diesputnikdie

Hi everyone, I’ve spent the last 18 months bringing a 2004 Cayenne S (4.5L V8) back from the dead. It sat outside for 5+ years and had a laundry list of issues. I just finished a massive diagnostic session and wanted to document the specific failures and fixes, especially regarding the "0L" CAN bus error and a terrifying compression test result that turned out to be a false alarm. The Patient Vehicle: 2004 Porsche Cayenne S (non-Turbo). History: Sat for 5 years outside in PNW. Incorrect turbo injectors installed by previous owner. Crank no-start (clogged drains, soggy floors caused the common splices under the carpets to disintegrate) Initial State: Running Condition: The car would crank and start after fixing the splices, but ran incredibly rough and would not idle without holding the gas pedal. Communication: Impossible. The Durametric scanner showed "Link Error" or could not find modules. The OBD-II port showed "0L" (Open Loop) when testing resistance between CAN High/Low (Pins 6 & 14). Phase 1: The "Invisible" Electrical Break The Symptom: I couldn't scan the car to diagnose the rough running because the Gateway wasn't talking to the OBD port. Multimeter showed "0L" (infinite resistance) across Pins 6 & 14, where it should be ~60 Ohms. The "Aha!" Moment: On 2003/2004 models (specifically my VIN with the 10th digit "4"), the Gateway is inside the Instrument Cluster. It is not a separate box under the dash like later models. The Fault: I traced the wiring and found: Continuity between OBD Pin 6 and the Green Plug on the back of the Instrument Cluster. NO Continuity between the OBD port and the main CAN splice under the Passenger Seat floor. The Fix: I bypassed the broken section of the dashboard harness. Spliced into the CAN High and Low lines near the OBD-II port. Ran a twisted-pair jumper wire directly to the factory splice point under the passenger seat carpet. Result: Resistance returned to 60 Ohms. The scanner immediately connected, showing "No Codes Found" (initially), confirming the network was back online. Phase 2: The "Smoke & Misfire" Scare Symptoms: With the electronics fixed, I could finally see what was happening. Smoke: Massive cloud of White/Grey smoke smelling strongly of raw fuel. Codes: P0300, P0303 (Cyl 3), P0308 (Cyl 8). Scary Symptom: A loud "Ticking" noise from Bank 2 (Driver's side), which often signals the dreaded bore scoring. The "False" Diagnosis: I performed a dry compression test and got terrifying numbers: Cylinder 3: 60 PSI (Dead) Cylinder 8: 100 PSI (Very low) Spark Plugs: The plugs on Cyl 3 & 8 were "steam cleaned"—the ground straps were perfectly white/clean, while the center electrodes were black. The Real Diagnosis (Fuel Wash): I performed a "Wet Compression Test" (added a tablespoon of oil to the cylinders) to see if it was rings or valves. Cyl 3 jumped to 190 PSI. Cyl 8 jumped to 230 PSI. (!) Conclusion: The engine block is healthy! The low compression was caused by Bore Wash. The cylinders were so flooded with gasoline that it washed the oil film off the walls, preventing the rings from sealing. The "Ticking" was likely a dry lifter or piston noise from the lack of lubrication. Phase 3: The Injector Diagnosis I had installed "Remanufactured" Bosch injectors (Part # 0280156101) thinking I was doing the right thing. Wiring Test: I tested the injector harness voltage (Key ON, Engine OFF) to ensure the DME wasn't shorted and holding them open. Bad Cylinders read ~7-8V. Good Cylinders read ~7-8V. Result: Wiring is perfect. The DME is functioning correctly. The Verdict: The "Remanufactured" injectors were mechanically stuck open immediately upon installation (likely due to debris in the rail or just being bad "reman" units). They were dumping fuel, washing the cylinders, and killing compression. Summary of Fixes No Comm/Rough Run: Fixed by running a dedicated CAN-Bus jumper from OBD port to Passenger Seat splice. Low Compression: Disproved engine failure via Wet Compression test (Results: 190/230 PSI). Misfire/Smoke: Identified stuck-open "Reman" injectors. Current Status: Waiting on Brand New injectors. The fuel rail is getting a deep clean, and the gas-contaminated oil is being drained. The 230 PSI result on the "Ticking" cylinder confirms the engine is saved! Hopefully, this helps someone else who sees "0L" on their multimeter or "60 PSI" on their compression tester. Don't scrap the car—check the wiring and the fuel!