bruce7

Will the car go into closed loop mode? The status shown is open loop
but you may have taken the picture just after startup and the system
had not yet entered closed loop mode.

Check the ignition wire set insulation for breakdown or bad connections.

I would run secondary ignition waveform tests. This will quickly identify
which cylinders are not firing properly. Also do a current ramp test on
each coil. To do these tests you will need an oscilloscope (labscope, DSO)
and a trigger sync pickup, secondary ignition inductance pickup, and a
low amp current probe. I can post example waveforms from my car if
you get this far for comparison.

Find and fix any VRAM vacuum leaks. The long term fuel trim shows it's
adding fuel for the right bank (cylinders 4-6). BTW, the reported misfire
codes cannot be depended upon to be 100% accurate. The misfire may
be on the other side. This is a tedious job without a special tester but
you can do it with a hand vacuum pump and gauge. The cool tool to
use now is a CO2 tester.

Change the fuel filter if not done recently.

Verify the oxygen sensors are working properly. They degrade over time.
Some say to change out at 60K miles. You are at 80K. I went 100K but
they started failing at 90K. In retrospect I would change at 80K. To verify,
you need an oscilloscope (labscope, DSO) and need to check these parameters:

1. max voltage >= 850 mV
2. min voltage <= 150 mV
3. voltage > 0 always
4. period ~ 2 secs
5. rise time < 80 ms (use a snap-throttle test)
6. fall time < 100 ms (use a snap-throttle test)


Good that you changed the cap and rotors. I recently changed mine and
it made a huge difference. I went 45K miles but I thought I could go 60K.
Nope. Visually and resistance tests did not reveal anything but evidently
the air gap was eroded and making for a slight roughness that I have not
completely eliminated. I will now change them every 30K miles. It is an
unfortunate aspect of the ignition system that they wear so fast.

Don't think a leak down test is needed yet. If the secondary ignition waveforms
show a longer than normal spark burn time then low compression would be a
suspect (valve seating or rings) and a leak down test might be something to do.

Haven't mentioned fuel injectors but these can get clogged up and drip fuel.
It's not too expensive to send out to clean and at some point you will want to
do that. I just did it and it really cleaned up the O2 waveforms which showed
some random fuel related misfires.

I would only replace components when testing indicates they need service.
Over time I've tried to acquire the equipment and learn how to use it rather
than depend upon someone else. Good luck and let us know what you find.

BesideTheBox

Here is a *link* to an old post with explanations of some OBD-II parameters.

Some thoughts about your OBDII parameter values:
Intake air temp looks normal for a 60 - 70 degree F day.
Ignition advance at 4 degrees is normal for idle, but it can bounce around a little, and later it shows 10.
Your 'coolant F', actually cylinder head temperature for our engines says 266, so you did not just start up your engine and I don't think that you are in open loop due to SAI.
I think that your short term fuel trims display 0 because your 'fuel sys 1' and 'fuel sys 2' show that you are in open loop mode and the computer can't calculate the delta from the expected fuel delivery that would have been supplied if the engine was in closed loop mode.
In open loop mode, the computer is NOT relying on the O2 sensor voltages to vary the injector 'ontime' to vary the amount of fuel supplied to the engine.
I suspect that you are in open loop mode because your pre-cat O2 sensors may be beyond their useful lifespan.

I agree with Bruce7 that you need to take a good look at your pre cat O2 sensors.
With your Actron, you may get a reasonable assessment of their condition.
I see the left side pre-cat O2 sensor (O2S11 - O2S bank 1 sensor 1) shows .650, and your right side pre-cat O2 sensor (O2S21 - O2S bank 2 sensor 1) shows .150.
Hook up your Actron and watch these two values over a couple minutes time while at idle and also at 2K RPM.
I say a couple of minutes because our DME uses 9600 baud to deliver the OBD2 data out the OBD2 port.
Since it is sampling data, the data might not be requested at the exact top or bottom of the range.
Monitoring over time helps to get a better picture of the true range.

Please post what you see for your min and max O2S11 and O2S21 values for each RPM value.

pp000830

Don't dig too deep. New caps and rotors and a bottle or two of Techron and you may be done. Also make sure none of the little vacuum lines have slipped off.

sacman

rich, did you ever resolve this issue?

Watson

Also interested in the outcome!

@sacman : do you also have this issue?

rich c4s

Issue ended up being the timing chain. Once in there, ended up doing more.

sacman

Thanks for the update Rich. I'm suspecting mine being that too because I had addressed all of the ignition stuff (distributor belt, plugs, wires, rotors,caps and O2 sensors).

sacman

My started out with O2 related sensors. I replaced all 4 sensors but 2 are still not receiving signals so I just reset and they come back right after about 30 mins of driving. Then, I got P0303 as the car felt like stalling for 1 minutes. Again, I reset the code and eveything is running smoothly. My next step is to do the following next week while changing the oil after a giving the fuel system cleaner treatment with GB 44K:
1. Check for loose connections (plugs, injector, distributor, etc). Most ignition stuff (dist belt, plugs, wires, rotors and caps) were replaced 5K miles ago.
2. Check for Cam shaft Sensor.
3. Air leak.

I'm not sure if how to check for timing chain if the timing is actually the cause. This probably requires bringing it to the shop.

QN

EduardoForesti

Another P0303 sufferer.

1997 993 C2, cabriolet. 100K miles

The P0303 code started about 150 miles after a big job, which included:
- Plugs, wires, caps, rotors, distributor belt
- Upper and lower VC gaskets
- Clutch, DMF (don't judge me ), etc
- SAI ports spa treatment (port clean/flush re: 0411 0410 codes)
- Clean ISV
- Air filter, fuel filter, alternator, oil and filter
- Engine (plus cats/exhaust), got a bit of an (external) bath given all of the accumulated oil from leaky gaskets
- Note: Has Porsche / OEM belts from before "the big job" (noting this because it is a known culprit for misfires)

Other Symptoms (beyond CEL and code) and info:

• The engine definitely sputters at idle and in driving, but I drove it yesterday and the sputtering was intermittent for parts of the drive (like it had gone away, but...it came back).
• When the P0303 first popped, it popped with a P0411 and P0410 (freaked me out), but I've reset twice now and the P0411 and P0410 have NOT appeared again).
• Plug wires for cyl 3 are set/tight at plugs and d-caps and the wires from d-caps to coils are tight.
• OBD stats attached (Bank 1 definitely looks out of whack - but only via inference given the huge difference to Bank 2; not because I know any better)

I think the recommendations from this thread is now for me to (net of work performed to date)?:

• Find and fix any VRAM vacuum leaks. I don't have any testing equip other than a OBDII reader, so I can look for disconnected vacuum lines?
• Figure out to test the hall / Pulse sensor https://rennlist.com/forums/993-foru...op-manual.html (I responded to that post looking for procedure)?
• Check the grounds https://rennlist.com/forums/993-foru...l#post10388201 ?

Given other's experience and expertise and the attached OBD stats, is there anything glaring that would you lead you to "the source"?

I have a service manual, but it is incomplete and is totally missing section 28 ("ignition system")...ugh...

Many thanks for any insights!

PS: The shop (that I love) that did the recent work is +/-90 minutes from me, so if this can be fixed from home, I'd be a happy camper...hence my reaching out to "the Rennlist brain-trust"...