Misfire

[nile306gti6]

Hi all, I'm after a bit of advice. My gti6 has developed a misfire and hesitation under load, it only happens once the car has warmed up after being driven 3-4 miles gradually gets worse to the point it wont idle by itself. I've replaced spark plugs, coil packs, cleaned icv valve. Still the same afternoon replacing these. Anyone had something similar before? Also what diagnostic tool is compatible with the 6's, Any ideas ? 
Cheers!

[Ben_w]

Is it using any coolant? Have you done a compression test?

[Mighty306]

Cheap scanners bought off the web won't read these. Lexia3 / PP2000 is the way to go but even then you might not get a code that points to something specific.  (Have had a similar problem n it just said fuel trim was out, which can be caused by a lot of stuff). Where in S Wales are you?

Vehicle is in open loop when cold so small air intake leak would get ignored until warmed up a bit. Could poss be lambda too. That's where I'd start. Emissions check at garage would help rule those out.

Beyond that a poor signal from other sensors (e.g. coolant temp, MAP, air intake temp) could cause poor running / misfire. Reference voltage to sensor as well as sensor itself need to be investigated. Have you got a multimeter?

This a a very useful site with a page specific to misfires.  Ignore the bit about misfire codes ...that's for later OBDII vehicles. https://www.aa1car.com/library/misfire.htm

[nile306gti6]

Is it using any coolant? Have you done a compression test?

No it's not using any coolant, I don't think this is down to compression tbh. Think I'm going to replace sensors next. If it had low compression in one of the cylinders wouldn't it be misfiring the whole time rather than after getting up to temp?
Cheers

---

Cheap scanners bought off the web won't read these. Lexia3 / PP2000 is the way to go but even then you might not get a code that points to something specific.  (Have had a similar problem n it just said fuel trim was out, which can be caused by a lot of stuff). Where in S Wales are you?

Vehicle is in open loop when cold so small air intake leak would get ignored until warmed up a bit. Could poss be lambda too. That's where I'd start. Emissions check at garage would help rule those out.

Beyond that a poor signal from other sensors (e.g. coolant temp, MAP, air intake temp) could cause poor running / misfire. Reference voltage to sensor as well as sensor itself need to be investigated. Have you got a multimeter?

This a a very useful site with a page specific to misfires.  Ignore the bit about misfire codes ...that's for later OBDII vehicles. https://www.aa1car.com/library/misfire.htm

Hi mate, I've seen some of them on eBay, reviews are very mixed. I'm from Carmarthenshire, just down from Swansea. You? Nope I don't have one. Need to pick one up, I have coolant temp, map and air intake sensor s on order.
Cheers

[Mighty306]

Ah, you're not that near me then (Bristol Way). Not much point in offering for you to pop over to plug in to PP2000. Am pretty sure there will be someone closer with it.

I had a similar problem a few years ago n like you went down the route of replacing all the critical sensors in the hope of solving the problem. It's a fairly hit n miss strategy n potentially expensive too. You could replace them all n find you still have the issue. Like I did. That's why I'd approach it differently now, particularly as using cheap replacements can make things worse.  I used an unbranded MAP sensor & it ran like a dog. Now use Bosch if poss, or Intermotor or Cambierre likely to be OK too. 

Many of the sensors can be tested to a certain extent with a multimeter n checking they receive the correct reference voltage is important. The 306gti6 site has a guide. http://www.306gti6.com/forum/showthread.php?id=80340.

Btw, my misfire was, in part at least, due to a poorly fitted cam belt which had altered the valve timing slightly. I haven't mentioned it before, but the EVAP system is also a potential source of issues. Paying a good garage (with a reputation for quickly diagnosing issues) could save you money in the end.