No spark, won't start ! (1.9 GTI)

[mmatthej1 1]

About a month ago, took car for MoT, started fine - the tester then left engine running for a longish time, to test exhaust gases, put it up on ramps and we saw a squirt of water, presumably from header tank overflow. Fan had kicked in OK, so I saw this as no major issue, just same as sitting in traffic. Anyway, the car wouldn't then re-start.

 

Being at friendly garage, I asked them to sort this for me and they diagnosed 'intermittent spark' and fitted a new coilpack - car then started & ran just fine. However, a few days later, it just turned over and wouldn't fire up. I whipped a plug out and rested it on rocker cover - when I turned the key, I saw a spark as soon as reached the position prior to starting position, which seemed a bit odd - I then saw no spark, as I turned the engine over.

 

My suspicions pointed me to the ignition amplifier but - rather than diagnose myself - I called in RAC, who reached same conclusion, without my prompting..

 

I bought a replacementb ign. amp., fitted it but unfortunately still no spark. (The 'old' ign. amp. was after-market, with BLUE top, whereas 'new' one is also after-market with BLACK top, btw)

 

I've checked any wiring connections that I can see in engine bay & under dash, removed/refitted various relays 'just-in-case' of tired connections, tried a different H/T lead from distributor to coilpack, checked rotor arm.

 

So... my plea is for any further suggestions, please!

[DamirGTI 323]

Is it Jetronic ? or Motronic ?

 

If Jetronic , and if the new coil and module didn't fix it , likely it'll be bad dizzy signal cable . It goes from the dizzy pick up coil to the ignition module and it's the first main signal source of the engine initial motion/rotation for the ignition module and tachymetric relay while cranking the engine via starter - very important piece of cable ! essential needs to be in good condition .

 

There's 3 wires in it , pick up coil + and - , and third wire is just a shielding .

Often the pick up coil signal wires break (partially or completely) , due to age/wear and tear , and also cause they're pretty thin gauge wires ...

 

Check that cable , for the test remove it and connect the dizzy pick up coil with the module connector with two wires just the + and - signal , shielding is not really needed .

You'll need 2x 2.8mm female and 2x 2.8mm male spade connectors and obviously two wires of any kind you have laying around .. connect and try to start it up , see what happens .

 

Should fire right away if it was the bad cable .. from the stuff you've already tried without success , most likely it'll be that signal cable .

 

D

 

 

Edited July 14, 2022 by DamirGTI

[mmatthej1 1]

Thank you -I don't know if Jetronic or Motronic - how can I tell the difference, plse?

 

I think I know the cable you refer to - it used to have a connector block, just behind engine but we had endless trouble with it and replaced the joint with fixed, soldered jointing. I have an auto electrician coming round, probs next week, so will point him at this are, first of all.

 

Can replacement cabling be sourced these days or might my leccie have to make up a new set?

 

 

[SRDT 146]

On the Motronic engine you will have a simple distributor with no signal wires sticking out, also the AFM are not the same.

Slanted top for the Jetronic:

Flat top for the Motronic:

[mmatthej1 1]

Thanks - will check this out, be good to know which type I have! (pretty sure that it's Jetronic)

 

[DamirGTI 323]

Can take a look on the ECU casing too ...

 

If it's Motronic it'll have "Motronic" embossed onto the ECU alu. top casing , if Jetronc it'll be black label/sticker . 

 

New signal cables are me thinks non available .. but it's really easy to make one out of old knock sensor or CAS sensor , cut just the sensing element leaving the cable and 3pin plug on the end .

 

D

Edited July 15, 2022 by DamirGTI

[Anthony 1,000]

Assuming that it's Jetronic, before condemning the signal cable mentioned above, it's worth checking / cleaning / WD40'ing the pins inside the yellow 3-pin plug on the end of it - they can be notoriously flaky if it's corroded or damp as it's such a low-voltage signal, and if water got in there when the header tank overflowed that could certainly cause the sort of intermittent behaviour you're seeing.  Usually just popping the two connectors apart, a squirt of WD40 and inserting/removing the plug a few times tends to resolve it unless it's notably corroded.

[mmatthej1 1]

At long last, my auto electrician has found the fault - a break in one of the 'pigtail' wires coming out of the distributor - it LOOKED OK , could be pulled as a quick test of connection but continuity test showed it up !

So thanks for all ideas & help, this was a weird problem, now - thankfully - resolved!

 

[Anthony 1,000]

That'll be the signal cable mentioned above - normally they break on the outside which in turn breaks the inners too due to the increased strain, but it's not unheard of for them to break internally and look OK externally, just a bit odd that it occurred at the same time as the expansion tank overflows.  Glad that you've found the fault and it's now resolved.

 

What I tend to do is to clip or cable tie that signal cable to something - dizzy vacuum advance capsule, coolant hose or whatever - to stop it moving around excessively and causing it to suffer fatigue failure from the excessive flexing.

[mmatthej1 1]

Actually, the history to this is that we endured a lengthy period of problems with the pigtail connector blocks frequently failing in their contacts, so just learned to reach round and 'waggle the wires' to make it work again - no way to run a railroad really so, in the end, my auto electricial recommended just cutting out the blocks and making soldered connections, shrink sleeved etc - this actually worked fine & resolved the 'waggle-need' problem for a long time but - now - his tracing efforts found that connection in one (red) wire, whilst appearing solid, had somehow failed.

 

He will now come back and remake the join and, to your point, will also secure the cables to minimise movement.

 

There's always 'something' going on with old cars, eh!?!