spinaker

I'm not quite sure what happened but when I tried to start my 928 today, I heard a bang then smoke came out from under the hood. I shut it off immediately although it didn't start.

Upon examination, the passenger side metal intake runner was blown from the rubber hose connections and a piece of the plastic air intake on the same side has been broken off.

It also looks like there is oil(?) in the fixed intake runners.

Does this sound like the fabled leaking injector outcome?

Open to any suggestions and diagnosis including possible extent of damage and how repairable with my home garage skills.

I have to run out for a while right now but will check back in here in an hour.

Thanks in advance for everyone's input.

Shark Attack

this does happen. I have heard of it this s few times now. I think it is computer related. i am sure. More folks will chime in here soon, sit tight

the flyin' scotsman

Doug...........is there a strong smell of gas?

Try jumping the fuel pump relay and view the fuel rails and injectors....relay #XX

Garth S

One quick check you might make is to pull the vac lines from the fuel pressure regulator and dampers ( there are 3 - 2 of one and 1 of the other - depending on year), and turn on the key to pressurize the fuel lines: look for fuel.
If one of the diaphrams had ruptured, raw fuel will be drawn into the intake ..... lying in wait for a spark.

spinaker

Thanks for the feedback.

There is no smell of gas. I suspect if there was gas in the rail, it burned up quickly, although I would have thought that if there were fumes or gas in the intake, there would have been a much bigger boom.

I don't have time this afternoon to start to actively diagnosis but will do so starting Monday.

Any further suggestions are appreciated.

Bill51sdr

This happens infrequently to those of us who own or have owned a 32V 85-86, and no one has a definitive answer why. My suggestion would be to check and set the cam timing. I did this to an '86 I once owned and the problem seemed to stop. Happened to me twice, btw. Blew off both plenums, destroyed the filter box and put two dents in the hood.

spinaker

Thanks Bill. No dents in my hood. Only the passenger plenum came off but it appears to have broken a piece of plastic off of the intake behind it.

Do you think the misfire takes place in a cylinder (i.e. - leaky injector) or in the plenum?

Where do I find a write-up on resetting the cams? That may be beyond my mechanical capabilities but I will look at it anyway.

Bill51sdr

Doug,

I don't buy the "leaking injector" theory because there is nothing in the intake tract to ignite the fuel/fumes, not to mention this seems to occur the very second you turn the key! Look in the archives under "cam timing" and you may find the procedure, or maybe even Greg Nichols' site. It's a little involved if you're not mechanically inclined.

Big Dave

Check out PorKen's cam tools. They're MUCH easier to use than the factory method.

http://liftbars.com

Factory cam-setting method

Jim bailey - 928 International

fuel in a cylinder only sees a spark when the valves are closed ! The injectors spray into the intake port above the valve so fuel sitting on top of an intake valve becomes vapors in the intake manifold...since all eight injectors pulse at the same time some always spray on a closed valve. It pretty much needs a spark at the WRONG time to light up the intake.

heinrich

leaky injectors. I had this on my 85 and after replacing the injectors, no more.

Bill51sdr

Heinrich, not to be difficult here, but how exactly do those leaks get ignited in the manifold?

heinrich

Bill I deserve that, I know .... all I can tell you is my result. Injector timing is LH .... Ignition timing is EZF ... nothing else is different and yet I have a very reliable engine now -- with a snall hood dent Theory? Perhaps . I guess ... maybe .... who knows ... an intake valve opens as a LOT of fuel is still in the chamber .... and the explosion continues longer than we expected ... all that excess wash of fuel in the cylinder now gets a wash of oxygen ... and ... BOOM!! But then all I know for sure is .. big boom, now no boom.

ZEUS+

I agree with Jim. Possible cross fire in dist. cap(s). Unrelated vehicle, but have seen faulty GM crank sensors cause air filter housings to blow apart.

a4sfed928

I have seen this on motorcycles with CDI. For some reason when the ignition switch is turned to the on position the system will develop a spark as soon as the ignition circuit powers up. I would ***,u,me if the rotor was somewhere between cap conductors it may jump to the wrong cylinder and light off vapors in the intake. My .02.