So... I figured out what my cars issue was (not starting issue). The fuel pump was barely alive. Alive enough to pump gas through the filter. But not alive enough to get any sort of fuel pressure readying on the fuel rail (on the engine).
So... I ordered a new fuel pump. Installed it, and started up the car. Started and ran like a CHAMP. Immediately too. ;o) Yeah!

This is what happened when I started it up a few days later (car is not a daily driver). I turned my key and I heard a loud "Ba-BANG"! The sound came from the engine area (not exhaust). Lots of smoke... but no fire or anything. I took off the airbox/air filter assembly, took a look at it and didn't see any cracks or anything. MAF sensor and everything looks like new. So I figure I'd try to start the car (leaving the box assembly off). The car starts but runs like you see it in the video. Low "popping" sounds coming off the top of the engine area. I know the older porsche engines (70's - 80's) could easily blow the airbox. Does anybody care to take a guess at what my brand new(ly) created problem might be?

Make sure to look at the video, and keep in mind all I've done is replace the new fuel pump (and new battery). Previously the car ran absolutely flawless.
I replace the full pump.... try to start the car and hear the loud "pop" smoke comes out of engine area. Now the car runs like what you see in the video. What the heck??

 

That noise (popping) is coming form the top area on the engine. NOT the exhaust.

 

Wished you had held the camera steady when the noise was happening. I wanted to see if the engine was reacting to the noise.

Any chance you dislodged a vacuum hose in the engine compartment? Doesn't really sound/behave like a vacuum leak though.

Sounds more like a misfire from a very bad coil or possibly a loose spark plug. Even then though the noise doesn't really sound like a coil/plug misfire or a loose plug.

Any chance of some piece of hardware in the crankshaft pulley? It might be my imagination but I thought I saw the tube with the blue cap give a brief shudder at one point the noise was heard.

Are all the accessory drives free of any excessive play? What shape is the belt in? Any sharp edges? Missing lengths of the small v's on the working surface of the belt?

 

Before I replaced the fuel pump everything ran perfectly. I would not have knocked a vacuum hose off, etc... those POPPING sounds are coming off the top of the engine. I'd say inside those black plastic things on top the engine. The engine might be moving around a little more than normal because it's not exactly running as smooth as it did right before the (BIG) Ba-BOOM sound (when I turned the key to start it up after replacing my fuel pump).

Like I mentioned in my first explanation...
1). Replace fuel pump.

2). Big "Ba-BOOM!" sound with smoke from engine bay (not exhaust) when I turned the key 1st time to start it up after replacing fuel pump.

3). Now when I start the car up it's runs not too good and it's making those popping sounds from the top black plastic (boxes?) on top the engine. Those popping sounds I am POSITIVE are the results of that LOUD "Ba-Boom" sound that came from the engine bay when I started it up for the first time after replacing the fuel pump.

 

Not sure what you are referring to by those "those black plastic things on top the engine".

There is the intake manifold which is a large black plastic thing. There is a secondary air injection pump off to one side of the engine over in the left hand corner of the engine bay. This is not on top of the engine though. Other than some black lines that criss-cross over the engine that's about all the black things on top of the engine I recall.

The first loud noise with smoke could have been something electrical shorting.

The sounds in the clip are rather distinct and thus I don't necessarily believe they are coming from inside the engine. The engine doesn't act like there's an intake leak.


One possibility is the noise is the engine spitting back through the intake. The engine spits back through the intake if it is lean. (It backfires through the exhaust if it is rich.)

A lean engine lean enough to spit back through the intake suggests then something with the fuel system. Insufficient fuel or fuel pressure.

Sorry but that's all I have right now.

 

Ok... worked on the car a bit more today. I think I pin-pointed the issue. The intake plenum (I guess its called)
on the passenger side of the engine. The POPPING sound is defiantly coming from this area (see arrow in photo).

I believe when it made the BIG "Ba-boom!" sound, that might have blew my intake plenum loose. Looks like the
clamp was knocked askew (see photo). I'd like to gain access to the top of the engine area right above that plenum...
to see if the plastic (black plastic) cracked when it made the loud "ba-BOOM!" noise. My car is a cabriolet... but it
doesn't look like I can gain access via the rear deck area where the convertible top rests in the down position.

Does anyone know if there is a trick to gain access to the top portion of the engine???

 

A friend of a friend (who's a mechanic, but not for Porsches) stopped by took a look at the car for about 20 min. He's going to stop by tomorrow to look a bit more at my car but told me to get a PCV valve for it... as that might be part of the problem. Cant find a PCV valve as a part I can purchase for the 996 engine (1999). He also suggested to pick up a Fuel Pressure Regulator as they might have been my actual issue from the start.

I can buy a Fuel Pressure Regulator for around $120. Since I can't seem to find a PCV valve listed as an item I can purchase for the 996... does anybody
know what Porsche may call a "PCV valve"?

 

AOS: Air Oil Separator

 

I was thinking this is (photos I posted) a hose that connects to the plenum... two clamps on each side of the (1 inch) hose.

Looks like the explosion, blew the clamp and hose out of their "normal" place. Now an air-leak's causing my problem with running (LOTS of "popping"). And inability to actually run smooth and steady. Sounds HORRIBLE.

 

Sorry to say but it sounds terminal. For these cars to backfire and blow off some intake hose/clamp generally means the cam timing is way off.

Try to find someone with a durametric and see if your cam deviations are way off the charts.

If you continue running it, you'll get more collateral damage. I can only speculate at this point that your chain guides and or tensior(s) could have failed. They could also have collateral damage from the IMS tensioner paddles. Once again, these are only guesses at this point.

You could borescope each cylinder and see if you have any piston to valve contact. That way at least, you know if the damage is limited to only the top end.

I would also drop the sump and inspect for any debris and inspect the oil.

Good luck and don't run it any more.

 

Figured it out today. The loud sound had blown the two large intake hoses (with their clamps) slightly off from where they should
be. BOTH hoses on the passenger (right) side of the engine had blown off enough for a serious air leak. Took me an hour of not fun work to get those hoses and their clamps back on. What a P.I.T.A. But... SUCCESS!!! Soon as I saw how bad they had blown off I knew that I'd found the problem. After the final tightening of the hose clamps, and turning that ignition key, the car started like a CHAMP! Now runs smooth as you'd possibly want it to run. ZERO issue. Unbelievable. And... almost imperceptible to the human eye, to see what actually had happened. If it weren't for that ONE hose clamp (that my friend spotted) slight askew, I would'nt have had any idea of what the cars issue could have possibly been.

SO... what did we all learn? If you hear a huge POP! then some smoke from your engine bay after changing your fuel pump. And the car runs like sh*t, then go directly to your intake plenum area and look at those 4-5 inch diameter hoses with the hose clamps. They WILL be the source of your problem. Hook-em back up and you'll be back on the road.

 

You probably have some underlying issues you may not be aware of. Intake hoses just don't pop off for no reason and the "BA-boom " sound you describe could signal something more drastic.

It may be running ok now but would be interesting to see how long it lasts.