I re-read your original post and I have a question. When you removed the cats and installed the cat delete pipes did you have the ECU re-programmed? If not this could be the issue.

 

No, I did not reprogram the ECU just bolted on the cat bypass pipes and enjoyed until this happened

 

When throwing parts at a problem I prefer to throw the right parts.

I would resist the temptation to use the Champion plugs and instead install a full set of the proper plugs.

You want as many unknowns as possible.

Besides the misfires are there any other error codes? Any pending codes?

I can't help but think the problem is something else. I mean assuming the plugs are not the culprit you've replaced the MAF, plugs, coils, and the AOS.

If you pull the plugs and they have oil on them you have to suspect the AOS and it is for some reason passing too much oil vapor through and this is then going to the intake and fouling the plugs.

Usually I would suggest you monitor the fuel trims to see if the DME is desperately trying to find a suitable fueling setting which can be a sign the VarioCam system is acting up but this is usually limited to one bank or the other.

With misfires from cylinders of both banks this suggests a common failure mode and I kind of like the AOS for this.

 

Great advise. I'm thinking the issue is the DME not being re-programed. If the AOS has been replaced that isn't the issue .. if it was. Proper plugs is also the way to go. Can't do anything with a Porsche on the cheap.

 

This is the problem.

 

Whether or not the DME has to be reprogrammed with the exhaust change I can't say. I would hope if the maker of the exhaust mod if the mod required a DME reprogram would say as much in the instructions.

If the instructions do say this and you didn't do this... well, then do it. Then install the new/fresh plugs before you road test the car.

If the exhaust mod maker doesn't require a DME reprogram, or perhaps just leaves this up to the owner to figure out on his own, that is not a company I'd want to do business with.

But moving forward, you'll have to explore what others have done with this same mod in order to get max benefit from the mod without of course the misfires.

 

I'm okay with this, however, simply removing the cats (his only mod) with delete pipes usually require a DME re-flash. Sometimes not for a short period but it will always catch up to you. IMO

 

I've ran cat bypass before on stock ecu with no issues. I think the OP should trace his work back. It really sounds like a loose connection or faulty coil(s) even though it may be new.

 

Let the car sit for days with the battery unplugged in hopes that the car would clear memory and forget that I was running catless and probably rich.

Started up the car and rough idle but not as bad as before. Gas some gas and engine turned okay but some tapping noise but figured that's because it's been sitting around forever and not having it run for more then 15-30 seconds.

One thing I did notice is the CEL started flashing again but after giving it some gas the CEL burned steady which is better then a flashing CEL but after I let go of the gas the engine just died LOL WTF.

Codes for generic overall misfires and misfires in cyl 1 and 4.

Going to order some NGK 4 prong 3199 double platinums and see if that helps. Going to also order two more coil packs. Damn, I have like 12 NEW extra coil packs and starting to forget which ones were good and bad....

 

No need to disconnect the battery to cause the DME to forget fueling settings. Use the OBD2 code reader to clear DTCs. This resets all the learned fueling to the defaults.

I really do not like disconnecting the battery unless absolutely required.

Too late now but you have to be sure to keep the new hardware and the old hardware separate.

You have to be sure the coils and plugs are good. Installed correctly and the right type of plugs. The proper plugs are of the extended tip style. This type of plug runs hot at low engine speeds which helps keep the plug from fouling. But at high engine speeds the tip is cooled by the incoming fresh charge which keeps the plug from breaking down from the heat.

I'm not convinced the plugs or the coils are the problem now.

The behavior suggests the engine is not being properly fueled at cold start. Normally I would suspect the coolant temp sensor because if this delivers the wrong temp the DME is not going to add the right amount of fuel. Generally the engine is fueled too lean and you get spit back not backfires.

But the flashing CEL signals a rich misfire. This suggests an overly rich fueling situation. It is hard to overfuel a cold engine. It can be done but it is not common. Signs of an overly rich mixture could be due to an injector problem, one or more leaking injectors, or possibly too much fuel pressure.

However, say one injector leaks. The DME would detect an overly rich condition and dial back the fueling for that entire bank. Thus what could happen is the good cylinders go into lean misfire condition while the rich cylinder could reach some sort of (barely) suitable fueling condition.

Thus I'm less in favor of a bad injector but more in favor of a fuel pressure problem.

I recall you installed a different exhaust and intake? Did you upset the fuel pressure regulator?

Last thing touched and all that...

But before you tear into the fuel pressure regulator...

Another possible source of misfires is the VarioCam Plus system is not working properly. Early in a cold engine start the VarioCam Plus system changes intake valve timing and selects low valve lift. Valve timing is a bank wide adjustment. Valve lift is independent to each intake valve lifter. If the low valve lift isn't working right on some cylinders misfires occur.

Now you mentioned hearing some ticking noise? My references state that if valve lifter "chatter" is heard concurrent with the misfires and the CEL coming on this can be a sign the intake valve lifters are "dirty" and the low lift feature is not working because of this.

I'm not advising you to tear into the VarioCam Plus system right off the bat just covering all bases.

Be sure of the coils/plugs. Be sure the fuel pressure regulator is ok and any vacuum lines that connect to it are ok.

Monitor intake air temperature (a reading from the MAF) and coolant temperature at cold engine start to be sure they are close to ambient.

Also, if possible monitor fuel trims. If while the engine is running the engine misbehaves if you see the fuel trims swinging rail to rail (so to speak) this can be a sign the DME is attempting to compensate by fueling what is lacking due to the low lift not working with some cylinders.

Also, I recall you installed some kind of bypass?

As others have suggested this can require a DME reprogram to accommodate. I have no first hand experience on this but it is plausible.

This should not be dismissed as if not the sole reason for the behavior a contributor at least.

When things go to heck with say the VarioCam Plus system the DME will attempt to get the desired/expected readings from the #2 sensors by varying the fueling. If those sensors are not connected, or the exhaust bypasses them and they are not working properly, the DME can have a conniption fit (so to speak) in trying to make sense of the readings or lack of readings.

The #2 sensors play a vital role in properly fueling the engine.

When my Boxster's VarioCam solenoid failed I viewed the short term fuel trims and they were wildly erratic. I kind of suspected what this meant and the tech confirmed it. Because the cam timing on the one bank was not right the # 2 O2 sensor reading on that bank was off. The DME was adjusting the fueling to try to get the #2 O2 sensor reading it expected. The tech told me that had this condition continued the engine would have begun to misfire from the fueling. However, an engine shut off and restart had the failing solenoid working ok again and afterwards the fueling was ok, for a while. The failure was at that time intermittent.

 

If you deleted cats your downstream O2 should eff up your a/f and should be detectable on fuel trim readings. That would explain the poor performance.

 

Thanks all for the thoughts and tips. I started the car and gave it more gas and kept it around 3,000rpm for longer then the usually 30 seconds or less I was doing before. The knocking or ticking sound is now gone. The rough running is also gone while holding down the gas. Engine is turning smoothly until I let go of the gas and it just dies.

Before I could at least start the car and rough idle on its own. Now I can't start the car without giving it gas and keep the gas pedal pushed in. Immediately when I let go it just chokes out, stumbles and just dies.

Did a search for stalling on a 996 and found some had issues with the crankshaft position sensor. My previous experience on another german car was that it would start up but once it got warm after several minutes it would just die. A new crankshaft position sensor solved the problem for that previous car. As for now the C4S just dies. Fix one problem and another one arises.

 

Good evening, I saw this post you started but I did not see if you ever resolved the issue. Did you happen to remember what the issue was? I am having the same issue but I have been chasing my tail so any help would be great.

 

Don't wait for a response - he hasn't posted in almost two years so maybe he's moved on. Maybe someone else will jump in with suggestions.

 

Thanks. I figured but it was worth a shot. I will keep on and try a couple more things.