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Sun Jun 18, 2006
14:37
Well, I thought it would be quite a while before I got a change to post again, but I was wrong! I've been tinkering on our 95 Jetta lately, getting it ready to sell. It was running poorly after I jump started it, so I hooked the laptop running VAG-COM up to the car to look for clues. I've found that the OBD-I Volkswagens are very poor at helping to troubleshoot problems, and this time was no exception. There were no diagnostic codes stored in the ECU, yet the car was running terrible. So I put away the laptop and started troubleshooting the old fashioned way. It had been quite a while since I had thoroughly inspected the ignition system, so I decided to start there. The distributor cap and rotor had a lot of carbon buildup (black crusty stuff) on the contacts, so I spent some time on them with a piece of emery cloth and a small flat-head screwdriver. They're pretty inexpensive parts to replace, but as long as the cap isn't cracked and the cap and rotor contacts aren't worn too much then some cleaning will probably get you by.

I wasn't worried about the spark plug wires, because I replaced them with a quality OEM set when I bought the car a little over 3 years ago. The plugs themselves, however, I hadn't checked since I installed them (at the same time I bought the car, again). It's easy to put off inspecting the plugs on A3 Golfs and Jettas, because the intake manifolds almost completely block access to the plugs for cylinders 1, 2, and 3. The 4th you can get at easily, though. Definitely take the time to disconnect the intake manifold if you want access to the spark plugs, because I can almost guarantee that you'll ruin at least one plug wire otherwise. There's just no way to get a good grip on the plug wire ends with the intake manifold attached, and if you can't get a good grip on the end of the wire, then you'll most likely end up pulling the wire lead out of the end - and then you'll be stuck having to buy new plug wires.

The intake manifold isn't difficult to remove, but there is a lot of stuff that attaches to it. The obvious bolts are the ones in front, in plain view - they hold the upper intake manifold to the small lower section (the small lower section attaches to the cylinder head). For access to the spark plugs, you only need to remove the upper portion of the intake manifold. There are also 2 bolts on the back side of the intake manifold that attach it to a bracket mounted over the exhaust manifold. They're tricky to find at first, but fairly easy to remove. There are many electrical connectors and hoses that will also need to be disconnected - they will vary slightly from car to car (for example, depending on OBD-I vs. OBD-II and whether or not an air pump is equipped, etc).

Here is my upper intake manifold, disconnected and moved up out of the way:
intake manifold removed

Here is a closer look:
intake manifold removed

To get even more room, disconnect the blue electrical connectors from the fuel injectors, and you can pull that whole mess of wires down through the lower intake manifold. The long, plastic clip that guides the plug wires can also be easily removed, which will help a little bit. Here is the same view, but with the fuel injector wiring and plug wire clip out of the way:
intake manifold removed, looking at plugs

After pulling the plug wires off from the plugs, blast around the plugs with compressed air so that no loose debris will fall down into the cylinder bores as the plugs are removed. My plugs all needed to be re-gapped (one of them was a whopping 45 thousandths). If you've never gapped spark plugs, it's easy. Take a look at this picture here:
spark plug electrodes
The "gap" they refer to is the distance between the center electrode and the side (or ground) electrode (the ground electrode is that "L" shaped piece that sticks out of the bottom). Correct gaps are specified by the vehicle manufacturer, so check your shop manual for the specs. Checking the gap is easy, you just need something for a "guage" if you will. A set of feeler guages will work for most plugs, and they're handy to have for lots of other things too. You can also get little guages designed specifically for gapping spark plugs. In any case, the basic idea is to take a small piece of material that is known to have a thickness the same as what the spark plug gap should be, and carefully bend the ground electrode until the piece of material is a very close fit. The end of sparks plugs (around the center electrode) are very brittle, so you have to be careful not to crack it. Make very small adjustments to reduce the plug gap, because trying to increase the gap without ruining the plug can be quite tricky. I decrease the gap on mine by lightly gapping the ground electrode against something real solid, like the head of a large hammer or a metal vise or a large chunk of scrap metal. It usually doesn't take much.

When reinstalling the plugs, make sure to use a little bit of anti-sieze compound on the threads and be very careful not to cross-thread any of the plugs. Be gentle starting the plugs, and don't force them. Watercooled VWs have aluminum cylinder heads, and the threads of the plug are steel. That means that cross threading will do far more damage to the cylinder head than the spark plug. Also, don't over-tighten the plugs or you could strip out the threads in the cylinder head completely. Your shop manual should tell you the correct torque for the plugs, and you may be surprised just how little it is. In general, they should be good and snug, but not very tight.

After I reinstalled the plugs and the upper intake manifold, the Jetta ran a little better... but still had serious issues. Here is the end of this part of the story - stay tuned for the next post to see what I ended up finding and how I fixed it. It's a good one.

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