spark plugs are unevenly colored, advice please?

[hzoltaan]

I must confess, this is not a Skoda, It's a carburetted Saab 900, that's pretty much the same idea as a Skoda 105 engine, just bigger. 

There's 1 carb, a single Pierburg, sits in the center of the intake manifold. 

 

So my quick question, and i'm off, Offing the Skoda forum.

 

My N1 and Nr4 plugs are  dry black, while the 2 middle ones are white, a bit too white for my taste. (on carburetted cars i usually have them nice and light brown)

 

Just checked valve clearances, they are OK.

Big Big suspect is intake manifold and carburettor, but i though it never hurts to ask about. What would you guys check, adjust, clean replace and in what order? 

 

Thanks a lot! 

Z

[Warrior193]

Hello, are the plugs all the same heat range? Your description sounds as if cylinders 1 and 4 are running too rich - while 2 and 3 are too lean. It's hard to understand how the carburettor or inlet manifold could do that. Have you checked cylinder compressions? How does the engine run - any loss of power or misfiring?

I'd suggest fitting new, correctly-gapped plugs and recheck after a reasonable mileage.

[hzoltaan]

Compression is even on all 4 cylinders... I wanted to tell you the exact numbers, but i don't have those pictures any more. 

Time to make a new test! 

 

Plugs were replaced (correct heat range) after buying it (maybe a 1000kms before) , and it always had cold start problems.

(It's a project car taken for a walk every now and then, mostly used to learn welding. )

It usually starts up on 3 cylinders, and you have to play a lot with the choke, accelerator to get all 4 on board. 

I started throwing new parts on it as i also did not understand the issue. It has now new plugs (double electrode versions, I hoped it will help... It did not), cables, distributor. 

Ignition is electronic, but timing is manually adjusted and distributor is mechanic. Ignition was checked with a strobe, it's set correctly. 

Carb was rebuilt and i was fiddling a lot with the float height to get it start better, but as you said.

Having 2 cylinders run rich and 2 lean on a single carb system does not make much sense. 

 

I can only think of some tiny leak in the manifold... there's an old stuck EGR valve still on it. I disconnected the vacuum control hoses to it, but who knows... 

Hence if no better ideas present themselves, I will take the manifold off and close all the extra holes. 

 

Any other ideas? I think i sprayed it with brake cleaner once to see if there's any leak on the intake manifold and did not manage to find any... 

It baffles me really.

 

Thanks for the advise, and sorry it's not a Skoda

 

The Felicia has no such issues apart of lacking power just off idle on LPG, I think i need to raise pressure a bit now that it's colder.  

 

[Breezy_Pete]

Where does the vacuum connection to the brake servo come off the manifold?

[Warrior193]

Is there anything unusual about the cold start method on that carburettor type - does it use the usual butterfly flap?

Is the LPG conversion a standard, commercial unit?

My step father ran a Taxi on LPG in NZ- I seem to recall him saying it was easier to start in winter by temporarily switching to petrol, as it was difficult to optimise the engine for both fuels in dual fuel. If I recall correctly, that situation was made even worse if using CNG.  

 

I'd suggest blanking-off or replacing the faulty EGR and check any vacuum connections for leaks.

Edited 22 December, 2023 by Warrior193
grammar

[hzoltaan]

Hi Pete, 

It comes off at the corner where Nr1 cyl is connected: Marked in blue. This picture is not my car, it's off Wikipedia, but it's the same model, Engine, B201, with the single Pierburg carb. 

Do you suppose there's a leak around the vacuum line...? Why not? I pulled it out quite easily last time i fiddled around the alternator... 

And now i see that on this picture under the EGR, that hose connection is made to the valve cover... That's a weird thing. On mine it's blanked off.

 

Warrior193, I'm sorry, the LPG bit was about my Felicia, not the car in question.  

OFF of the OFF topic: For starting with petrol, it's absolutely right. Over the years i had 5 cars on LPG (it's very popular here) and on the carburetted ones we used just a manual electric switch that would close off the petrol line and open the LPG line. You started on petrol, then switched your ON-OFF-ON switch to OFF, waited till the petrol went low in the carb then turned to LPG and off you went saving the globe. 

On the injected cars it's all automatic. It starts automatically on petrol then switches to LPG once the coolant is about 40 degrees. I never would have thought that LPG was available in New Zealand... I thought guys down under either drive V8 pickup trucks and SUVs or Japanese key trucks. (I own a Suzuki carry as well)

 

[RicardoM]

@hzoltaanAre you sure your car has a carburetor and not a single-point injector? The service manual for B201 on Saab 900 mentions only fuel injection.

If it has a carburetor indeed, what Pierburg model ?

[hzoltaan]

Hi Ricardo, my car is exactly like that one from the Wiki picture i added. Somehow I lost my own photos about it, so You gotta take my word for it. I changed diagraph in that carb so i'm sure it's a carb.

Yeah, there were Bosch injected ones but the simple 'pikey' models were carburetted. 

Saab B engine - Wikipedia

Mine sadly has the Pierburg 175CD carb, that's pretty rare compared with the Zenith. But you can fin it on some Mercs, and there are tons of those in Poland. 

 

[RicardoM]

OK then. So we are looking for a variable in the engine combustion. Since you said that the engine is mechanically fine, we have to address the fuel/air mixture in each cylinder and the spark.

The carburetor delivers the same mixture to all cylinders. From your description, the mixture is rich. You will have to address the carburetor issue separately, otherwise the fuel consumption will be excessive and the engine will run like crap.

So we are left with two variables: extraneous air in cylinders 2 and 3, making the mixture lean OR bad spark on cylinders 1 and 4, or both. If the spark plugs are all identical and in working condition (forget the multiple electrodes spark plugs, stick to the factory recommendation) the conclusions are:

• vacuum leaks in intake manifold
• bad distributor cap
• bad high voltage leads
• a combination of the above

I like the Gunson Colortune gizmo to see what is going on combustion wise.

[Warrior193]

3 hours ago, hzoltaan said:

Hi Pete, 

It comes off at the corner where Nr1 cyl is connected: Marked in blue. This picture is not my car, it's off Wikipedia, but it's the same model, Engine, B201, with the single Pierburg carb. 

Do you suppose there's a leak around the vacuum line...? Why not? I pulled it out quite easily last time i fiddled around the alternator... 

And now i see that on this picture under the EGR, that hose connection is made to the valve cover... That's a weird thing. On mine it's blanked off.

 

Warrior193, I'm sorry, the LPG bit was about my Felicia, not the car in question.  

OFF of the OFF topic: For starting with petrol, it's absolutely right. Over the years i had 5 cars on LPG (it's very popular here) and on the carburetted ones we used just a manual electric switch that would close off the petrol line and open the LPG line. You started on petrol, then switched your ON-OFF-ON switch to OFF, waited till the petrol went low in the carb then turned to LPG and off you went saving the globe. 

On the injected cars it's all automatic. It starts automatically on petrol then switches to LPG once the coolant is about 40 degrees. I never would have thought that LPG was available in New Zealand... I thought guys down under either drive V8 pickup trucks and SUVs or Japanese key trucks. (I own a Suzuki carry as well)

 

Yeah, we Kiwis were trying to save the planet starting from the late 60s - especially every time it kicked-off in the middle east - hell, we even cancelled NZs first shot at running a round of the World Rally Championship in 1974.

Don't tell anyone, but it was our neighbours from across the Tasman who were more into big V8s - us poor Kiwis couldn't afford the fuel 😇 

[Paws4Thot]

5 hours ago, hzoltaan said:

It usually starts up on 3 cylinders, and you have to play a lot with the choke, accelerator to get all 4 on board.

Which makes me think of the HT leads.

[J.R.]

6 hours ago, hzoltaan said:

Having 2 cylinders run rich and 2 lean on a single carb system does not make much sense. 

 

A lot of contributors are overthinking this.

 

It makes absolute sense that a single carb 4 cylinder in line engine would have different combustion mixtures on the inner and outer cylinders, one glance at the compromised inlet tract lengths will show you exactly why.

 

I would however have expected the outer cylinders to run leaner with fuel condensing on the manifold walls.

 

I can see that its a X flow engine so does not have a hot spot joining the inlet and exhaust manifolds which usually favours the inner cylinders, does it have a water heated inlet manifold or a thermostatically controlled exhaust heated inlet to the air filter? These are all things to check.

 

The other thing is that spark plug colour is a very good indication of combustion conditions but only if the test is done under the correct conditions known as a "plug cut test".

 

For a race engine this will be done when under sustained full load, either on a dyno or test track, for a road car its done at a fast cruising speed with the engine at full operating temperature, after a couple of miles at a constant cruising speed on the flat with a constant throttle opening you declutch and switch off the ignition, you cruise to a halt and then check the plug tip colours wearing gloves or after having had a pint if you can coast to a pub 🤣

 

It sounds like you have some work to do if its not firing on all cylinders on start up, you were right to confirm the compressions before anything else.

Edited 22 December, 2023 by J.R.

[J.R.]

1 hour ago, RicardoM said:

I like the Gunson Colortune gizmo to see what is going on combustion wise.

 

They are ok for setting idle mixture but not for cruising or full load, also you really need 4 of them and they dont spark anywhere near as good as a spark plug under lean burn mixtures.

[nta16]

My thoughts -

Might not be one single thing but a combination (or might be one one thing) so I am now looking at things in the round rather than lasered down to plug colours only (and I agree with you can have two sets of two colours of plugs from a single carb).

 

I would have a look at the Triumph forums that use a similar engine  for some clues perhaps to your issue(s).

 

Starting on three suggests that's an issue too, are you sure it's three, suggest HT side from cap to plug, or is it two getting too much or too little fuel as per plugs.

 

Electronic igniter heads can go off and dissy caps being crap is not uncommon from the cheaper makers  / suppliers (and their rotor arms).  Also electronic dissy top leaves usually very worn and never very long lasting mechanical dissy bottom (well British ones anyway) and rebuilt last a couple years of use before wobbling out again but perfectly useable for a couple of decades perhaps.

 

Bosch rotor arm have a 5 whatsit resistor in them that can start to break down before it fails that might also hinder starts and setting up and running, if the rotor arm is still in good condition you can sweat out the resistor and remove it and bridge the gap.  If you have what is called a red rotor arm from one of the cheaper suppliers you get what you pay for but even Bosch and Beru can go.

 

Sparks plugs are genuine and not counterfeit or the very cheap ones from the cheap suppliers of cheap ignitor heads and ignition kits and cheap HT leads.

 

The shut off test previously described is very good if your able to do it and you can get and handle what will be hot plugs (easier on a X-flow than when the exhaust manifold is within skin blistering error area).

 

Vacuum hose is best to be marked vacuum hose or thicker wall not flimsy thin walled old rubber.  Thinking of which what colour is anything coming out of the exhaust tail pipe after full engine warm up at idle?  Care must be taken with where any hoses off the engine come and go and blanking off.

 

You put your engine was same as the Wikki photo but then that there was a variation, are you able to see a period photo of your exact engine set up to your model and year in case there are other variations, owners alter things over decades so unless you have a concours correct car exactly the same model and year it is difficult to know which is correct (from factory at least).

 

I would be going back to just after setting valve clearances and rechecking everything, if you know someone with the same parts, and they are fully working well, you could try swapping over your parts to their car to test them and their parts on your car.  Just because something has been rebuilt doesn't always mean it has been done well or mistakes not made or faulty parts fitted, just because a part is new doesn't mean it cannot be faulty, or even the correct part sometimes.  I had 30+ years of buying and fitting ****-poor "classic" car parts, generally period New Old Stock parts (if still available) or working or serviceable genuine old parts are often much better than new made parts. (well for UK anyway) .

 

A different person looking at or working on the car can sometimes spot the obvious you have overlooked or previously checked or not bothered to check as "it won't / can't be that".

 

Wow, that was a lot, enough for now.  😄

 

Edited 22 December, 2023 by nta16

[nta16]

More (quick) thoughts.-

As ignition coils start to get towards failing they can sometimes do odd things and not just the one thing many say.

Electronics and electrics (items, wires, connectors) can sometimes function differently or not function at different operating temperature so fine, or not, when cold or hot and not function or so well at different temperature.

I am personally not keen on Colour Tuner as it is a bit subjective and in the UK at least different petrols and different petrol additives, one ethanol and lead replacement additive gives the the plugs a salmon or darker salmon colour.

 

 

Edited 22 December, 2023 by nta16

[RicardoM]

2 hours ago, J.R. said:

It makes absolute sense that a single carb 4 cylinder in line engine would have different combustion mixtures on the inner and outer cylinders, one glance at the compromised inlet tract lengths will show you exactly why.

Not to the extent described by the OP. Two black and two white is FAR from being a result of shape and length of the inlet tract.

Now let us wait for the OP collect relevant information. The ball is in his yard. Remember that he has full access to his car, while we decide based on breadcrumbs of information.

[hzoltaan]

Wow, thanks for all and happy new year! 

I was out for a good week visiting family with no access to internet or the car.

Thank you all the myriad answers, I'll try to go/check point by point:

 

What we know of this engine:

After buying the car a few years back as a project car (actually I learned to weld on it) it was always difficult to start. Once you got it going on all 4 pots, it ran good though. Not too strong. Always felt that it supposed to give a bit more umph.

Everything in the engine bay looks original, not tampered with, full of old SAAB bits. Stickers and whatnot make me feel that it was very well maintained till like 2016 when it got exported from Sweden. (I bough it in 2020)

It's a 1988 model, the simplest 99hp version with that Pierburg carb. 

Intake is hooked up to the coolant, and yes, airfilter gets hot air off the exhaust downpipe region. All of that was tested and works. Even the Thermostatic gizmo works to regulate intake air temperature. 

 

Work done:

After the purchase carb was re-built, new diagraph, cleaning, etc. It had lousy power due to a tear in the diagraph. That's got fixed. 

As it was still difficult to start, everything after coil was replaced. Lead set, plugs, distributor. 

And as it did not change a thing, I tried again with a different brand of leads, plugs, no change

Early on EGR was disconnected, (controlling vacuum hoses taken off between carb and thermostatic valve in intake manifold (the green little thing on the picture) 

Just now checked for valve clearances, all perfect.

...

...

and you know what, now that i'm looking at that picture i noticed that the vacuum hoses are connected differently...

Hang on.... Sadly there are not many pictures online of the carbureted engine, most are the more glamorous  injected... I'll have to verify that in the workshop with my manual.

It never occurred to me that somebody might have messed up reconnecting the vacuum hoses. 

For example the connection under the EGR that goes to the valve cover is blanked off in my case, 

 

I'll have to check that. 

 

Yesterday I had an idle few minutes in the workshop so i took off the EGR entirely. I'll properly blank it off with a flat plate. 

Need to get the fancy threaded bolt to close off the exhaust gas to EGR too. 

 

Give me the afternoon to check those vacuum lines.

 

Once again, great thanks for the help, much appreciated! 

 

 

 

 

 

[RicardoM]

One more relevant question is related to the history of the fault. Since you got the car, is this the first time you checked the color of the spark plugs?

Which one is true?

1. the engine had even combustion for years, then suddenly deteriorated.
2. the engine had uneven combustion all the time for years.

[hzoltaan]

Nr1 is true. After I got it  in 2020, i did a basic maintenance and plugs were evenly light grey then. (a bit too lean for my liking, my other carb'd car an '85 suzuki carry has light brown)

I was surprised to see black/white/white/black plugs now. 

No change in starting up though, it always felt like 3 cylinders fired up correctly and the 4th took a lot of play with the choke, a bit of throttle etc. 

(If i used it more often like every day I had no issue firing it up.  After a few days it would do it's usual 3 cylinders.)

Now it's in the workshop as i did some bodywork and thought of finally getting to the root of the issue. 

 

Just checked my Haynes, and there's no picture that would help me with the vacuum lines. 

 

[Paws4Thot]

@hzoltaan @RicardoM Back in the day, the usual UK cure for issues with a Pierburg carburettor was to buy a correctly jetted Weber direct replacement for $engine. Whether these are even still available I don't know.

[nta16]

I am not saying the following will be directly relevant to to your case just an example.

 

I bought a pre-converted larger engine (and brakes, tyres and suspension of course) British "classic" car and it had different (oversized) carb (Holly, with Offy) and vacuum pipes off.  Ran fine except at certain point of the rev range when accelerating it was like turbo lag (no turbo or supercharged fitted though).   As I couldn't borrow another of the same carb off a mate of a mate he recommended I take the car to a specialist in those carbs.  He had the carb for a week and could find nothing.

 

Then luckily I was recommended to an old school rolling road tuner, he had the car running outside the rolling road shed as there was a track-toy running something in on the rollers, he spent about 10 minutes running the engine, scratching his head and having a fag and then suddenly said something pulled a vacuum hose off and shoved a big long screwdriver down it and smiled.    Cut the hose to a stub, put a setscrew and small Jubilee clip on the stub to act as a temporary  blanking and said "Take it for a good run boy and see 'ow it gooes".  It ran marvellous.

 

When I returned from the run and asked he said the Americans have vacuums for this that and the other on their cars, he had no idea what that one was supposed to be for but wasn't needed on a British car, he didn't do American cars.  He didn't even want to take any money, he did something similar again on an unusual problem with another car of mine, spent 20 minutes on it, refused to fit the new carbs linkages parts I'd bought just in case and apologised for taking so long to remember the solution from a previous time (bent hinge pin on organ-type accelerator pedal).  Un fortunately soonish after he died.  A fantastic old school chap, too modest to even take a personal monetary tip let alone rip anyone off - so different from too many others I've meet in the English  motor trade.

 

[hzoltaan]

I guess they are, Webers are pretty famous. 

And here it is.

https://classiccarbs.co.uk/product/weber-40-dcoe-139-twin-carb-classic-alfa-romeo-1750-2000cc-twincam-engine/

 

It's only 700 quid! 

 

I paid about 800 for the entire car.

[RicardoM]

3 minutes ago, Paws4Thot said:

@hzoltaan @RicardoM Back in the day, the usual UK cure for issues with a Pierburg carburettor was to buy a correctly jetted Weber direct replacement for $engine. Whether these are even still available I don't know.

People dumped easily Pierburg carburetors because they are more sensitive to vacuum leaks. Any vacuum leak makes you wanna dump the car i a ditch and set it on fire. Sealing perfectly the underbody of the carburetor makes you love your very economical car.

So, no need of any Weber carb from my part.

[hzoltaan]

nta 16, sadly i miss contacts like that over here, moved a lot over the years, and more often than not i meet with mechanics who are utterly untrustworthy / incompetent or both. 

Fortunately for the Skoda Felicia I've happened to stumble upon a decent chap. But he is Skoda only, and only his Dad would poke around a carb anyway... Them Kids, don't wanna touch anything that's not injected.

 

Knowledge like that what you mentioned is simply priceless! 

 

Got an oil plug to seal off the EGR exhaust port (M16x1.5 thread) and set of new plugs. I'll try to find the time and put it together. 

 

I still feel that if it were carb issues, the sparkplugs would not be colorcoded like blakc/white/white/black. Hoping for a small leak around the EGR connection / valve cover air connection. I'll fix that up and report back.

(Might take a few days, I have a few projects running)

 

[RicardoM]

12 minutes ago, nta16 said:

I am not saying the following will be directly relevant to to your case just an example.

Obviously. The OP has very different combustion in 2 cylinders. It has nothing to do with the carburetor. I know myself too a lot of stories about "smart old school wizards" who in reality are a bunch of amateurs with zero knowledge about understanding engine diagnose and the effects of "miracle" solutions. Usually the effects are higher consumption and higher pollution. Irrelevant for street garage tinkerers.