Quick question about spark plug heat range and gap

"DAWRX - The Herb Strikes Back" (karsonkinja) 08/14/2019 at 12:07 • Filed to: None

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Its a long-ish story, but to keep it short, I took my car into the dealer for some issues I’ve had with the engine stumbling under power or WOT. They blamed the spark plugs and said I need to check with my mechanic who changed them to make sure that they’re OEM or NGK plugs of a certain part number.

He calls me back and tells me that his parts supplier sent him the wrong ones (Denso plugs for a 2016 Impreza as it turns out), and he didn’t double check when he got them delivered because his parts supplier insisted they were OEM. Hes going to take care of it and put the right ones in today.

Anyway, according to the part number they have a heat range of 22 (equivalent of 7 for NGK plugs) and a gap of either .04 or .044. My car requires a heat range of 8 (colder than 7) and a gap of .02-.022.

It seems like this is a recipe for preignition however I never got any CELs. I’ve only driven ~6k miles on the wrong plugs. I’m not that aggressive of a driver, I rarely go WOT and it took me a couple months to notice there was a problem in the first place (I went WOT from a near standstill to jump into a gap in traffic and had no power until my car dumped a bunch of black smoke, it hasn’t done this since). It drove almost normally lower in the rev range.

Based on the difference in specs and my driving habits/mileage should I be worried about piston erosion? Should I insist on a compression test?

CarsofFortLangley - Oppo Forever > DAWRX - The Herb Strikes Back 08/14/2019 at 12:15

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It’s fake news.  Just throw whatever in and it will work

jimz > DAWRX - The Herb Strikes Back 08/14/2019 at 12:15

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if you’re not hearing pinging or chattering, you’re probably fine. A heat range difference of 1 isn’t necessarily going to cause preignition unless you’re already teetering on the precipice.

I’ve been there, done that. When I had an SRT-4, spark “blowout” was a common thing if your spark plugs were old and the gaps had opened up. it was much more noticeable than just a stumble.  Even on stock engines.

gettingoldercarguy > DAWRX - The Herb Strikes Back 08/14/2019 at 12:27

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How many miles are on the car?  I’m going to assume you have an fa20 engine? Check and re place coils if necessary once correct plugs are reinstalled . Stock if you’re looking to save a bit, https://www.ignitionprojectsusa.com/ if you’re a bit spendy. How’s your intake tract look for carbon buildup? I also take it you didn’t have anything to monitor dam, or knock feedback?

DAWRX - The Herb Strikes Back > gettingoldercarguy 08/14/2019 at 12:36

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66k miles

FA20DIT/FA20F

What could cause the coi l packs to go bad if I may ask out if curiosity.

When you say intake tract you mean the part of the intake right before the head?

No I don’t have anything like that.

I like cars: Jim Spanfeller is one ugly motherfucker > DAWRX - The Herb Strikes Back 08/14/2019 at 12:38

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Worst case I would think is incomplete combustion, which your cats take care of. Did you notice a change in fuel economy? To clean it out, I’d drive balls to the walls heavy on throttle for a few hundred miles to get rid of any deposits that may have formed. Worst case you’ll have a good time.

DAWRX - The Herb Strikes Back > jimz 08/14/2019 at 12:39

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When my car blew all that smoke I definitely heard some kind of pinging. Sounded like it was below me in the cat though,  like dropping a bunch of screws down a metal surface is the best way I can describe it.

What would chattering sound like?

gettingoldercarguy > DAWRX - The Herb Strikes Back 08/14/2019 at 12:40

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They fail from getting hot

DAWRX - The Herb Strikes Back > I like cars: Jim Spanfeller is one ugly motherfucker 08/14/2019 at 12:41

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Yeah probably ~2mpg less on average normal driving. Hwy driving was more or less the same.

gettingoldercarguy > DAWRX - The Herb Strikes Back 08/14/2019 at 12:41

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Yeah, carbon buildup  can show up as misfires, too hot of a plug and poor ignition overall can exacerbate the situation. I wouldn’t have the place that installed the plugs do a compression test, they have reason to come back with good numbers.

DAWRX - The Herb Strikes Back > gettingoldercarguy 08/14/2019 at 12:42

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Yikes, I’ll tell my mechanic to take a look at them I guess. Thanks for the tip.

I like cars: Jim Spanfeller is one ugly motherfucker > DAWRX - The Herb Strikes Back 08/14/2019 at 12:43

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Yeah, sounds like you’ve been dealing with incomplete combustion. I’m assuming highway driving your revs sit mostly constant and pretty low, when spark sits at a constant advance and your mix leans out.

jimz > DAWRX - The Herb Strikes Back 08/14/2019 at 12:43

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that’s what I’ve usually heard in a car.  When I had my Dyna (Harley) I pinged it a few times when I forgot to downshift after nearly being run into the curb and lugged it too low.  those finned air-cooled cylinders rang like bells. 

DAWRX - The Herb Strikes Back > gettingoldercarguy 08/14/2019 at 12:44

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Looks like a walnut blast might be in my future then...

Just as a quick defense, my mechanic is a long time family mechanic who owns his shop that we have gone to for years and years with no issue. I think he got complacent with my car unfortunately, but I do still trust him.

DAWRX - The Herb Strikes Back > I like cars: Jim Spanfeller is one ugly motherfucker 08/14/2019 at 12:45

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I religiously use cruise at 65mph. Sits a little under 2.5k rpm if I recall.

gettingoldercarguy > DAWRX - The Herb Strikes Back 08/14/2019 at 12:47

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Ah, cool. Yeah walnut blasts suck?  You may want to look into an air oil separator/catch can and egr delete. The egr delete will require an ecu to check off the corresponding p codes. You’ll have much smoother cruising and much less buildup.

DAWRX - The Herb Strikes Back > jimz 08/14/2019 at 12:47

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THATS EXACTLY THE SOUND. wow. In my car it was pretty brief though. and I was only able to replicate it a couple of times for like half a second at WOT and then it stopped doing it al together, it would only stutter and lose power.

DAWRX - The Herb Strikes Back > gettingoldercarguy 08/14/2019 at 12:49

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So you’re saying don’ t do a walnut blast?

gettingoldercarguy > DAWRX - The Herb Strikes Back 08/14/2019 at 12:50

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Not at all, just that or sucks when you need one.

gettingoldercarguy > DAWRX - The Herb Strikes Back 08/14/2019 at 12:51

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But those two other things will keep your car running better longer.

DAWRX - The Herb Strikes Back > gettingoldercarguy 08/14/2019 at 12:53

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O h okay. Appreciate all the advice. Those items were on my radar but not as urgent items. I should probably get serious about getting them done.

gettingoldercarguy > DAWRX - The Herb Strikes Back 08/14/2019 at 12:54

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It’s right there if you're doing the walnut blast, so labor should be much cheaper

Snuze: Needs another Swede > DAWRX - The Herb Strikes Back 08/14/2019 at 12:55

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I dealt with spark blowout on the Cruze early on. There was a miscommunication between GM and the supplier over who was gapping the plugs, so they never got gapped. On top of that GM was a little aggressive wanting like 0.35 or something. Going to a tune was a nightmare because the increased boost made blowout worse. After my tune and my car ran terrible, I pulled my plugs and found gaps ranging from 0.22 to 0.36. GM corrected their spec to 0.28, which is what I set mine to, and the car has been fine ever since. Well, not fine, it’s had lots of other crap break (stupid PCV system) but the plugs have never been an issue since.

Modern ECUs are pretty good at compensating for problems, and yours probably recognized the problems and pulled a lot of timing out, which explains your lack of power. That likely saved your pistons, so I wouldn’t be too worried about them. 

gettingoldercarguy > DAWRX - The Herb Strikes Back 08/14/2019 at 12:59

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I'd really like to see what your dam dropped to.  Drive it like somebody else stole it until plugs get fixed.

gettingoldercarguy > DAWRX - The Herb Strikes Back 08/14/2019 at 12:59

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Don’t drive it like that, get your plugs swapped

gettingoldercarguy > DAWRX - The Herb Strikes Back 08/14/2019 at 13:32

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I meant don’t drive full throttle from what was suggested above, keep low load in the engine. I also noticed that you live in h  town.  I'd s uggest running a 90/10 mixture of water/antifreeze with a surfactant like Amsoil dominator coolant boost, unless you travel to somewhere that gets seriously cold.

DAWRX - The Herb Strikes Back > gettingoldercarguy 08/14/2019 at 13:44

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I figured he suggested that for AFTER I get the plugs swapped. Which I’m sure would be okay, correct?

Im assuming all hat stuff helps keep the engine temp lower?

gettingoldercarguy > DAWRX - The Herb Strikes Back 08/14/2019 at 13:49

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Yeah, especially the cylinder heads which greatly reduce chances of detonation.  The stock 50/50 or 40/60 are meant for places that have three seasons of winter and one of spring.

brianbrannon > DAWRX - The Herb Strikes Back 08/15/2019 at 22:01

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The gap is why you had an issue at full throttle. Not enough voltage to jump the larger gap. Your engine is fine and don't mess with your coolant. It's antifreeze and antiboil and also protects against corrosion