donbayers

OK, my new to me 70 LS-5 has been running rough since I got it a little over a month ago.

I did all the general maintenance items.

New R-43T plugs
New cap, rotor
Compression test (170-160 on all)
Rebuilt carb (professionally)
New correct plug wires from Lectric Limited
Set correct timing and dwell according to book
adjusted idle speed needles

Engine still running rough so I did the ole trick last night of running it in the dark.

All kinds of arcing coming from the plug wires and pops of ignition blue flame, especially on number two. So I made sure the boots were on the plugs properly and I still had arcing.

Another strange thing was that I could see blue luminescence at the point were the braided shielding was coming off from around the wire to where it gets grounded to the valve cover.

I can only think of two things so far.

1. Really bad set of wires

2. Something going on with the voltage of my coil causing way too much voltage and the wires can't insulate properly

A. I did not change the coil. It looks like an old standard black coil

B. I don't see a resister/ballast anywhere and don't know if it should have one.

I'm going to look in the books to see what I can read about but wanted to put it out for help.

One of my first thoughts for testing would be to go to the parts store and buy some modern wires and put them on to see how it will run then.

the Part B above has me wondering though.

Thanks for any help

Don

doorgunner

Rookie comment: If the original resistor wire to the coil + has been replaced with a standard wire, it could be producing LOTS of spark.....for a few weeks---until the coil melts....(don't ask...LOL)!

grumman41

Don, I have the original spark plug wires on my 71 LS5 and I get the same arcing. It doesn't seem to affect my engine too much, great power and throttle response.

Kevin

jnb5101

Is the plug gap correct?

donbayers

Ok. Plug gap is .35 per book.

Learned there is no ballast resister only special resister wire that goes to coil.

I put in a standard replacement coil and new standard wire set.

Running the same.

What am I missing here. My brother suggested checking voltage on coil to see what that is. Said if voltage regulator bad then it could be causing it.

Engine Guru's of the CF Unite and help me solve this problem!!!!!

Best

Don.

ajrothm

The problem is the spark plug wires...Not anything else..

Throw a cheap set of regular rubber insulated wires on it and see if it solves the problem... If so, then you know your high dollar repro wires are junk...

I'd be willing to bet the wires are junk..

No such thing as too much ignition voltage...More the better....Just need good wires to get it to the plugs.. As long as you are seeing/hearing the arcing when the hood is open at night, the engine is going to miss...

69Vett

yep wires are toast/breaking down. replace them.

donbayers

I wish that was it but apparently not. I put on Accel hi-temp 8mm wire set very carefully ensuring all plug to wire and cap connections were 100%.

I still have the same problem.

Measured voltage.

Can not running
At Alt is 12.86 volts
On positive side of coil is 7.10 volts with key on

Car running
At alt is 14.20 volts
At coil is 11.10

Keep guessing guys.

Thanks for any help.

MarkEdmondson

I also have a 70 LS5 with M20 C60 PS PW Tilt, Stereo; no PB or rear defrost but mostly original. Do you have photos?

My experiennce is that the reproduction braided plug wires for these cars are crummy. They may be as good as the original ones (don't know; before my time), but they seem to cross fire and leak voltage a lot.

For the street, I've had good luck with Taylor Spiro Pro 8mm wires. I currently have their braided steel custom set for big blocks with black insulation and 135 degree plug boots. They fit in the factory looms and under the shielding, and since I didn't install the SS boot covers (silly looking things) that come with them, they look stock to the casual eye.

What a difference!

http://www.taylorvertex.com/spark-pl...ting?id=219865

The coil isn't causing the arcing you see, but they do break down over time so replacing it with a new one is a good idea. I kept my original coil and repro wires for shows. The car runs crummy to/from the event but is correct.

The original engine harness has a resister wire to the coil, so no external ballast resister is used.

Also, make sure the distributer and its timing are working properly. Lars has a nice post somewhere detailing issues with worn distributers causing sloppy timing. Check the mechanical and vacuum advance calibrations. Past mods (like bypassing the TCS with full manifold vacuum, replacing weights and springs, too much initial timing, etc.) by folks not knowing what they're doing can cause drivablity issues (roughness, over heating, poor performance, etc.)

MarkEdmondson

BTW, the 180 degree bend isn't good for your braided resister wire. Consider rotating the coil to avoid that.

MarkEdmondson

Looking at the photo of the yellow spark plug cables...

It couldn't hurt to use cables of proper length and routed properly so they don't touch the air cleaner, valve cover, master cylinder, each other, etc. Each is an opportunity for arcing.

donbayers

Thanks for the post Mark

I can't vouch for the condition of the distributor but here is what I've done.

Replaced points and condenser

Dwell set at 29-30

New rotor and cap

Read Lars pub and books. Set timing at 6 with vac advance disconnected and plugged on carb side. Per book

As you can see in pic I followed Lars paper and replaced the springs with the ones he said to from the Mr Gasket kit.

I've not found any obvious vacuum leaks and if I pull off the main hose on the manifold and the PCV thing and plug it makes no difference in the way the engine runs.

Did the wires, coil and voltage check above. No help

I'm ouT of knowledge.

MarkEdmondson

If the concern is voltage and cross firing (the light show you mention), then focus on the plug cables. Be sure they are high quality and they are routed properly. From the photos, it looks like this needs attention.

69Vett

the only way you will see Flash arcing surrounding plug wires,
is if the insulation of the plug wires is breaking down. no other reason will cause this.

68Thunder427

Wrong spark plugs. Should be 43N or equivalent not T.

BBCorv70

I have a 70 LS5 as well, shielded wires bought from the dealer back in the early 90's, GM wires, not repops. No issues as the OP is experiencing. I could try starting it up at night, look for arcing.

If there is any arcing it could be due to inductance, voltage being generated on the shield wiring, not leakage from the core.

dochorsepower

Yep, the big blocks had this problem with the original wires even when they were new back in the late '60's. Time to get quality wires.

Zoomin

Hey Don - just curious if the Accel plug wires provide the nightly light show?

MelWff

Looking at the picture of the coil both the bracket for the coil and the bolt look rusty and the screw for tightening the coil is missing. Could you have a poor ground for the coil?
Why did you read Lar's article and replace the springs and then set the timing to 6 degrees initial when you should have set the timing to 36 degrees total?

dugsgms74

Hmm, I have a similiar set-up(lectric limited wires, etc.) and works fine. The only difference is that I got non-resistor plugs(ngk B6ES). Not sure itll make much difference but should lower the max voltage in the primary side.

BTW, you do have a ballast resistor, its the positive wire to the coil, different(non copper) strands that act as a resistor.