Popping Plenum on a GTV6

[shane wescott]

Hi Guys

Had some issues with rough running which turned into no start on the GTV6.

Got some new sparkies (Golden Lodge HL USA Plugs), and was told to check the plenum.

Sure enough, problem 1, Bosch spark plugs - no self respecting Alfa would run on those, and prob 2 Yes I had amanaged to pop the plenum.

So loosened the clamp, gave it some strategic pushes and belts with a hand, tightened the clamps and purring like a kitten again (or roaring like a tiger depending on revs)

My question is how common is it to pop the plenum. When I bought the car I was told not to touch the accelerator when starting as it would pop the plenum.

Is this a common "feature" of the 2.5 V6. Happy to live with it, just curious how common it is.

Catch ya

Shane

[Jekyll and Hyde]

My question is how common is it to pop the plenum. When I bought the car I was told not to touch the accelerator when starting as it would pop the plenum.

As said - tap the throttle at the wrong time when you start it, plenum will blow off.  I think every single GTV6 with a stock plenum will pop it under the right conditions (Meaning an intake backfire due to too much air, not enough fuel - which is very easy to do when starting it).

[Evan Bottcher]

First time I jumped in a 75 3.0L I pumped the pedal while turning the key and *bang*.  I was so embarrassed - I am so used to old cars on carbs.  I got a stern message about not using the throttle on any car with injection - fair enough...

[shane wescott]

Yes a lesson learned indeed for myself. Some extra grey hairs and i almost caused my neighbour to have a heart attack.

Catch ya

Shane

[Colin Byrne]

Sure enough, problem 1, Bosch spark plugs - no self respecting Alfa would run on those

mmmmm, not sure about that.

[Brad M]

Sure enough, problem 1, Bosch spark plugs - no self respecting Alfa would run on those

mmmmm, not sure about that.

I was waiting for your response on that. I'd be interested to know the reasoning behind it.

[Victor Lee]

My standard GTV6 2.5 I had years ago popped the plenum a few times....however, I don't believe spark plugs was ever an issue. 


My GTV6 3.0 litre 24 valve does it occassionally:

It did it when the battery was close to flat ... typically if it is in the workshop and is just being started, moved in/out of the workshop over a period of a week or two without the opportunity for the battery to recharge.  The very split second the key is turned, the plenum popped.  What we believe is that the Autronic ECU at that very moment didn't know what position the cams were, and fired a spark erroneously which ignited the any unburnt mixture which then went up the open inlet valve to pop the plenum.

Benincas has solved this problem by programming the ECU so as the crank has to be turning at least 200rpm at start up before allowing any spark to fire.  This way, it gives the opportunity for the ECU to determine the position of the cams (from the cam sensors) before firing the first spark.