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Old 05-30-2010, 03:59 AM   #1
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Power loss after replacing spark plugs

I recently replaced the spark plugs in my VX

Old plugs were NGK ZFR5F-11. When I removed them the gap was somewhere between .65 and .70 on all of them.

New plugs were NGK ZFR4F-11, gapped at .44.

The car ran fine with the old plugs but I was hoping to see a gain in mpg by using the stock plug.

After the install it did seem to run slightly smoother and mpg may have improved very marginally, however, now whenever it is hot out (90+) my car seems to lose a lot of power. I live in Southern California so it is quite common for it to be hot here. Also, while going through my Owner's manual I noticed that it recommends ZFR5's for hot climate, which leads me to believe the issue may have to do with the heat range of the plugs.

Has anyone had a similar problem? Does this sound like a likely symptom of running plugs that are too hot?

I know that I can always just spend 15 bucks on new plugs and find out if that was the problem, but a lot of the posts I have read here recommend the ZFR4's so perhaps there is weak link somewhere else?

Also I am curious if anyone knows whether the stock plugs for California VX's might have been different from 49-state VX's. If that is the case, could swapping in a Federal ECU clear up my problems? I am planning on doing the swap anyway once I can find an ecu for a decent price.
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Old 05-30-2010, 05:10 AM   #2
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i don't know honda or plugs that well, however it's not too uncommon for symptoms to appear after a tune-up. did you blow out the tubes w/ compressed air before changing them? funny that you would have a LOSS of power afterwards.

btw, i've seen NGK single platinums on sale for $2.50 each. that's if you don't want exact stock ones tho.
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Old 05-30-2010, 05:44 AM   #3
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Here's a hypothesis- It could be that the 4F is a hotter plug (higher tip temperature) than the 5F and this is causing a little spark knock that that knock sensor picks up. When the knock sensor sends this signal to the ECU, the ignition timing is retarded slightly to reduce the knock- but power and fuel economy suffer.
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Old 05-30-2010, 12:06 PM   #4
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Quote:
Originally Posted by Erik View Post
Here's a hypothesis- It could be that the 4F is a hotter plug (higher tip temperature) than the 5F and this is causing a little spark knock that that knock sensor picks up. When the knock sensor sends this signal to the ECU, the ignition timing is retarded slightly to reduce the knock- but power and fuel economy suffer.
This seems like it might be a possibility. I just found the old plugs I pulled out of there so I think I will regap them to .44, put them back in and see if the problem goes away.

Also when I installed the new ones I just used a regular ratchet, not a torque wrench and I did not use compressed air to blow out the tubes. They looked clean. I doubt that would affect the performance, but I suppose there is a minute chance.
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Old 05-30-2010, 08:14 PM   #5
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I would have writen the same thing as Erik. Those old plugs must have been really old, or overgapped on purpose. If they aren't too eroded, they should work fine. How is their color? NGK has a chart on their website.
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Old 05-30-2010, 08:36 PM   #6
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Originally Posted by fowljesse View Post
I would have writen the same thing as Erik. Those old plugs must have been really old, or overgapped on purpose. If they aren't too eroded, they should work fine. How is their color? NGK has a chart on their website.
I am fairly sure they are just old. The center electrodes are worn down to the point where there is no V-groove visible anymore.

I will put them back in tomorrow and see how the car runs. It seems that will be the only way to really figure it out.
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