Need help with plug reading
 

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?

http://forums.pelicanparts.com/uploa...1562605542.jpg

Addition to my plug post
 

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

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.

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.

look here simple chart..
http://datsun1200.com/uploads/newbb/...a6882bd01c.jpg

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.

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

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

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.

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?

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.

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.

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

Ivan,

Can you further explain that dynamic?

Thx,

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.

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.

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.

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.

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.

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.

t77..in mechanics language "bone stock"--for me it is an original miles and engine no rebuilds and yes it matters;-)

Ivan

bigfan911....let`s see how it will be with those new plugs..you say 1000 miles,right? Try to drive it a little harder as suggested by Kuehl i think?

Ivan

I might try taking the car out and run it hard. Red line pulls in 2nd and 3rd. Then pull the plugs and check them again.

Rule out Intake leak theory:

Grab a can of brake cleaner (starting spray & fire extinguisher).
Start engine when it has been cold for a while (not running).
Let it warm up for 5 minutes.
Note your rpms.
Spray around the LH intake, watch for drop or rise in rpm.
Ditto RH intake (caution around the air filter plenum).
It would be nice to have a AFR gauge or CO gauge but rpms can tell you.

you better get a new book:D

dealing with people on line (not in person) (probably in person too).
there meaning of "bone stock" and yours is NOT the same and THAT can leave you chasing you hind end.

t77..never mind i just understood when he said bone stock...maybe you did not because you kept asking about rebuild .....again never mind, your technical comments do not help the OP;-) unless this is about English grammar;-DDD

Ivan

check all the intake bolts and exhaust bolts.
do what kuehl said then try swapping injectors from left to right.
start with easy stuff.

Thanks for all the input. Don't want to start any arguments here. For clarification, the engine has never been rebuilt. Original 45K miles since new.

I talked to a local mechanic and he has a course of action that isn't invasive at this time. He noticed that injectors 1-3 come out of the ecu from the same point. Injectors 4-6 come out from a different connection point in the ecu. The signals run to the injectors. The plan is to check the pulse width at the injectors to see if they meet specs (or see if left and right are the same at least)

First course of action will be to do a smoke test to see if there is a leak anywhere in the left bank.

Like someone said, "do the simple things (obvious things) first.

After looking at the plugs in person, as opposed to the pic you see, he said things didn't look all that bad but there is a difference. I think the pic magnifies the problem a bit.

big..to be honest...the car runs great,right, no missing at all, no problems when you give a gas...after all no problem just you took the plugs out on a car which did 5 k in 6 years....
i would really say, what is the worry--drive it, man...
Ivan

I hear you. That's my plan but still want to do the simple tests I listed. With the left bank running lean I just didn't want to risk burning a piston or something. Then again maybe it's a little OCD kicking in.

While it runs great it might even run better if the left bank gets all the fuel it needs. Also don't want to burn any valves. Maybe the difference is negligible however.

I realize this is not an emergency so won't get around to checking things for a month or so. I'll keep people posted if I find anything substantial.

With the cost of rebuids a little preventative maintenance never hurts.

As far as I know there is only 1 injector driver circuit in ECU, so if both banks are firing they will have the same pulse width. Pins 14 and 15 will be bridged inside the ECU to supply the ground signal to both banks of injectors.

If my plugs looked like that, I certainly would have noticed. Mine would have sputtered just taking off unless I ran my throttle up to 3k and slipped my clutch like a torque converter.

My take:
I'd put 6 new plugs in
I'd put a torque wrench on the intake runner nuts because it's a known source for leaks
I'd do a few pulls with it then check the plugs.
Another easy test is a infrared temp sensor on each exhaust port. See if your left and right bank ports have about the same temp.
One more easy check: Pull your oil cap and see if the rpm's drop. If you hear a difference in the engine, you probably don't have any big leaks.

BTW, Sal suggested I put in a wideband o2 gauge which was some of the best advice I think I have received here. There's a lot of money in that engine compartment, why guess at what's going on?

Here's kind of where I'm at after digesting all the suggestions.
1. There are new Bosch plugs in now. That's why I pulled the old ones.
2. If 76FJ55 is correct and there is a bridge to terminal 14 and 15 within the ecu it's probably not a fuel injection/ecu problem since all plugs are firing and the pulse widths should the same.
3. I'll do a smoke test before tightening the intake manifold bolts to see what's happening. I'd like to see if it's the intake manifold or not first. Otherwise I won't know if the problem is fixed for a long while. I did the oil cap test already. The engine does change rpm.
4. I can do the exhaust manifold IR test now. Easy enough to do.

Reading the plugs will show you mostly what was happening when you shut off the engine. So I expect what we are seeing is after the engine slowly rolled up to the house with no load and then idled for a bit before it was shut off. Not that useful of a reading.

As to the unevenness of the plugs: At the age of these cars it would be common for there to be at least some small level of vacuum leak at idle that would make some cylinders lean and some rich.
- The Motronic uses "batch injection" which means all the injectors fire at once so depending on when the specific cylinder is in the induction cycle different cylinders will have different results from a port leak. So if the intake on a port opens during or right after the injector fires a vacuum leak on that port won't make much difference. The charge is right there and will get sucked into the cylinder.
But if a port has the injector fire right after the intake closes a vacuum leak has the whole rest of the cycle to draw the intake charge back up the runner into the plenum so some of the charge gets sucked into another cylinder.
In other words: At the high intake vacuum of idle your mixtures can be all over the map.

But at full throttle when the manifold vacuum is next to nothing any port vacuum leaks won't have any real effect.

- All this is well and good if you have leaky manifold gaskets.
__________________________________________________
But it all comes back to how to correctly read your plugs.
To correctly read plugs you need to cut the engine at a point in its operation where you want to see how it is running.
- That means under full throttle acceleration and generally in the middle of it's torque curve. Then you will get color on the plugs that really means something.
In a street car you need to be very careful that you don't turn the key and lock the steering column and kill yourself (or even worse, crash the car). You'll need to be able to coast to somewhere where you can do the plugs. If you are on the track you need to make sure you don't have someone run you over when you cut the power either.

You do this and then you will get something worth looking at on the plugs.

^^^^
Or you could throw plug reading right out the window and just go buy a wideband o2 setup and KNOW what your engine is doing at various points from idle, to tip in to WOT.
But yeah, if you want to know what it's doing at various stages, gotta kill it like quick said. Me, I just look for an overall picture. I want to see something on the chocolate milk end of the spectrum

But seriously, we have engines that are worth at least 10K... isn't an investment of a few hundred to know what the engine is doing a worthwhile thing?

wide band O2 sensor
 

I had M&K install an additional bung in the cat bypass that I purchased and then installed a wide band air fuel ratio gauge. It is without a doubt the best thing by far that I have added to my 82 SC. It is extremely helpful when tuning mixture and it provides a window into what the mixture and other related components are doing at all times/conditions. Now that I have it, I would feel blind without it!

Just my thoughts.

Dave

Is the car parked on a side slope?

No slope involved, car is parked in the garage when it's shut off.

If reading the plugs after a plug change is not ideal I think the next step has to be a smoke test to see if there's a vacuum leak. Probably long overdue on a 30 yr old vehicle anyway. Maybe next a valve adjustment. Last one was 6k miles ago. All just regular maintenance.

The idea of a wide band is very intriguing. Maybe in the future.

I live in an area of CA that doesn't require smog testing unless a vehicle is being transferred. Maybe I can get a "test" smog check that supposedly doesn't get reported to the state. Not sure if I believe that or not though. After all this is Kalifornia...