V6 Misfire Nighmare

[Guest danny.s]

That looks identical to a clip from a photo frame that has a sheet of glass and a backing sheet, but no frame around the edge.

 

 

:blink: How stupid do i feel !!

Anyway I have removed the coil pack, there doesn't appear to be any obvious sign of damage. I am trying to source a replacement to try out ,,fingers crossed.

[Sharanfx]

Engine Speed sensor is also a common failure on the VR6. It does sometimes starts as a misfire and eventually gives up the ghost.

 

Basically the ECU wont know that the engine is turning, hence does not fire the coilpack.

[Guest VR6!]

Engine Speed sensor is also a common failure on the VR6. It does sometimes starts as a misfire and eventually gives up the ghost.

 

Basically the ECU wont know that the engine is turning, hence does not fire the coil pack.

 

You really need to get the codes read! IIRC a crank sensor/engine speed sensor isn't a cheap part! but then if the engine isn't running the crank sensor will show up as faulty! DOH ;)

and then there is always the cam sensor? a cheaper part that sometimes causes rough running/misfires and is a cleanable part! the sensor can get gummed up over time and cant get a true reading hence the misfire!

[Guest danny.s]

Right lets have a recap:

Initial problem was a misfire and loss of power :D

Leads replaced

plugs replaced

misfire still present ! car then ceases to start, it turns over but wont fire up :wacko:

Coil pack replaced

still wont start :D

Would a mobile electrician be a good idea at this point, or are there more checks i can do myself. The ECU has been mentioned can anyone give me any idea of its location ? pictures would be good.

Thanks

[Guest danny.s]

I have just spoken to an electrician who said it sounds like the crank sensor !!

Does anyone know where i can get a downloadable Haynes type manual

[dipsomaniac]

have you got a good spark (will it jump 2 inches) at the plugs? If you have it must be fuel related. if not, as you have replaced the plugs, leads and coilpack it must be a sensor or relay. you need the fault codes read.

 

haynes will probably not help if you have the v6 you need the manual from bentley publishing if you want to sort it yourself.

 

i still mantain that the cheapest option now is to get a good mobile auto electrian to spend an hour of there time sorting the problem -

[Guest danny.s]

have you got a good spark (will it jump 2 inches) at the plugs? If you have it must be fuel related. if not, as you have replaced the plugs, leads and coilpack it must be a sensor or relay. you need the fault codes read.

 

haynes will probably not help if you have the v6 you need the manual from bentley publishing if you want to sort it yourself.

 

i still mantain that the cheapest option now is to get a good mobile auto electrian to spend an hour of there time sorting the problem -

[dipsomaniac]

1. remove one of the spark plug leads at the plug end - the most accessable one if you don't have the correct tool is the front L/h
   
2. remove spark plug (or use a spare one) and insert into plug lead cap
   
3. hold the lead with a suitable pair of insulated pliers so that the end of the spark plug is approx 2 inches from a metal part of car
   
4. ask someone to turn over engine
   
5. look for a healthly blue spark jumping from the plug to metal part
   

[Guest danny.s]

Thanks Dipso,

I have still yet to check for a spark but am planning to have a look this weekend. I would love to get an auto sparky in but unfortunately I have run out of money so have resorted to the DIY approach. My next check if a spark isn

[Guest danny.s]

Hi all,

Well the saga continues !!

I have finally checked and can confirm there is a spark, so as previously sugested the problem may be fuel related. would a failing pump or blockage explain the misfire problems ??

[dipsomaniac]

you really do need to read any logged fault codes. where do you live? someone on here with Vag-com maybe able to help.

[Guest danny.s]

Strong smell of fuel ,, I have removed a plug and there seems to be alot of fuel on the tip is the engine flooded ?? That kind of rules out the pump or a blockage theory anyway.

[sepulchrave]

...Sounds like the plug you just pulled is misfiring if it's that wet!

 

I simply cannot think of any mechanism which could cause such significant overfuelling without the ECU being aware of it and going to failsafe mapping.

 

The only unmonitored system is on the HT side, everything else is under ECU control. Are you absolutely certain that ALL your HT leads and Spark plugs are 100% good. I say this because a mate of mine had an Astra which came back from service with a misfire, this turned out to be one of the brand new spark plugs which had a cracked insulator below the electrode!

[Guest danny.s]

you really do need to read any logged fault codes. where do you live? someone on here with Vag-com maybe able to help.

 

 

I'm in gosport so if there is anyone in the portsmouth,fareham,southampton area with vag-com who would be willing to have a look, let me know i would be forever greatful. i'm at the stage were i would drive the bloody thing off a cliff if i could get it started. :blink:

 

...Sounds like the plug you just pulled is misfiring if it's that wet!

 

I simply cannot think of any mechanism which could cause such significant overfuelling without the ECU being aware of it and going to failsafe mapping.

 

The only unmonitored system is on the HT side, everything else is under ECU control. Are you absolutely certain that ALL your HT leads and Spark plugs are 100% good. I say this because a mate of mine had an Astra which came back from service with a misfire, this turned out to be one of the brand new spark plugs which had a cracked insulator below the electrode!

 

The misfire did start a few days after a sevice and i'm not 100% certain the plugs have been checked its had so much done to it from various garages i've kind of lost track. I was kind of hoping the non starting problem was due to the failing of the part that was causing the misfire in the first place. I'm so close to throwing in the towel !!

Could the engine temp sensor have anything to do with the overfuelling ?

[MrT]

I assume that you checked there is a large spark on every lead, not just one of them? The lead with the petroled plug sounds like the one that seriously needs checking. You really need to check this lead and also make sure that if it does produce a large spark to earth that there is no damage on the cable where it normally lies. You also need to check this spark plug, whilst a spark may jump from the body of the plug to to earth, can you see the spark coming from the electrode as well, it may jump from the centre electrode to earth or you may just see the spark jumping from the plug body to earth. The plug itself may have a centre electrode to earth path that means it is not sparking where it is meant to.

 

This really does sound like an HT problem.

[Guest danny.s]

I assume that you checked there is a large spark on every lead, not just one of them? The lead with the petroled plug sounds like the one that seriously needs checking. You really need to check this lead and also make sure that if it does produce a large spark to earth that there is no damage on the cable where it normally lies. You also need to check this spark plug, whilst a spark may jump from the body of the plug to to earth, can you see the spark coming from the electrode as well, it may jump from the centre electrode to earth or you may just see the spark jumping from the plug body to earth. The plug itself may have a centre electrode to earth path that means it is not sparking where it is meant to.

 

This really does sound like an HT problem.

 

Only one lead was checked, the easiest one to get to as I don

[MrT]

All you have checked with one lead is that the lead you disconnected works and that part of the coil pack is producing a spark. It does not prove the other 5 leads and other parts of the coil pack are working. You need to check these.

 

If you removed a lead from a cylinder I would expect that plug to get covered in fuel. By removing the lead from a plug then running the engine you would be pumping fuel and air into that cylinder and as there was no spark to ignite it, the fuel would be deposited in the cylinder and the plug. Some fuel/air would also be pumped into the exhaust where it could ignite.

 

Petrol turns to vapour, very quickly in a warm engine, so I would not worry about that.

 

If you had lost one or more cylinders due to an HT problem you car would get very thirsty as it uses 6 units of fuel for every two revs but only outputs one power stroke for each remaining working cylinder for every two revs. So if you lose one cylinder, your consumption will be approximately 120% of normal and for two cylinders 150%.

 

I would still suspect an HT problem on your car.

[dipsomaniac]

you say that you have replaced ht leads, plugs and coilpack. are you sure that all of the leads are connected correctly? is the wiring harness to the coilpack ok?

[seatkid]

You've got fuel in the cylinder, so I reckon the problem is ignition (as in 90% of petrol no-start cases)

 

Did you get a brand new coil pak?

 

Were the new leads an OEM brand e.g. Beru or Bosch?

 

What is the make/model of the new plugs? (i.e. are they the correct heat range)

 

I had exactly same symptoms with my Golf - in the end down to faulty lead(s) (insulation breakdown) . Don't be fooled a weak (white) spark. You need a big fat blue spark willing to jump 3 - 4 inches.

 

Once you flood a petrol engine you have to either

 

Wait a loooong time. (minimum half hour, maybe hour)

 

or Take out the plugs and turn it over and refit.

 

or Try a tow start.

 

Having flooded the engine, once its started don't run it aggresively, just let it idle lightly, as the CAT may be saturated. If the CAT starts to get stinking hot or you smell bad things from the exhaust, switch off immediately and leave it an hour for the CAT to evaporate the petrol and cool down.

[dipsomaniac]

the engine will run on 3 cylinders and in the old days would start if you had a spark and fuel. however, these days you have a (insert collective noun) of sensors reporting to the ecu.

 

as i have said earlier the cheapest option is to get in a good mobile auto electrian. it will cost approx

[Guest danny.s]

the engine will run on 3 cylinders and in the old days would start if you had a spark and fuel. however, these days you have a (insert collective noun) of sensors reporting to the ecu.

 

as i have said earlier the cheapest option is to get in a good mobile auto electrian. it will cost approx

[DaveM]

Good luck !

 

if it's any use, my 2.8 V6 developed a misfire immediately after a service.

I went back 'banging the table' and they replaced all HT leads for me free of charge !

 

But, it still misfired !

 

went back again, this time they checked the coil pack and there was some arcing across a couple of the pots. He did point out the slight discolouration on the black plastic, but you needed bloody good eyes to see it !!

 

drove away happily with no misfire, but on checking, I noticed that they had put my old HT leads back on, (bugger !)

 

They only charged me for the coil pack, (no labour charge for install or diagnostics)

[dipsomaniac]

is it sorted dan?

[Guest danny.s]

is it sorted dan?

 

The auto electrician (who came highly recommended ) came and had a look on thursday, sorry i didn't get back straight away, me and the family had to go to yorkshire for a funeral. I borowed the sister in laws Zafira :bigemo_harabe_net-196: , Me the wife + 4 kids = bugger all boot space !!.

 

Anyway,the guy read the codes and stated the hall sensor has failed he explained that this info was slightly missleading and the ins and outs regarding the relationship between the cam and crank sensor and the hall effect and all that. He said that because the engine was cranking the cps would appear to be ok. He is convinced the engine wont fire up because the cam sensor has failed and needs replacing. He did say that in his experiance if the cam sensor has failed the crank sensor would not be far behind so it may be a good idea to replace both.

 

[dipsomaniac]