Strange starting problems

[pi quattro]

Thanks in advance for any advice on my next step.

My van 1.9 DG petrol had a hiccup when starting, the engine would turn over and "catch" just as I let go of the key.
I had this before and immediately thought the ignition switch was the culprit. (I had this symptom before)

It didn't start at all a few weeks ago and it wasn't "catching" so I replaced the ignition switch with a brikwerks one and it started immediately and I tested it again half a dozen times or so.

Came back to it 2 days later- nothing can't get it running at all.

Checked all connections, already cleaned up earth crowns and replaced the earth strap at the front of the gearbox last year, now not sure where to turn?

There are two wires going into the coil, only one has any power through it when starting and ignition on is this right? (wiring diagrams have me scratching my head)

How can I test the output from the coil? My multimeter only goes up to 600v and I believe the output is much higher?


P.S. 99.9% sure it ain't a fuel problem, I can smell the petrol very strongly

[ghost123uk]

Hi there.

Firstly, you cannot test the output of an ignition coil by measuring it's output voltage with a meter because it is in the region of tens of thousands of volts. One tests in two ways. One is to get a spare spark plug, connect to to any of the 4 spark plug leads, hold the body of the plug onto a clean bit of alloy on the engine and get an assistant to try and start the engine. One looks at the plug tip and you should see a spark. The whiter the spark the better, though they always have a blue tint. IMPORTANT = You have to do this VERY carefully as if you get it wrong you can get a nasty, even dangerous electric shock (thousands of Volts). I usually earth the body of the plug by holding it with a very dry towel or similar and make sure it is held firmly against that (good) earth on the motor.

Secondly, you can test the windings inside the coil are in good nick by measuring their resistance with your meter. Details on how to do that are in our wiki here -> https://club8090.co.uk/wiki/VW ... ition_Coil" onclick="window.open(this.href);return false;

However, and here I have to admit that my knowledge on "our" ignition systems has let me down, I could research it, but someone will be along soon to clarify. Your symptoms are those of a cold start voltage boost circuit fault, known as a "ballast circuit", but I am not sure if our vans use this system. Many vehicles of our vintage did, but I think mainly on the more basic points style ignition systems, not on electronic ignition systems like ours.
The following in small type because it is purely information only and as said, might be irrelevant on our vans) = A "ballast system" coil actually runs off 8 Volts normally, it only gets 12 Volts whilst actually starting the engine (to boost the spark). Once the engine is running a resistor drops the voltage to 8 Volts. So, if the resistor or it's wiring is faulty, the motor won't receive sparks whilst cranking, but for that 1/2 second after you cease cranking it will. This causes the symptoms of not "catching" whilst cranking, but sometimes succeeding in "catching" as you release the key. Someone will be along soon re this "ballast" or "no ballast" thing (I'm now thinking we don't have it )

So, test your coils resistance as per wiki. Carefully test for an actual spark. Or, if you have a friendly T25 owner nearby, you could test the coil via substitution.

If it turns out not to be the coil, the next, and quite common thing to fail is the ignition amp. A little black box on the bulkhead, just forward of the coil, about the size of a fag packet. Testing for a problem there is best done by substitution with a known good one. I always carry a spare one of these.

Let us know if you can find a good spark.

[pi quattro]

Ghost thanks for the reply!

The ballast theory sounds entirely plausible as the symptoms sounds fairly similar. We did try the spark plug against the engine and my friend told me it only sparked as I let go of the key and stopped cranking - hence I replaced the ignition switch.

I will defo try the testing of the coil as you suggest and at least that could confirm/deny its operation. We did try a spare coil but the connectors seems different - after reading the wiki link I now see why.

Is there any way of testing the output of the ignition amp? I don't have a spare one of them to try. I am sure that I checked the plug from the amp to the coil and there was no output when the ignition was on?

[ghost123uk]

I still don't know if "we" have the ballast system on our vans, but I am leaning towards not.

I know of no way of testing the ignition amp. I haven’t read on here of any way of testing them other than by substitution.

However, another distinct possibility has come to mind. How fast is your engine spinning over on the key ? Reason = another cause of your symptoms could easily be that when cranking the voltage from the battery is dropping too low to work the ignition system. When you release the key, the huge drain that the starter motor creates disappears, the voltage rises and the ignition system could then start to work for that 1/2 second before the engine stops turning. By far the most common cause of this, especially at this (cold) time of year is a failing battery. It is quite easy to "borrow" a known good battery off another vehicle to test this. Just be VERY VERY careful that the +ve and -ve terminals are the same way round as the ones on the vans battery as there is a 50/50 chance they are the other way around and you DON'T want to get that wrong !!!!!!!!!

Other causes of sluggish turning over and associated excessive voltage drop are bad connections on any of those very heavy cables from both posts on the battery and also from the engine to chassis earth (which is on the front "nose" of the gearbox. You can temporarily test that latter one by connecting a black jump lead from a clean, solid bit of the engine to a body earth, the latch for the tailgate (by your knees as you stand there) is a good place. If the engine spins better with that in place your engine to chassis earth is in poor condition.

First off though, get a known good battery connect it, up making sure the red lead is on the +ve terminal and try that.

Let us know how you get on.

[Ian Hulley]

Is there any way of testing the output of the ignition amp?

When they fail they just stop working ... zilch, nothing, no notice.

[pi quattro]

Battery is a good one. Brand new last year and I have a voltmeter on the dash! I check it often and the battery is in tiptop condition. With all the cranking we have put a charger on it too.

Have checked earths but I will try the jump lead trick.

I had an issues with the engine revving flat out when I first started it, would a poor ignition amp cause this? I am leaning towards this.

[ghost123uk]

I had an issues with the engine revving flat out when I first started it, would a poor ignition amp cause this? I am leaning towards this.

No, the ignition amp would not cause that. That is 99% likely to be carb related. Best not to "worry" about that right now as, whilst it might need attention, it is unlikely to be the cause of your current non firing symptoms.

[pi quattro]

Tried another coil and another ignition amp, that are known to be working, still wouldn't start! Now totally baffled.... Will be getting a tow to a garage today I think.

[pi quattro]

Update -

The van was bump started with a tow and was taken to a vw specialist. After a good look, it was diagnosed as having a fault with the hall sender part of the distributor. Brickwerks rebuild kit already ordered. Will update results. If I remember, I will ask the garage if our vans have the ballast system as described.

Cheers.

[ghost123uk]

The van was bump started with a tow

This indicates I might have been correct re low battery voltage. My money is on a failing battery. We get this type of issue on the forum quite often at this time of year.

Let us know.

[pi quattro]

Well the "hall" unit was rebuilt and it starts first turn of the key! I was told that some sort of analyser was put on the output and it was described that the output should be "stepped" like a pulse. Mine was flat with no output. Batteries were fine. Cheers