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Re: Misfiring at 20 PSI, high RPM. Spark Plug suggestions? (Longitudinal)

I assume you have decent plug wires? Under high boost levels you could blow the spark. 2 things to try are a smaller gap (which you are doing) - Colder plug (same thing)- then If you keep having problems you might want to try a better plug wire - or aftermarket ignition if you are not running one allready.
 

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Discussion Starter · #4 ·
Re: Misfiring at 20 PSI, high RPM. Spark Plug suggestions? (rivethead)

Quote, originally posted by rivethead »
I assume you have decent plug wires?

New Bosch. I have not yet been convinced I need any more than that.
Quote »
Under high boost levels you could blow the spark.

Extinguishing the spark is exactly my concern.
Quote »
Colder plug (same thing)

Actually the NGK numbers run backward. The 5 is a hotter plug. I should be considering a COLDER plug to try to keep spark alive?
Quote »
or aftermarket ignition if you are not running one

That might be necessary. Right now, it's Bosch KS with a turbo 5K coil. The turbo coil is known to work very well for 18+ PSI, and I am firing it earlier in the cycle than most, which should make the job of sparking easier (sparking under lower cylinder pressure than if timing is retarded a lot.)
.028", eh? By what interval should I adjust gap? I was thinking .005 closer (like .025",) but it seems like maybe I should take very small steps until the misfire goes away?
This FI tuning is mostly new to me. Previously, on NA engines, it was mostly set it and forget it.
 

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Discussion Starter · #6 ·
Re: Misfiring at 20 PSI, high RPM. Spark Plug suggestions? (Jefnes3)

Quote, originally posted by Jefnes3 »
NGK BKR 7E
(copper plug 2 steps colder than ~stock N/A plug)
Gapped to .022"

-Jeffrey Atwood

Thanks. I don't recognize that part number. Is it still a large (21mm hex) spark plug?
 

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Re: Misfiring at 20 PSI, high RPM. Spark Plug suggestions? (Jesusloves20v)

I run ngk bkr7e plugs gapped to .024 at 15psi. No probs here.
ignition is handling buy some stock GM coils(SDS provided) and some 8.8 Accell wires.
 

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Wow, same problem I had a few months ago.
ABA head on a 1.8, above 20psi and 6K it just shuts down pretty much. Lower the boost it will go to 7K, lower the RPM it will go past 20psi.
I dont know if I fixed it, but my first shot at it was getting an better ignition box. Plug wires alone wont do much for you, unless you are arcing out the side of them, or you have junky ones.
I bought a MSD 7AL-2 off a Mustang board, and converted over to a Ford ignition coil.
Once Iget the car back together(I changed ALOT of stuff on it at the same time), I will see if it helped. I know Im going to be getting hold of Magnecore for some wires too.
 

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Discussion Starter · #10 ·
Re: Misfiring at 20 PSI, high RPM. Spark Plug suggestions? (Jesusloves20v)

Quote, originally posted by Jesusloves20v »
No, that plug is for x-flow, 16v's, vr6's, 20v's

Youll need a 7 range plug in a NGK and do what Jeff said, gap that sucker down to .022

Figgers. So, I want maybe a BP7ES? I put in a set of BP6ES today, gapped to .022", and had every bit the misfiring problems as before, and probably a bit more severe and more frequent (every pull to/above 6KRPM instead of every now and again.)
Is a cooler plug gapped the same actually going to help? I will admit almost total ignorance when it comes to spark bolts.
 

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Re: Misfiring at 20 PSI, high RPM. Spark Plug suggestions? (Longitudinal)

If the reasoning is that there is so much pressure that the spark cannot jump the gap whay would a colder plug be a way to go? I would think something that would jump the gap easier would be the way to go [ie smaller gap, stronger coil, etc.].
I had a smiliar problem many moons ago and the engine would not go past 5 psi boost. After several attempts of adjusting the wastegate I figured out it was the coil. I would think that since the coil you are using was never designed to see 20 psi and that that is one heck of a lot of pressure for the spark to jump thru I would check that. Another think might be that since spark will go to the least resistance I would think that maybe the wires/resister ends are where the spark is finding ground. Those shielded plug ends are difficult to find those shorts that only occur under load.
 

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Re: Misfiring at 20 PSI, high RPM. Spark Plug suggestions? (Butcher)

do your plug wires have beru ends on them? I had this problem way back they are plastic right above the metal and break run and idle fine and then when you start driving or racing the move and break up...that is when i switched to magnacore....try replacing them with other wires once...
 

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Re: Misfiring at 20 PSI, high RPM. Spark Plug suggestions? (German VR6)

Why a cooler plug? From BDS (Blower Drive Service) info page. Forced induction is forced induction.
Spark plugs should be one or two heat ranges colder than the recommended stock factory plug (never use extended tip spark plugs). The colder plugs need to be used due to the higher cylinder pressure created by supercharging; higher cylinder pressure means more heat.
A cooler plug helps to keep pre-ignition levels down under high heat conditions (high boost). Since some plugs will actually glow after high boost, high use running. Plus running a cooler plug under high boost conditions helps to eliminate erosion of the tip over time.

High densities (like those under boost) require more voltage to spark.
Thus sometimes the smaller gap needed. This can be a detriment to optimum performance - You should run the widest gap possible. So the need for a more advanced ignition system at high boost levels.


Modified by rivethead at 9:25 AM 9-12-2005
 

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Re: Misfiring at 20 PSI, high RPM. Spark Plug suggestions? (rivethead)

Quote, originally posted by rivethead »
Why a cooler plug? From BDS (Blower Drive Service) info page. Forced induction is forced induction.
Spark plugs should be one or two heat ranges colder than the recommended stock factory plug (never use extended tip spark plugs). The colder plugs need to be used due to the higher cylinder pressure created by supercharging; higher cylinder pressure means more heat.
A cooler plug helps to keep pre-ignition levels down under high heat conditions (high boost). Since some plugs will actually glow after high boost, high use running. Plus running a cooler plug under high boost conditions helps to eliminate erosion of the tip over time.

High densities (like those under boost) require more voltage to spark.
Thus sometimes the smaller gap needed. This can be a detriment to optimum performance - You should run the widest gap possible. So the need for a more advanced ignition system at high boost levels.
Modified by rivethead at 9:25 AM 9-12-2005

Thanks for the ignition lesson
but the question was how does a colder plug help a misfire under high boost. I know about heat ranges in plugs but I do not understand how that helps with misfires under high boost and maybe someone can enlighten my premadonna ego.
 

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Discussion Starter · #17 ·
Re: Misfiring at 20 PSI, high RPM. Spark Plug suggestions? (German VR6)

Quote, originally posted by German VR6 »
how do you know if your blowing out spark??

Well, the dyno shows mixture running much richer from the moment the misfire starts, indicating both 1) ample fuel is present, and 2) that such a rich AFR following a not-so-rich one tells me that maybe combustion is stopping. Also, when driving the car and encountering the misfire, I can actually smell raw fuel on deceleration.
Cooler plugs (NGK BP7ES) gapped first to .028, then to .025 have changed NOTHING. Peter recommends the W6DPO, but $12.50 each is a big plunge.
This problem is irritating because the car would love to rev to 6K or slightly more, but I can't rev past 5500 without encountering the misfire. Sometimes, if I get everything nice and hot, I can occasionally rev to 6K, but never any higher.
Oh, another indication to me that I am extinguishing spark comes when I change gears after the misfire occurs. I rev it out and it misfires. I change up one gear, then lean back into it. The engine stutters in the exact same way it did with the misfire for a second or two, then clears its throat and gets going. This, I believe, is the gasoline-soaked spark plugs drying off before they can spark effectively again. Does this make sense?
 

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Re: Misfiring at 20 PSI, high RPM. Spark Plug suggestions? (Longitudinal)

What a/f's are you running when the misfire happens?
If you were blowing out the spark (too rich), the wideband would read it running lean as there is a lot of oxygen in the exhaust stream now since it wasnt used in the combustion process.
 

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Re: Misfiring at 20 PSI, high RPM. Spark Plug suggestions? (Mad Mel)

Quote »
Thanks for the ignition lesson but the question was how does a colder plug help a misfire under high boost. I know about heat ranges in plugs but I do not understand how that helps with misfires under high boost and maybe someone can enlighten my premadonna ego.

I have been busy wiring up my tec3 trying to get the caddy ready for a run this weekend. I am not the expert by any means. But here goes. From what I can remember with plugs on old blower motors - The colder plug helps with pre-ignition which can sometimes be diagnosed as a missfire. A colder plug from what i was told has a shorter insulator which has a bit to do with helping the spark in a boost application. We used to run a surface gap plug with no heat range on very high horsepower motors. If you were not to careful you could foul up the plug quickly. The best solution outside of ultra high HP motors is probably a projected tip plug - Though you have to check piston clearance or (and I have not used them) the bosch pt+4. The other reason for a colder plug is that over time you can wear the tips on plugs - If you are changing plugs regularly this is not an issue. One way to see if you are running the right heat range of plugs is to look at the condition of the plug - You want a light reddish-brown tint.
Champion plugs used to have a formula for heat ranges - 1 range colder for every point of compression increase. Don't remember the forced induction other than 2 ranges colder to start with.
 
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