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Spark plug issue???

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Morris

Morris

Yoda
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Okay, so my car has been doing weird things lately. It surges when cruising through town. And on the highway, it is experiencing radically shifting AFR (air/fuel ratio). Coupled with this is an erratic vaccum signal which bounces up and down a few CmHg then settles, then bounces around.

I checked for vaccum leaks as well as checked timing and compression. Everything looks good. I checked the plugs. They had a thick reddish brown coating (indicating a good clean burn, right?) which I removed with a wire brush. After I did this, the vaccum signal and idle seemed much more stable.

I have a new generic brand coil and an old Luminition system. I am running Bosch Platinum plugs gapped to .31.

This one really has me stumped. Do any of your brilliant minds have any ideas as to where I should look next?
 
Ditch the platinums dude......

Go fur NGK BP6ES gaped at .025 /ubbthreads/images/graemlins/thumbsup.gif
 
HooBoi... I agree with Dave... 0.025"~ 0.028" but no more. The colour you're wanting to see is close to "Cadbury light". /ubbthreads/images/graemlins/grin.gif

...can't believe I said that. /ubbthreads/images/graemlins/devilgrin.gif
 
Cadbury light?........What happened to almond brown?

How many chicks read plugs?
 
I had read in another post that guys were gapping up to .37 on the plats. I thought that was a bit extreme, but it seemed to run real nice for a while at .31.

Anyway, I'll grab the NGKs and see what happens.
 
The standard coil is 17,000 and will work w/ .025

The 40,000 volt coil can jump a .035 gap.

(about the only thing this helps is cold starting)

Yer not gonna git 10 hp out of a tenth inch gap /ubbthreads/images/graemlins/jester.gif
An ya don't gotta turn yer plugs into weld'n rods /ubbthreads/images/graemlins/grin.gif
 
Well, I am very sorry to say replacing the plugs did not fix my problem.

Where should I look next. Could it be my Lumenition box is going bad?

Or should I give up on ignition and look elsewhere?
 
Try disconnecting yer vacuum advance (& plug it)

Go fer a lil' drive & see if it is slightly better.

(This won't cure anything.....)
It's more academic curiosity /ubbthreads/images/graemlins/grin.gif
 
Tried that one. Made it run really lean and all other symptoms continued.
 
(It only does it during cruising/partial throttle?)

Usually Vacuum leak or carb component loose or worn out.

Could be something really wierd like plug wires /ubbthreads/images/graemlins/confused.gif
 
I just had a major headache with my new Lumitron electronic ignition.
Dead miss at low speeds. After I replaced the head gasket, checket the valves and pistons for holes, replaced the intake gasket, and cleaned out the carby twice, I discovered a warped disc under the dizzy rotor. This rubbed the metal off the magnet on the disc causing a miss at low speed.
I give up on electronics. 4 different ones and I am back to points.
 
First, I was going to say "Check your float level"...then I remembered this is your car. /ubbthreads/images/graemlins/jester.gif

The vaccum signal should bounce around as you open the throttle, but not at steady state. Are you sure you don't have a vacuum leak?

IF you have an old set of points around, it wouldn't hurt to see if they help. Does your coils shoot out a nice, hot spark that'll jump at least 3/4" or so?

I have a Petronix system and standard Chevy-type coil. It has been bulletproof for 4 years and is a pretty common setup among my friends with similar racers. Cost about $100 total.
Also, do you have any crossfire or voltage leaking from the coil, cap, wires, etc. Run the engine at night in a dark area and spray water (from a plant sprayer) on it. If it lights up like a Christmas tree, you've found something.
Is your O2 sensor well shielded? Sometimes, if they get a blast of cold air, it drives them crazy. The position of the O2 sensor in the exhaust manifold can also lead to erratic feedback.
Maybe midrange is just lean....how are you "mapping" your system?
 
Okay, here's an update.

I took the distributor apart and found the my mechanical advance was in need of attention. I lubed everything up and repalced on of the spring with one from another dizzy I had.

Next, I started probing around with my Fluke. I am getting six volts at coil (after ballast). I got to thinking "hmmm, my Lumenition box picks up power from the (+) terminal. 6v is probably not enough." I gave the Lumenition box 12v switched.

On the way to work this morning, everything seemed to be going much better. But once I got up to temp, everything went bonkers.

I am running a Chevy coil, too, Nial. It really seems to me that the coil is the source of my woes.

What say you?

BTW, I am pretty sure it is not O2 or map sensor error. I am not allowing the O2 sensor to correct my mixture, and still AFR jumps around and my injector pulse width reflects the jumping. Also, I hooked an analog vaccum gauge up to see if it jumped around when digital vaccum gauge did. Yep, it did.

Also, I have thoroughly sprayed all possible vaccum leak zones with various aeresols and always the idle stays steady.
 
Would replaceing condencer be in order, maybe you have an old one to try? How about the coil, have another you can hang in there for a test?
 
I have an electornic ignition system, so no condensor. I do have another coil, but I am pretty sure it is trashed, too. The coil I have in there now is still under warrenty, so I may try to get it replaced. If not, it only cost $15.00, so I can just buy another.

wick
 
I sure suspect something silly like that. Of course your wires are good, how about a crack leak in the dizzy cap. Something that changes when it gets hot?
 
I think I see yer problem.....

You got way too much high tech stuff in there.

Remove everything that has a metric fastener holding it on & start over. /ubbthreads/images/graemlins/jester.gif
 
[ QUOTE ]

I have a Petronix system and standard Chevy-type coil. It has been bulletproof for 4 years and is a pretty common setup among my friends with similar racers. Cost about $100 total.

[/ QUOTE ]

Nial - would you mind elaborating on your ignition system mods? I'm running the stock setup and I'm always looking for an upgrade /ubbthreads/images/graemlins/grin.gif
 
Are you sure you don't have a vacuum leak? Check again.
 
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