spark plugs and fuel econ

[Execut1ve]

I put all kinds of miles on this car, 30k mi is about 2 yrs of driving for me. On one occasion I put 3k miles on it in a 1 month period lol

[EdKiefer]

Originally Posted by some_other_dave

I'm surprised at "mixed" results. My experience with the common variety Bosch platinum plugs has been almost uniformly negative. The expensive ones are fine, but the (relatively) cheap ones you can get everywhere suck. Lousy quality control. And the +2 and +4 are the same crappy plugs with extra electrodes welded on.

NGKs only for my CRX.

-soD

Well I didn't want to say mostly negative because I have limited usage , most were from 1980-2000 performance type vehicles (turbo's) .
The OEM were better and on my own XR4ti they never worked right to me .

I will note these were single electrode ones not the +4 types (I don't believe they were out yet) .

[Execut1ve]

someone above mentioned indexing the plugs. I'm familiar with the basic idea, but wouldn't I have to have the head off the engine to see where the intake valve is to make sure the ground strap is on the side opposite the intake valve?

[ChazInMT]

The intake valve is in the top of the cylinder....duh...just have the ground strap face down.

If you don't like that answer....check this out! Take note of points 3 & 4.

NGK Spark Plug Installation Guide

[Execut1ve]

I realize it's in the top of the cylinder... however the spark plug mounts pointing straight down (or nearly so) so it's not a question of the ground strap pointing up or down but rather left, right, back, forward, etc.

[ChazInMT]

(That was a joke) Did you check out the link? (It is serious stuff)

[Execut1ve]

I did, if definitely has me thinking. I haven't made up my mind either way on it. if I could find a picture of the underside of the head of my engine that would be sufficient I think

[topcat]

Last weekend I replaced the plugs on my Toyota 1ZZ-FE engine, after 66k miles. I replaced like for like with standard NGK copper plugs BKR5EYA-11. These are supposed to have a 1.1mm gap.
I went through all the decisions, like surely if it is not misfiring, then don't bother changing them. Surely a longer spark gap from the old eroded plugs would give better economy, due to more complete ignition.
My decision to change them was mainly as you say guilt! And also to give the coil packs an easier time, and thus less likely to burn them out.

Well, after 66k miles, the gap on the old plugs was more like 3mm! As I replaced them, I made a note to index the plugs, i.e. face the open side towards the air intake manifold if possible (front of car on _this_ engine- back of car on most other engines). This was luckily where 3 of the 4 naturally ended up. Unluckily, the 4th one ended up facing the exhaust manifold with the correct torque wrench setting, so I gave it an extra 1/4 turn and it ended up side on, 90 degrees out. The new plugs, I set to the manufacturers recommended 1.1mm gap.

I am sad to say that my fuel economy is slightly down after doing this. My 20 mile trip to work usually gives 54 MPG (imperial) but this week I have got about 52 MPG.

So my conclusion would be, for best FE, use the longest spark you can before misfires occur. But for longevity of coil packs, use the recommended spacing. A trade-off as always.
Tom

[Ryland]

A sharpie marker does wonders when indexing spark plugs so you can keep track of the ground leg while threading the plug in and if you are unsure where your valves are in relation to the plug then you should be able to find a photo of your head online or even in your shop manual.

Originally Posted by Execut1ve

someone above mentioned indexing the plugs. I'm familiar with the basic idea, but wouldn't I have to have the head off the engine to see where the intake valve is to make sure the ground strap is on the side opposite the intake valve?

[Execut1ve]

that may be but I'm not certain which direction the plugs would need to face to get the best gains from indexing, toward the intake or exhaust or what