help reading spark plugs

Won · 11-09-2005, 11:18 PM

I'm going to see Al S on the weekend and ask for his opinion on the "coffee grinder" sound. that story here.

Meanwhile, I got the correct spark plugs and went ahead and changed them. Now I'm not very good at reading spark plugs, hence this post, but this seems interesting.

from the left, cylinders 1 to 6.

It's not clear in the pictures, but all the plugs from the left bank (cylinders 1, 2 and 3) have considerably more white residue than those from the right bank (4,5 and 6). The ones from the same bank look identical, so basically all the ones from the left bank look like the one on the left of the next picture and ones from the right bank, the one on the right.

Quite obviously each bank is running in different conditions. What could be causing the difference here, injectors, intakes? I did a compression test and all cylinders show about 155psi. Could it be the fact that catalytic converter is on the left side and it's causing that side to run hotter and knock?

TerryH · TerryH's Garage

Those plugs don't look bad. White fuzzy stuff on plugs usually just shows they are old and have been in there a while. Fuel additives leave deposits.

I would install a new set and check them again in a few weeks to get a better indication.

Reading plugs isn't as easy as it was in the days of leaded gas, carburetors, and computerless cars.

RickM · RickM's Garage

They all look pretty good to me as well.

Nine9six · Nine9six's Garage

As I understand it, plugs should be read only after a good spirited run, with the motor well up to temp and turning at least 5K rpm. From that rpm range, push in the clutch, shift into neutral, and pull the plugs for a read.
I am sure there are other opinions on this...

Won · 11-12-2005, 03:39 PM

cool... just curious, if I'm interested in the state of the engine at lower rpm where it pings, then wouldn't it be better to pull them out after running at the rpm of interest as the plugs can be "rewritten"?

Nine9six · Nine9six's Garage

Take it to a smog check station. Not very costly, and a smog check can tell you alot about the health of an engine.

HFR_Racer · HFR_Racer's Garage

Looks like the left bank is running a little lean. The right is too hard to tell from the photo.

HFR_Racer

Won · 11-12-2005, 06:37 PM

smogged(AirCared) in June by PO, for "driving test" which is done at 25mph CO is 0.05%, for idle test 0.00%, with cat and O2 sensor connected.

As the weather got colder I unplugged the O2 sensor and I could push the metering plate up quite a bit before rpm started to drop back, richened the mixture 3/4 a turn, was hunting when clutch in, leaned out 1/4 turn and it's fine... as far as I can tell.

Should I be alarmed that one bank is running leaner than the other? I'll replace injector seals soon and also check the rubber connection between intake runners and the airbox.

stlrj · 11-13-2005, 12:45 AM

What's your CO set at? How was it running with those plugs?

Won · 11-14-2005, 06:39 PM

I never checked CO with an analyzer. But the car was definitely running lean, and the seals for the injectors were/are bad too. I met Al over the weekend for the noise issue and apparently his car makes the same noise too, from the transmission. Also he thinks, and I agree, that there could be some pinging due to those seals that are inaudible or a part of the noise.

Thank you everyone for your replies!