ddubois

I just finished a bunch of maintenance on my recently purchased 59,000 mile, '91 C2 and I'm debating whether I should replace the ignition wires. I changed engine and trans oil, new spark plugs, adjusted valves, new dist. caps and rotors, new dist. belt (it was in fact disintegrated), and I measured the resistance of all the wires. They ranged 2.6 k-ohm to 3.6 k-ohm. There is a slight intermittent miss at low and high RPMs which has me wondering about the wires. The old plugs looked great and consistent across cylinders. I have built my own diagnostic interface and have run DougB's scantool and get no errors or values out of range. Due to some electrical work on the alarm system the DME has been reset, but due to where I live (winter), I haven't had a chance to drive the car and adapt the DME. Likewise, I haven't done the scantool adaptation yet.
Would you replace them?

Thanks,
Doug

911URGE

As far as the resistance I cant comment. Can you hear any "snapping" sounds from the distibutor and have you tried the water mist test in the dark to look for arcing? That may sway your decision knowing these plug cables are not cheap. Arcing plug wires can lead to a host of little gremlins.

springer3

Age and mileage both take their toll. If the wires are original, you are on borrowed time. Resistance is not the story. Insulation breakdown is the concern as high-voltage systems age. Stray arcs are the problem, because they can damage the electronics in a modern engine. I developed the Christmas tree effect the day after Christmas on my 92 at 59,000 miles. I did the fluids, distributor belt, plugs and valves two years ago. I am now doing the rotors, caps, wires, coils, and, of course, new plugs. Who needs a 964 that breaks down in the middle of Alabama, or anywhere else for that matter?

Dave R.

I recommend Beru wires instead of Bosch or other, for the simple reason that the Beru set comes with rubber grommets and various hardware installed (which also pre-sort the wires too).

See e.g. pic here

Bosch set I installed had only the wires.

ddubois

OK. I'm convinced to replace the wires with Beru. But how about the coils? Do they tend to have aging issues? Any suggestions for testing?

TIA,
Doug

Wachuko

When I replaced my wires I went ahead and replaced the coils while I was there... look at it like required maintenance. Several Rennlist sponsors carry a complete maint kit that includes everything but the coils. Add the coils and change them as part as your next service. My two cents of course.

colo964

I think driving for years with bad wires led to my coil failure - just a theory. Seems like if there are stray sparks from the wires, more current goes through the coils, making burning more likely. Sounds like you are in the same boat. Coils are way cheaper and easier to install than wires, might as well, or you might find yourself with a dead car at an inopportune time, all for a $50 part or two.

Indycam

If you do replace the coils , make sure that the new ones are not from Brazil .

I would have a looksee at the old coils before replaceing them , if they are fine looking , why replace .

TR6

I don't disagree with not replacing them if they are fine, but what does a bad coil look like? To me, they've always looked exactly like a good coil. The elements that fail are not visible externally. Unless 964 coils are different than all the other kinds of cars I've worked on.

I know on my BMW 3.2 M series, its well documented that if you let the spark plugs go too long past their service life and the plugs begin to fail, it will cause the coils to fail prematurely. And on a BMW M series, the coils are very expensive...

Indycam

"but what does a bad coil look like?"
Weak spark , tracking around the top , leaking oil , etc .

If the top is clean and smooth / no tracking , is putting out a big blue spark , is dry as death valley , why spend a penny to replace them ?
And if you replace a good euro coil with a Brazilian coil , your doing yourself some harm .

ddubois

I discovered that one of my coils was bad (no spark). FYI, it looked fine from the outside, the only measurement that was off was the resistance across the secondary. It was 2.2 kohm vs. 6 kohm spec.
So when you say Brazilian coils are bad - do you mean the Bosch that are made in Brazil, or some off brand made in Brazil?
Lastly, is it normal for the engine to run better on one of the distributors vs. the other? When I run it on the secondary dist which is connected to the intakes it runs smooth, but when I run it on the primary dist (exhaust spark plugs), it runs like crap. I'm suspecting the wires which I haven't received the replacements for yet. Recall from the start of this thread that the caps and rotors are new.

Thanks,
Doug

Dave R.

No, not normal.

Indycam

Bosch Brazil is an oxymoron .
If you buy a factory new bosch coil for your car , look real close at the label , if it is made in brazil , try to find another .

"I'm suspecting the wires"
How are the plugs ?

KirkF

You could replace just the wires and use your existing ends.

This thread is a link to a person who can sell you the wires cut to length, in a couple of different colours.

https://rennlist.com/forums/showthre...ferrerid=10545

Kirk

Dave R.

Color would be fun, no?

Recommend you try the water mist test in post #2.

I found I had visible arcing (visible in the dark with & without water mist, but more dramatic with mist) between spark wire boots at the distributor cap, so I would not have trusted the insulation of my end boots enough to re-use them with new wires. YMMV.