VR6 Missfiring problem (stuttering)

[ip 0]

Hi All,

Real tale of woe here. Bought a VR6 back in Jan/Feb. Ran okay initially but, after first long drive in Feb, started to judder/missfire if pulling a heavy load at low revs (full car in second gear for example). Only happens from 900rpm up to 1500rpm, after that smooth as you like.

Now, back in March I set about replacing the following:

Plugs

Coil (recon unit)

MAF

Temp sense/sender

Thermostat

All to no avail. Then, thanks to some great advice from a forum I tried replacing the HT leads and all was good. No judders, fuel economy improved, the works.

So, imagine my despair this morning when after the same long drive (300 miles) as last time, the problem has returned!!!! Pulling away from a roundabout in second and the car suddenly starts missing terribly.

Not sure what has happened. Now I've had it a while I am happy that, most of the time, it runs really well for a VR6 with 100k on the clock. I get 28mpg round town and 35mpg on the motorway. Plugs are a nice biscuity colour so mixture must be about right and it uses no oil or water at all (oil stays very clean too). So overall, the engine seems sweet.

So, what else could this be? Anyone has any thoughts it would be great to hear from you.

Cheers,

[slim5878 1]

coil pack!!!!!

[ip 0]

As mentioned in the original post, I fitted a new (alright, reconditioned) coil pack 2 months back. I did this before changing the HT leads and it made no difference. As I say, last time this happened, it was the leads that fixed it.

The replacement coilpack is clean as a whistle with no cracks etc. However, it is probably worth putting the original pack back on and seeing what happens. I'll try to find time this week.

My gut feeling is that I am not looking at a coil issue though since it was a dry day and only started to happen after 5 hours of driving (engine bay would be warm and dry as toast by then). So, any other thoughts?

Meanwhile, you'll find me stuttering around thwe streets of Edinburgh in my not so smooth VR6.

[matty.vrt 120]

make shure all your leads are on properley.also if there are any connections on your maf wires make shure they are good and there no leaks inbetween the maf and engine.

[ip 0]

Hi Matty, good tips. The air inlet system seems nice and airtight up stream of the MAF though so I think all is well there. I'll double check the MAF wiring but it was fine two months back when I swapped out the MAF (no sign of any wear and tear on wiring or connectors).

Given the simplest explantation is usually best, I reckon you could be on to something with the HT lead connection theory. If they were not pushed on correctly, they would work fine initially until arcing caused a resistive connection to form. I gave them all a quick check last night (none appeared loose) but I'll give them a more thoruough exam to be sure.

Either way, until I get the plugs out for a quick exam I won't really know what is happening. Seriously, these cars a nightmare.

[ip 0]

I've also heard that cam sensor issue can cause these problems to occur. Anyone have any experience of this? How much will the G40 sensor set me back?

[matty.vrt 120]

think if it was g40 it wouldnt run good at all never mind 300 miles ano there a bit of a nitmare like ive almost replaced every sonsor on mine.

[matty.vrt 120]

(sensor*) hehe

[ip 0]

Yeah, it seems unlikey that the G40 sensor would only affect a specific rev range. Also, I wouldn't expect to see 35mpg if the timing was far out.

Since it was HT leads last time it points to HT leads this time. I'll check I installed them right. I'll also see if I can borrow my mates spare set (his VR6 is more problematic than mine) and see what they do.

[craggsy 91]

Have you ran vagcom on it to check all the sensors out

[ip 0]

The last time this happened I ran vag-com and found no errors at all.

In fairness though, I have not rescanned since the problem started again yesterday (got home late, too tired and pissed off to bother after a 6 hour drive). So you are quite right, the answer might be logged waiting for me in the ecu. It's the first thing I'll try when a get a free ten mins (hopefully tonight).

I guess I am sceptical though since it didn't help last time this problem occured.

Thanks for the comment.

[manzi 0]

you put the leads in yourself?

i had a rough running problem with mine not so long ago, plenty of money spent on replacement parts but in the end, the garage i took mine to hadn't put the leads in properly. don't think they had the tool to do it. it was proper cowboy'd.

runs smooth now!

[ip 0]

I did put the leads on myself and would like to think I was smarter than that, but we all have off days.

I'll pop all the leads off and on (with tool) and see if I messed it up the first time.

Cheers.

[manzi 0]

would like to think I was smarter than that

just to make sure, i never said anythin like that, thought i'd give it a mention since i replaced the throttlebody before lookin at leads. :S

[ip 0]

Classic. Well, if it turns out that it IS my throttle body then I'll know who might have a spare for sale.

[VR6BOY 2]

The throttle body has to be adapted with VAGCOM each and every time they are disconnected or the battery dies

[ip 0]

Got some time to play tonight. Found the following:

1. Vagcom, all good, no fault codes

2. Throttle angle. Nice and smooth across whole range

3. Plugs, all clean. No sign of rich or lean running

4. HT leads all correctly fitted

So, basically found nothing. All is well, so why's it missing/hesitatiing under load?

Does anyone have typical adaptation values logged for their engine? I'd be interested to compare in case that throws something up.

I had 1.178 for idle, 0.897 for partial thrttle and 0.9 for full throttle. All within spec according to vagcom.

Anyone have any other thoughts?

Cheers,

ip

[ip 0]

Has anyone ever tried testing coils as per the instructions from the Bentley manual?

http://forums.vwvortex.com/zerothread?id=793322

Obviously most of the instructions relate to testing the signal from the ECU but the last two indicate expected impedances from the coil pack. If anyone has a known duff coil it might be interesting to measure as described and post the results.

Cheers,

ip

[Charged VR 0]

Had a Hessitation on my friends VR that got worse when hot, Took me ages to find it, But ended up being the wrong plugs were supplied by G/S/F, Bought genuine ones and no problem since. Also is the little vacumn hose from the inlet manifold to the fuel pressure reglator intact?

[ip 0]

Thanks for the tips but the plugs are the recommended NKG platinum ones and the vacuum hose you mention is tidy. Are there any other hoses I should be having a look at?

[juliet 0]

I know this might seem a litle daft but mine regularly does this. Its fine for a month or two then it starts spluttering at low revs but dissapears above 3 to 4 thousand. I simple disconect the batery for two mins and reconect and go out for a drive this always cures mine, worth a try.

[vr6newcomer 1]

interesting this, mine has been doing exactly the same thing over the las few weeks, going to change spark plugs and leads this week, ill update you then.

[ip 0]

Hi Homer, it might sound daft but you are dead right. An ECU reset might be all it needs. If the adaptation values drift for some reason then it might cause something like this to occur. I'll give it a shot when I get a chance to play. Thanks for the tip.

ip

[ip 0]

Hi vr6newcomer. I'm prepared to bet that you'll just need new plugs and leads. From what I can see on most forums, this clears up 90% of misfire issues. Please do let me know what you find though.

Cheers,

ip

[vr6newcomer 1]

will do matey, my only real concern is that if a plug & lead change cures the problem again, this will be the 3rd new set of leads on the engine since my rebuild about 18 months ago, so if this next set also goes in about 6 months, i guess it must be a fault with my coilpack which i bought from an engineering company in essex, but ill get back to you as soon as ive got the new leads and plugs in.