Tuesday, March 22, 2016


A couple of weeks ago, I had the $500 Jetta suddenly stall in the driveway. Today's post covers the root cause investigation.

P0341: cam position sensor
P0422: o2 sensor
So, Boo is standing in the driveway next to her idling 2001 VW Jetta (named 2dot0) when it suddenly stopped running. There was no special noise, nor did it gasp on it's way down. It was just running one second and not running the next. My mind ran through a few scenarios, but I landed on electrical because of how quickly it shut off.

What You Should Do
Since a gas engine runs with the correct combination of fuel, air, compression and spark, These are the things that should be checked, and checked in that order, before you start swapping parts... even if you think you're sure you know what's wrong. If you have a more modern car, get a code reader and pull the codes from the computer. Sometimes, the computer won't give you a code for a while. I didn't get these codes here until after I'd figured out what was wrong through the steps below. The P0341 code confirmed my findings.

fuel pressure regulators
(new on right)
Simply put, verify that you have fuel at the injector. To radically simplify things, I verified that I had fuel at the fuel pressure regulator by removing the regulator and letting the fuel pump cycle. I had fuel bubbling over. Pulling an injector can be difficult, so for me, this demonstrated that I had fuel at the rail. The probability of all 4 injectors clogging so badly that the fuel wasn't making it to the chamber was so low, I ruled out fuel, but replaced the fuel pressure regulator anyway since the old one fell apart on extraction (see picture).

Check the air filter. It is completely clogged? It's probably not the issue. Check the "snow snorkel" that runs from the air box to the outside. Sometimes something can get jammed in there (like snow), preventing the engine from getting air. Remove some intake piping between the air box and the metal bits so you can see the little gate on the air intake. When the foot pedal is moved, does the flap move? You're probably getting air. This would be a good time to check the air sensor. This usually would throw a code, but to verify it isn't that sensor, unplug it and try to start the car. If it starts, that sensor is bad. The car will run without the sensor, but badly. Sometimes this sensor can prevent a start, but that wasn't the case with me. I ruled out air, and put everything back together again.

This is where I should have checked compression, but I was convinced it was an electrical thing, so I skipped ahead to Spark. Don't. Checking your compression is easy, and it reveals some very interesting info about your upper end, the mechanical timing and, possibly, a lower end issue.

2.0 ignition coil
Grab your compression tester (they are pretty cheap, if you don't have one) and test your cylinders one at a time. It's best to remove all four plugs, and test each cylinder multiple times. Take care how you manage your plugs and wires so you don't set yourself or your car on fire nor do you lose track of which wire goes where. Unplugging the coil is the simple solution. Anyway, if you get any reading under 100psi, try squirting a little oil into the cylinder and retest. If the reading is better, your rings are going and you'll need a bottom end rebuild soon. Start saving. If the reading doesn't change, its a valve-train issue. Assuming all of your reading are within 15% of each other and they are all above 100psi, move on to fuel.
Had I done this step before Spark, I would have found all 4 cylinders at 0 PSI, indicating a broken timing belt. This was verified by removing the timing belt cover and not seeing the belt. Yikes.

Remove the spark plug that's easiest to get to. In the 2.0 engine, that's #4. Take care how you remove the plug wire. Now, with a partner turning the key, hold the plug against the engine block (forming a ground) and watch for the spark. No spark? Could be your issue. I was way overdue for a tune up, and the plug socket fell off the plug wire when I touched it, so I concluded replacing plugs and wires was a good idea. 2dot0 still didn't start. I should already have checked compression, but still, I should have stopped here and gone back to it. I continued down the electrical gremlin path instead.
The new plugs and wires didn't do it. So, I got a new coil. And then a new battery. And finally a new crank position sensor. Still no start.

no, I'm not a Packer fan
It wasn't until I got to this point that I reverted to the compression tests and learned that I had just thrown over $100 of new parts plus a battery into a large boat anchor. The timing belt broke, throwing off the timing and causing the valves to hit the piston tops. The engine was effectively blown. Tiny fragments of valve and piston will work their way into the deeper recesses of the engine while the breaking belt could have damaged rollers or the coolant pump. I sold the car for scrap and its gone.

Watching 2dot0 get towed away, I ran a quick accounting. I bought the car for $500, and had it running for another $30. Since then, I only bought tires and oil, so that's probably another $600 or so. Rounding up, I was probably into that car for $1200 before it broke and then threw another $300 into it. That's $1500 for a car including maintenance for 18 months minus the salvage I was paid, means it cost me less than $70/mo. Since you can barely rent a car for a weekend at that rate, I think we did extremely well. I just wish I had performed the timing belt maintenance.

That's all for today. After 2dot0 broke, I served my penance for not doing the timing belt by riding mass transit for a few weeks. Today was my first day back driving to work. It is such a luxury, though I do kind of miss the light rail. Thanks for following along-

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