Misfires on cyl 3

[Citgot]

My joy after replacing the AOS, IMS and RMS was short. My car ran well for a few days but yesterday it started hesitating and it felt like I lost a cylinder. The engine light started flashing whenever the speed exceeded 20 mph. I limped to a friend’s home nearby and then the right exhaust started smoking and a petrol smell was obvious.

 

Fault codes are P0300, p0303 and p1229. I have tried with replacing the spark plug and the ignition coil on cylinder 3 but that did nothing. The spark plug is drenched in petrol. There is voltage in the ignition coil cable on cyl 3.

 

What is my next recommended step? Compression test? Anything else?

 

Edit: 996 3.4 2000

[JFP in PA]

26 minutes ago, Citgot said:

My joy after replacing the AOS, IMS and RMS was short. My car ran well for a few days but yesterday it started hesitating and it felt like I lost a cylinder. The engine light started flashing whenever the speed exceeded 20 mph. I limped to a friend’s home nearby and then the right exhaust started smoking and a petrol smell was obvious.

 

Fault codes are P0300, p0303 and p1229. I have tried with replacing the spark plug and the ignition coil on cylinder 3 but that did nothing. The spark plug is drenched in petrol. There is voltage in the ignition coil cable on cyl 3.

 

What is my next recommended step? Compression test? Anything else?

 

Edit: 996 3.4 2000

 

You need to find out if the injector on that cylinder is stuck open, probably the easiest way it to monitor the engine off fuel pressure to see if it drops off due to leakage.  You need to address this quickly as the unburnt fuel will wash the oil off that cylinder wall and lead to scoring.  Once you fix it, change your oil and filter as the oil will most likely have a lot of fuel in it.

 

Good luck!

[Citgot]

Thanks. Engine off fuel pressure, is that what is described in Workshop Manual section 20-2 with a special Porsche tool?

[DBJoe996]

Yes, that is the correct Workshop Manual section.  Maybe someone with experience will weigh in on the pressure testing tool.  I don't believe there is anything unique about the pressure testing port (schrader valve on the fuel rail), maybe a local auto supply stores might have one that will work. What you want to see is if the fuel  rail stays pressurized with engine off, or if it bleeds down, meaning the fuel injector for #3 is stuck open as JFP pointed out.

Edited June 13, 2020 by DBJoe996

[Citgot]

Thank you! Found in some other older thread that I need a M14x1.5 to M15x1.5 adapter for a standard pressure tester. That confuses me, why would not a M14x1.5 to 1/8” NPT adapter work? I thought 1/8” NPT was the standard pressure tester connection.

[Citgot]

Looking through the fault codes a bit more thorough p1229 seems to address the fuel injector in cylinder 5, not cylinder 3. Is that correct?

[JFP in PA]

14 minutes ago, Citgot said:

Looking through the fault codes a bit more thorough p1229 seems to address the fuel injector in cylinder 5, not cylinder 3. Is that correct?

 

P1229 is a shorted injector on cylinder 5. 

[Citgot]

So cylinder 3 misfires could be something else than a fuel injector? Isn’t it strange that problems on two cylinders in different banks occurred at the same time?

[JFP in PA]

3 hours ago, Citgot said:

So cylinder 3 misfires could be something else than a fuel injector? Isn’t it strange that problems on two cylinders in different banks occurred at the same time?

 

Not at all strange or unusual.  “Fecal matter occurs” and all that.

[Citgot]

OK, thanks. I’ll do a pressure test and see if it indicates that any injector is leaking. I guess I’ll have to check the wiring on bank 2 as well.

Are injectors known to go permanently bad on 996 or is it just a matter of removing and cleaning them?

[DBJoe996]

What version is your DME?  Error codes differ for version 5.2.2, 7.2 and 7.8, and since your car is a 2000, it could be 5.2.2 or 7.2

I would say generally that they (injectors) don't go bad, but just get clogged up.  They  can be rebuilt by a professional/specialist.

[Citgot]

I don’t know which version I have. I can’t find it anywhere with my scan tool. Didn’t know the fault codes differed but that would explain why it looked like cyl 5 also had a bad injector.

[Citgot]

I have got e-gas on mine so I guess that makes my motronic a 7.2 which means the fault codes are all on cylinder 3. Makes sense now. Thank you for your help.

[Citgot]

Bummer, looks like I pinched the wire going to the cylinder 3 injector when remounting the intake when I did the AOS. I guess that happens when working only by feel with no visual possibilities.

I guess it is more likely that that is the problem than a faulty injector then.

Seems like a tough match to repair the wire so far in the engine bay. Can anyone tell me how that wire is wired, I mean can I unplug it somehow to repair it outside of the car (if it is broken that is)?

[DBJoe996]

No, the engine wiring harness is a whole unit that connects to the X51 connectors in the engine bay.  It would be extremely difficult to replace just the cylinder 3 wires in the wiring harness.  Maybe you can find where the wire got pinched, and repair just that wire.  Agree, it's going to be difficult in that location but it has to be done.  What if you were to lower the engine to the frame and see if you can reach it?  You had to do that to replace the AOS.

[Citgot]

Thanks. Yeah, I know where the cable might be broken as it sat wedged between the upper intake manifold and the lower part. I’m surprised that the car ran at all, must have been some air leak because of that cable being there.

I have already lowered the engine a bit as I was about to replace all the injectors. That’s when I found the cable being stuck. Actually I replaced the AOS without lowering the engine, bad call...

I shall try to peel back the insulation on the wire to find if it is cut. But it is very very hard to reach it with both hands. Maybe I can solder it and tape it back together. Would probably be easier from underneath but the cable is far too short for that.

As the fault code indicated that the injector was shorted to ground, can I assume that it is at least the live wire that is broken or could a cut ground wire give the same code?

[JFP in PA]

It may help if your disconnect the harness from all the injectors to get more room to work.

 

DO NOT TAPE IT BACK TOGETHER!  If the wire is damaged, you need to open up the damaged area, even cutting the wire although it is still intact, and sliding on a heat shrink tube before soldering the wire back together.  Then you can slide the heat shrink tube over the joint, shrink it, and you have a fully insulated, water proof repair that will out live the car.  Fix it right, fix it once................

[Citgot]

Of course, heatshrinking before taping is a must. I was a bit unclear about that but I had no intention of doing a hasty and ****ty repair.

[Citgot]

This is how I found the cable after getting it out of the intake, which was harder than expected. I guess I have found my problem.

 

So as I now have 6 new injectors, would you recommend that I replace them when I am in there or should I sell them and cut my losses, or maybe save for when a injector stops working?

[JFP in PA]

25 minutes ago, Citgot said:

This is how I found the cable after getting it out of the intake, which was harder than expected. I guess I have found my problem.

 

So as I now have 6 new injectors, would you recommend that I replace them when I am in there or should I sell them and cut my losses, or maybe save for when a injector stops working?

Yeah, that one ain't happy.

 

While I hate to use weather worn phases, it would not be a bad idea to swap them out "while you are in there".  Injectors wear and foul more than people would believe.  There is also a market for used injectors that people buy to have refurbished and installed.

[Citgot]

I decided not to replace the injectors right now as I didn’t want any more possible faults before I sorted my last one. So I soldered the wire and put everything back as before. Measured the voltage and the resistance in the soldered wires and they seemed ok.

I then started the car and it didn’t show any check engine lights. Success! At least I thought for a few seconds but the my garage was filled with smoke from the right exhaust. And I mean totally filled with smoke!

So is this expected and will stop after all the unburnt fuel is gone or have I missed something when putting everything back in the car?

[JFP in PA]

Probably just unburnt fuel; take it out for a run and see if it clears up.

[DBJoe996]

When you replaced the AOS, did you remove the TB and left intake?  There may be some residual oil in the intake.  The AOS vents to Bank 2, the right side of the engine and left exhaust pipe.  Having a bunch of oil in Bank 1, and right exhaust pipe, does not sound good.  Thinking on it....

[Citgot]

Yes, I cleaned the TB and the intake manifold from all oil after replacing my AOS. I have driven a few days after the AOS job without any smoke, so the smoke most likely has something to do with my latest injector cable problem.

I’ll take it for a spin and see if it clears up. I hope there is no risk of any fire in the cat?