I checked the compression on my 92 Toyota MR2 but I forgot to disconnect the distributor. Now, I am not getting any spark. What did I screw up?
Did you inadvertantly pull the center wire out of the distributor cap or coil? That’s the first thing I’d look at. Then look at the small wires going to the coil. Did either of them get disconnected?
Sometimes electronic ignitions don’t like being disconnected from the plugs they were designed to spark…All that voltage has to go somewhere…
No, and I suspect that’s the problem. I didn’t disconnect anything from the distributor during the compression test.
Yes, it obviously didn’t like being disconnected from the spark plugs during the compression test. So, all that voltage went somewhere . . . and damaged what?
Considering your previous post, you probably didn’t have any spark before you did the compression test. The centershaft bushing on the distributor is often the cause of no spark, it could also be the ignitor. My experience is that when these items start to go, the follow each other so the best bet is to get a remanufactured distributor and be done with it.
BUT, if anything gets damaged from not unpluging the ignitor, it would be the coil. That is pretty unlikely though as people do compression tests all the time without unplugging the distributor and no harm is done.
To check your center bushing, remove the distributor cap and rotor. Turn the engine until one of the vanes on the shaft aligns with the line on the ignitor. Use a stainless steel or brass feeler gauge, 0.010", to check the clearance. With the feeler gauge in place, push on the shaft and see if you can grow the gap. You have to have the feeler gauge in there or you won’t see the gap change.
If you can “grow” the gap to where a .017 fits, the bearing is worn out. You wont get a stable gap between the vanes and the ignitor and you won’t get spark.
The engine ran before the compression test it was just down on power. The compression is around 130 (with normal being 142 to 178) but with 138,000 miles I’m not surprised it is below “normal.”
Thanks for your suggestion. I will check the distributor bearing as you suggest.
To test the coil, use a multimeter, and check the ohms between the primary coil, which is the two small wires, the 12V power and ground wire. The ohm reading should be around .5 to 1.5 ohms. Then test the secondary by using the 12V power and the center electrode. This ohm reading should be around 10K to 14K ohms.
Did you compression test just do one cylinder? You’re supposed to test each cylinder, and compare the results across them all. Plus, since you have low compression in that one, did you add a bit of oil, and do a wet test? This will tell you if that cylinder is low due to rings.
BTW, 138,000 miles is nothing if the maintenance was done correctly. I had a '90 Toyota pick-up with 251,000 miles on it, and compression was good averaged close to 150 psi , with only 7% difference between them. That engine had 325,000 miles on it when the truck was totaled.
Did you have the throttle wide open when you were cranking the engine to get those compression readings? If you didn’t, that’s why they are low.
Also, check the fuses, if you haven’t already.
Maybe you lucked out and it blew a fuse.
BC.
The ignition coil is likely damaged. When the engine is cranked, with spark plug(s), or wires, disconnected, the spark plug wires must be connected directly to ground (the engine block); else, the spark makes a path through the coil windings, to the coil body, and to ground any which way it can.
You probably fried the igniter/ignition module in the distributor. When there’s no place for the high energy spark to go it overdrives the igniter/ignition module where it overheats and is damaged. That’s why they make the calibrated spark testers for checking spark. So igniter/ignition module isn’t damaged.
Tester
Thanks, I’ll take the ignition module in and have it tested today.
The coil (secondary) was fried. I replaced it and all is well. Thanks for your help.
Wow, That is highly unlikely. HV circuits dont have this issue. They are made from tough stuff(like 100,000 miles tough). You cannot over drive the ignition module, does not happen at all. If no current is flowing there is NO HEAT. There can be other issues but heating is not one. Usually a bad capacitor can cause this, but it was already bad just not causeing a problem. You do not need to have the plug wires grounded to do the test but you may need to unplug the computer so that it does not see a fault.
Thanks for letting us know. Most coils are oil filled so cranking them without the center wire grounded usually doesn’t hurt them. Epoxy filled coils, on the other hand, cannot tolerate this.
Thanks for coming back with the news that the ignition coil was fried. If you were to test it further, you might find that the ignition coil is shorted internally. The spark plug wires must, always, be connected to ground if the coil signal isn’t disabled.
Coils, and other voltage transformers AREN’T as tough as most people assume. In fact, they’re rather fragile.