Denso + NGK plug problems ?

[stevepudney]

one of the main reasons for plug breakdowns is the ht leads!
as the spark tracks down the outside of the plug and causes it to crack!
early ford mondeo's were notorious for this.

if you find this has happened to your plug then change that lead at the same time as theres a good chance that it will happen again;-)

the only plugs i will not buy for any vehicle due to many probs in the past are: champion! they are truly useless and a waste of money

i generally use ngk's on any vehicle i work on, but denso and bosch also are not far behind in terms of quality.

however you do occasionally get a faulty batch of plugs that do not work properly, ive had this a few times even with ngk, so just return them to wherever you bought them and get yourself another set!

That's odd because after I had the crack happen to me I called Denso Europe and spoke to one of there technicians, he told me it was due to a faultly plug (a weakness in the ceramic) some plugs are more prone than others.

This has also happened to me in the past with a set of HKS plugs (made by Denso). A few weeks after fitting, on routine inspection I noticed one of the plugs (pot 2) actually had a lump out of the ceramic so I swapped the damaged plug for a new one and by chance fitted brand new 8.5mm Magnecor leads at the same time.
Again a few weeks down the line I checked the plugs and the plug in pot 4 had a crack running down the ceramic.

Even the chap in Sparkplugs.co.uk told me it was the plug at fault, hence he replaced my damaged one.


Steve

 

[Fazz]

Just an update on my experience with plugs.

Car was fitted with NGK Grade 9's goin on research on here.

Car went for mapping with RC and couldn't be done due to miss so changed plugs to HKS's and all mapped fine.

Car developed slight miss month later, I checked plugs all seemed fine. Swapped back to the NGK's to see if any difference (also all appeared fine), the car missed a lot more with the NGK's.

Swapped the Leads and no difference, turned out to be dizzy cap but point here being the car wouldn't run on the NGK's. Suffered badly from miss in every gear.
No such problems with the HKS's and going perfect.

I know which I'm sticking with.


FYI - running 1.5bar on 3071.

 

[turblio]

Well thats interesting Fazz as I am running NGK 9's and have a missfire whats the exact number for the HKS plugs you are using?...

 

[Shaun]

That's odd because after I had the crack happen to me I called Denso Europe and spoke to one of there technicians, he told me it was due to a faultly plug (a weakness in the ceramic) some plugs are more prone than others.

This has also happened to me in the past with a set of HKS plugs (made by Denso). A few weeks after fitting, on routine inspection I noticed one of the plugs (pot 2) actually had a lump out of the ceramic so I swapped the damaged plug for a new one and by chance fitted brand new 8.5mm Magnecor leads at the same time.
Again a few weeks down the line I checked the plugs and the plug in pot 4 had a crack running down the ceramic.

Even the chap in Sparkplugs.co.uk told me it was the plug at fault, hence he replaced my damaged one.


Steve

Hi Steve,now this is just a thought mate,i noticed the other day that my Denso plugs actually have a resistor fitted to reduce noise,now here's the thing,when i had my R5 turbo i fit some hi power leads not realising that my local motor factors had given me a rotor arm with a resistor fitted a few weeks later it developed a missfire,when i found the culprit the resistor in the rotor arm had actually melted :shock: and the tip of the rotor arm was barely hanging on so do you think that with you running a high power ignition system could be causing problems with the resistor in the Denso plugs and 1)causing the missfire and 2)Causing them to crack when the resistor expands under the extra heat that the high powered spark produces?Have you tried a sparkplug without the resistor fitted?

 

[stevepudney]

Hi Steve,now this is just a thought mate,i noticed the other day that my Denso plugs actually have a resistor fitted to reduce noise,now here's the thing,when i had my R5 turbo i fit some hi power leads not realising that my local motor factors had given me a rotor arm with a resistor fitted a few weeks later it developed a missfire,when i found the culprit the resistor in the rotor arm had actually melted :shock: and the tip of the rotor arm was barely hanging on so do you think that with you running a high power ignition system could be causing problems with the resistor in the Denso plugs and 1)causing the missfire and 2)Causing them to crack when the resistor expands under the extra heat that the high powered spark produces?Have you tried a sparkplug without the resistor fitted?

Hi Shaun

Interestingly enough the same sort of ish thoughts have gone through my head, hence I have some NGK 9's coming today.

My theory is:

1. the standard factory ignition of the Pulsar SR20DET was designed to do what it does on the standard car and it did it quite well in it's day and all things considered still does 13 - 15 years later. Then people like us come along and we push the boundaries of this system to the limit with bigger very efficient modern turbo’s and it basically boils down to the system in standard form not being able to produce enough power for the demands were putting on it. What seems to be surfacing as the problem is the distributor.
2. So to help boost the power of the standard ignition we use the MSD/Mallory/Crane/Magnecor ignition equipment, this without a dought helps and it definately produces more power as we do get a bigger/stronger spark, so generally we can push things a little further forward but the same problem surfaces itself and stops us going any further forward, the fact that the Pulsar uses a distributor.

I think it very important to match all the various components of the whole build because they are all only as strong as the weakest link in the chain.

If using the higher power MSD/Mallory ignitions I think we should consider the weakest links to be the distributor cap, rotor arm and plugs.

In my case I think the Denso plugs are showing the first signs of weakness with this misfire, because they were fine when first fitted. So hopefully the NGK 9's that have just arrived will help and last a little longer.

We shall see




Steve

 

[Fusion Ed]

Shaun raises a very good point here. I have been reading up on this in a few books I have and it appears that the resistor fitted components should be avoided for these reasons.

I have a gtir distributor here on my desk, I have just been playing with its cam/crank outputs, in an attempt to see weather it would be possible to read these and make a unit that distributes the signals to separate coils / wasted spark system. It certainly seems possible. There is also the option for those with e-manage ultimate to do this, again needs to be tested with firmware 2.12, as up until now its not been working. I may also try this today.

Ed

 

[turblio]

Well the dizzy is the only part I have not changed (other than the injector loom or lambda sensor) be very interested to see what you find Edd

 

[stevepudney]

Well the dizzy is the only part I have not changed (other than the injector loom or lambda sensor) be very interested to see what you find Edd

You miss my point Frank, your distributor isn't the "problem" the problem is that unlike most other high powered turbo cars the Pulsar "uses" a distributor.


Steve

 

[Fazz]

Well thats interesting Fazz as I am running NGK 9's and have a missfire whats the exact number for the HKS plugs you are using?...

Hi Mate,

Think they're the S45's. Give Rc a shout they do them fairly reasonable at £40 I think. Same as the NGK's.

Also check your leads and Dizzy Cap as a few of us have experienced these as problems also.

Hope it resolves for you mate.

 

[campbellju]

I did a post on this on another forum I'll dig ot out and copy it across.

Its got my own tests, others theory and experiments and my own conclusions.

 

[campbellju]

WARNING: This is for electronics geeks only at the moment!!!!

I've been doing some research and testing of my own ignition system as I moved to a Mallory Capacitive Discharge type, I have some Magnecor and OE leads and can vary my plug gaps as much as I want. If I can optimise these then I should be able to get a more efficient spark.

For reference, A few resistances I've been checking from my parts:

Nissan OE leads resistance are between 6K - 11K (About 20K/m)
Magnecor 8mm (blue) leads resistance are between 3K - 6K (About 11K/m)
Magnecor 8.5mm (Red) leads resistance are between 6K - 11K (About 20K/m)

The Nissan and Blueprint rotor and cap have negligible resistance
The secondary coil resistance of the OE and Mallory coil are about 10K


I found this interesting post from an airplane based site that I thought I'd post up in the meantime as it filled in a few gaps for me.

I have some preliminary thoughts but no conclusions but thought I'd post where I'm up to.

Jim
---------------------------------------------------------------------------------
Recently an interesting thread on this newsgroup discussed the relative merits of resistive plugs as used on many Rotax engines.

In order to get to the bottom of this Spark plug vs. resistance story I decided to do some experiments. I am a electronics engineer (when I am not flying , so I have the tools for the job.

First a coil was rigged for the job to create the high voltage required for the plugs. I used a standard car coil combined with an electronic interrupter/generator. Spark plugs with and without resistors as well as caps with and without resistors where obtained. The plugs where all equally gapped to 0.4mm. I used a scope to monitor the voltage at the plug tip as well as at the coil (via high impedance probe - scopes are expensive !). The result was quite interesting.

As expected, the voltage at the cable (before any resistor) rises at the same rate regardless of resistance until the point of firing. Thereafter however the picture changes.

The coil generates a certain amount of energy. This energy wants to go somewhere. At a voltage of about 7KV the plug fires (irrespective of resistance). Until that happens NO CURRENT FLOWS. Whether you have resistance or not does not matter. A paltry 5KOhms does not do anything when compared to the nearly infinite resistance of the gap itself (until the plug fires that is).

Once the plug fires the resistance comes into being. The coil cannot get rid of its energy in the shortest possible time due to the resistance.

This reduces current flow in the spark and it takes quite a bit longer until the energy in the coil has expelled itself via resistor and spark gap. This results in a longer spark. However the spark is weaker due to energy loss in the resistor.

The scope shows this very nicely and it also gives reason why the resistor helps to suppress RF. With the resistor changes in the rate of current flow are much less resulting in "flatter" edges on the voltage vs. time curve that the scope shows you. This implies less high frequency components of the signal in the cable feeding the spark plugs.

Conclusion: It is quite safe to insert a resistor. It will not stop the plug from firing at all. High values will however lead to a weaker spark -but it is going to spark, no matter what.

However, contaminate the plug with fuel (even just a little) and a high value resistor will cause the plug not to fire. 10K plugs as are used on some motorcycles now are about maximum I would guess.

I do not recommend you use resistance plugs or caps at all on inverted Rotax installations due to the possibility of plug contamination by oil and fuel.

As further experiment I increased the resistance value to see what effect this is going to have. I tried values 10K, 47K, 100K, 220K, 470K, 820K and 1M.

Even with 1M the plug (dry, not contaminated) still fired but noticeably weaker and longer (you can actually see it firing longer !). But contaminate this plug even slightly (a little moisture by exhaling onto it) and you get no spark.

Finally, a disclaimer: All of the above has been found out by a little experimenting. Use the results at your own peril. Don't get back to be with a heap of bent metal that used to be your plane claiming it is because I said you should put 1M resistors into your spark plug leads. I did NOT

 

[campbellju]

here is another good site I just found from NGK Oz, a surprisingly pragmaitc FAQ from a supplier:

(Link gone)

Some more interesting reading:

(Link gone)


http://www.stealth316.com/2-sparkplugtech.htm

 

[campbellju]

Summary, non geek friendly:

Aftermarket capacitive discharge systems: Better for high boost high rev applications than OE. Will not give more power on their own but will allow more accurate tuning of the ignition map so in "theory" more power (At high boost/rpm)

However, their short duration is why they have to fire many times at low rpm with lean mixtures. Without this "feature", CD systems will misfire. Inductive OE systems with longer durations don't have this problem. However, running small plug gaps on an OE system would give similar problems.

Plugs, leads, caps

If you'll excuse the pun these are just noise. Yes they will make a difference but assuming your ignition system is in good order for the application, this is just fine tuning.

Plug Gaps

This is where the coarse tuning mainly comes from. When you look into the detailed theory, even with a fancy CD system, I would agree with this quote from the NGK site:

"In most cases, the largest gap you can run may still be smaller than you think."

So in my opinon, what is the optimum gap for a given car, I'm sure this will make the non-geeks laugh, its excert from the "eng-tips" car website:

"I spent a day just varying the gap and observing the results. I adjusted the timing to optimum after each gapping as well. I got the best performance with a gap just smaller than that which caused a misfire. I also noticed that the smaller gap caused pinging more readily. As mentioned, real-life compromises dictate the best overall gap."

After all this nonsese theory, this is still the best way to set a plug gap!!

 

[campbellju]

Update:

Again here is my favourite quote from NGK

"In most cases, the largest gap you can run may still be smaller than you think."

On an uprated ignition syetem I've seen the spark jump over an inch to some random pieces of metal in the area. There is a lot of energy generated. The rotor has no resistance, after market leads can have lower resistance. This means the resistance in the plugs are more critical for controlling duration. Low resistance is good for high boost high rev but makes life more difficult at low load/lean mixtures.

Too much energy through your ignition system will wear it out faster making caps/leads and plugs more consumable.