Mk2 16v Poor cold starting - think I might have finally found the problem..

How odd... ETKA lists two different part nos:

Pre-90: 191 905 115 A
Post-90: 211 905 115 D

Not sure what the difference is, and they must be interchangable I suppose since I had the supposedly earlier one on my old late car..

Not to worry anyway - the main thing is it works now

 

Hmm.. how strange

The problem has reared it's head again - a week or two after fitting another coil apparently sorted the issue, it's now just turning over and failing to fire.

Given how well the coil sorted it last time I'm thinking it's still got to be something electrical - either the new coil coincidentally breaking down, or something else that was temporarily disguised by the coil.

I replaced the leads and dizzy cap today and that made no difference (although they were items off the old car they worked fine when it was running). I had considered that once I've replaced bits and cranked it a few times it might still fail to start due to wet plugs.

I pulled and earthed one of the plugs and that seemed to be getting a decent spark; if it was one lead I've had thought it'd be a bit rough till it got warm but it's fine.

Thinking it might be a shifty earth - have cleaned and greased the big one on the gearbox as well as the battery terminals and those on the coil; is there anywhere else I should try? Perhaps something like a short at the starter might be responsible?

 

Cheers John, no I havn't checked the sensors in the head although I will do if the problem persists. Funnily enough it started from cold almost immediately yesterday, and again pretty quickly when I tried it earlier; so I'm thinking it might have been dodgy leads (they looked original) and the engine just wouldn't start after I changed them as it was flooded from all the cranking. Will see how it goes.

Thanks again for the pointers

 

Did you manage to get this problem cleared up dude? Sounds a lot like the one I'm having.

 

Nope, the car's still being a complete cock

The saga has continued over the holiday, although I haven't updated this thread much.

In summary, on the ignition side the car has had replacement leads, plugs and coil (all known good, off the old motor). There seemed to be a fair voltage drop across the battery during cranking so we replaced it; still nothing. Going to try another starter motor when I can get the car in the workshop.

As regards fuelling, the control and system pressures appear fine. I thought it might be leaking injectors flooding the engine overnight so I whipped them out and stuck them in glass jars for a day or so. There was no fuel in the jars (I suspect it evapourated) but once the injectors were back in it started on the first turn of the key. Thinking this was the problem I swapped over the injectors from the old car; problem persisted.

Replaced the cold start valve which didn't help.. havn't checked the thermotime switch but the injector works when cold, and since it's either on or off I'd have expected a problem with the thermotime switch to cause it to fail to shut off after 8s or however long it is, so this shouldn't affect starting.

It's really starting to p*ss me off now - perhaps it's a problem specific to late small bumper Tornado Red 16vs

 

Mines just started doing the exact same thing, just cranks over and wont fire but then almost does as the key is released, got it sorted though by changing the cold start valve, fire's instantly now, hope this helps in some way

 

Cheers Dan, tried that already though.

Replaced the starter motor yesterday; outside in the f*cking snow so I didn't have to start it to get it into the workshop, and I could see the fruits of my labour immediately.

Once the new one was on it started second turn of the key - as has happened many times before I thought it was sorted, until I can to start the POS today and it was back to 30 seconds of cranking before it would even humour the idea of firing.

Really getting p*ssed off with it now; going to try a direct feed to the coil from the battery tomorrow to see if that makes any difference.

Properly running out of ideas now..

 

I read on the last page you'd replaced the coil. As I mentioned a couple of posts back I had almost exactly the same issues as you... I swapped my crappy GSF coil for a Bosch coil and it's been perfect (touch wood) since. Measured the resistance of the coil and it was way too low. As you just mentioned, might be worth investigating your coil more closely. Could be two duds...?

 

I know originally that you were wondering if the ignition switch could have been at fault. Perhaps it's worth eliminating this still? There are actually several terminals that should make contact when you turn the key, and it could well be that the terminal for the starter solenoid is okay (so it turns over just fine), but the +15 terminal on the ignition switch is worn (which could affect ignition during cranking). (Rubjonny may need to confirm this.)

As a simple test for the above, I may be tempted to hook an inductive strobe lamp to one of the ignition leads while cranking just to see that the plugs are firing.

If something like this does turn out to be the cause of the problem, then it may seem strange that temperature should affect it, but temperature affects everything.

 

Thanks for the support gents

Hmm.. what's the resistance supposed to be? Tbh I'd rather test stuff properly as you've done, but usually end up substituting instead. The replacement coil was off the old motor and was working fine then, but then it hasn't been used for a year. Glad you got yours sorted anyway

Cheers Trev - didn't think about using the inductive timing light, although we did have one of the plugs out and held it to earth when trying to start it, and we did get a spark.
I'm assuming that ignition switch controls the ignition circuit via a relay, so were the switch knackered presumably it shouldn't throw the relay and hence shouldn't get a spark at all.. correct? I suppose it might be possible for the relay to oscillate if getting a dodgy feed from the key.

I think the problem is more time than temperature dependant tbh; once started and run for 10 seconds there's no problem starting. I can't see the engine producing enough heat in that space of time to make much difference to any of the components. In support of this, I started it eventually a while ago whilst it was really cold (probably -2ish), left it for 4-5hrs and it started instantly again.. would have thought that in this time the system should have been back down to ambient temperature again.

What's most frustrating is it's generally randomly started OK after much of my tinkering (having the injectors out, changing the coil, changing the starter motor) only to consistantly fail again in the days that follow...

 

I tested mine like this:



As far as I know, it should read between 7k and 12k. My faulty coil read around 4k. My spare Bosch coil read mid-7k.

I was convinced, as you are, that it was temp related. Turned out the coil had died (and it wasn't very old). Possibly due to the freezing weather - it had actually started to leak it's coolant out, the low resistance suggested it had failed aswell internally.

I'm not certain it is the coil, but your symptoms sound so much similar to what I had going on. Gradully got worse and worse to start - starter motor spinning but no ignition. But would eventually pop into life. Once started, would start again on the button. Leave it over night or while at work, and it would be back to impossible.

 

Cheers for the info dude

The trusty (!) Haynes manual states the following resistance values for the coil:

Primary winding (between low voltage terminals 1(-) and 15(+)): 0.6-0.8Ω
Secondary winding (between terminal 1 and the central high voltage terminal): 6.9-8.5kΩ


First I tested the coil I took off the car:

Primary: 0.9Ω
Secondary: 7.55kΩ (Taking liberties with factors of 10 here, since I'm confounded by the scale on the multimeter)


Then I tested the coil currently fitted to the car, which came from my old motor (not from cold unfortunately, since I had to drive to get a new battery for the multimeter):

Primary: 1.2-1.3Ω
Secondary: 9.50kΩ (Again with the wonky scales)


So both are out of spec according to the Haynes manual, although not hugely (unless the secondary winding values are actually 10 times what I think they are).

Anyway, I also tried starting the car with two batteries connected in parallel and it started a hell of a lot easier, so I'm thinking it's definitely an electical fault of some kind.
Will probably replace the coil, although I'm not relishing the idea of chucking 70 at parts when I'm not 100% sure that's where the problem lies..

If I'm feeling particularly proactive tomorrow I might chuck the old coil back on again, as this seems less knackered judging by the resistance values..

 

I wouldn't recommend a GSF coil if you do replace it. Mine was only a few months old and it's toast.

 

Cheers - tbh I'm a bit of an OEM tart anyway, so will be on the phone to TPS on Monday

The old man is always trying to push all manner of aftermarket sh*te on me; most of the time he gets told where to stick it

 

Cheers John. I've just had another fiddle and the plot appears to be gaining viscousity

I checked the resistances across the coil again (this time after the car had been stood for a good 20hrs, last time it had been started some minutes beforehand). The resistance of both the primary and secondary windings was less than last time (closer to being within spec) so I'm not convinced that this is the problem.

Following yours and Trev's advice, I ran a jumper from the battery to the positive terminal on the coil, and it fired first time. As usual I did p*ss about somewhat and ended up priming the fuel pump several times, so I'll repeat the procedure tomorrow to rule out this occasion as being a fluke.

Based on the above it appears that I have a fault somewhere in the ignition system; it appears that the feed from the switch is direct and doesn't have a relay, so that's one less thing to have gone wrong. I'll check, clean and grease all the electical contacts I can get my hands on (dirty/dry contact somewhere perhaps?), then I suppose the next logical step is to test the resistance across the appropriate terminals on the ign. switch both before and after starting. Not relishing the prospect of replacing the switch if it does turn out to be knackered..

Thanks again for all your help

 

My jetta does exactly the same thing. Before xmas it was started at least once a week, although reluctant it would eventually start. It hadn't been started for a few weeks until tonight and just wouldn't start when turned over. Tried for ages but would not fire. Changed the plugs and fired straight away. Whats going on?

 

if its any crumb of comfort i'm in the same boat as well, but ive been putting up with it for 3 years, the car was my mums before that and she too put up with it since 2000!

my problem is maybe not quite as bad though, it generally fires after 10 seconds or so (just long enough to get amused looks from passers by!) and once or twice a month it starts on the button, but that happening is rare enough to give me a suprised expression for most of the morning

no service items have ever cured it, new fuel pumps when the originals gave up had no effect, coil is 100%, battery and starter are nearly new as these get changed nearly as often as my pants due to this issue being so hard on them, motor and box came out for unrelated reasons a couple of years ago and i secretly hoped their reinstallation would have an affect... no.

in fact the only thing thats not been checked/tested/changed is the accumulator, but ive not pursued this as a knackered acc. would not allow it to occasionally start on the button??

my latest route my brain is slowly trying to work its way down is related to the throttle-closed microswitch on the throttle body. i may be barking up the wrong tree, but sometimes (more often than not) it doesnt close under normal use and needs a flick of the right foot to get it to settle down. im trying to figure out with a process of elimination if the switch being open is causing the failed starts as my current starting technique is to turn the key with my foot off the throttle, if it doesnt fire straight away i then bury the throttle until it fires. if i dont touch the throttle im looking at a flat battery and no start.

ive been doing this every morning for the last 3 years, so for the last few weeks ive been meaning to check the switch position before attempting a start, but the lack of caffeine in my system at that hour means im in remote control so i keep forgetting and doing the above.