Single misfire event every 3 seconds

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Re: Single misfire event every 3 seconds

Postby aleksanderk » Sun Oct 11, 2020 2:55 pm

Long time since my last update.
I came to think about a fouled spark plug that I had a while ago, that I was sure was caused by my cheap and wring plug wires. Replaced spark plug and wires.

Today I started the car up for the first time since my last post here. Fired up nicely, but still misfiring. Decided to disconnect one injector at a time, and listen to how the engine was running.
Cyl. 1, 2 and 3 it obviously misfired because it was only running on 3 cylinders, but the random misfore was still there. Disconnected cyl. 4 and the random misfire went away, just running on 3.

Pulled the plug and it looked decent. A bit wet, and black, but not caked or anything. Tried another plug I had lying around, but then it wouldn't fire at all on cyl 4. Found another one and it ran again with random misfire. Opened up the gap and tried again. No misfires at all! AFR stabilized, and the engine ran smoother than I ever can remember!
Took the car for a test drive, and the misfires came back. Took the plug out and saw that the porcelain was cracked and was covering the electrode. This was a crappy cheap plug.

Off to buy 4 new plugs this week. I feel really stupid for not taking a closer look at the plugs.
The OEM plug is a BPR6ES, but since it's turboed, I run BPR7ES wich is one step colder. Would I get some form of gain by changing to an Iridium plug or some other "fancy" plug, or even just keep the hotter plug that it has originally?
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Re: Single misfire event every 3 seconds

Postby katana » Mon Oct 12, 2020 3:56 am

In my experience, and unless you are using BIG boost, cooler running plugs are not required with turbos! I think this is a hang over from the past when fairly uncontrolled fueling and boost controls were the norm. Modern plugs don't tolerate fouling AT ALL - generally a carbon'd / fuel soaked plug is scrap these days. Modern plugs are designed to run lean and hot so a little extra fuel - for power or cooling - is tolerated but change the plug spec for a cool running one and trouble ensues. Iridium plugs are great in 'lean burn' engines but not so much in 'power' engines - the tips whilst not fouling can glow red hot so promoting pre-ignition / detonation which isn't good with forced induction! IMO - just use the regular plug and - if & when - the plug looks to be suffering, then maybe swap out for the 7's
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Re: Single misfire event every 3 seconds

Postby aleksanderk » Mon Oct 12, 2020 10:02 am

I'm running 1,6 bar/ 23-24 psi of boost. If I change to BPR6ES, how will i know if it's not "right"? Detonation, or just poor performance?
BPR6ES are stock for this engine when it's N/A, or OEM low pressure turbo. (0,3 bar / 4 psi).

If the pros outweighs the cons, then I will try a 6 instead of a new 7. The 7 might even be the reason why I hade to make this thread in the first place?
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Re: Single misfire event every 3 seconds

Postby stevieturbo » Mon Oct 12, 2020 12:08 pm

If the 7's are in and there are no fouling issues....keep using them.

Although 6's would probably be fine too. A lot depends on fuel and actual usage.

Many will say readings plugs can tell you whether the heat range and many other aspects are right....but that is a bit of an art and requires new plugs each run and fairly specific run and shutdown to get a good picture ( 1/4 mile type run )
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Re: Single misfire event every 3 seconds

Postby aleksanderk » Mon Oct 12, 2020 2:11 pm

It could be fouling that caused my problems. The mixture has been all over the place sometimes, and that might had a negative impact on the plugs.
A new set og plugs are needed anyway. I think I'm going with 7's, and if these problems return I can try 6's.

A big thank you to all of you that have helped me along the way! :D
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Re: Single misfire event every 3 seconds

Postby katana » Tue Oct 13, 2020 9:27 am

aleksanderk wrote:I'm running 1,6 bar/ 23-24 psi of boost. If I change to BPR6ES, how will i know if it's not "right"? Detonation, or just poor performance?
BPR6ES are stock for this engine when it's N/A, or OEM low pressure turbo. (0,3 bar / 4 psi).?


That's pretty good boost so 7's may be right. Using 6's too hard would show evidence of electrode burning / melting. It could be that a 6 is the right heat rating but the plug design leaves the tip too or under exposed - not all plugs are created equal!
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