Need help with plug reading

[big911fan]

I recently changed the plugs on my '89 Carrera after about 5K miles. Attached is a pic of the plugs. As you can hopefully see plugs 1-3 look like they burned very nicely.

Plugs 4-6 are clearly slightly fouled. The difference between the two banks of plugs is noticeable.

Does anyone have an opinion on what would make plugs 4-6 burn uniformly the same but more fouled than plugs 1-3?

[big911fan]

Sorry. I forgot to mention that the plugs were NGK BPR6ES.

[proporsche]

before you look for problem solver..let me ask you why did you use these plugs anyway? And what made you look at 5k on them??

Ivan

To your question..when was the last time you did a valve adjustment?


I only use one type for 30 years...Porsche Spark Plug - Bosch WR-7-DC+

When i take the cat off, i use these..Spark Plug WR4CC.

[big911fan]

From prior posts on this site a long time ago the NGK plugs were recommended as well as Bosch. I replaced the NGK's this time with Bosch Super Plus WR 7 DC+.

The NGK's were installed in 3/2013 and had about 5K on them. I changed the dist. cap, rotor, and plugs this time.

Last valve adjustment was about 6K ago by an independent Porsche mechanic.

[proporsche]

look here simple chart..

[big911fan]

Yes I've seen and used those charts. My question is "Why is there a noticeable difference between the two banks of cylinders.

Cyls 1-3 look fine to me. Cyls 4-6 are lightly carbon fouled. What could cause this?

If the valves were the problem why are they good on 1-3 and uniformly bad on 4-6? I can see an individual valve being off but plugs 4-6 are all pretty much the same.

[piscator]

Reading your plugs, I see that you are about to meet a dark haired stranger...

[big911fan]

I see this board isn't what it used to be. Namely helpful....

[tirwin]

Well since it’s Motronic EFI, what is common to one bank? Fuel rail pressure? Something to do with the cam on that side?

Could it be something as simple as the last time a valve job was done they valves on that side weren’t adjusted? Or done properly?

In these situations I try to remember Occam’s Razor — the simplest explanation is the most likely.

[kuehl]

Originally Posted by big911fan

My question is "Why is there a noticeable difference between the two banks of cylinders. Cyls 1-3 look fine to me. Cyls 4-6 are lightly carbon fouled. What could cause this?

Off the top of my head, in a perfect world:
If the gaps are the same, the valves are adjusted the same, compression and leak down are the same, injectors are the same, and so forth: you might have excessive air coming in on one bank compared to the other (intake manifold gaskets).

My preference is NGK Iridium's but the model NGK you have should work for now.
Although, all your plugs look a quite 'sooty (carbon or oil fouled).

What is the history of the motor (rebuilds, compression and leak down, mileage, is the engine management system stock, etc)?

If you are stock your DME and 02 sensor should be "trying" to keep things clean for the most part when at idle and cruising; if they are working.

When you drive it do you lug it or keep the RPM's up?

Have you pull off your distributor cap and looked at the rotor and posts in the cap?

[Bill Douglas]

Originally Posted by big911fan

I see this board isn't what it used to be. Namely helpful....

piscator is being helpful. Reading your plugs, I see that you are about to meet a dark haired stranger...


I think what he means by this is the Dark Haired Stranger is your engine rebuilder.

[big911fan]

Thanks for the ideas. The engine is bone stock with only 45K miles. I've never checked compression or done a leak down test. The engine runs well so I had no need. When the NGK's were installed I also changed the cap and rotor as always. All the gaps from the removed plugs are just about right at .030. It runs very well after the recent plug, cap, and rotor change. Never had smoke at start up, acceleration, or trailing throttle.

Not sure if the fuel rails could supply uneven rail pressure but maybe. Worth checking out.

I'll admit to not running it hard very often. Something is clearly different between the two banks.

I'll run it a little harder for the next 1K miles and take a look at the new Bosch plugs at that time.

Thanks.

[proporsche]

I just realized that the WR4CC are actually for my engine because i have an Euro model...so stay with the WR7DC ...and i would just drive ...plugs will last you at least 10-15K miles no need to always check them;-)
Ivan

[famoroso]

Originally Posted by proporsche

Ivan sez...

I only use one type for 30 years...Porsche Spark Plug - Bosch WR-7-DC+

When i take the cat off, i use these..Spark Plug WR4CC.

Ivan,

Can you further explain that dynamic?

Thx,

[T77911S]

as kuehl mentioned first thing I was thinking of was maybe an air leak on the left side.
you could swap injectors form the left to right.
check for exhaust leaks on the left.
I also thought about cam timing, maybe. don't know if it would make the right look that bad.

is that original miles or a rebuild.
you might consider a comp and leak down test.
if a rebuild were the heads rebuilt with new guides.

the right side really looks like guides or rings. but I would rule out the other stuff first.

[kuehl]

I believe, usually, cylinders 6 and 3 run hotter. However, you have the opposite issue going on.

As T77911S mentioned, 'cam timing' can do that; if someone did not set the cams properly when puttin the chain back on. If you have the past history of repair orders handy (that pile of papers you ask for when you buy a used car), dig through them.

[proporsche]

boys..here ...the OP said this...
"The engine is bone stock with only 45K miles.".

Big fan 911....I would just add to this you need the drive it more often 45k is nothing .......

Ivan

Famoroso ,i have mentioned above you post my is Euro model engine and it takes WWR4CC spark plugs without the catalyst.

[big911fan]

Yes, I'm guilty of not driving often enough or hard enough. Too many vehicles...

The theory about the left bank of cyls running lean makes sense. If there's a vacuum leak on the left side maybe the the ecu is overcompensating causing the right bank to over fuel. It's definitely dry and carbon fouled on the right side plugs. Not oily like I would expect valve guides to cause. The insulators on the left bank plugs are almost totally clean unlike the right side.

I'll dig through the old records to see if anything was done to the timing chain. I do remember a receipt for replacing a gasket on the timing chain cover but nothing about the chain itself.

[T77911S]

Originally Posted by proporsche

boys..here ...the OP said this...
"The engine is bone stock with only 45K miles.".

Big fan 911....I would just add to this you need the drive it more often 45k is nothing .......

Ivan

Famoroso ,i have mentioned above you post my is Euro model engine and it takes WWR4CC spark plugs without the catalyst.

does not matter.

what matters is if it has been rebuilt.


I bought one that had the cams 15 degrees advanced (not on purpose) and it would spark knock when you floored it above 4500.
got a good deal on it,
the guy read the dial gauge backwards when setting the timing.

[big911fan]

The car has original miles. I have records going back to '97. Mileage sequence looks consistent so no reason to believe any major work done.

The only repair of note was the left camshaft oil line was replaced in '07.