cilinders 1 - 3 not working

[Jeroen Wittock]

Hi all, new to this forum.

 

3 months ago I bought a 2002 996 targa with 175k km. I drove it for about 2000km. Than on a 30km drive home the engine started to sound more and more rough, more and more vibrations.

When the rpm got below 3000 I lost all power (engine did not die), and with full throttle it slowly picked up speed until it reached 2700 to 3000 rmp when all power returned and the car lept forward in a jerk.

Tried to make it home, but after 10km of this it finally stalled and did not want to start again.

During the last 10km of running, check engine light came on, fuel light came on, abs errors, pcm error all came and went.

 

Towed the car home and put a simple obd reader on the car.

I was greeted with the following codes:

• P0343: CMP sensor A bank 1 -high input
• P0303: cilinder 3 misfire
• P0302: cilinder 2 misfire
• P0301: cilinder 1 misfire
• P0300: multiple misfire detecte
• P1325
• P1341

 

At this point I called the Indy where I bought the car from and they said to replace the camshaft position sensor. Did not think too much of it, so I went ahead and replaced it. Cleared the codes with the simple obd reader, but the rough running remains.

At this point only code P0343 is coming back.

 

Putting a temperature reading on all cilinder exhausts shows that cilinders 1,2 and 3 remain cold, cilinders 4 to 6 warm up.

• I do have a fuel smell, so I assume cilinders 1-3 are getting fuel.
• Compression test on cilinders 1 - 3 gives between 126 and 128 PSI
• Took out coil of cilinder 3 and connected spare spark plug, it spraked but it was yellow.
• Used camera to inspect the cilinders, I am no expert what so ever, but my amateur opinion is that I did not see lines on the cilinder walls, and no damage to piston ( not hitting valves or anything)
• Only thing to note was that cilinder 3 had a lot of oil in it ( a puddle of 1 or 2 mm high), so I removed fuse for fuel pump and ignition, and with spark plug removed, ran the starter so it could pump out the oil. After which I put back the fuses and tried starting again, still no joy on cilinders 1-3.

 

I replace coils and plugs on cilinders 1 - 3. Still not firing. (I have not yet checked spark again to see if it is nice and blue, nor did I test on all 3 cilinders to ensure I have spark)

 

With the cmp on bank 1 disconnected, the engine behaves the same as when connected.

• Question 1: So if DME decides not to use cilinders 1-3, why do I still get spark and why do still smell fuel? I would think that if DME decides not to use a cilinder that it would not send spark signal and not trigger injectors?
• Question 2: I read that without cmp on bank1 the engine should still fire up (on all 6)?

 

 

I did some google-fu and found in the workshop manual to check signal wire from DME to sensor for short to B+.

 

Now I do not understand what short to B+ means, nor do I have special tool 9637. So I started measuring. Below you can find all my results, but short version is that all measurements I took for wires to and from cmp on bank 1 are the exact same as the measurements for bank 2. So I do not understand why cmp bank 1 is throwing error and cmp bank 2 is not.

 

Question 3: Can someone explain me between which points I need to make a measurement. And what should be disconnected before making the measurement? (note I did a lot of measurements described further in this post)

 

Question 4: the wiring diagrams say that the supply voltage should be 5V, but I measure 11V?

 

Measurements I took on the cable end that goes into the CMP on bank 1:

Let's call wire to DME gnd line A

Let's call wire to DME output/signal line B

Let's call wire to DME supply  line C

 

A - B: 10,7V and 49k ohm

A - C : 11.2V and 70 ohm

B - C :0.4V and 42k ohm

A to chassis: 0V and 0.2 ohm

B to chassis: 10.8V and 42k ohm

C to chassis: 11.2V and 70 ohm

 

Now if I disconnect pin C12 (cmp bank 1 signal) from connector to DME, than I measure no voltage between wire in plug to sensor and chassis.

Which leads me to believe that C12 is supplying voltage but 0.4V less than the DME supply wire to the sensor.

 

Now for the interesting bit, I have almost identical measurements for CMP on bank 2.

 

Question 5: Why is the computer still reporting high signal on cmp bank1 even though I get same measurements comparing CMP on both banks.

 

Another observation I made is that found very small oil leak at the bottom of the engine where it connects to the gearbox. Also the two connections between left and right air intake are oily. And if I open oil reservoir cap, there seems to be some negative pressure. ( I have ordered a second oil cap so I can drill a hole and add vacuum pressure meter to see if AOS might be bad) Will report measurements here once I get those parts.

 

Question 6: Could the above indicate a bad AOS? It was replaced already in 2017, and reading about AOS does indicate I should consider replacing every 6 or 7 years?

 

Question 7: IF it theory is bad AOS, how does that explain only cilinders 1-3 not working.

 

Question 8: What parts of the engine are dedicated to one cilinder bank? So that I can test by swapping or measuring those components to try and understand why bank 1 is not happy?

 

Additional info that might or might not be related:

• AOS, IMS and RMS where replaced around 2017.
• It started raining on the drive home, first time I drove it in the rain.
• Before driving home, the car was parked on a hill side. Front right wheel was highest, rear left was lowest.
• No smoke as far as I could tell.
• I was almost out of gas, so I thought it might be running out of fuel during the rough running, so I fueled up, but rough running remained.
• On the last drive before the return home drive, at points in time I thought I heard ticking (for lack of a getter word)
• When trying the start the car when towed home (and before doing any work) there was again a subtle metal ticking that went away after a few seconds of idling.
• After replacing cam shaft position sensor, coils and plugs on bank 1 (cilinders 1-3), this ticking is completely gone.

Edited August 3, 2023 by Jeroen Wittock
typo

[Jeroen Wittock]

Forgot to add that I removed and check the two variocam actuators as well. The left one (timing?) was fine, the right one (lift adjustment?) was stuck. A healthy dose of brake cleaner and a lot of testing with a 12 V battery got it loose again and working fine even when putting pressure on it. Put it back, no change whatsoever.

[JFP in PA]

P0343 indicates that cam position sensor 1 is reading out of spec or is shorted.  As your electrical test show it seems to be working, the next question is where is the cam timing.  Next step should be to read the cam deviation values with a Porsche specific scan tool like the Durametric system or a PIWIS, both banks should read +/- 6 degrees or less; if bank 1 is high, you have a cam timing issue.

[Jeroen Wittock]

I am trying to buy a duratech tomorrow to get better readings. However, someone pointed out to check the ground connection from the fuel injectors on bank 1. It is located behind the bracket that holds the wire to the cps, it is right below the AOS. I did remove the bolt holding the bracket to get to the ground, it was dirty, so cleaned it to bare metal. And now the P0343 seems to be gone. I cleared code, started engine, stopped it, read codes again and it was no longer there. Will test again tomorrow.

 

However, before cleaning the ground the car would keep idling, now it idles for a few seconds and than dies.

 

Now that the car does not keep idling I cannot do the vacuum measurement on the oil refil cap that I was planning to. I read somewhere that 4 to 6 inches of H2O indicates good AOS, 6 to 8 or more inches of H2O would indicate a bad AOS.  Any chance AOS is part of the problem?

 

Since fuel goes to fuel rail for cilinders 4 -6 first and than through hose to rail for cilinders 1 -3, could too low a pressure cause not enough pressure to remain on bank 1 for cilinders 1 -3 to fire up?

Edited August 3, 2023 by Jeroen Wittock

[JFP in PA]

I cannot see the AOS being any part of the issue at hand; even when completely failed, cars with a dead AOS run fine, they just idle funny and smoke a lot.

 

You can check your fuel system for pressure and delivery by connecting a test gauge to the Schrader test port on the fuel rail.

[Jeroen Wittock]

Ok, I'll test that tomorrow and report back. I suppose I will find what pressures are expected in the workshop manual?

 

Any chance this is timing related?

Edited August 3, 2023 by Jeroen Wittock

[JFP in PA]

Your fuel system should retain 3.8+/- 0.2 bar (around 55 psig) with the engine off, and sow 3.3 +/- 0.2 bar (48 psig) running at an idle. With the engine off, your fuel pump should deliver 850 ml of fuel in 30 seconds.

 

Which timing are you questioning?

[Jeroen Wittock]

Timing of bank 1, any chance the bolts that hold the sprocket in place came loose causing timing to shift?

[JFP in PA]

7 hours ago, Jeroen Wittock said:

Timing of bank 1, any chance the bolts that hold the sprocket in place came loose causing timing to shift?

 

Unless it had been touched by someone, I've never seen that happen on one that had not be messed with.