Intriguing discovery about spark plugs-got the right ones?

[Ade]

To cut a long story short, my turbo has been a bit of a bitch this week, 3 days it failed to start when cold in the morning, flatted the battery trying and ultimately got it going by bump starting but with a horrendous misfire until slightly warmed up, by which time all seemed normal and it would start up again fine throughout the day, just not, apparently, after being left overnight in the cold and damp, such was the weather here for somewhat of the past week.

I had been experiencing a slight misfire from cold for a little while but it would disappear after literally a minute or so of running and I attributed this to possibly my coil or ignition module having seen better days (rest of ignition system components all new when engine was installed in the car about 3-4 months ago but the coil and the trigger box were taken from the blue one and as far as I know, original). As this eventually seemed to manifest as a total failure to start, I sourced a new module and coil. For interest, the OE Bosch coil/trigger box assembly IS still available if you quote the actual Bosch part number rather than going by registration or engine code as these methods don't seem to yield the correct, if any, results. The number, if you want one, is 0 221 600 066. A google search of this initially reveals trigger boxes without coils but if you quote this to GSF, for instance, and tell them you want a genuine bosch one, they will get you one from germany and it's the complete OE assembly. There's none in the UK at present, or at least there weren't last week so I ended up getting an aftermarket trigger box from MVC in Coventry, who are great and managed to get it same day and while I was there picked up a coil for a Saab 9000 with N/A B202 engine, which has a very similar setup. Any will do really (as long as it's for electronic ignition) but the connections on this one for both the king lead and the trigger connections are spot on and the good news is that it's cheap and readily available.

After fitting my newly cooked up ignition assembly the car did feel better and so I was hoping 'problem solved'....

Then came the following (cold, wet) morning

Wouldn't go again. I eventually managed to attribute this to a faulty temperature sensor but along the journey of delving into the rest of the ignition system just to be sure (the memories of misfires pointing me wrongly in that direction), I made an interesting discovery regarding the spark plugs that were fitted that wouldn't have been helping my cause on a cold, damp morning with out of tolerance sensors at play. On the subject of which, any of the electronics gurus know what the jetronic would do if it detected like 25k ohms at the temp sensor? 0 degrees is supposed to be around 6.8K ohms? Would it have been flooding me and wetting the plugs thinking it was like minus 150 degrees or something silly, given that resistance goes down with temperature or is there some threshold tolerance at which it will react in some other way? Be interested to know... the look of the plugs wasn't too bad, didn't look like it had been suffering too much of an over rich condition (although maybe the sensor wasn't too far out of tolerance in the upper ranges) but anyway, onto the interesting contributing factor of the aforementioned spark plugs...

It turns out they're the wrong ones for the engine, and not just the turbo as all engines take the same OE spark plug and the worrying thing is that I've been given these spark plugs before and they are also to be found in my recently acquired B18FT, which shows that there is mass circulation of an incorrect spark plug that is supposedly for our engines but is in fact wrong. I had never really payed that much attention to the spark plugs apart from buying them (quoting my engine code) and fitting them. Shocking really that I never noticed the difference before when taking old out and fitting new but during my ignition system adventures I decided to change back to a different set of plugs that were quite new at the time I took the engine out of my blue one and stripped it down, hence why I kept them, and this time, I did notice the difference. The plugs that I was supplied with previously were in fact the correct ones for the engine and these are an NGK ZGR5B. This format of NGK part number denotes a plug made to an engine manufacturer's specifications, not a part of NGK's own standard range. Their own range has a different part number format and these incorrect plugs are from that range and the part number is BPR7ES. If you have been given BPR7ES's as the correct plugs for your engine, they are not. The ZGR5B is the plug made to the original specification for these engines and when you compare them, there is a hell of a difference Have a look for yourself if your interested, tells you how to read the code on the plug-


https://www.ngk.de/fileadmin/Dokumente/ ... ode_en.pdf

There is an oddity though. If you have 'read' the codes, you will notice that both spark plugs are denoted (in a different format) as being a 14mm thread with a 20.8 A/F hex and 19mm thread reach. When compared, the ZGR5B is noticeably longer than its supposedly identical counterpart. Like a 1/4" or more. This is massive in terms of electrode positioning inside the chamber

The 'Z' part does denote 'extended gap' but I'm not sure this is anything to do with it as the electrode on this plug is V grooved and I would imagine it is referring to the spark gap being extended by virtue of this rather than the whole thing sticking out more. Perhaps the extra stickout is some part of the 'special design' denoted by the 'B' but either way, the point is, that aside from the heat range difference (the cooler plug not necessarily being a bad choice if like me, you give your turbo a good hoofing and like boost ), there is a big difference in the overall position of the electrode, the OE spec protruding much further into the chamber, facilitating a better combustion, albeit it at increased risk of knock, although it's not only electrode stickout that determines the heat range of a spark plug, in theory you could have a '7' or cooler heat range plug in the engine with its spark gap positioned correctly if the design was right. It would be good to find a better suited cooler plug for this engine for hard driving, something I might look into if I ever find the time... In the meantime, if, for instance, I do a track day in it again, I will switch back to the BPR7ES's as it will run ok on these, as it has in the past and the cooler plug with less stickout is safer for this type of driving. For daily use, it runs much much nicer on the ZGR5B and I can see why. I can also see why the BPR7ES would have compounded a cold start issue caused by the temp sensor, with the electrode tucked so far up, there will be much less tolerance on the conditions required inside the cylinder to achieve a combustion on a shitty cold damp morning, so incorrect fuelling is all you need

With the whole ignition system from module to spark plugs and everything in between now less than six months old, the temp sensor sorted and the correct spark plugs, she runs better than ever and she wasn't bad before, or at least not until last week This could explain the until now inexplicable mystery of why some sets of plugs have seemed better in this engine than others over the years. I think some were right, some were wrong and I can't believe it's taken me this long to notice

So there you have it, a bit of hopefully slightly less than useless and nevertheless intriguing info about spark plugs. Go and pull your HT leads off and let me know what spark plugs you have It would be interesting to see the mix, other manufacturers numbers should easily cross reference to one NGK plug or the other, or maybe more

Wonder what the actual Volvo spark plugs are like, does anyone know off hand if the centre electrode is V grooved on them or whether it is in fact NGK that makes them? The ZGR5B is supposedly the OE spec plug, be interested to know if it is in fact identical to a Volvo one or whether its got a bit of NGK development for the application in it as well, like the V groove for instance. Might get some genuine plugs next time just to satisfy my curiosity if no one knows!

Every day with a 480 is a day of discovery.....

[dcwalker]

Interesting!

Having gone around the houses over the years with different makes, for some years now I have always used genuine Volvo spark plugs in my cars. I know someone else makes them etc etc, but this way I feel I can be certain to have the right ones, they seem of good quality, and usually not expensive.

Aiming to service Lily very soon, including a spark plug change, so if I remember I'll post up a picture or two on here of the genuine article.

David

[jifflemon]

Interesting..... remember I changed the plugs recently?



Bosch left (old) NGK right (new).

Looks like I'll be changing them again!

EDIT: Just re-read Ade's post - I've got the right ones! Phew!

[AleksanderHugo]

I have also noticed that the plugs are different length, despite being all listed for Volvo 480. I had Bosch plugs for some time and I replaced them with Champion rn7lcc, which are noticeably longer. However, I didn't notice a big difference in the way the engine is running.

[Ade]

However, I didn't notice a big difference in the way the engine is running.

OK, maybe I was over egging it a bit when I said "much much better" But there's definitely a perceptible difference I think, albeit a subtle one that perhaps only an engine nut like me would really notice! It makes sense that there would be, with bowl in piston style combustion chambers, the electrode being tucked right up in the head is certainly not going to do the combustion quality any favours, as I remember when taking the head off (with the correct plugs fitted, the ones that are now back in), the plugs didn't protrude overly far anyway so those incorrect ones must barely reach into the chamber at all, the net result of which will be a shit flame propagation through the cylinder. Out of interest, which engine does your car have? The difference may be less noticeable (certainly in adverse starting conditions) in a N/A engine given that it has a higher compression ratio and thus the mixture is already hotter at TDC on compression and so easier to ignite. Obviously the cylinder pressure thing goes out the window when a turbo is on boost as ultimately the absolute pressure in the cylinder will be higher than N/A because of the forced induction, regardless of comp ratio, but for starting and gentle cruising, the N/A's will be less affected I think. Of course, if yours is turbo then who knows???? Maybe I'm imagining it (although I don't think so) or you need to pay more attention to the subtleties of your engine I jest, of course, no offence at all intended!

Jeff, looks like the bosch ones you pulled out are the equivalent incorrect plug to the NGK BPR7ES and yes, the new NGK ones you have are correct. Be interested to have another opinion on whether you can perceive any difference in the way it runs from one to the other.... also, can't see brilliantly, but does that bosch one look more fouled than the correct one? Both sets looked ok for me but there was a difference in colour (just erring towards fouling but still quite a nice grey/brown) on the cooler plugs but not much. Although I hammer mine daily (it goes over 4K revs at WOT at LEAST 5 times a day, often more ) and so the cooler plug probably would have reached sufficient temperature to 'self clean' in my scenario, whereas one driven perhaps less often and a little more forgivingly may not. All interesting stuff anyway....

[Ade]

but this way I feel I can be certain to have the right ones, they seem of good quality, and usually not expensive.

Aiming to service Lily very soon, including a spark plug change, so if I remember I'll post up a picture or two on here of the genuine article.

Sensible really, I'm discovering more and more stuff supplied by motor factors that isn't listed correctly. Off the top of my head (for turbo at least) ignition coils, valve stem seals, lots of sensors and management components and now spark plugs seem to regularly be incorrectly listed. For what it's worth, jogging my memory, it seems that GSF tend to yield better results than Euro, talking main factors. I know my incorrect plugs were supplied by euro, as were some incorrect stem seals when rebuilding the head (much to my dismay when I'd been planning to put the valve gear back in that day ). I have a feeling my correct plugs and correct stem seals (I gave up with euro on these although it turns out they did have them in stock but just not listed correctly but I thought 'bollocks to you' out of principle and went to GSF instead!) were supplied by GSF. Steer clear of euro car parts for 480 engine parts, seriously, you will end up taking most of them back Their database really is fuck awful where the 480 is concerned, worse than most.

Pics of the genuine plug would be nice if you do get a chance

[Robou]

A correct spark plug for starting the engine doesn't exist. As long as it is clean, that is has no carbon deposits or is soaked, and the gap is not too large, that is let the spark go the easier way by jumping inside the coil or the distributor or between the leads, any plug will do.
A correct spark plug is determined by the temperature inside the cumbustion chamber and this again is determined by the way you use your engine. The plugs are ranged from warm to cold and the hotter the temperature in the cumbustion chamber the colder the plug should be. The colder the plug, the better it transports the heat from it's tip to the mounting area.
This is all there is to it. So if there is a starting problem better check the mixture at that point by the co-pot than worry about the right plugs.
By the way, for over 10 years now I use the NGK BPR8ES under all conditions and it suits me well. I have no need to follow the car manufacturers' specifications and look for plugs which are hardly obtainable and if, are too expensive. The location of the tip in the cumbustion chamber is purely theoretical, it may ideally lead to a more effective combustion. But the transport of the heat is less effective and because of the whirling mixture it at the most is a matter of microseconds.

The ignition of the turbo is not the best Bosch could have incorporated at those days. The dwell is fixed, which means the spark is not optimal at low revs and then dies out at about 6000 revs. This means the fuel stop in the Jetronic is practically superfluous, the spark will die sooner. There are two versions of the ignition module, one with a bipolar transistor and the other with a mosfet. The letter has less voltage loss while switching the coil so delivers a stronger spark. This may make a difference at cold starting. The Saab module probably was like this. The module does nothing but amplifying the pulse from the EZ210K, it does not change any of its shortcomings.

[Ade]

A correct spark plug for starting the engine doesn't exist.

I know that

The plugs are ranged from warm to cold and the hotter the temperature in the cumbustion chamber the colder the plug should be.

Hence me saying I would put the cooler plugs back in for a track day to reduce the chance of knock

I have no need to follow the car manufacturers' specifications and look for plugs which are hardly obtainable and if, are too expensive.

They are easily available and not expensive, it's just the point that when you request an OE spec plug from a supplier, you should get it, not another plug that's deemed suitable, even if it is. It's a happy coincidence that this plug is good for hard driving of this engine but nevertheless you should not be given it as the 'correct' plug. Choose it of your own free will.

So if there is a starting problem better check the mixture at that point by the co-pot than worry about the right plugs.

Changing the temp sensor has cured my problem and I just happened to discover something about incorrectly supplied spark plugs (they were and are, in the UK at least supplied by some as OE plugs for this engine) that answered a little nagging query I've had for a while about the SUBTLE difference in running I have noticed between changes of spark plugs, having never realised the plugs were so different. And what would the ecu do given my 25k ohms resistance at ambient? Too much fuel, or no? Wouldn't the spark occurring further away from the theoretical ideal than with the OE plug make a small difference to the point at which an incorrect mixture would refuse to ignite?

The location of the tip in the cumbustion chamber is purely theoretical, it may ideally lead to a more effective combustion.

This is all I'm trying to point out as a matter of interest to those people who do pay really close attention to the way their engine runs, because you can notice really subtle things in engine running with changes like this. Look, I take my hat off to you, or I would if I had one, for your knowledge of the electronics in these cars and you obviously know your engines as well but believe me, so do I, albeit from a different perspective, I've been fascinated by them since I can remember and I was around them and working on them not long after and striving to understand them better all my life and I have ended up working professionally in motor racing. I do not possess your knowledge of the electronics but I have a good ear and feel for engines and I do stand by the fact that my engine runs better on these plugs, and not just now but in the past as well with hindsight, reason being that the spark is occurring in a closer to theoretically ideal place, thus better combustion.

My gut tells me that the shorter plugs weren't helping my cause, albeit by an immeasurably small amount, given my sensor issues with the cold damp start, that's all, and I was just sharing a little knowledge and experience along the way. My gut is normally pretty good when it comes to such things and the fact is that with the temp sensor sorted and the OE plugs, my engine starts as it should and runs like it did when (in the 'unknowing about the different spark plug' days) it seemed 'happier' with a particular set of plugs it happened to have. I agree, colder plug for hard running with high temperatures but for the daily drive to work she feels a lot nicer on the stock plugs in the lower rev ranges. Go and get a set and see for yourself, I swear to you if you drove the car with one set of plugs, then swapped them and immediately drove it again with the other, you'd notice a difference if you were paying enough attention.

There are two versions of the ignition module, one with a bipolar transistor and the other with a mosfet

How do you tell them apart? Is the part number for the module and coil assembly that ends 066 (which supercedes the one ending 065) one type and the superceded 065 the other? What type would a typical modern aftermarket one be in all likelihood? Just to be clear, my module/amplifier whatever you want to call it is referenced to the 066 number and is the right one for the car, the saab bit is just the coil itself, I thought it couldn't hurt to have a new one along with the module. Don't forget, I had plausible reason to suspect an ignition problem, especially given the age and visual condition of the existing parts and a pre existing slight misfire from cold. Potting resin on the module was cracked open for one so I thought that moisture ingress might be a problem, damp mornings were the problem after all. Thought maybe once it warmed up a bit, it dried out, you know? The spark plug thing was just an interesting discovery for me along the way that I thought I'd share and it did shed some light on a previously unanswerable query of my engine being on the BPR7ES's (and safer for giving it some, happily) but being on the ZGR5B's in terms of general smoothness and refinement of running. Not unreasonable when the spark is occurring quite a bit closer to the optimum point, no?

[Robou]

We agree and disagree on some points, to my opinion minor ones. There's theory and practice, and the latter is chaos with too many parameters to be sure of the ideal solution.
About the ignition module I'm not sure, if the part numbers are different choose the newer. I never bothered because I'm using the module as trigger for a self contained ignition system.