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Discussion Starter #1 (Edited by Moderator)
Hey. New member, longtime thread browser, I have read countless threads on this issue, but have never come around a definite cause or solution.

I have a stock 2005 Volkswagen Passat 1.8t, engine code awm, 100,000 mile on odometer with regular oil changes every 4,000-6,000 miles using Castrol edge 5w40, Bosch or mobil1 XL oil filters.

About four months ago I started having a starting issue, felt like the battery was draining well the car sat over night or sometimes over 5 hrs, no flashing or solid CEL, just a drag to the startup. So tested the relatively new battery 12.4v off 14.8v on. This continued for a little over a week and then finally got a code stored P0302, I was in the process of gathering everything to do my 100,000 mile maintenance anyway and had just purchased a bundle of parts off of eBay from someone who had given up on their project car. It came with, new oem NGK spark plugs gapped 0.32, new red topped Audi ignition coils, Bosch remanufactured fuel injectors, urospec 4.0 fpr, new maf sensor, everything needed to replace pcv system, new center exhaust pipe with flex pipe, exhaust coupler and gaskets, (my flex pipe had been leaking and wrapped for several months and coupler is on its way out) green CTS and retaining clip, and dipstick tube, along with a bunch of odds and ends, gaskets, relays, fuses, so on.

I started with plugs and ignition coils and she started right up, all was right in the universe again for about a month and then got P0300, P0302 and was getting a flash CEL at startup, I dove into looking for a vacuum leak and ended up finding that the pcv tube had split perfectly in half right before it goes into the rubber T. Replaced elbow and pcv check valve and again started right up, I patted myself on the back and got another three weeks to a month of no issues till one morning flashing cell P0302.

I then swapped injectors #1 with #2 and instead off getting any results it ran fine for about a week only to have the miss come back to cylinder 2. Now I'm really confused so I decided f**k it I’ll replace the injectors and again starts fine, one week later P0300, P0302. Now I’m banging my head on the hood. I do some reading and read about the dreaded coolant leaking into cylinder 2 and even though I wasn’t loosing coolant anymore because I had replaced my coolant reservoir months before due to a slight leak from a heat crack and the coolant flange before that. I decided to check the plugs and see if I could get a look at the piston, plug #2 was a little fouled and wet with gas as expected with the misfiring and the piston along with #3 had a thin buildup on it, possibly from excessive oil being pushed into the engine from failing pcv components, luckily no coolant. Cleaned everything up and reinstalled and you guessed it started right up!

Two weeks later P0300, P0302, WTF! This goes on for about another month, replace a part all is good, back to misfire and yes I had planned on replacing all these parts anyway and keeping the old parts as backups but hoped something would fix this problem. I came to the conclusion that maybe this is beyond my skill set and tool set, even though I had been maintaining and fixing my own cars for over 20 years maybe this time Germany engineering had gotten the better of me, so off to the only vw mechanic I trust.

He starts with the basics swap plugs one and two along with coils, misfire goes way for two weeks, but he continues to start her up every morning, it misfires once again plugs her into Vag-Com and all systems come up fine, he let’s it sit over night and starts it in the morning no misfire and has started right up for the last month and has been at the mechanics for two months now and has only misfired twice sense he’s had the vehicle, of course before moving into the wiring he would like it to misfire again and I had pulled back the boots on the ignition plugs and everything still looked new so unless it’s a short I’m thinking no need to check the wiring, because how could a single cylinder misfire be caused by wiring unless it’s further up the # 2 wire. Would build up on piston cause misfire and could this have burned off? Am I missing something any input would be much appreciated.

P.s I have replaced almost everything I got in the bundle except exhaust components, and some pcv hoses. I even replaced fuel pump relay and fuel filter, which both ended up clearing up miss from about a week and tested fuel pump and fuel pressure and all were normal. I also pulled and cleaned most of the pcv lines and hoses and evap hoses, intercooler hose from turbo to throttle body, and the throttle body it self. I did come across a small amount of oil in intercooler hose maybe 2tsp and a couple drops at the throttle body inlet, but the intake manifold looks pretty clean and cold and warm compression test came up normal 170-180 on all cylinders.

I’m sure I’m forgetting something, but the stack of notes I compiled over the two months I spent under the hood was more than I could imagine rewriting and more than anyone would want to read, I already feel I should apologize for the novel. ~(;

Thank you for reading and I look forward to any insight or thoughts.
 

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Discussion Starter #3
Thank you for the reply. That definitely is something I should look into, but would I only get misfire at startup if the camshaft position sensor was failing? I counted it out only because I figured that if the timing wasn’t synced I would be getting misfire under load and on multiple cylinders, at this point I’ll try anything.
 

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For this problem to keep coming back to cylinder #2 would indicate a mechanical problem. I would still check the crankshaft and camshaft position sensors and the wire harness supplying the #2 injector and coil. Just to eliminate those as suspected culprits.
I would then do a compression test to verify your statement about the coolant, and also to see if you have a problem with the cam followers on cylinder #2 and or broken rings.
It's a remote possibility one or more of the cam followers have collapsed causing intake or exhaust valve to not function properly.
 

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Discussion Starter #5
Tested the camshaft position sensor and it is within specs. Testing the coil wiring and injectors wiring harness on Monday and checking the levels of Combustion gases in the coolant reservoir just to rule out the coolant possibility. If that all comes back good, doing a leak down test and hopefully that will reveal something. Thank you for your suggestions!
 

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For this problem to keep coming back to cylinder #2 would indicate a mechanical problem. I would still check the crankshaft and camshaft position sensors and the wire harness supplying the #2 injector and coil. Just to eliminate those as suspected culprits.
I would then do a compression test to verify your statement about the coolant, and also to see if you have a problem with the cam followers on cylinder #2 and or broken rings.
It's a remote possibility one or more of the cam followers have collapsed causing intake or exhaust valve to not function properly.
Yeah I was also gonna say that if it isnt electrical (cps), there is a chance that a valve is getting stuck open.
 

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Tested the camshaft position sensor and it is within specs. Testing the coil wiring and injectors wiring harness on Monday and checking the levels of Combustion gases in the coolant reservoir just to rule out the coolant possibility. If that all comes back good, doing a leak down test and hopefully that will reveal something. Thank you for your suggestions!
Did you also check the Crankshaft Position Sensor, the cam position is less likely and doesnt cause too much of a problem.
 

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Discussion Starter #9
I’m thinking that is definitely going to come down to pulling the valve cover and intake manifold if all of the other tests lead to a dead end and start a visual inspection of valves, guides, springs, and lobs. Hopefully not head and head gasket. 🤞
 

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Crankshaft position sensors are only three years old, I forgot to mention that. I will add that to the list of things to check out, I know sometimes even new parts crap out.
Thank you for your thoughts, it’s much appreciated!
 

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Crankshaft position sensors are only three years old, I forgot to mention that. I will add that to the list of things to check out, I know sometimes even new parts crap out.
Thank you for your thoughts, it’s much appreciated!
Ive seen CPS's go in 3 weeks. Especially if its not an OEM part. I still keep a spare in the car. I dont want to bug you about it but its just an easy test before you have to start pulling the cover. Resistance I belive should be between 725 and 1000 ohms.
 

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Discussion Starter #12
I’ll definitely test it! Even though it is a oem part I’m sure they could be defective sometimes too.
 

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Before you start tearing the car apart check the fuel regulator for leak and vacuum. Also check all your fuel injectors for that clacking sound make sure they are actually working properly. Basically what you are looking for is to make sure they all sound the same and have the same rhythm. I'm sure there's tutorials on here to do both those things.
 

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Discussion Starter #15
Before I swapped injectors 1 and 2 I had done a visual inspection of the fuel pressure regulator and vacuum hose and there were no signs or smell of fuel leaking and for good measure I ran the vehicle with the vacuum hose disconnected to no avail and seeing that I had a new urospec 4.0 fuel pressure regulator I replaced it even though the Bosch oem 4 bar still looked good, I also took a long screwdriver and listened to the fuel injectors firing and all sounded to be running in time. Still waiting on the results from the actual firing pattern and timing of the fuel injectors and plugs. Thank you for the response and look forward to getting to the bottom of this. I really miss having her on the road!
 
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