my 91 Passat GL just died on the highway yesterday. It was running at
70 miles per hour and then the engines shut off. It did not overheat, there is enough oil. It seems to be no spark. I took the wire off the spark plug and tested it on the engine as ground. No spark. When I turn the key and the car is in gear it does move, the battery is brand new and not discharged. The starter is rotating. All belts are ok. I took the distributer cap off and everything looks fine too including rotor.
What else could go wrong? Ignition coil? ECU? Any other tests one would recommend?
1) Distributor -- This is easy to test. Just take the coil wire off the distributor cap and see if you get a spark from there when you are cranking. This will check both the distributor and the plug wires. Its probably more likely the distributor than the plug wires, cause a single plug wire isn't going to stop the car, and what are the chances that multiple plug wires failed at once.
2) Hall sender -- This is a little tougher to check, but definitely neccessary. The hall sender (on the distributor) has 3 pins. The two outer ones are power and ground. Verify on a volt meter that the harness is supplying these properly (with the ignition turned on). If not, suspect a broken wire or ECU or something along those lines (bare in mind, I think ECU failures are unlikely). Once you've verified good power/ground, figure out a way to monitor the center pin with the harness connected. This is tough without a special adapter or something. I've found that you can get good results by sticking a wire in, just make sure you're only on pin #2. With the ignition on, slowly turn the engine. Pin #2 should switch between about 10 and 0V (4 times per cam revolution, or 2 times per crank revolution). You can spin the engine either by putting the car in reverse and pushing it backward, or spin it with a ratchet with the car in neutral (to make it easier you can remove the spark plugs so you aren't fighting compression.
3) Check coil resistance: primary (1 to 15) = .6 to .8 ohms, secondary (4 to
15) is 6500 to 8500 ohms.
4) Remember, its always possible the coil wire failed.
(Also, I'm assuming the engine sounds normal when you are trying to start, as opposed to spinning really fast which would indicate your timing belt went).
1) I took the coil wire off the distributor and tried to start the car. There is no spark going to the engine.
2) The engine speed seems to be normal - not fast. I havent checked if the distributor rotor is actually rotating - but I did take off timing belt cover and checked that the tension is ok. Also when I put the car in gear and try to start it it does move forward. Isn't that an indication of the fact that the timing belt is ok?
Will try do the rest of the stuff tomorrow. I guess a) check the coil resistance b) check the hall sender all is what I can do.
I am wondering about this part. Taking the coil center wire off of the distributor would cause no spark to go to the engine if you just pulled the wire from the distributor, but had a large spacing from that wire to engine metal. I think what was being suggested was to unplug the high voltage coil wire from the distributor and arrange things so that the free end had perhaps 1/8 inch (4 mm) to the engine block, and to watch in dim light to see if there was a spark.
That is probably what you did, but I just wanted to make sure.
MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.