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The Hobby Car

2003 VW Passat GLX 4motion Wagon

This is my Passat. Looks great but doesn't run. Hence has become a project now. While the previous owner seems to have kept it pretty well with regular maintenance, but the car misfires. The reason needs to be determined. I have a list of the problems that I see for now, and the tests I do to go about diagnosing it. 

Problems

  1. Oil leakage on the Bank 2 valve cover

  2. Misfire on bank 2: Cyl 4,5,6

  3. Bank 1 O2 sensor downstream

  4. Rocking front axle

  5. Vacuum Leak

  6. Foggy headlamps

  7. Ignition cut off when gear changed into Drive.

Error Codes

  1. P0300 – Generic Misfire

  2. P0304 – Cylinder 4 misfire

  3. P0305 – Cylinder 5 misfire

  4. P0306 – Cylinder 6 misfire

  5. P0141 – O2 Heater Circuit (Bank 1 Sensor 2)

Diagnostics

1. PCV System

The PCV system ensures that no excess pressure is built up in the crankcase. The excess pressure can cause the oil to leak from the valve cover. Replacing the PCV valve fixed the oil leak from the sides.

Problems

  1. Oil leakage on the Bank 2 valve cover

  2. Misfire on bank 2: Cyl 4,5,6

  3. Bank 1 O2 sensor

  4. Rocking front axle

  5. Spark Plug wires broken on connectors at coil

  6. Vacuum Leak

  7. Foggy headlamps

  8. Ignition cut off when gear changed into Drive.

Error Codes

  1. P0300 – Generic Misfire

  2. P0304 – Cylinder 4 misfire

  3. P0305 – Cylinder 5 misfire

  4. P0306 – Cylinder 6 misfire

  5. P0141 – O2 Heater Circuit (Bank 1 Sensor 2)

2. Vacuum System
Vacuum lines.png

I couldn’t identify any broken vacuum line or open line to find the leak. However, old vacuum lines were plastic and became brittle overtime. Could easily brake. Replaced them with new vacuum lines that are more flexible and easier to work with. Checked Vacuum pressure at the end at each end of each connection. Seemed to be holding just fine.

Problems

  1. Oil leakage on the Bank 2 valve cover

  2. Misfire on bank 2: Cyl 4,5,6

  3. Bank 1 O2 sensor

  4. Rocking front axle

  5. Spark Plug wires broken on connectors at coil

  6. Vacuum Leak

  7. Foggy headlamps

  8. Ignition cut off when gear changed into Drive.

Error Codes

  1. P0300 – Generic Misfire

  2. P0304 – Cylinder 4 misfire

  3. P0305 – Cylinder 5 misfire

  4. P0306 – Cylinder 6 misfire

  5. P0141 – O2 Heater Circuit (Bank 1 Sensor 2)

3. Foggy Headlamps
Foggy lamps.png

This is an easy fix hence I did it quite in the early stages. It was a 4 step process with an online available DIY kit

Problems

  1. Oil leakage on the Bank 2 valve cover

  2. Misfire on bank 2: Cyl 4,5,6

  3. Bank 1 O2 sensor

  4. Rocking front axle

  5. Spark Plug wires broken on connectors at coil

  6. Vacuum Leak

  7. Foggy headlamps

  8. Ignition cut off when gear changed into Drive.

Error Codes

  1. P0300 – Generic Misfire

  2. P0304 – Cylinder 4 misfire

  3. P0305 – Cylinder 5 misfire

  4. P0306 – Cylinder 6 misfire

  5. P0141 – O2 Heater Circuit (Bank 1 Sensor 2)

There can be a whole bunch of reasons for misfires. From here onwards I try to go with all the checks that you would for a misfire diagnosis. Critical observations here are that the misfire Exists in all cylinders of one bank. That is a good starting point, but while I can, I check all the components as I go. 

4. Spark Plugs

Physical Inspection

Spark plug.png

Visual

In the visual inspection I am looking for the gap between the center electrode and the grounding electrode (aka electrode gap) which seems to be perfectly fine. I am also looking for any signs of oil / fuel breaching and the color in general of the plugs. I am also looking for any settlement / burn marks around the center electrode to indicate the health of the combustion.​

Smell

Smell test is a little tricky but combined with the visual test for any burn marks/ settlement can he helpful. I got a strong smell of unburnt fuel which could indicate the rich mixture before burning or the spark plug inadequately or only intermittently igniting the mixture.

Spark Test

Spark Test.png

In this test, I pulled out the spark plug and disconnected the corresponding injector to avoid unnecessary fuel. I grounded the grounding terminal of the spark plug and cranked the engine. I repeated the exercise with each cylinder. I found that all the spark plugs were igniting just fine.

5. Cylinder Compression 
Compression.png

It is also possible that there is damage to the cylinders, and they are not holding pressure which is why the rpm won’t rise above 3000. The compression tool is plugged into the spark plug thread and the engine is cranked for a few seconds. The pressure should be around 190 psi and should be consistent throughout the cylinders. This seems to be the case, which would imply that the engine in fact is good.

6. O2 Sensor Swap

The error on the OBD tool indicated that Bank 1 Sensor 2. The downstream sensors exist only for emission reporting and do not have any role in controls. However just for the sake of covering all bases, I swapped out the O2 sensor to see if the error persists. I swapped out the O2 sensor without plugging it in, essentially simulating perfect air. It seemed like after plugging in the sensor, the error for the O2 sensor went away, however the engine did not run any better.

7. Wiring Harness

The whole of bank 2 misfiring can also indicate the error with the harness going to the bank 2. To check if the electrical wiring is okay, I did a continuity check by connecting the positive of the voltmeter to the wire injector connector and the negative to the ground (vehicle chassis). The wires seem to be continuous and hence this is not the problem.

8. Spark Plug Wires

Wires:

Spark plug wires can also be a source of shorting near the metal body of the engine. This can be due to worn out insulation. This can be checked via spraying some water at the wires and looking for any sparks. The vehicle passes this test as well. This indicates that insulation of the wires is not the problem.

Spark Plug wire connector.png

Connectors:

The next test is to visually inspect the wires at the connector ends. After plugging the wires from the coil pack, it was noticed that the wires were broken from the edges. This could cause a loose connection during vehicle operation causing intermittent missing. It might be worth replacing these wires.

9. Fuel System

To check the misfire and the ignition cut off for drive gear I checked is the fuel system. There are 2 things that could be going wrong.

Fuel Pressure Check:

Fuel Pressure.png

Insufficient fuel pressure can be due to a problem with the fuel pump or a clogged fuel filter. I replaced the fuel filter and checked the fuel pressure with a pressure fuel pressure gauge. Although,  a clog in the fuel line would cause misfires in all the cylinders, but its good to check for peace of mind. 

Clogged Injector:

Clogged Injector.png

A clogged injector can also cause misfires. For this test, I pulled out the injector rail with the injectors connected and cranked the engine. I was looking for the fuel exiting the injectors on the tissue placed underneath. It seemed like all the injectors were firing. However, when I repeated the test, the injectors on bank 2 did not fire. On repeating the test for the 3rd time, I found that all of them firing again. This is concerning because intermittently occurring issues are the hardest to diagnose. There might be something wrong with the wiring or the computer.  

10. Visual ECU inspection
ECU.png

Watermarks: Over time water can cause rust on the metal parts. This can cause the metal parts to break causing.

  1. Short Circuit: While the ECU is covered under a properly protected weather box, water has entered at some point due to a leak or temporary removal of the ECU.

  2. Insufficient supply of current to a specific cylinder causes the misfires.​

Physical damage:

  1. Any physical damage to the outer body and hence the motherboard can cause unpredictable behaviour.

  2. Broken pins at the connector end can cause missing signals essential for the right vehicle performance.

 

Results: From the visual inspection the ECU seems to be alright. No marks no water signs.

11. Upstream O2 Sensor
O2Sensor upstream.png

​Although unlikely the pre-cat oxygen sensor might be causing the problem since is not reflected on the OBD scan. To eliminate the concern, I loosened the O2 sensor while the vehicle was running and checked for performance differences. Loosening the O2 sensor enough to let the outside air have enough space to move in was enough for the vehicle to show an evident difference in performance. This rules out the bank 2 upstream O2 sensor from being the issue.  

12. Cam Timing Adjuster Solenoid

This diagnosis is to check if the cam adjuster solenoid on bank 2 is operating fine. I followed three steps to ensure it worked fine.

  1. Resistance

CAM adjuster.png

While the exact value of the resistance through the solenoid is unknown, I use the solenoid of working bank 1 as a reference and compare. The result was that both the solenoids were at the same resistance. While the exact value of the resistance through the solenoid is unknown, I use the solenoid of working bank 1 as a reference and compare. The result was that both the solenoids were at the same resistance.

 

2. Swapping solenoids

 

The next way to verify is to isolate the solenoid and see if the issue follows. This can be done by swapping out the cam adjuster solenoids of the two banks and seeing if the misfiring now happens at bank 1. On swapping the solenoids the issue still stayed with at bank 2 indicating the solenoid is not the problem.

3. Cam adjustment degree

Cam adjustment angle.png

In this test, I check the cam adjustment angle with a scan tool. The cam adjustment angle when the vehicle is idle should be between -3 0KW and 6 0KW. It seems like the values for both the banks are in the range but have a 3 0KW difference between them (-5 0KW and -2 0KW for banks 1 and 2 respectively). While I don’t know what the defined specification of the adjustment should be, it might be worth getting both aligned to the same angle and observing the difference. But before that, it might be worth checking the cam adjusters themselves to see if that is the reason for this misalignment.

13. Plugged CAT
Exhaust_Cat.png

Noticing some exhaust smell and my friend Niko pointed out the exhaust coming out of the intake. This is an acute case of plugged catalytic converter. He removed the oxygen sensor on the misfiring bank and violla, misfires vanished. This is a moment I will never forget, my first success after months of disappointing results. 

Reason: Since the exhaust was completely plugged, exhaust air was pushing back on the exhaust valves at the bore, This caused cylinders to not produce enough vacuum to pull in air and not combust properly. The exhaust air found its way back to the intake. 

The previous test on the oxygen sensor did not bring out the same results because the O2 sensor was only loosened and not removed completely. Since the CAT was completely plugged, the loose threads in the sensor fitment were not enough to let all the exhaust from 3 cylinders out at the rate it was supposed to. The pressure of the exhaust out of the O2 sensor hole was very strong and given the strength and heat, it is not wise to let it on for long. There are electrical wires on top of it that can melt. Considering the age of the car finding a harness would be just as hard.  

No Misfire.png

Measuring blocks 15 and 16 gives the misfire counts in bank 1 and bank 2. All indicating 0 is very satisfying to watch. Given the condition of the CAT, air pressure cleaning would not work. The cascading effects of misfires and heat from incomplete combustion caused the CAT to melt into a plug. Hence a 'plugged' CAT. 

The vehicle had gone into limp mode because of the misfire issue. It is quite possible that the vehicle would cut off fuel when pushed into drive. The reason is unknown but the car seemed to drive with the issue gone, so problem number 7 was also resolved. 

Solution: The only solution is to get a new CAT. The car has 2 banks, the CATs from both banks merge into a muffler/resonator before splitting into 2 exhaust tips. All I need is the driver-side CAT which has the preCAT and catalytic converter.

Problems

  1. Oil leakage on the Bank 2 valve cover

  2. Misfire on bank 2: Cyl 4,5,6

  3. Bank 1 downstream O2 sensor

  4. Rocking front axle

  5. Vacuum Leak

  6. Foggy headlamps

  7. Ignition cut off when gear changed into Drive.

Error Codes

  1. P0300 – Generic Misfire

  2. P0304 – Cylinder 4 misfire

  3. P0305 – Cylinder 5 misfire

  4. P0306 – Cylinder 6 misfire

  5. P0141 – O2 Heater Circuit (Bank 1 Sensor 2)

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