ignition problem

[JeffW]

Can you use any coil type? Like say a accel or MSD coil? Also do I need to change ignition module with coil? I posted earlier about my car missing when hot, does fine on the interstate or at high speed but in traffic it builds up heat and misses or dies.

Thanks,
Jeff

[Early_S_Man]

With the stock Bosch CDI-system ... NO!!!

[CamB]

Warren is pointing you in the direction of the correct Bosch coil. You know you have found the right one because it is the most expensive coil in the world (3x the price of a normal one!).

But.... it may not be the coil.

What sort of condition are your ignition wires? Any "corona effect"? Do you know how to check the condition of the Beru connectors (search for "Beru")?

A few people (me included) have had Berus which failed as the engine got hot. The Berus are the resistor connector on the spark plug end of the wires.

I guess we need more info...

[RoninLB]

I smashed open a few old Beru connectors. Man, I don't like the design....all those little parts waiting to cause problems... What does the serious mechanic do besides putting a meter to them???

[Early_S_Man]

You put the engine on an ignition scope or analyzer ... and can see the output 'LIVE' and tell if any individual cylinders have problems!

A really well-equipped shop (quite rare) can put the car on a chassis dyno and look at the ignition system under loaded/simulated driving conditions!!!

[JeffW]

My plug wires "appear" to be in good shape. They are the ones with all of the ground cables on them. The car starts doing this after it get up to temperature in traffic. If I drive on the insterstate for extended periods it seems ok but if I try and stop the gas alitttle I can feel it hesitate. I had it die on me in a drive-thru line the other day and it wouldn't start until I let it sit for a while. Can I install an MSD 6a and coil and get rid of the bosch? I'm not sure what to replace this stuff with.

Also... I don't want to spend an outragous some of money on this since I plan on putting a 3.6L in by end of summer...

[CamB]

If you went to an MSD 6a and high vibration coil, and the Berus were intermittent (ie non-functioning when hot), you will have EXACTLY the same symptoms.

Ask me how I know...

I am the source of an unsubstantiated rumour that MSD units are very hard on aging Beru connectors too.

The hard part for you is that the problem only happens when the engine is hot. This makes it tough to test.

[Targa77]

Try this site http://www.permatune.com/Technical%20Support/Porsche/911.htm. It has a lot of useful info even though you may not be using a Permatune CDS box.

[JeffW]

where are these Berus locatedand what do they do? I've never heard of them.

[Targa77]

http://www.pelicanparts.com/catalog/shopcart/911M/por_911M_igniti_main.htm. Also do a search for Beru under a search engine and you'll find lots of stuff out there.

[Superman]

If your ignition wires are 25 year-old factory wires with grounded stainless steel braided covers, then I'm betting they are not doing the job. AT LEAST remove the SS braid (it is not needed) since this is likely to be grounding some of your sparks, causing misses. A better fix would be new wires, but with the braids off at least you could see the arcing at night.

[steveW]

A quick check on plug lead condition is to run the car at night (in the dark) and watch the light show - can be pretty spectacular!

This by no means accurate, but if you see the show, replace the wires.

cheers

[JeffW]

So wires without the grounds are better? For some reason I thought they were needed.. Maybe I'll do a tune up on the engine then...

[JeffW]

yes? no?

[CamB]

The groudns were installed by the factory to reduce RFI. No-one KNOWS whether they do much, but it appears not.

Steve Weiner at Rennsport Systems recommends Magnecor wires as replacements (especially with MSD units). They aren't cheap (at $150ish), but are less expensive than factory ($200 from Pelican??, no braiding).

Alternatively, you could test the Berus, which look like this:



This might prove fruitless if it only happens when hot though...