My little ZX is starting to be a pain in the arse!

rossnunn · Unread post by **rossnunn** » 05 Jan 2004, 04:22

Alwight? All had a good Xmas?
Ok time to get down and dirty.
My sweet little 1.4 Carb'd ZX is starting to be a right pain in the arse.
When I first bought it all was well (about a yeart ago). But after the blat home down the motorway it started to cough, as you rev it up the rev's dip the rise again. I lived with it until about a month ago when I had a run down south. So I booked it in to the local garage for them to look at. That afternoon I get a call to ask if I could come down. They showed me some VERY black sparkplugs, and said it needed some ajustment and recommended a service at the sametime. OK.
Went to Hastings, came back slight coughing again, back to the garage couldn't find anything. now it has flatspots, the revs dip - it's getting worse!!.
I have new fuel filer's inline and they are clean, there is a good supply of fuel too.
I'm looking at selling the car soon and would like to clear this up beforehand.
Apart from that it goes like a rocket! - I'm sure it's got the legs on my 1.4i I have just bought!!
So can anyone help me shed some light??
Thanks to you all
R

AndersDK · Unread post by **AndersDK** » 05 Jan 2004, 04:44

The sooted sparkplugs indicates the engine gets enough food - but can't digest it properly.
I'd suspect a nasty little problem somewhere in the ignition system. Give the ignition system a thorough overhaul - testing each HT lead with an ohm meter - looking for carbon tracks in dizzy cap etc. etc.

rabenson · Unread post by **rabenson** » 05 Jan 2004, 20:48

try starting the engine up in a dark place with the bonnet up (don't gas yourself though). You can easily see any surface tracking on leads etc.

rossnunn · Unread post by **rossnunn** » 07 Jan 2004, 01:23

ok I'll try some of that at the weekend and let you know the results.
Cheers people.
oh what should the ohm meter reading be for a HT lead??
Thanks again
R

AndersDK · Unread post by **AndersDK** » 07 Jan 2004, 01:50

HT leads these days have build-in resistance to decrease the peak spark current - thereby decreasing radio interference.
Depending on the cable lenghts - expect some 2K - 10K ohm readings.
The point is to test if they are totally disrupted - i.e. have insanely hi resistance.

rossnunn · Unread post by **rossnunn** » 07 Jan 2004, 21:29

cheers
I'll give a go tomorrow - forgot my meter today!! DOH!
R

rossnunn · Unread post by **rossnunn** » 12 Jan 2004, 16:28

right, using a auto-ranging meter this is my results:
Reading the HT leads form RIGHT to LEFT:
2.285 ohms
2.696 ohms
2.846 ohms
04.01 ohms
1.168 ohms < this is the short lead that goes to the coil.
Any thoughts?
Cheers
Ross

arry_b · Unread post by **arry_b** » 12 Jan 2004, 19:26

They look OK to me.
Do the readings change significantly if you bend the leads around while measuring them?

rossnunn · Unread post by **rossnunn** » 13 Jan 2004, 01:39

erm, no I don't think so - didn't really try to be honist. what about the 04.01 one??
Ta
R

AndersDK · Unread post by **AndersDK** » 13 Jan 2004, 02:07

The 4.01 ohms one seems odd to me -
(it's not 4.01 KILO ohms ?)
First off - you can not really do an ohm measurement to more than within 0.5 - 1 ohm accuracy - except in laboratory conditions.
Simply because of varying contact resistance on the probes.
Next off - this cable seems to be a duff "service" replacement at some time - using improper cabletype.
It should not really be bad to the spark energy transferred to the plug - but it's definately a problem in your radio - this cable would enable you - and any other nearby - to "watch" your engine rev's through any shortwave receiving.
My real concern is that this cable may cause arcing from it's surface - because of it's lack of damping - thereby giving you the odd missings on your engine.
Shop around to find a supplier which stocks single HT cables in a range of lenghts - ready prepared with contacts fitted.
MUST be silicone cable - with the odd carbon/fiber center lead - best you can get.
Cable colour is indifferent.
Then simply remove & clean the original caps from the old cable - for re-use on the new cable.
Other cable values looks fine to me - if you DO in fact mean K (kilo) ohms to these ?

rossnunn · Unread post by **rossnunn** » 13 Jan 2004, 02:42

Ok thanks,
I've been thinking about this, if it was a spark issue, wouldn't a timing gun show this up??
Thanks
R

AndersDK · Unread post by **AndersDK** » 13 Jan 2004, 03:47

To some extent - yes.
It depends on where the spark goes really.
If the spark is igniting as it should on the plug - ok
If the spark is cable (or cap) arcing near the plug - after the timing gun insertion point - then it does not really tell you anything - but the engine does [;)]
If the spark is constantly arcing in the dizzy cap - or is not produced at all - then the timing gun does not indicate - but the engine does [:D]
Intermittent sparking can be seen with the timing gun - as it won't indicate coinciding with the engine misfiring.
No matter the exact problem - be sure to positively trace the symptom as either of 2 :
1) ignition problem
2) fuel problem
If you don't do that - you end up replacing random parts in panic - to no help.
By the laws of Murphy - you would only solve the problem by replacing the last possible part - the car [:D]

rossnunn · Unread post by **rossnunn** » 14 Jan 2004, 21:13

ok I'm about to give it a go, i'll let you know the results.....
Cheers
R

rossnunn · Unread post by **rossnunn** » 14 Jan 2004, 21:50

right just checked it with a timing gun, and it all seems 'normal' on tickover and up the rev range. Its quite difficalt to make it do it this way because the engine isn't under load.

AndersDK · Unread post by **AndersDK** » 14 Jan 2004, 23:30

Yeah - well.
Seems your car don't wants to part you - trying to punish you for that [:)]
I have to admit that such problems may take for ever to trace down - especially as the problem is not possible to clearly provoke at no-load condition.
There is only one way to trace down such problems :
- excluding known good working parts/elements from your symptom tracing.
This means a systematic look after on all bits involved with ignition & fuel feed.
The point is to be systematic [}:)] - above all [8)]
If you keep up to be systematic - it won't even be that time consuming - as you then KNOWS that previous tasks performed ok - no reason to go back.
examples :
- there is no point in tracing & suspecting the carb - if the problem is water in fuel tank - or dirt clogged vent hose to the fuel tank.
- there is no point in suspecting the ignition coil or module or plugs or cables - if the problem is moisture in the dizzy cap.
What I'm trying to say is - that we do not yet have a sure pointer to your problem.