So in one of my cars (not the lovely Godzilla) I turn the key and BOOM!!!! Smoke pours from under the hood ..... HOLY ****!! Open the hood, find the entire intake plenum blown to pieces, airbox destroyed.

LOL :-) Another day in the life of a 928 junkie.

So... I'm almost done replacing the injectors (after checking the belt)

 

Sounds like you had plenty of spark and fuel.

What year is that car?

 

Holy Smokes (pun intended)!!! This must have been an 85-86.5 engine, right?

What would a leaky injector detonation do to a later model engine and its intake?

 

WOW! So please explain what caused said BOOM? ?Or was that an injector exploding?

 

Best guess: Leaky injector flooded cumbustion chamber, spark detonated fuel, high pressure from detonation went into intake, intake hoses ruptured... It's been done before.

 

Hman:

Pictures would be nice for those with morbid curiosity. Hope it is not as bad as it sounds!

 

My guess is that it is an 85-86 and that you now have a couple of dents in the hood! BTDT unfortunately so I know how you feel. As for the leaky injector theory, there is nothing in the intake tract to ignite the fuel and the plugs only spark when the valves are closed, so that is not likely. My 86 had Autothority chips in it (which I removed) and I later found the camshaft pulley on the passenger side was not timed/indexed properly. This "explosion" only happened twice. I do not know for sure which of the two things I did cured the problem, but it never occurred again. A lister in the LV area now owns the car and I sold it to him with the Autothority chipset reinstalled. Haven't heard or seen anything posted...

 

Vertex Auto (no affiliation) sells a little flappy/check valve to keep this from happening on the older 911's. It requires drilling a hole in the airbox. It looks like it would fit the 928 airbox as well. You may wanna look into it.

 

My 79 does that every once in a while. Hasn't done any damage to the airbox, but it has taken years off my life. I think I have a slightly leaky injector and every once in a while, it clears its throat. Big bang and then a cloud of smoke!

First time it happened, I almost wet myself trying to get the fire extinguisher out of its hold-down...

 

if thats the case, lucky he didnt bend somehting. Fluids dont compress at TDC

 

mine did that years ago. even dented the hood!!! boy was I happy

it's also caused by revving the motor and turning off the key before it's back to idle after too many glen livets, glen fitches, all the glens, etc.... cost me an airbox, hood repaint, lots of littlle rubber parts.

bummer man!!!

 

The red one?

 

Good point - I was just speculating, based on past such stories, and should have made that clear.

But if you have a much larger-than-normal detonation in the combustion chamber, would the valve seal be strong enough to prevent pressure going back into the intake? If so, what else could have ignited the fuel and where?

 

You'll blow a ring before you'll blow past a closed valve. The more pressure you put on them, the better they seal.

Also, if you have too much fuel you'll get a burn, but no bang. You'll be too 'rich' for detonation.

 

Timing is I think fine. It' an '85. Otherwise in fine shape. It is possibe that an injector leaked into the intake. Remember the injectors fire straight into the intake runner toward the port in the head. So I don't know, but I have replaced all the injectors with refurbished ones, she ran fine before and we'll see if she's fine now. No reason for me to suspect timing .... as I say it checks out passnger side and I'll verify driver's side too. Hood has a small dent yes, I'll have that removed I guess. I feel fine thnks .... ws quite funny, I laughed out loud ... might have been worrying had this been my only 928.