TheOtherEric

Maybe this is a dumb question...maybe not. I posted recently about visible arcing between my king lead and the distributor cap. After trying a couple times to re-seat it, I'm still periodically seeing arcing. So out of curiosity I just unplugged the king lead altogether, fired up the engine, and it ran pretty much the same. Huh?!?! No difference. Still a little on the rough side. Is it possible I'm running on 6 plugs and losing power? How can I check this, apart from buying an oscilloscope? Any advice appreciated!

chris walrod

Without loading the engine, it may be difficult to tell a difference when running on 12 vs. 6 plugs. To verify the dizzy belt is not broken, unplug one coil wire, run the engine. Then turn engine off, reconnect that coil wire and unplug the other, run the engine...

Not sure if that helps. You may need to replace the plug wire altogether. At least ohm them out to see if you have a wire or two that has high resistance..

Steve Weiner-Rennsport Systems

Eric:

The engine will drop about 150-200 RPM at idle if its running on 6 plugs.

To check the drive belt, simply remove the lower cap and see if the lower side rotor spins freely. It should not,....

You didn't say how many miles are on your car but you have more than 50K on the original set of wires, I would respectfully suggest that you consider investing in a new set.

Plug wire arcing causes misfires which are VERY hard on the catalytic converters.

Derrick B.

Is there a warning light that tells us if the distributor belt is broken? I thought we'd get a light on the dash if that happened.

Randall G.

Nope, no warning light. Other than pulling coil wires (as described above) or performing a visual inspection, the only way you'll know is the engine running poorly. When the belt broke on my old 964 engine at about 75k miles, the engine had some low-RPM stumbling, and felt lethargic in general.

Oh, and for the distributor check (expanding on what Chris has written). As I understand it, the engine will run on only one distributor. If you pull a coil wire, and the engine won't start, that suggests the connected coil/distributor is bad. If it's the secondary distributor that's connected, the belt is likely broke, and is no longer being turned by the shaft.

I replaced the caps and rotors on my car Sunday, and the 48k miles belt was in perfect condition. I'll post pictures later today.

TheOtherEric

The engine will DEFINITELY run on one distributor. I think I noticed what Steve mentioned-- that the idle RPMs were a tad lower when I disconnected the top distributor last night.

So if you're running on 6 plugs and you pull one of them (thus disabling 1 cylinder) will that cause a failure to start? Right now I'm thinking that I am running on all 12 plugs, but the arcing at the king lead is really confusing. My car has 42k miles, by the way.

flatair

As Steve pointed out, make sure your wires are in good shape, that is key. I even put a 'cheapo' replacement set of wires on my 73 911S that were actually faulty - one of the end connectors broke internally and was not even firing one cylinder (the spark plug was squeaky clean!). Incidentally these engines are so inherently balanced that I couldn't believe it ran so *smoothly* on 5. After that little incident I bought a nice set of Magnecors.

Brad

Rick Lee

Another way to check is if you have a local shop with the Porsche factory tester. A few in this area have them and at our last PCA tech session, Roger and co. from Autotherapy were checking fault codes for all us OBDII folks for free. When they did my car, they were able to shut each cylinder down, one at a time. Slight drop in idle for each one, but it confirmed they were all working and showed me what it would feel like if one failed.

Randall G.

Eric,

There's lots of great information on the belt here:

http://www.porsche964.co.uk/technica...r_vent_kit.htm

Written for a 964, but applicable to the 993, as well (except for the vent-fitting part).

Incidentally, my belt looked just like the one in the picture provided by Thom Fitzpatrick.

TheOtherEric

Wow, thanks for the info guys. I guess I might just need to make a trip to the [cringe] dealer. Rick- do you happen to know if they have some standard set of diagnostics to check that everything is working properly?

kkim

Couldn't you just use the inductive pickup of a timing gun on the plug wires to confirm if signal is passing through them? If the timing gun flashes, you have spark... no???

Rick Lee

Eric, there has to be a cool indy in your area who would run your codes for you. The factory tester has some program that runs through everything.

I would let my woman (who can't drive stick) take my 993 to Jiffy Lube before I ever take it to a dealer. They are incompetent thieves. I'd feel less robbed if they used a gun on me.

Ron

If this test is done are you just confirming that the belt is intact? Or can you see it to determine how it actually looks too? Like is it cracked and ready to break?

Randall G.

Hey Ron,

It's not the end of the world to get to the belt, but it's not as simple as checking your oil, either. You have to remove a couple connections (e.g., for the rear shift valve, rear blower temperature sensor), remove some ducting, take off the caps without stripping the screws, remove the rotor, finally the shield. This is all described on Robin's website, besides the link I put above. Here's a picture of a good belt, copied from that link:



If you're just looking to verify the belt is intact (as opposed to its condition), removing the primary coil wire and making sure the car still runs (on the secondary distributor only) is a much easier way to go.

Ron

Thanks Randall, I think I'm going to inspect that belt in the near future. I've read that they might should be replaced when 5 years old. My 97 has 12K miles and I wouldn't think it would be necessary unless the material that the belt is made of degrades substantially over time, which it may.