Sunday 21 February 2021

Troubleshooting misfires and no start saga. Maintenance - oil change, clean MAF, throttle body and IACV porsche 996 911, coil pack spark plug tube change

 Oh, how much fun it is to keep old cars alive.

Few weeks back (early Feb 2021), the 911 developed a big misfire just as I was coming home - managed to limp it into the garage.

Symptoms: Flashing then solid CEL, really rough idle, audible misfire.

Pulled codes;

  • P0341 - Camshaft Position Sensor 1 - Signal Implausible, Short to Ground, Short to B+
  • p0300 Misfire Damaging to Catalytic Converter
  • p0306 Misfire, Cylinder 6, Damaging to Catalytic Converter
Plus a bunch of old codes relating to the alarm and microswitches - irrelevant to engine. So, time for initial troubleshooting.... misfires often due to
  1. ignition (spark) problem - plugs, wires, coilpacks, crank position sensor, MAF, throttle, idle control valve
  2. fuel problem - pump, filter, injector
  3. compression problem - valves, head, piston, bore scoring etc (this is the scary expensive problem!)

as usual... start with cheapest, easiest investigations first before going into expensive, difficult investigations. Basic maintenance first.

1) Drop oil, check filter. Found a few small bits of orange sealant/RTV in the oil filter, but no metallic particles. Wonder where this is coming from? Ususal suspect is oil sump gasket, but I've not seen this orange sealant at any prior oil change.

Mobil 1 5-50 now a recommended oil for 996s.

Removed and cleaned MAF with some CRC spray, dried and reinstalled.

Checked throttle body for any signs of oil (which can be a sign of AOS failure - was really clean before and after throttle. Gave it a clean anyway. Note this is a cable throttle early 996.1

Removed Idle Control Valve - tested with a 9V battery and found it to be pretty sticky. Cleaned it out and retested to make sure the flap opens and closes easily, then reinstalled. The gasket and bolts were a bit worn out - replacement parts ordered. Checked all connections after the MAF were secure and no obvious problems like loose hoseclamps or bolts.

Raised the rear of the car and placed bricks under the rear wheels for a bit of space, removed coilpack cover on right, and accessed coilpack on cylinder #6.

Coilpack removed had a fair bit of oil all around it and missing the end collar.

Ordered a couple of replacements (on the left)

Pulled Cylinder 6 spark plug - a dirty NGK, but no big signs of carbon buildup oil oil deposits - promising! If it was very oily, this might indicate oil getting past valves, seals or piston rings ($$$ problem). Brand new Bosch replacement FGR6KQE 4 prong plug replacement.

Used a mini endoscope to check inside the spoark plug tube - no obvious cracks in the tube, a little oil or fuel pooling at the bottom of the tube.

Top of piston - fairly caked on fuel/oil, no obvious damage to top of piston.

Pulled cylinder 6 spark plug tube - was an aftermarket replacement with O rings well worn. Made a tool with a long bolt and end waser to yank out the spark plug tube. New OEM spark plug tube and O rings from local dealer reinstalled.

Bolted everything up, checked coolant and oil levels, put the battery on a C-tek overnight.

Started everything up.... and no improvement! Hard to start, and when everything kicked over, idled very low with audible misfiring. With a few revs - just over 1000rpm, things did even out a little.

Pulled codes-  same P0341, P0300 and P0306, plus a P0305 now - for a misfire on cylinder 5!

Will recheck all wiring today - just need to make sure all the coipacks are plugged in 100%. Next step is to recheck fuel pump (though I imagine a fauly pump would cause misfires on all cylinders), check fuel filter for blockages, then.... more research required!

What am I considering right now?

- Car cranks over OK - starter is fine. I do have a spare new starter motor bought a while ago ready to replace. RPMs moves on crank - crank position sensor is OK. Replaced this part a couple years ago.

- Fuel pump issue (check working by bridging fuel pump relay), blocked fuel filter (replace, it's a cheap part), blocked injector(s) - bit harder to investigate. That said, a fuel pump problem will most likely cause multiple misfires on all cylinders rather than just 1, or 2. An individual fuel problem is most likely the injector associated with the cylinder.

- No compression - to check with compression tester. Potentially related to variocam problem (fairly common for variocam solenoids to get sticky/stuck on one cam setting), but also chains have broken. The P0341 code is a potential red flag, though related to bank 1 (cylinders 1 2 3) rather than bank 2?

Hoping it's not a compression problem, because this is where things will get expensive quickly. Ultimately I'm realistic about the potential problems a motor with 258,000km will have. Not really worth my time or money to pay for expensive engine overhauling (haven't decided what my limit will be) as the resale value of this car was always going to be modest. Never bought this car with the intention of it being a garage queen, just a cool daily driver. Worst case scenario if it's an expensive engine job is to sell this car in parts, or in whole to a wrecker. Best case scenario, I find a fuel issue and fix it myself. 

Here's hoping!

Update 28.2.2021 - Jumped the fuel pump relay with a fused wire - fuel pump runs and sounds good. Tried starting the car, bypassing the relay with the same fused wire to ensure the fuel pump is running all the time - same problem where engine barely fires up and runs poorly.

Now to check output after fuel filter, and at fuel pressure regulator.

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