How big a spark should there be?

strupgolf · 07-18-2006, 05:02 PM

Searched but didnt find. I'm trying to find a miss of my 86 3.2 911. I pulled the plug wire off and installed a good plug into it, held the wire, and started the motor. How big a spark should there be? It is so small that it's hard to see the spark. I thought there should be a big bright arching spark but no. Any ideas on this. The rotor and cap seem to be fine and fairly new. Oh, and when I hold the wire, should I hold it to a ground, or just let it lie on a towel. Thanks

Early_S_Man · 07-18-2006, 05:21 PM

Here is the test spark plug I recommend ... and, YES, it should be grounded!

KD Tools 2756 or 2757:

defcon65 · 07-18-2006, 05:55 PM

Sparks should be bright and blueish, visible in daylight. Reddish to yellow can indicate a weak coil or ignition module. Check the ground connections too, that can cause a miss sometimes.

strupgolf · 07-18-2006, 06:26 PM

I could barely see the spark at dusk, but again they were'nt grounded like Early s said. I just held the plug wire with a channel lock with a new spark plug attached to the end. At start-up, it really POPS loudly, and then calms down some. But its still there when driving. Where should I check for the ground connections?

911pcars · 07-18-2006, 07:30 PM

A good spark should be quite audible too. A loud snap is good.

Sherwood

Eagledriver · 07-18-2006, 08:14 PM

The spark should jump at least a quarter of an inch to ground. You can check other cylinders to compare.

-Andy

lateapex911 · 07-18-2006, 10:10 PM

Well, if the plug isn't grounded, the spark isn't going to be very strong, LOL. Test again, but with the plug grounded. Imperitive.

defcon65 · 07-19-2006, 06:17 AM

Strup, you can check the ground strap from the engine to the body and see if it is loose or corroded but from your description of a weakening spark, it's probably the ignition module in your 86. Test the spark by laying the metal body of the plug against a good ground, like a metal engine component when you crank the engine. A miss could also be a bad fuel injector, though - have you had those tested/cleaned? Is the car high-mileage?

Superman · 07-19-2006, 08:08 AM

I'd pull the wire from the center of the distributor cap and hold it (using insulated pliers) near a metal engine part. Have someone turn the engine over. The spark should be blue, snappy and should be happy to jump at least a half-inch. I've seen them jump more than two inches.

defcon65 · 07-19-2006, 10:04 AM

I checked Pelican's parts catalog and it looks like the factory ignition unit is not available for your car if it is indeed bad. You might try the aftermarket MSD ignition; a lot of Pelicans use those.

strupgolf · 07-19-2006, 02:12 PM

Thanks for the help guys. Yea, it SPARKS when you ground the plugs. I get good spark to all plugs so I dont think its the wires, great!!. Now, I've run a can of FI cleaner for about a hour, but it still POPs. How do you check for a bad injector, it could be that.

911pcars · 07-19-2006, 05:50 PM

"How do you check for a bad injector, it could be that."

To help isolate a weak, non-contributing cylinder, perform a cylinder balance test. With the engine at a high idle, disconnect a spark plug wire one by one and note how much the engine speed drops each time. The cylinder that drops the least is the one not contributing. That could be due to a bad plug wire, poor cylinder compression, bad plug .... perhaps a faulty fuel injector. Don't run the engine too long with a disconnected plug wire - it puts a strain on the ignition system if the 15,000 volt spark can't find a ground. Unburnt fuel also collects in a disconnected cylinder.

You can perform the same test by disconnecting each injector harness connector in turn. That might isolate a faulty injector. Swap injectors in cylinders and retest.

Sherwood