Plug Reads?

[Jetaway]

Wasn't sure where to put this thread. Thought of Help Me! but its not an emergency. Electrical, probably, but that's only my best guess, so I thought I put it here under Engines as system.

I have a 1972 240Z with stock intake system and a dizzy from an early 280ZX. The dizzy uses the E12-80 ignitor. MSA premium exhaust system, but stock exhaust manifold, installed last August. My idle has been a little rough lately and it felt a little down on power, but nothing major and its sometimes its just one's imagination.

I pulled the plugs today and took some pictures of them. The plug numbering goes from left to right in each photo (1-3 and 4-6). My plugs are usually pretty consistent, at least within each bank (carb), but this time two really stood out, the #2 and #6 plugs. While the other plugs weren't exactly as I like to see them, I had never seen any quite like these. They weren't glazed like from overheating, just clean, I guess. While you can't see it in the photos, one of the other plugs had foul shorted with a chunk of something between the electrode and uh, the other electrode? Anode, I guess. I replaced the plugs with some cleaned up ones that I had removed early in their life back when I was getting a handle on adjusting the carbs and wanted to get a clean read.

I pulled the dizzy cap, found the dirtiest looking contact, and sure enough it was the #2. The #6, though didn't seem much different than the rest. But they are physically next to each other. I took sandpaper to the contacts and the rotor, buttoned back up and took off for a test run. Felt much zippier. Don't think it was my imagination. And the idle was smoother.

I richened the carbs up a week ago and installed a 195 thermostat maybe six weeks ago. I'm having a hard time coming up with a scenario as to how those changes would have only affected two plugs, one in each bank. But that's why I'm asking here.

I bought the car a little less than three years ago, have put around 30,000 miles on it since. Can't remember if this is the second or third cap/rotor I've been through, but I do remember being surprised that the set immediately before this one had to be replaced. Does that make sense? The previous cap/rotor set didn't seem to last long.

Is it a reasonable hypothesis to assume that the "white" plugs were caused by a weak or missing spark? If so, could it have been due to sloppiness on my part installing the rotor cap or symptomatic of a deeper problem, perhaps a warped shaft or worn bearings of some sort? Anything cheaper / simpler that could cause this that I've overlooked?

Chris

[beandip]

Chris, I have been using the same ignition for 11 years and swear by them. First off are you using NGK plugs? Try a set if them BPR6ES. I have a question about the ignition wiring. This could be the problem. Try removing the wire from a troubled plug and use that wire on one that is burning cleanly. Of course I am saying to remove the wire and installing it on the different position on the cap also. I clarify because some readers would just switch at the plug only.

See how this works . If the problem changes from one plug to another then replace the plug wires. With the ignition that you are using the plugs should last for 20K easily. Set them at .035"

What is the timing set at? I am running at 16* BTDC but if you do this, do it after clearing up the present situation.

All the best, Gary. Portland Or.

[FastWoman]

Those are some pretty odd looking plugs. Ideally (and ordinarily) they would all look approximately the same -- preferably somewhere between your #1 and #2, but a bit closer to #2.. If your carbs were out of balance, you'd have two different plug appearances in the two banks.

So I'm thinking maybe you've got some ignition problems on just some cylinders, but not all? Are your wires good? Are your spark plug gaps all the same? Do you consistently hit on all 6 cylinders, or does your engine miss a bit?

I'm also wondering whether you have any compression issues. Your two nastiest plugs are adjacent -- the #3 and #4. Head gasket problems?

The whitish coloration of #2 and #6 is from lean running. The carbon buildup on the other plugs is from incomplete combustion and/or oil combustion. Causes could be...

*rich mixture

*extreme lean mixture

*cylinder misfiring (bad ignition)

*low compression

*oil leakage into cylinder (valve guides, rings, head gasket)

Maybe it's a weak link sort of thing. For instance, maybe your ignition coil is failing, and your #2 and #6 plugs consistently spark, having a very slightly closer gap than the other plugs, which aren't consistently sparking. Could be many things. Dunno.

Edited February 14, 2011 by FastWoman

[Jetaway]

Chris, I have been using the same ignition for 11 years and swear by them. First off are you using NGK plugs? Try a set if them BPR6ES. I have a question about the ignition wiring. This could be the problem. Try removing the wire from a troubled plug and use that wire on one that is burning cleanly. Of course I am saying to remove the wire and installing it on the different position on the cap also. I clarify because some readers would just switch at the plug only.

See how this works . If the problem changes from one plug to another then replace the plug wires. With the ignition that you are using the plugs should last for 20K easily. Set them at .035"

What is the timing set at? I am running at 16* BTDC but if you do this, do it after clearing up the present situation.

All the best, Gary. Portland Or.

I've used several types of plugs, but like you, have settled on the NGKs. I run the gap at .035 -- .038. Timing -- currently is at 17* BTDC _but_ I'm running it advanced because the vacumn advance has been nonfunctional since I bought the car.

Checking the wires is a good idea, but at the moment (after changing plugs and cleaning up cap/rotor) its running pretty sharp so I don't know if a wire swap would tell me anything. I'll check with an ohmmeter and see if they come in around the same, allowing for the different runs to the plugs.

I have a couple comments for FastWoman and I'll add a couple of my own thoughts to the end.

Chris

[Zs-ondabrain]

Although #2 and #6 look lean, they look better than the incomplete burns on the others.

I use nothing but NGK plugs and Wires. But I use BP6ES plugs. Should I use the BPR's??

What are the advantages of those?

Anyways, as Gary said, NGK!! New wires never hurt, go with the Blue NGK wires.

The increased Burn marks on the Inside of the Cap on #2 and 6 could also mean that they are getting better spark than the others. Typically, the wearing away of metal in a cap means the electricity is hitting that contact better. What's the possibility of a wobbly Dizzy?

I guess it sounds like I'm throwing stuff out there, It's late and I'm gonna go to bed and think better in the morning.

Let us know what you find.

Dave

[Jetaway]

Those are some pretty odd looking plugs. Ideally (and ordinarily) they would all look approximately the same -- preferably somewhere between your #1 and #2, but a bit closer to #2.. If your carbs were out of balance, you'd have two different plug appearances in the two banks.

So I'm thinking maybe you've got some ignition problems on just some cylinders, but not all? Are your wires good? Are your spark plug gaps all the same? Do you consistently hit on all 6 cylinders, or does your engine miss a bit?

I'm also wondering whether you have any compression issues. Your two nastiest plugs are adjacent -- the #3 and #4. Head gasket problems?

The whitish coloration of #2 and #6 is from lean running. The carbon buildup on the other plugs is from incomplete combustion and/or oil combustion. Causes could be...

*rich mixture

*extreme lean mixture

*cylinder misfiring (bad ignition)

*low compression

*oil leakage into cylinder (valve guides, rings, head gasket)

Maybe it's a weak link sort of thing. For instance, maybe your ignition coil is failing, and your #2 and #6 plugs consistently spark, having a very slightly closer gap than the other plugs, which aren't consistently sparking. Could be many things. Dunno.

The #3 plug had a piece of crud where the spark normally jumps, I'm thinking it basically shorted out. I know its hard to tell from the pictures -- the desk puts a warm glow over the plugs, but when I tried white paper, the darker plugs disappeared into darkness. I think the #1 is the most normal looking -- tan insulator, not many deposits. Not an expert at this by any means.

Up until this time, the plugs have been pretty consistent within each carb. And, he says with a small sense of accomplishment, increasingly consistent across the carbs. Except this time.

The engine was idling rough, but didn't seem to miss once up to 800 rpm or so.

Compression / Head Gasket? Could be. I haven't checked the compression since last summer when it was a trifle low, but consistent, across the cylinders.

Ignition coil? Jeez, hope not. Replaced the stock one with an Accel during Summer of '09.

I'm wondering if the change to the 195 thermostat has anything to do with this. I've always ran a 180, which consistently kept the gauge right in the middle. With the advent of winter -- not that wintery, but cooler, it dropped a pointer width. I thought I'd try a 195 to bring it up a bit. It does, too much, I think, because now it consistently runs two pointer widths hot.

Also, an embarrassing thing to admit, but I'm a short shifter. Unless there is a need for tactical speed, I'll be in 4th by 35 mph, and sometimes go really crazy and drop it into 5th. Also, the proportion of in-town versus highway driving has been higher than usual for the last two months -- in fact about when I changed to the 195 thermostat.

So, maybe the higher engine temp, combined with less high speed running (3000 rpm and over) is causing the carbon build-up (which is much worse than normal), and bad wires or a wobble in the distributor, or sloppy placement of the dizzy cap is causing the white plugs. That's whats so puzzling -- it wasn't running that bad, wasn't missing above idle, there doesn't seem to be an obvious richness difference between the carbs, the plugs have always been consistent or if not, could be traced to an obvious problem (fuel richness, dizzy cap wear, etc.) but there are three distinct plug sets -- the fouled, the suspiciously clean and the perhaps divinely protected normal one.

I'll check the wires on Tuesday, probably switch back to a 180 termo then too and, well, drive and watch.

Chris

[Jetaway]

Although #2 and #6 look lean, they look better than the incomplete burns on the others.

I use nothing but NGK plugs and Wires. But I use BP6ES plugs. Should I use the BPR's??

What are the advantages of those?

Anyways, as Gary said, NGK!! New wires never hurt, go with the Blue NGK wires.

The increased Burn marks on the Inside of the Cap on #2 and 6 could also mean that they are getting better spark than the others. Typically, the wearing away of metal in a cap means the electricity is hitting that contact better. What's the possibility of a wobbly Dizzy?

I guess it sounds like I'm throwing stuff out there, It's late and I'm gonna go to bed and think better in the morning.

Let us know what you find.

Dave

I was thinking that the burn marks meant a lesser spark. But what you said is in more concordance with what I'm seeing. #2 and #6, physically next to each other getting a good spark while the others starve to a greater or lesser degree.

I'm thinking this might take a couple of months to resolve. And while under some circumstances a "Wobbly Dizzy" sounds sorta fun, I'm thinking it will be a bit of a PIA in this context.

Thanks all, I'll get back to you on the wires Tues/Wed/Thurs. Busy week ahead and I can spend _way_ too much time here reading posts on other topics.

Chris

[Carl Beck]

If your plugs have been in the car for say 1000 miles and you have driven in all manor of conditions {stop and go, highway, short trips where the engine barely gets warmed up etc. etc. - - then pulling the plugs will really tell you very little about how any specific aspect of your ignition and air/fuel mix are operating. There are simply too many variables involved there.

If you are going to "read" your plugs - you have to install clean plugs and then run the car though its normal operating RPM range. A higher speed loop around the interstate and then home to pull the plugs. No short shifting and lugging the engine at low speeds....

"R" on the NGK plugs indicates "Resistor" - they cut down on electrical noise that can be a problem with radio reception.

FWIW,

Carl B.

[Diseazd]

Is it me or is the center plug in the first picture missing an electrode? I always replace all basic ignition parts when you get a new Z........points,plugs,condensor,rotor and cap if the engine doesn't run perfect from day 1.

[esmit208]

Is it me or is the center plug in the first picture missing an electrode? I always replace all basic ignition parts when you get a new Z........points,plugs,condensor,rotor and cap if the engine doesn't run perfect from day 1.

I thouhgt the same "D":ermm:

[Gary in NJ]

It's either missing or has morphed into a fine-wire plug.

[FastWoman]

I think you're right, Diseased. I hadn't noticed that. That would certainly be consistent with lean running. Yikes!

Jetaway, the crud stuck in your #3 plug would have been a dislodged chunk of carbon. You've got a really bad problem with incomplete burning. One hazard of this is that you'll throw chunk of carbon that lodge in the exhaust valve, resulting in burning of the valve and seat. You might want to give your engine a SeaFoam treatment to wash out the carbon. (And then do an oil change, of course.)

I don't think your cruising in high gears is a problem, as long as you don't do it under power. I've gotten in the habit of dropping to higher gears myself whenever just maintaining a steady speed. I'll make a long run down a flat 35 mph road in 4th, just like you. Fifth gear is a bit much, though. I'll drop down to 5th at 40-45. When I need to accelerate, I'll always downshift first, and I make it a point to do at least some brisk accelerations with each drive after the engine warms up. I've driven like this for almost 20 years with my '92 Saturn (bought new) and more recently with my Z, and I've not experienced any carbon deposit problem in my engines. If it did, I would have stopped the practice long ago.

FAIW, I've driven Zs for a total of 20 years (2 different cars and two different stages in my life), and I've always used the standard NGK plugs. They've always worked great for me. I also have about 15 years experience with the inductive core (non-resistive) NGK wires, which I can't say enough about. Your rotor and cap could probably use a refresh, but those aren't as critical parts. And I doubt any cap misalignment would have resulted in the plug reads you've gotten.

Edited February 14, 2011 by FastWoman