Help Needed With Very Random Non Starting Issue

[Weser 30]

So I thought I had solved this issue but after going to my car this morning it wont start again. Its a standard 1.9 8v gti 92.

 

I have had the problem a few months now. Basically the car will be absolutely fine for a couple of weeks starting straight away and running lovely. Then out of the blue it just wont start. Turns over fine but wont fire and start. If I leave it a few hours or go to it the next day it usually starts fine and again wont give any trouble what so ever for a while.

 

When it doesn't start there is no spark. I have tried an ignition amp, coil, dizzy, cap and rota arm. The problem seems to still be there. I thought I had solved it with a replacement dizzy - mine turned out to have oil in it and the car had been fine for the last 3 weeks but this morning it wont start again.

 

I haven't tried leads and plugs because I am convinced they are fine because it runs perfectly when its running.

 

I reckon I must have a wiring problem some where, dodgy connection, corrosion or broken wire. However I am seeking input from the forum for what else to consider and test. Could a taccy relay cause my problem, I did put a know working second hand one on not long ago.

 

As you can image its starting to bug a bit and would like to fix it so I know I can rely on it a bit. Thanks

[Tom Fenton 1,526]

If the tachymetric relay is intermittently not working then absolutely it could cause this problem. When it does the non-start then check to see if the fuel pump has power when cranking and you'll know.

[Weser 30]

Thanks for the reply Tom. Sorry should of said. The fuel pump primes fine but I haven't tested power when cranking. However thinking about it I may have just answered my own question as I ran the pump constantly, so effectively bypassing the tachymetric relay and it didn't start so I suppose that rules it out, unless it does control something on the ignition side? but I don't think it does, maybe wrong.

[Tom Fenton 1,526]

The tach relay also powers the ECU and ignition, so if its not working then even if you frigg the fuel pump, the engine still won't run.

[Weser 30]

Great cheers for confirming that. I will have to get hold of one and put it on and see if that sorts things out. If I want to test to see if powers at the ecu and ignition would I do what you suggested earlier and see if the pump has power when cranking? I presume its all in the Haynes somewhere so should beable to work out what pin on the ecu I should be expecting power on.

[Anthony 1,000]

Ignition isn't powered by the tachymetric relay on Jetronic Tom - it's only the fuelling side of things (fuel pump and injectors) that are.

 

Ignition feed comes straight from the brown plugs as wire #2 (thick red). Easy enough to check for 12v at the coil when it won't start to rule that out anyway.

 

Have you tried another signal cable from the dizzy? I used to have an intermittent non-start issue some years back and it was down to this, in particular a poor connection at the 3 pin plug where it meets the loom where I presume it suffered enough volt drop that under cranking there wasn't sufficient signal strength to trigger the ignition amp as like yours, once it did start it ran perfectly.

[Tom Fenton 1,526]

My mistake apologies.

[Weser 30]

Thanks for all the replies.

 

Sweet I will check there is power at the coil on the 12V when it wont start again - hopefully tonight. If there isn't what does this point towards?

 

As for the signal cable on the dizzy. I replaced the dizzy for the one I bought from yourself Anthony but can remember if yours came with a signal cable or not. If it did I would of left it on there. If not would of used the one that was on mine. Will have a look at the dizzy I took off and see if I can work it out. However there is no reason that I could have a problem with the 3 pin connector plug on the loom though instead of the one on the signal cable side. Might be worth a little look at.

[hoodygoodwood 70 3 Cars]

Another vote for the lead coming out of the dizzy , when it happened to my 1.6 GTI about 20 years ago you could still get them new .If you get a friend to turn over the engine and you wobble the wire about a bit it might fire up .The outer insulation often fatigues and cracks close to the dizzy connection .

[welshpug 1,627]

Could also be the ignition barrel or wiring if the switched live is problematic, so there's a few things to check but as with many issues until it does it its hard to say specifically what it would be.

[Weser 30]

Hit the nail on the head there Mei! So hard to check everything as it hardly ever stops starting when I have time to go over things. Then when I Have got time its working again! Ok so I guessing the switched live you are talking about is the 12V (red wire) feed to the coil? Will go over a few things when I can and report back.

 

Where does the 3 pin plug signal cable from the dizzy wire to so I can bleep it out with a multimeter, is it the ignition amp. Will have to get the Haynes out later I reckon.

[205gtiloz 1]

Hit the nail on the head there Mei! So hard to check everything as it hardly ever stops starting when I have time to go over things. Then when I Have got time its working again! Ok so I guessing the switched live you are talking about is the 12V (red wire) feed to the coil? Will go over a few things when I can and report back.

 

Where does the 3 pin plug signal cable from the dizzy wire to so I can bleep it out with a multimeter, is it the ignition amp. Will have to get the Haynes out later I reckon.

Hi there couple thing I would check are ignition barrel and old imobalisers not always removed compleatly and still cause problems also the blue ecu temp switch check the wires on the plug

[Weser 30]

There is no immobilisers on the car I know that for sure as I removed all the ones that were there. Bloody shoddy alarm installs are a nightmare. Also checked the coolant temperature sensor connector - had problems with a bad connection there before. When it first started to happen I thought it was a dodgy connection there but I am pretty sure its ok.

 

I will make sure the ignition barrel is working well thanks.

[jackherer 543]

You can rule out the ignition barrel and any immobilisers etc by temporarily hotwiring the coil positive. My money is on the dizzy signal cable as said above though. The ECU temp sensor wont cause lack of spark.

[Weser 30]

Just an update there is power at the coil and we have ruled out the ignition barrel. Thanks for all the help guys I am thinking the same sounds like something to do with the dizzy signal. Now I don't think it's the signal cable on the dizzy itself unless I am very unlucky to get two bad cables as I have replaced one already. I think it's in the loom.

 

Could someone that knows about the engine loom be kind enough to tell me where the 3 wires on the dizzy signal cable go. Do all of them go to the ignition amp?

 

On another note and just to rule it out it can't be a problem with the dreaded brown plugs can it?

 

Thanks

[welshpug 1,627]

they go to the ignition amp, pull the boot back on both the three pin plug and the 7 pin on the amp and make sure the terminals are all secure, DCC had a 1.6 a few years back he spent weeks trying to figure why it wouldn't run, till I pulled the plug to buzz through the connections and noticed all three terminals weren't anywhere near touching its corresponding male plug and its terminals

 

unlikely to be any of the brown plugs IF you have confirmed a good 12v switched live, the one in the engine bay will only have auxillary stuff.

Edited June 23, 2014 by welshpug

[Anthony 1,000]

Are you sure that there was a signal cable fitted on the dizzy I sent? It was a few weeks back so I can't be sure either way but I didn't think that there was one on it, which would suggest that you're still using your old (and possibly faulty) one.

 

(easy way is to see if there's one still attached to the old dizzy I spose!)

[mrfirepro 127 1 Cars]

Andy,

 

I have a spare dizzy lead here if you want to try it on for a while, I work in Witham so you can pick it up from me if you want to try it, or I could post it to you.

[Weser 30]

Sorry guys was at wimbledon yesterday so a little busy. Its a hard life drinking pimms and eating strawberries

 

Anyway back on topic. Anthony your right I looked at the removed dizzy and it didn't have a signal cable on so I must have used my old one. I reckon this is the first port of call. However I have a bit of time tomorrow and Friday night and at the weekend so will bleep through some wires to make sure.

 

Paul thats a very generous offer - I might take you up on it. However I would like to buy one as I reckon this could be the cause of my issues so would need one anyway. However I really appreciate the offer. P.S very impressive resto!

[mrfirepro 127 1 Cars]

No problem,

 

I'd let you have mine, but want to keep it as a spare as I have heard they are scarce and do break.

 

I wouldn't need it back quickly was just thinking that it would prove the point before you fork out for one...

[Weser 30]

Like I say I really appreciate the offer - I understand that you would want to keep it. I will be on the look out for a spare too now!

 

The thing is I don't know how long I would have to test it for - last time it was nearly a month before it gave trouble again... If I have no luck in getting one in the next week or so I will 100% be in contact.

[farmer 327 1 Cars]

I have new ones coming to the UK shortly.

 

Part number on those are 5911 34.

 

Same one/type as Paul was offering.

Edited June 25, 2014 by farmer

[Weser 30]

Only just seen this, I have one on its way so hopefully it will sort my problem.

[Weser 30]

So just to update this. Changed the Dizzy signal wire 3 weeks ago and haven't had a problem yet. Hopefully it was the issue. I think the car seems to be starting quicker as well, but that could be my imagination. Cheers for the help guys.