Help-Intermittant Missing Problem

[VR6_Pete 0]

Last year I was driving down a lane on a wet day and was forced to drive through a pothole filled with water causing lots of water to be splashed up through the n/s/f wheel arch. Car immediately started running rough and not on all cylinders... stopped at side of road, switched off and popped bonnet to see what had happened. engine bay was soaked, even the sound deadening on the underside of the bonnet was dripping! Anyway - started her up again and she ran fine, and did ever since...

 

until... last weekend. The same thing happened but at first start-up after car had been sitting (in the rain) for two days. Despite several attempts at switching off and restarting the problem did not go away. It would switch between running smoothly and cutting to not all 6 cylinders. From my previous experience I hoped that after a few minutes of running the engine bay temperatures would sort out any moisture that had got into the electrics. Exactly this happened but it took ~10 mins to clear. The engine would run rougher when you tried to accelerate, but would run fine if you kept the revs steady. I believe this is a tell-tell trait of an electrical problem?

 

Since last weekend, the problem has reoccured intermittantly, just occasionally missing a beat, so something is still not quite right. The car's just had its 100k service and had the plugs changed.

 

Has anyone else experienced such symptoms? Are there any tests I can do other than replacing the HT leads / Coil pack??

 

Cheers,

 

Pete.

 

p.s - sorry about the lengthy description this has turned into!

[ardandy 0]

From the thread title it sounds like you've got a intermittant missing problem?

[selbekk 0]

sounds like you got some water in through your air filter, or whatever. where is it placed? or do you have the original box?

[lukeage 0]

Thew not an easy one - i would just start checking all of your contacts are clean and not erroded MAF connector, HT Leads etc etc.

 

Also get a VAG-COM on it - that could save you a lot of time.

 

I am far from an expert and i am sure someone will come along who could help better, or tell you i am talking bull.

[Walesy 0]

I'm not an expert either but it sounds like a leads gone to me?

[lukeage 0]

I'm not an expert either but it sounds like a leads gone to me?

 

Yep - suprising the amount of cr6p can get down the plug wells.

[Roger Blassberg 0]

This is uncannily similar to what has been happening to mine.

 

First off, are you absolutely confident that the new plugs are of the correct specification? NGK BKR5EKUP, about £3.60 each from http://www.sparkplugs.com

Secondly, are you sure that the mechanic didn't damage the HT leads by just tugging them off when doing the service? They should be taken off with a proper tool.

 

I strongly suggest that you look at the HT leads; with the engine idling, spray a mist of water onto the coil pack ends of the leads (in the dark is better); look and listen for leaking sparks when you sharply rev the engine. A weak insulator cap will spark and crackle as the revs increase. There may also be a general deterioration and leakage of spark anywhere along their lengths. So, then change the offending lead(s) as necessary.

 

BE CAREFUL WITH LIVE HT LEADS. YOU WON'T FORGET THE SHOCK OF 40kV FOR AS LONG AS YOU LIVE, WHICH MAY NOT BE AS LONG AS YOU WOULD LIKE. Sorry for shouting, but it's an important point.......... just jumping back and slashing the top of your head on the bonnet catch can be quite enough to ruin your whole day.

 

If you still have a problem look very carefully at the coil pack itself for hairline cracks in the moulded plastic and replace as necessary (about £120 if you shop around, and they come up on eBay quite often). It is easy enough to change once the HT lead guides have been taken off. A temporary repair is possible with the likes of Araldite, but you are only putting off the fateful day, (which will, without doubt, be at 3 a.m. on a remote windswept hillside in the pouring rain.)

 

Best wishes

RB

[bcstudent 0]

It does sound like classic coil-pack failure.

[STORM 2 0]

TBH, the only definate conclusion you can make from the information you have supplied is that there is an intermittent electrical problem, probaby a short. As mentioned the best thing to do is to get VAG-COM plugged in before you pay over £100 for a coilpack. There is a reason loads come up on ebay - most have been replaced only to find the coil pack wasn't the problem in the first place!

[double-6s 0]

did you see the old plugs when they came out mate?

sounds like an electrical problem as everyone has said, but who knows.

good luck

[VR6_Pete 0]

Thanks for all the responses guys,

 

Car drove without missing a beat on the way back from work this evening (16 miles), although the ABS warning light stayed on for the whole journey-some thing which also happened for the first time a couple of days ago, but is also intermittant-switched off engine when I got home and restarted and ABS was happy again!

 

I doubt it, but is it possible that the ABS and ignition problem are related? Is the ABS system controlled by the ECU or is it separate?

 

I will have a proper poke around the engine bay at the weekend and check connectors, HT leads etc. But i'm guessing that it is a moisture related problem, as it seems to affect the car only when it is cold+damp in the morning and before it is warmed up. We'll see what happens tomorrow morning after a good run this evening!

 

Roger - I replaced plugs with Bosch FLR8LDCU type-the only type listed in bosch catalogue. I read your thread on your HT leads and I will be checking mine if the problem persists. Although is it more likely to be a connection rather than a dead lead seeing as it's an intermittant problem and seems to be temperature/moisture sensitive?

 

Also, do coil packs usually fail catastrophically or can they fail such that only one or more cylinders is affected?

 

Cheers,

 

Pete.

 

 

p.s - Why is it that cars run fine for ages and then everything goes wrong in a short space of time!? Murphy's Law?

[PBSTORM 0]

I've got the exact same problem with my VR.

 

I've changed changed the plugs the leads and the coilpack. I've also cleaned the ISV and the MAF.

 

It drove fine for a couple of days and then started to misfire intermittently again.

 

I've also noticed a funny smell from the engine bay since the coilpack was changed. Like burning plastic-cant see anything though...

 

Hope you have better luck finding the fault than me!!

[Roger Blassberg 0]

Pete,

 

the ignition system is based on 3 coils with an ht lead connected to either end of each one - both ignition circuits in the pair have to be earthed for either of them to fire.

 

This arrangement means that there is a spark (in fact a number of very closely spaced sparks) not only at the the very end the compression stroke but at some other time in the cycle too corresponding to the optimum timing for the associated cylinder.

 

If you have an earth leak, such as a dodgy lead where the ht can still find its way to earth, then the other one of the pair will still fire. If you completely disconnect one lead, its twin will not fire either.

 

I have heard that coilpacks tend to fail progressively, especially in damp conditions. I can't confirm that from personal experience.

 

Best wishes

 

RB

[Socrates75 0]

I had this problem...

 

I went through a huge puddle, the car went into fail safe.

 

Once dried out, say 10 mins, back to normality.

 

I always steer clear of the deep ones now :afro:

[Socrates75 0]

Must admit I did sh*t it.

 

The last time it ran on 3 Cylinders I'd destroyed my rad :)

 

I assumed I'd soaked something electrical, nothing has happened since.

[VR6_Pete 0]

Thanks 4 replys.

 

Car's been fine since last thursday now - which may be down to the weather OR the problem dissapearing. Time will tell.

 

I had a poke around under the bonnet and checked the HT lead connections etc. but not done anything much further yet. I will do though because something obviously isn't quite how it should be, and like roger said:

 

you are only putting off the fateful day, (which will, without doubt, be at 3 a.m. on a remote windswept hillside in the pouring rain.

 

Cheers,

 

Pete.