Sunday, April 19, 2009

spark test

Plan for today was to paint. Minivan had other plans - it was once again doing a solid impression of a heavily-graffitied rock, and we discovered that the ignition problems really are a lot more serious than a dead battery. (First bad sign: JDH put the suspect battery into the other junker minivan, his Town & Country which sounds like there is an angry man inside the engine with a baseball bat, and it fired right up.)

So we went back around with the usual round of troubleshooting: battery is sending voltage? Check. Coil is getting voltage? Nope. Spark plugs are sparking? Nope.

Excellent, replace coil. Reassemble.

No spark. This is a massive sad.

For the historical record, and mostly as a note-to-self, here's the rough order of things tried:
  1. Car does not start. Massive sad. Starter cranks, slowly.
  2. Jump battery. Starter cranks much faster. Car does not start. Last time we waited a while and tried again, and it worked, so we were like OMG YAY!!!!11!! and burned rubber around the parking lot and celebrated victory and then called it a night.
  3. Test current to positive side of ignition coil. Intermittent before, now zero.
  4. Look up wiring. Discover that current in to coil is controlled by a relay, the Automatic Shutdown Relay, or ASD. It shuts off current to the ignition coil, the fuel pump, and the injectors when the key is on but the engine isn't running.
  5. Look up ASD on internet. Discover that it basically connects red wire (J2) coming from battery, to green-and-black wire (Z1) which powers the rest of the motor.
  6. Hard-wire red wire to green-and-black wire. Fuel pump now audibly runs whenever the key is on! We now get 12V to the coil while cranking the starter! Car still does not start.
  7. Grrr.
  8. Test spark plugs (again) to see if they are making sparks. They are not making sparks.
  9. Pull ECU, which in this car is amusingly called the SMEC. Stare at it dubiously.
  10. Try all of those previous things again, in lots of different orders. Halfheartedly price replacement SMEC.
  11. Go back to reading about computer, and start testing wires. The negative side of the coil connects back to the SMEC as well. The computer provides ground to the circuit, and sometimes suddenly removes the ground, which causes the coil to dump all of its accumulated charge onward, thus powering the distributor. The moral to this story is that even without the ASD, the SMEC needs to be happy in order for the whole thing to work.
  12. Figure out how to make the check engine light blink out the numeric codes which indicate why it's firing. Look these up. Discover it's complaining about several things, including the ASD relay. Yeah yeah, we know.
  13. Following instructions from the internet, we hard-wire pin 10 on the SMEC to the output of the ASD, which happens to be the positive wire to the coil, thus bypassing the ignition part of the ASD cutoff entirely. Heh heh. 12V to the coil all the time now, bitches. How you like me now?
    (Secondarily: JDH notices that the ASD is clicking on at startup, then immediately off again. This seems suspicious, like the cpu is seeing something it hates, and getting angry.)
  14. Car does not start.
  15. After some research, discover that there's another sensor, a really important sensor, called a Hall Effect sensor, which lives inside the distributor. Its job is to detect the distributor firing off spark plugs, and send this back to the SMEC, which uses it to get timing information. (Newer vehicles just use crank or cam position sensors.) If this sensor is not working, the cpu will stop the engine from firing. Remove sensor, clean it, try to test. Perfect continuity on the wires to the sensor. The sensor itself starts to fragment during cleaning. Bad sign? Maybe. It's just a little plastic UFO with lots of fragile wires in it.
  16. Discover that the guy at Kragen has never heard of a "hall effect sensor", nor of an ignition reference sensor or distributor sensor (its pseudonyms), nor can he look one up, or order one. Same for Autozone, and, disturbingly, the same is apparently true for parts stores on the internets. Pick-n-pull it is, then.
  17. Sad!
  18. Clean up. Try to start the van a few more times, just for the hell of it. Sadly this does not work. How cool would it have been if it did, though?
  19. Beer and tacos.
Some links which turned out to be incredibly useful in this process (the heavily-tabbed Haynes manual that we inherited from the previous owners being largely useless):
Update: Yep, totally the HEP sensor. Jdh installed a pick n pull special, and she fired right up. :-D

1 comment:

  1. Hey boys - sorry to hear about your problems with the pickup coil (hall effect sensor). Idiots at Autozone and Kragen should have had no problem finding it. Autozones number is a CR121 and is $50. Yeah, I'd have got it from the junkyard too. Make sure you grab a spare one for the race! Also make sure the one you get is the same as the one you have - the newer 2.5's use a different sensor and wont interchange. I had an '89 Caravan turbo back in the day and totally miss it. We'll see you in Reno! (Rich from Team Chevy High Performance)