Spark Plug Diagnosis

[Michael A.]

I recently replaced the plugs in my 66 327/300 as part of the spring tune up. They had been installed last spring prior to my trip on Route 66. They have between 6,000 and 6,500 miles on them. I don't know the actual mileage because the odometer failed on our return trip... but that's another story.

Before the tuneup, the car had developed a bit of a miss with a bit less power. After the tune up, the car is running much better. I don't have that much experience diagnosing spark plugs so would appreciate some experienced eyes taking a look at them, so here they are:

• Image 2193 shows the set of plugs. It's interesting to see the discoloration on the ceramic on the 2,4,6,8 plugs vs. the 1,3,5,7 plugs. What might that be from?

• Image 2197 shows the #8 plug which is the one that had the most carbon on it. Could this be the plug responsible for the miss?

Any other thoughts you might have would be appreciated. Thanks in advance for the education. This is a lot of fun.

Cheers,

[Gerard F.]

Re: Spark Plug Diagnosis

Mike,

Can't tell from the group picture as they all look kinda black. The ceramic should be more of a brownish color for normal conditions.

Your number 8 has some black deposits indicating a miss or an oil problem. I think I'd check the plug wire for that cylinder. Are you using a lot of oil?

In a post sometime back, I had one that looked like your #8, the others looked OK. It was the plug wire for that cylinder.

[Bill C.]

Re: Spark Plug Diagnosis

They all look bad, but for sure #8 was just along for the ride. Assuming the rest of your ignition system is up to par, I have always found the AC plugs to run to cold, a champion or Autolite equivalent of one heat range hotter is a better choice. This is all based on the fuels available to us for use today.
The end all plug I currently use on all of my cars and will use without exception in customers cars is the AC Rapid fire, its plug #7 for use in all small blocks, replaces all heat ranges. Works great, will probably be the last set you install, assuming someting else does not foul them, even then one could clean them. They will stay clean and cure LOTS of Ills! Without fail every customer who gets them is amazed at the difference they make, including ( and they advertise this) a smoother idle

They are about $5 each and readilly available, if your local Delco cannot help, Ecklers carries them.

The later style heads with the smaller "peanut" plugs are #2

BTW, same is true for all the BB car, use #4 in this case
Guess what plug comes installed in the new crate motors such as ZZ502's?

Try a set, you will not be sorry you did
Save the AC's for the field

[Larry M.]

Re: Spark Plug Diagnosis

Agree with Bill and Gerry, they all appear to be carbon/oil fouled and too cold of a heat range from what I can see. Suggest going to AC 45 (or R45S) or AC #7 as Bill suggests.

I used to run AC 44, but switched to AC 45 a year or so ago. Car runs much better and plugs don't foul out.

You may also want to check the condition of your plug wires with an ohm meter to see if they are still good. I don't remember the acceptable ohms/foot length, but its in the archives.....or I can post it later if needed.

Larry

[Michael B.]

Re: Spark Plug Diagnosis

Michael,

If this is after a tuneup (was that plugs, wires, cap, rotor ...) and limited miles then one last thing to consider is if the rings on 8 are on the way out. As other have mentioned 8 appears fouled but this condition will probably return.

You can't do much except measure the ignition cables but you might want to pull the distributor cap off to check the rotor, points, cap - maybe, if your lucky, just 8 on the cap is arc-carbon fouled - but others don't look that good. It's also possible wire 8 was not fully seated in which case there would be evidence of arcing . This is the cheap stuff to check.

If you have been replacing the plugs yourself but not experienced be careful with the torque on the plugs and give a light coat of oil on the engine side of the sparkplug gasket before reinstalling the plugs or putting the new ones in.

Good luck

Michael B.

[Bill C.]

Re: Spark Plug Diagnosis

Agree with Bill and Gerry, they all appear to be carbon/oil fouled and too cold of a heat range from what I can see. Suggest going to AC 45 (or R45S) or AC #7 as Bill suggests.

I used to run AC 44, but switched to AC 45 a year or so ago. Car runs much better and plugs don't foul out.

You may also want to check the condition of your plug wires with an ohm meter to see if they are still good. I don't remember the acceptable ohms/foot length, but its in the archives.....or I can post it later if needed.

Larry

Larry,

For sure, as I mentioned, my comments are based on the assumption that the rest of the system is up to snuff, plug wires are cheaper than the plugs, yes a PIA to install correctly but when done should last a few years., all the rest goes along, good cap, rotor, points/condensor ( or electronic system), distributor bushings, shaft play OK, etc.

Unless one is continually doing "spirited" driving with better than pump gas, I still fine the 45's to be to cold.

Not many are still doing much of that. More cruising than spirited. I as a rule run the cars a bit rich also so I can dial back in a bit more advance with the fuel, the rapid fires still stay clean even with the guy just put-putting around with the 350 hp he just got or had serviced.

I hear a lot of "but I always used them and they were OK" but the key new variable is the fuel.

I always know the combo is working because they are still happy (as am I with my 350's and BB's all using the RF's ) and been doing it about 5 years now.
I also find from my carb builders that not all states have the same fuel available, Conn has up to 20% "corn oil" so thats what I am dealing with, but 110 octane unleaded is also readily available at 8-9 dollars a gallon and of course, runs and smells better, but that gets too $$. Leaded is also available but not wanted/needed. So as a rule I need to tune and work with pump gas.

The champions and the Autolites I mentioned are of an extended reach design and help, the Rapid fire #7 is of the same extended reach design, and platinum as I understand. With proper maintenance should go well over 100K miles, this one plug is recommended to replace most of all of the span of cold-hot heat ranges ( ain't technology great? )

Anyway, would like to hear others experiences.
Bill

[Larry M.]

Re: Spark Plug Diagnosis

Bill:

You made me a believer. I will purchase a set of #7 plugs for my car and try them out.......but only after the AC 45 ones quit performing. Don't know when that will occur. Mike should also try a set.

As a contingency, I purchased a roll of Packard 440 wire a few years ago and will make my own spark plugs wires as well. Used to do this years ago with my performance cars, and the 440 wire always did well. Since my car has sidepipes, I don't listen to the radio anyway

Larry

[Michael H.]

Re: Spark Plug Diagnosis

If AC 45's are too cold, someone has mechanical issues. You can't "fix" bad valve seals, piston rings or over rich fuel mixture with the wrong spark plugs.

[Ken A.]

Re: Spark Plug Diagnosis

A couple of things I see are: They look oil fouled. You could have bad valve seals. Run a compression test, as well. Also see orange paint on some of the plugs. This will cause the spark to leak to the head area. NO PAINT on plugs. Test your wires with an ohmeter for proper resistance. Use your service manual for proper tune up procedure. PLugs should last 15-20K miles.

[Dale S.]

Re: Spark Plug Diagnosis

For around town, I always used extended tips spark plugs, like AC R- 45S. I have those in the glove box. My right rear spark plug is such a bear to change I have a Bosch platinium in that hole. I hope to be dead before I change that one again. Dale

[Larry M.]

Re: Spark Plug Diagnosis

For around town, I always used extended tips spark plugs, like AC R- 45S. I have those in the glove box. My right rear spark plug is such a bear to change I have a Bosch platinium in that hole. I hope to be dead before I change that one again. Dale

Dale:

I have a factory air car, and found that the two right rear plugs are best/easiest changed from underneath the car working up. Piece of cake that way.....except you have to jack up and support the car.

Larry

[Bill C.]

Re: Spark Plug Diagnosis

Bill:

You made me a believer. I will purchase a set of #7 plugs for my car and try them out.......but only after the AC 45 ones quit performing. Don't know when that will occur. Mike should also try a set.

As a contingency, I purchased a roll of Packard 440 wire a few years ago and will make my own spark plugs wires as well. Used to do this years ago with my performance cars, and the 440 wire always did well. Since my car has sidepipes, I don't listen to the radio anyway

Larry

Larry,
You will not be sorry. They work. Keep us advised when you do switch. I usually purchase a fresh set of Delco wires and they work OK, need to be cautious removing the dist boots to route them under the motor mounts easily. Recently in a picnch I bought a set of sb wires from Carquest. They were only $30 and other than the wrong color boots were super.

I have had good luck unclipping the wires from the oil pan clip and cutting the plug boot off and carefully taping the cut end of the old wire and the dist end of the new wire together, without overlapping them and just carefully "fishing" the new wires back down and up thru the v shields.
Saves a LOT of time and work, and I also always change the back rh plugs from underneath, including the shield. Having the lifts in the shop makes a world of difference!

I thought all Corvettes had side pipes? Radio? Whats that?
Bill

[Dale S.]

Re: Spark Plug Diagnosis

Larry, On my car, with SB, A/C, and K-19. I made a special tool with a 90 degree turn and a hook on the end to get the boot off. When you get the spark plug socket on the old plug you can only turn it with a flat whench. There is no room on the end of the plug socket for a rachet. I had tried from the bottom years ago and still had to use a flat wrench on the spark plug socket. It used to be a day getting it out and a day starting it without stripping the hole. The Bosch platinium has been in a long time and the other seven are easy. If I ever have to do it again I will look at the bottom again as the last time I changed it I had the smog pipes off. Just my thoughts. Thank you for the advise. Dale

[Joe C.]

Re: Spark Plug Diagnosis

I recently replaced the plugs in my 66 327/300 as part of the spring tune up. They had been installed last spring prior to my trip on Route 66. They have between 6,000 and 6,500 miles on them. I don't know the actual mileage because the odometer failed on our return trip... but that's another story.

Before the tuneup, the car had developed a bit of a miss with a bit less power. After the tune up, the car is running much better. I don't have that much experience diagnosing spark plugs so would appreciate some experienced eyes taking a look at them, so here they are:

• Image 2193 shows the set of plugs. It's interesting to see the discoloration on the ceramic on the 2,4,6,8 plugs vs. the 1,3,5,7 plugs. What might that be from?

• Image 2197 shows the #8 plug which is the one that had the most carbon on it. Could this be the plug responsible for the miss?

Any other thoughts you might have would be appreciated. Thanks in advance for the education. This is a lot of fun.

Cheers,

Hi Michael,

How "tarr'd" is your engine?

All 8 look rich, but can't see enough from the first picture. Take two head-on photos, closer, one bank at a time. The insulators surrounding the positive electrode should be medium tan, and the electrodes themselves should be dry and whitish/grey-to-dark grey/black. There should be no black particles present. #8 looks fouled, and with the carbon particles flying around in the chambers, this WILL short the plug. #6 looks like it has carbon particles on it also, from the profile view. You can try the good old "clean the carbon from the chambers with water" trick, if you dare. It DOES work, but you should be careful and "take it easy" if you decide to try it.

In any event, aside from the dark insulators/electrodes you have another problem with the right bank. There should not be any soot on the porcelain. It looks as though you have a fairly large exhaust leak on the pass side...........ESPECIALLY at #6 exhaust port, and slightly less at #8, with #2 and #4 somewhat less. Another possibility is that #6 plug was loose and leaking. You should have been able to hear either of these.

Joe

[Michael A.]

Re: Spark Plug Diagnosis

Wow, what a great series of input. Thanks to all.

Let me try and address a few questions raised. Joe asked how "tarr'd" the engine is. It is the original engine but the original owner had it rebuilt in 1990. When I bought it in 96 it had 780 miles on the rebuild. The only thing I really know about the rebuild is that they supposedly put a bit of a performance cam in it. The idle and vacuum seem to support that. I have driven it pretty regularly since then and put nearly 40,000 miles on it. It has always used about a quart of oil every 700 to 800 miles, although it's recently increased consumption to a quart every 500 to 600 miles.

To answer some of the other questions, the tune up I did last year before our 5200 mile adventure included plugs, points, condenser, rotor, cap and plug wires. The plugs installed at that time were the AC44 in the pictures. This year's tuneup included all of the items above except for plug wires. I also went with the Champion RJ14YC (AC45 equivalent) and am very happy with the results. Of course, based on what I pulled out, it had to be better!

Joe asked for some better pics on the spark plugs so here they are:
IMG_2232.JPG

IMG_2233.JPG

IMG_2234.JPG

IMG_2235.JPG
There is an awful lot of carbon although this view of #8 doesn't show the big chunk that you saw in the earlier pic. It is still there. Joe or others, any other thoughts on what you see here?

The comments on exhaust leak on the passenger side make some sense. Last June I removed the driver side exhaust manifold to have a flange fixed with spray weld. It was reinstalled (w/o gaskets) but it had two good clean surfaces and it appears to be sealing well. I did not remove the passenger side manifold, just retorqued it. I did remove the AIR tubes on both sides and installed plugs which made a big difference. The AIR tubes were leaking and I had all sorts of exhaust leaks.

Based on all of the inputs, I'm going take the following line of action:

• Replace the #8 spark plug wire, just in case.
• Check the torque on the passenger side exhaust manifold. Also check for leaks.
• Adjust the carburetor to "lean" it out a little bit.
• Continue to monitor oil consumption.

Thanks again for the advice. Keep it coming. It really is great fun learning and doing.