
\"a little man in a big world/\"
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Thanks for that oldman. I don't understand why it?s started doing now though, like all of a sudden?
I'll try your advice about unplugging the injector; although I feel removing the hall sender has the same effect and may be the safer option.
I ALWAYS start the car without touching the accelerator (as per handbook instructions). I do hold the clutch down though, so that in cold weather it releases some strain from the starter. Yesterday, when it was reluctant to start, it only fired with a partial throttle opening. Today, it's just totally uninterested and it'll run, on what sounds like only two cylinders, with the throttle open halfway, but this isn't getting it fully started.
I thought it might be a sensor failure of some sort, but I thought these only came to light when hot (if you can get it running, its fine).
What else should I try? (incidentally, we put more fuel in it just incase the gauge was telling porky pies, but obviously this hasn't helped any)
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I think that Roberson should widen the gap of an old plug (quite wide, 2mm gap, or so) to test the spark. As oldman says, under cylinder pressure, the sparking voltage required is higher. It is possible that the system can supply the relatively small voltage required to jump a typical gap at atmospheric pressure, yet break down under higher loads.
That the plugs are wet suggests all is well with the fuelling.
Has this problem only begun since you had the head off?
Number_Cruncher
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It isn't known as yet, whether the plugs are producing a spark, either under compression or at atmospheric pressure. It was assumed they were working satisfactorily as a timing light was connected to the HT leads, and when the engine was cranked over, the timing light works, signifying that some form of power was being supplied to the plugs.
Again, the plugs (new items) are though to be ok, thus could the problem be with the HT leads themselves, despite them being relatively new too?
My dad is bringing a multimeter home from work tomorrow so that we can check the resistances of the leads etc.
The problem has been a relatively sudden occurrence, and it?s never done this before. The car has covered about 800 miles since the head was off, all trouble free (apart from one tappet failing, and the ignition timing being about 2 degrees out, see above) It has gone from a 2 second rough idle, to two attempts at starting, to totally dead. Like i said before, once it was started on the day it took 2 attempts to do so, it ran fine all day, even when left for 4-6 hours. Leave it over night and its kaput.
It?s really got us bamboozled, so thanks for your help so far
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Ok, a further update.
As you may have assumed from my other thread here in 'technical', we measured the resistance of the HT leads, and they varied from 5.9-6.1 K Ohms (they should be 5 K Ohms and the king lead was ok). To aid us further into what was going on, we connectd a plug (earthed against the head), outside of the engine to see what kind of spark we had. Seemingly very weak, as it was a very dim orange flicker (with the occasional brighter orange spark). I thought they were supposed to be a blue/white spark?
I thought this could indicate the leads as the culprit, with coil being within spec, the rotor arm and dizzy cap being clean etc etc. So why the weak spark, if the slight increase in the lead resistance isn?t the fault? (oldman, N_C, you may be onto something)
Incidentally, we tried again today (24 hours later) and it sounded as if it was about to start, with one cylinder firing, but that was as far as it got.
ANY ideas much appreciated
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This should be a bright blue/white crack of a spark If you connect the plug to the King lead instead you will get more spares and will ellimate the plug leads. The spark if you use a peice of wire will jump at least 5 mm and even 8mm with a good healthy crack. Either you have an earthing problem, a faulty coil or a faulty igniton drive amplifier. Ideally you need a scope to see the drive LT waveform to identify the problem or spare parts from a scappie. Regards Peter
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sorry I meant you will get more sparks. I would also all thay I would not disconnect the injector connect and turn the engine to clear out some of the fuel put pull the fuel pump fuse out N/S Top Yellow from memory in it's own holder and crank over with a wide open throttle. Turn Ignition On and measure what voltages you have at the coil connector with respect to chassis. Regards Peter
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It sounds like you're getting near to the cause of the problem, Roberson.
If I were in your shoes, I would be checking
1) the voltage at the positive side of the coil LT, and at the hall sender, and at the ignition amplifier, both with the ignition on, and during cranking (sometimes there can be problems with ballasting - I don't know if your car has a ballast resistor)
2) the connection between the ignition amplifier and earth
3) the connection between the hall sender and earth
4) the connection between the hall sender and the amplifier
5) the low tension and high tension coil resistances
It may also be worth turning the engine over in the dark and watching for sparks jumping where they shouldn't.
BTW, your plug lead resistances are fine.
Good luck,
Number_Cruncher
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Thanks a million guys, this will give us plenty to go on tomorrow. I was thinking of giving up and booking it in at the garage, but we can't be far off now, so I?ll postpone that for now!
Incidentally, we've just tried connecting a jump lead from the negative terminal on the battery to the earth strap on the coil, then viewing what response we got from the spark plug. It was white this time, and a bit brighter, but not enough to allow the car to start. Thus earthling could be an issue.
Incidentally, where is the 'ignition amplifier'? Nothing of this mane is in the Haynes, but there is something connected to the coil (according to the wiring diagram) called an "end stage for ignition transformer", could that be it?
Thanks again
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>>"end stage for ignition transformer", could that be it?
Sounds like it to me.
If the system on your VW is like I **think** it is, the hall sensor in the distributor is quite a delicate switch, switching on and off as the distributor turns. It can't handle the current required to drive the coil.
So, there has to be an amplifier which reads the switching of the hall sensor, and switches the earth side of the low tension suppply to the coil - in almost the same way as contact breaker points used to do this job.
However, the end stage part of the description may mean that the amplifier itself is a multi stage device, with the low power stage residing in the ECU, and the high power stage residing on a heat sink by the coil. Your wiring diagram may help resolve this.
Having said all of this, the voltage and wiring checks are still valid. For example, it doesn't matter how exactly the switching is done; if you haven't got a good 12v supply to the coil LT positive terminal, you won't get a good spark!
Number_Cruncher
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That?s pretty much how the system works I think. Reading a bit more about it from the Haynes manual, it seems that the primary windings are charged by a voltage supplied by the ECU. As the engine rotates, the ECU is told by the output of the hall sender to interrupt the primary supply voltage. This results in the collapse of the primary magnetic field, which induces a larger voltage in the secondary coil. That latter sentence suggests what we seemed to find out from the wiring diagrams, that the "end stage for ignition transformer" is an integral part of the coil.
This made any testing of the ignition amplifier (if that IS it) very difficult, as I think its taking into account the coil as well. I must admit, I forgot to test the voltage being supplied to the coil. I take it I just connect the multimeter to the coil connector with the ignition on, and what kind of voltage should I expect?
If that is at fault (and it?s not the battery) then it?s into ECU territory, as this is what supplies the voltage to the coil.
Just thought I?d keep you updated.
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Incidently, we also fitted a second hand coil, which was known to work in the past, which made no difference.
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If it's an old model polo (they have an exposed old type fusebox) you could try removing the fuses, pushing the fuse holders closer together for better grip, then replacing the fuses with a bit of wd40 on the ends and turning them in their holders, for better contact.
It's also worth checking the coil is earthed well to the car body, sometimes there's also a copper strap between the coil and engine block, it's also worth checking the integrity of this strap if it's present.
If these steps don't work, you could then measure the voltage between the battery -ve terminal and the engine cylinder head while trying to start the car. This should be no more than 0.2v while cranking, if it's higher, your engine earth straps need cleaning.
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An update, just to keep you informed.
Over the last few days, me and my dad (the other person helping with it) have been very busy, and time to look at the car was difficult to find. I rang my garage who said they'd take a look, without an appointment, so all I had to do was get it there. We towed it the 6 or so miles at 7.30 at night to avoid the traffic, but still not something I?d want to do again in a hurry (he's slowing...ah, he's stopped...brake...harder...HARDER!)
To cut a long story short, the mechanic said he was on a while before he got it started, but why or how it started, we don't know. He tried a multitude of parts (coil, leads, complete new dizzy) but none of those helped, which is what I?d expect given the tests we had already done. However, the diagnostics constantly showed that the temperature sender was faulty, and the fault code continued to re-occur, so this was changed. I later read in the VAG w/s manual that if these senders go open circuit, the ECU thinks its -40C.
Knowing that the supply voltage to the coil was pretty much the same as the battery voltage (thus OK) we know the fault, if still present will be somewhere after that. Ruling out the possibility of faulty ignition components, it can only be an earthing problem, can't it? What is the best way to deal with checking and cleaning them?
The car made it home OK. Sometimes it seemed a little 'flat' and then sometimes not, but that could be me not driving it for a while. Idling isn't the best, but the timing could be out again (because they've had the dizzy off) but most likely its clearing its throat and getting settled after all these starting attempts, which threw a lot of petrol into the cylinders which wasn?t being burned.
I?m not confident it?ll start tomorrow, or whenever it?s next used after sitting all night. But I?m going out later, by which time it?ll have sat for about 7 hours??.fingers crossed.
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Final update on this.....
All appears to be well and the fault appears to have been the temperature sender. I left this update quite a while, giving the car a good testing before I reported back. Many starts and miles later everything is ok. Just came back from an arduous trip away to Yorkshire; 3 passengers, a multitude of camping equipment effectively meaning the car was fully laden and 2 trips across the hilly N. Yorks Moors with such a load, and it never missed a beat.
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