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[MG]

Hi

My V6 petrol starts as always first time with no problems. Runs a sweet as you like while it is cold. As it reaches normal running temperature it starts to run rough through the rev range up to about 2000 revs and then seems to be not too bad.

My thoughts were:

* head gasket going home

* Lambda sensor knacked

* DIS pack dying

Anyone had any of these issues which may have similar symptoms?

Appreciate your help with this - I just wish that the OBD diagnostics was available via an app. We have an MGTF that had a misfire problem which was traced to the Lambda sensor - which I easily diagnosed via the OBD2 diags port using free app.....

Thanks very much.

MG

[Nick W]

Start with the DIS, plug leads and plugs. By the time you've removed and inspected all of them(ansd a visual inspection is little more than an informed guess), it's probably worth replacing them all.


You'll be doing some dismantling to do that, so check as much of the intake as possible for damage and air leaks.


Proper diagnosis of the O2 sensors, by reading the live data under all operating conditions, is necessary before condemning them. I would be doing that to the MAF sensor first. Only very late V6s are OBD compliant, but there are cost-effective diagnostic alternatives although we can't discuss them here


Head gasket failure would present other physical symptoms, one of which can be visible on the spark plugs. Old age is making this a bit more common than it used to be on V6s, but it's still unlikely.

[MG]

Hi Nick.

Thanks for your reply and help. I will take a look at the DIS unit over the weekend.

Would the DIS cause issues when the engine warms up ? That is my only doubt that it might be this unit or leads/plugs.

However, I have noticed that the spongy material that forms part of the rear edge seal with the bonnet is soaking wet. This is just above the location of the DIS - is this a clue that the DIS may have deteriorated through water ingress from the spongy material losing its water-proof properties?

I have also noticed that when the rough running occurs the exhaust is smoky, white smoke and steamy looking. Hence my head gasket worry.

If the lambda sensor was not working properly would this cause lumpy running and white smoke?

Have had the car from new and so I know the history of it and have serviced it regularly over the last 20 odd years!!

Many thanks.

Regards,

Mel.

[Doctor Gollum]

Remove the foam, and give the DIS pack chance to dry out.

You may have caught it in time, but the DIS pack won't last forever...

[Entwood]

Similar problem on my old 2.5 many years ago ...  when the DIS pack was removed the amount of rust visible was quite frightening !!  My "guess" was/is that as the DIS pack "warmed up" it expanded sufficiently that corroded internal parts then failed to make decent contact.. hence the misfires ... new DIS pack sorted it ... wasn't cheap then, genuine from stealers ... lord knows what they are now, if still available !!

Some years later the 3.2 had a similar problem ...  check of the coil packs revealed similar corrosion... and they were around £100 each if memory serves !! 

[TheBoy]

The the scuttle foam is wet, remove the scuttle and thoroughly dry it. No need to remove the foam.

Whilst its drying, fix the cause of the foam getting wet, which is 99% usually the rubber around the screen is not secured *properly* to the screen along the bottom edge.  Sealing around the scuttle and removing the foam do nothing. Removing the foam significantly increases engine noise in the cabin.

The DIS probably can't be saved - if visual inspection shows *any* signs of rust on its core, or core delaminiation, replace it.

[Doctor Gollum]

Categorically speaking, removing the foam from adjacent to the DIS/Coilpacks does not increase cabin noise.

I would measure the difference to prove the point, but have neither an Omega of decibel meter to do so.

The scuttle is designed to allow water to drain down wherever it finds a route and gumming it up with sealant just makes a mess and makes it harder to remove on the very rare occasion you actually need to remove it...which is basically to replace the wiper motor.

 

[TheBoy]

Categorically speaking, removing the foam from adjacent to the DIS/Coilpacks does not increase cabin noise.

In my experience it does. Noticibly. Not quite as bad as driving with no scuttle, but close.

Opel didn't fit it just to increase weight and increase build costs.

[Enceladus]

Whatever about noise, water falling onto the coil pack will eventually knacker it. And also any replacement, unless you deal with the leak.

I assume the EML light is off, since you didn't mention it. But have you actually checked to see if there are any stored codes? You can do this easily via the paperclip method.

Check and see if any of the spark plug wells are full of oil. That would mean the cam cover seals have failed, which is to be expected eventually. This also causes rough running.

The 2.5/3.0 ECU doesn't have misfire fault codes. So in the absence of other faults, but with leaking scuttle and assuming the wells are clean it usually means the coil pack is foobar. If that's the case replace it with a genuine Bosch part from a Bosch dealer or you'll be doing the job again.

[johnnydog]

The the scuttle foam is wet, remove the scuttle and thoroughly dry it. No need to remove the foam.

Whilst its drying, fix the cause of the foam getting wet, which is 99% usually the rubber around the screen is not secured *properly* to the screen along the bottom edge.  Sealing around the scuttle and removing the foam do nothing. Removing the foam significantly increases engine noise in the cabin.

I totally agree with the above about leaving the foam as originally fitted.
Having recently found the lower rubber moulding at the bottom of my screen and lower retainer were loose, I thoroughly cleaned both, reattached the retainer and lower moulding (very lightly lubricating the tongue with rubber grease to aid it's reassembly). The lower moulding now sits very snugly against the screen and scuttle, and following the torrential rain over the last couple of days, the foam is bone dry.
I did put a thin bead of auto silicone on the edge of the body as per the guide, but this only needs to be narrow and about 1/8" high  at the most otherwise the scuttle won't sit properly and may be counter productive and allow water to pass onto the engine area around the coil packs / DIS pack.
I would personally leave the foam in situ.