spark plug testing - Honda Prelude Forum

jmcn · 12-15-2002, 01:38 PM

Question....how long do you have to use new spark plugs before they'll give an accurate reading of engine firing conditions? In other words, can I put in new plugs, do a couple blasts down the street at full boost, then do a WOT low-RPM cruise, then check the plugs? Or do they have to be in the engine for a while for evidence of running rich/lean, etc. to show up on the plugs?

Here is a picture of OEM 240SX plugs with about 10,000 miles on them, about 400 miles of which turbocharged at 4-psi:

Here's a picture of the new plugs I just bought and tested out running at 5-psi for only 20 minutes or so (under different driving conditions).

How do they look?

My set-up *should* be running extremely rich, and there is every indication of that with the pops coming from the exhaust, and the totally black exhaust tip. Jim Wolf has the reputation of tuning its ECUs very rich. I am still super paranoid about this though--although relatively to replace, my KA doesn't deserve to be blown up.

schwett · 12-15-2002, 04:47 PM

were you doing a hard run on those second plugs? the only way to "read" plugs accurately is to run the car, hard, like a couple wot runs through a few gears, and then stop and pull them right away. if you are just cruising around, the indicators of leanness or detonation will be wiped away by the normal happy fueling of closed loop, or whatever the nissan equivalent is.

i say that because the plug looks too clean to read!

jmcn · 12-15-2002, 07:58 PM

Well, "normal" driving of a turboed car means WOT runs doesn't it?

I'll pull the plugs out tomorrow and check them again. I drove it some more with the new plugs.

How does the first plug look?

BoYgUaN · 12-15-2002, 09:34 PM

looks fine imo
not tooo rich