GTV6 - bonnet mould blew off

[UNICO]

I started my GTV6 this morning to go to work as I've been doing every morning for the past year, however as soon as I tried to fire her up there was a loud bang in the engine bay and my bonnet mould blew off. Has this happened to anyone before? It was so bad that the nuts and bolts that secure the mould remained on the bonnet and the mould was on the floor. I think I need a new mould, does anyone have a spare, also, what would of caused the explosion in the engine bay?

Ed

[Sheldon McIntosh]

Did you have some throttle on as you tried to start it?

[Jekyll and Hyde]

The classic GTV6 popping plenum - caused by a backfire in the intake, blowing the plenum off the rubber hoses which mount it, some cars are prone to doing this if you give it some throttle while cranking.

[Sheldon McIntosh]

Or maybe an air leak somewhere?

[UNICO]

Thanks for the feedback, but I didn't have throttle on when I started it and the plenum box wasn't effected (I think, I better check it again). However I do have problems starting her when I haven't driven it for a couple of days. I have to crank it for about 30 secs before she fires. Very weird I think. What I'm concerned about is that the bonnet mould landed on the road!!!

Ed

[Al Campbell]

             "Have to crank it for about 30 sec."

The Cold Start Injector squirts for about 8 seconds and should then shut off. But if you have several attempts at starting, It'll squirt each time, filling the plenum with fuel. If you crank for too long you end up with a flooded motor.

Standard advice is not to touch the accelerator during starting or you'll get plenum pop. If  you've tried to start a few times,  open the bonnet and pull the connector off the cold start injector to stop adding more fuel.

Against this advice, I use the standard flooded motor trick and push the accelerator all the way to the floor. No pop. Yet.

One theory I've heard about the reason for putting the piece of plastic on the bonnet is so that you don't end up with a bent bonnet after plenum pop. Easier to replace a square of plastic.

AL.

[dehne]

ive had that happen in my 90 a few times, it was due to flooding. i just put it back on and tightened everything up a bit more

[UNICO]

I checked the plenum this morning and yes it is very loose, I can probably lift it off with one hand. I'll tighten it tonight. Going back to what I said in my previous thread, If I haven't started her in a couple of days it will struggle to start. I'll crank her over and if she doesn't start first kick (which she usually does) I'll have to keep her cranking continuously for about 30 to 40 seconds and then she will slowly fire up. Any ideas why she refuses to start?

[dehne]

ive had that prob with my race car not starting when i have not used it for a while i think its to do with the battery not quite charged enough to start it but has enough to turn over, i usually stick the charger on for 30-60 mins and its then fine

[UNICO]

That's what I thought it was, so I bought a new battery and it still gives me problems. Who I am kidding, it is an alfa after all, what more do I expect. When she does start, she drives  like a dream down to geelong and back everyday

[JOHN G]

This is from well known Alfa Guru Greg Gordon
(The dreaded plenum pop is not really caused by starting with the throttle open, however holding the throttle open will greatly increase the chances of a plenum pop. I will explain. The plenum pop is actually caused by air leaks upstream of the throttle body. However during a normal start, the closed throttle largely blocks the cylinders' access to these leaks. As soon as you open the throttle unmetered air can rush in from the leak between the AFM and the throttle and bang, plenum pop.

The most likely leak point in this case is on the underside of the accordion section of the main air intake tube, just after the AFM, however it could be somewhere else.

I know what I am writing here goes against the convention regarding plenum pop. When I first bought my GTV6 it had a horrible plenum pop problem. Once I fixed all the air leaks the problem went away. In fact I have experimented with this quite a bit. With all leaks fixed I can't make the plenum pop, no matter what I do, multiple start attempts, throttle position, nothing makes it pop. However, if I introduce a leak, flood it and start with the throttle open it will pop as often as not.)

So Ed read Gregs site hiperformancestore.com he sells the silicon vacume hose kit and explains how you can fix all the air leaks.

John

[Sheldon McIntosh]

it is an alfa after all, what more do I expect.

I'm always worried if my V6 doesn't start first go (which is very rare, and usually only when very warm).  In my limited experience, and all I've read, if they don't fire first go there is something wrong.  But don't worry, if you ignore them these problems never get any worse....

Have you read Greg Gordon's site re: air leaks?   http://www.hiperformancestore.com/Ljetronic.htm

Oops, we were posting at the same time....

[dehne]

you do know that if you badmouth an alfa that they only get worse, i give mine kisses and cuddles every day just to keep it informed that i do love it

[UNICO]

Dehne, can you post some photos of you cuddling and kissing your baby

As much as they drive me insane, I still love her and the other 4 that I had. I'll never learn.