Spark plugs for the six-pot

[Nick Jones]

I've got a couple of sets of these.......

Plasma plugs...... 

We had it cruising at 18:1 AFR without hitching but never got it mapped properly as the plugs were offending the ECU for some reason....  The second set has more holes but I've not tried them.

[richy_rich]

7 hours ago, Nick Jones said:

the plugs were offending the ECU for some reason

I would guess because most of the 'plasma' plugs are based on adding capacitors in parallel to the plug? 

There's some explanation as to how it works here : https://pulstar.com/how-it-works/patented-capacitor/

Not sure why that would upset your ECU though, maybe just added too much noise to the electrics in general?

 

[JohnD]

12 hours ago, PeterC said:

   Yet another sales pitch relying upon "quantum" to sell.  

I'ce seen one of those fan-plugs.....in a ModelT Ford.

Peter

There you go!  I said it introduced an imaginary time axis at right angles to normal time!   How do you think Henry Ford got to know about it?

J

[JohnD]

4 hours ago, richy_rich said:

I would guess because most of the 'plasma' plugs are based on adding capacitors in parallel to the plug? 

There's some explanation as to how it works here : https://pulstar.com/how-it-works/patented-capacitor/

Not sure why that would upset your ECU though, maybe just added too much noise to the electrics in general?

 

The link to the PulseStar plug decsribes the capacitor in series with the electrodes.    The video shows them in parallel, and it looks as if that uses a constant or high frequency high voltage, not a pulsed one, so I'm not convinced that it describes what happens in an engine. or what is happening in the PulseStar.    (The ad blurb claims that the capacitor is in parallel)

In the video, the constant/HF HV allows the capacitors to charge up and accumulate extra energy, which is then released in the next discharge.    That wouldn't happen with a PulseStar, as all the pulse of HV will be discharged through the capacitor before the next arrives.    I can't see what advantage that will give.

John

[Nick Jones]

4 hours ago, richy_rich said:

Not sure why that would upset your ECU though, maybe just added too much noise to the electrics in general?

It was a noise problem.  I've got better HT leads now so could try them again maybe.  No capacitors involved as far as I know and they are resistive plugs albeit lower resistance than "usual".

[Hamish]

Why would you buy anything else!!

 

[richy_rich]

2 hours ago, JohnD said:

The link to the PulseStar plug decsribes the capacitor in series with the electrodes.

I don't see that, it's built into the plug, but it's effectively in parallel between the electrodes, the 'negative plate' is essentially the thread of the plug.  They also explain that it's in parallel, for me it's identical to the setup in the video, just built in to the body of the plug.

I would suspect that this (or some version of it) is also what is in Nick's plugs, but I've also seen experiments with drilling the electrodes and not using a capacitor along with hand-wavy explanations about ionized gases so I could be wrong. 

[DeTRacted]

OK this is on a bike but still......:-

http://xlforum.net/forums/showthread.php?t=1555404

Adding a capacitor in parallel with the plug gap puts it in series with the coil. In a conventional setup that just lowers the resonant frequency of the  LC network which ought to slow the risetime of the coil voltage and allow some HF energy to flow directly to earth before the plug gap breaks down.  However, the value of the capacitance will be small and probably in the same order as the stray capacitances in the coil and leads, so any energy lost (or stored as they claim) may not be significant.

[JohnD]

Richy, you're right I missread the diagram, then read the blurb.

J.

[PeterC]

For really really big sparks: corona ignition:

 

[PaulAA]

On 5/22/2019 at 2:08 PM, PeterC said:

For really really big sparks: corona ignition

 

A remarkably foresighted piece of information, Peter...

 

Meanwhile, the three-pronged Bosch plugs have sat gathering dust on a shelf and only this weekend did I remember to swap them in.  Job done and...

BANG!

...what a difference!  The improvement is remarkable, particularly at low revs.  The engine loves these plugs!  It pulls like a train from 700rpm, even in top, and is considerably smoother and even feels more willing.  Thanks for the suggestion, Nick!

In contrast, the Benz Barge I've just bought for Junior has started running like a dog.  It's missing irregularly, which feels like an ignition problem.  Dizzy cap and rotor swapped without improvement and I was searching for the correct plug spec.  Interestingly, all the usual Benz forums recommend the most basic copper-core Bosch Super plug - no multi-prongs, no iridium or platinum fancy plugs.  And it turns out that getting hold of simple copper-core plugs (well, here, at least) is becoming difficult...

Paul

[Nick Jones]

Yep, Triumph engines love the three-pronged plugs, or the four pronged ones, or, I think, anything which is effectively a side-electrode.

As regards the Merc..... you (or he) haven’t picked up a dodgy tank of fuel somewhere? Assuming it’s injection, a pot of injection cleaner may help, especially if K-Jet.

[PaulAA]

Thanks, Nick

Ah, that's a thought!  Do you have a preferred brand for injector additive or will any do?

Paul

[Nick Jones]

Not alot of use to you...... but I usually use the Toolstation stuff - purely because it’s really cheap and seems to work. Wynns, STP etc all likely fine.

[PaulAA]

Thanks again, Nick - 3 quids' worth of STP laxative and combustion constipation is almost cured.  I'm going to replace the rubber boot between the throttle body/fuel control unit and the throttle gate, which is a common source of air leakage, apparently.

[Nick Jones]

The STP stuff is more than 3 quid here..... that’s why I buy the Toolstation stuff.

Had the the Merc been stood up / on light duties before it came to you?

[PaulAA]

Not sure - the PO had had it for two years, but I can't verify how much it had been used since being imported from DE.

I took it out this evening and it ran like a dog again... until it had fully warmed up. Then it ran relatively smoothly and was happy to pull (almost) smoothly from 1,000rpm in top.

It's a fair schlep to the new Mr Spanners, so the car will be warm when he sees it, which is not good.

[Nick Jones]

Running worse at low revs/light throttle and cold could indicate unmetered air - inlet leak somewhere?  Running "like a dog" is a bit ...... vague.....  Which engine is it and which injection?  (probably in your other thread but too idle to look.....)

[PaulAA]

Yeah, sorry for the excess of frustration there...

1990 230TE, so the M102.982 engine with the later KE-Jetronic system.

The dog-like qualities are most pronounced when cold - uneven tickover, extensive 'missing' which worsens as the throttle is pushed, no power under load. Dissy cap and rotor were replaced, without improvement.

Even when thoroughly warmed, it still misses intermittently, particularly when picking up from idle.

The throttle body boot is being done as I type, so I will update after the journey home.

It's a big space under the bonnet, but could it have baked its engine wiring loom over the years?  It does look pretty original and unadulterated under there...

[Nick Jones]

Ok..... KE is great when it’s working...... and the basics are simple and reliable...... but can be hard to diagnose and specialist tools (pressure gauges) are needed really.  It’s all about fuel pressure and control pressure. On the KE the control pressure is partially controlled by an ECU so could be a wiring or coolant temperature sensor. There may also be an O2 sensor if it has a CAT? Simple stuff like fuel filter shouldn’t be overlooked either.I’ve had few cars with the earlier and simpler K-jet but not messed with KE....

[PaulAA]

Just collected it and, hot, everything seems to be as it should - no missing, even idle, some more horses to play with.  The proprietor's more capable (and communicative) mate ran me through what he'd done (= what had evidently not be done first time) and it covered what you've just highlighted - adjusted the MU, balanced the pressures and visually checked the wiring.  It has a cat and I noticed that the insulation on the o2 sensor appears to have de-plasticised, so probably time for a replacement...  Oil, fuel and air filters replaced first time round, but he did suggest replacing the KE with a K-Jet Killer installation.

More of a test in the morning, starting from proper(ish) cold.

Paul

[PaulAA]

So, cold running is still rough, with a reluctance to pick up when the throttle is pressed.  Happy enough when warm, though.  Cold start injector, maybe?

 

[Nick Jones]

My experience with the cold start injector on k-jet is that it’s best disconnected electrically and left that way. The three cars I’ve had with it all started fine without even in the depths of winter, whereas having it connected caused issues. Basically over fuelling while cold but with some randomness thrown in. Might be worth a try.

[PaulAA]

So, briefly on the Benz Barge...

Found a proper enthusiast mechanic, who clearly eats, breathes and farts W124s.  His personal transport is a very comely 500E.

It took him two weeks to pin the problem down, but it turned out to be the combination of a fault in the ECU, a minuscule rupture in one of the throttle body diaphragms, an electrical fault in something with a long name (sometimes, I am defeated by the seemingly illogical Polish names for components) and, of course, a fault in temperature sensor no.2.

Fixed, admired and returned to base.  It is now a pleasure to drive.  I hope it is the same story after a cold start.

Paul

[Nick Jones]

Mechanic sounds like a good find......

Lets hope it’s done the trick