What's going on in 6

bwest

Drafting, not tailgating
May 18, 2005
502
0
0
HippieTown, CA
isnms-

How many miles were on the plugs? How do you drive the thing (pedal to the floor, stop and go, mostly freeway, etc)? Do you consistently use the same gas? Any fuel additives? All of these things will effect the carbon build up on the plugs.

Taking a blind stab without knowing any more about your car, I see a few things:

1. cyls 1 & 2 run the coolest, closest to ideal a/f, and generally run the the cleanest. I would imagine you are running an un-equal length manifold (1&2 have longer exhaust pulses).

2. cyls 3&4 look ok - #3 looks to either have too much fuel (slightly lower comp) or burning a hair of oil. regardless, the combustion process is dirty enough to leave its mark. Nothing to really worry about, but something to watch.

3. #5 looks par for the course. Looks like a little pre-ignition, which would make sense if your timing was off. It doesn't looks out of the norm with the rest.

4. #6 - what kind of oil are you running? It looks lean, but no more than the others under high heat (no additional graining or discoloration compared with the others), but is definitely funky under lower heat. Granted, #6 runs a bit warmer anyway (the egr design doesn't help), but I have never seen that much difference without there being another problem at hand. I personally would start looking at that injector (assuming the comp test and leak down performed with reason to the other 5). If you were eating a little oil (say rings that were begining to exit stage left), I could see increased cyl pressure helping minimize that. But I would also expect the electrode to show a little more of that.

Don't know if that helps you out much or not. I spent more than a few years tuning engines with spark plugs (and an egt if I was lucky) - the only way to know more is inspect the crown and combustion chamber, but it helps if they are clean beforehand.
 

isnms

United States of America
Mar 30, 2005
2,145
0
36
Oklahoma
i80.photobucket.com
Thanks bwest for that information.

About 10k on the plugs. Driving habits about normal, some interstate, some stop and go, some wot, mostly sensible. I got 18-20mpg average. I've been getting the 7eleven super. Manifold is stock. I've been running castrol 10w-30 syntecblend. No excessive oil usage, seems like maybe a quart per month and half.

I'm looking for vacuum leaks, need to check egr functioning properly, do a compression test and as you suggest maybe test my injectors.
 

bwest

Drafting, not tailgating
May 18, 2005
502
0
0
HippieTown, CA
How many miles does it take for that 1.5qt to blow out? On my stock 125k mi stock motor (with leaking valvestem seals and shot rings) I would do a 1qt every 3500-4000mi. When I first bought the car w/ 68k, it was less than .5qt every 3-4k.

On the new motor, its different, but that is a whole other can of worms. I would look into the comp test (and then a leak down if that doesn't point anything out immediately). I still think testing your injectors is a good idea.

while everyone has their opinion on gas, I find that chevron is the most consistent with the mileage tests I've done. But as they say, YMMV...
 

isnms

United States of America
Mar 30, 2005
2,145
0
36
Oklahoma
i80.photobucket.com
It uses about 1 quart per 1.5 month. That is probably about 1800 miles. I have a slow leak where the timing cover meets the block. Either fipg was not put where it should be or the block and timing plate were not machined together. Whichever, it's slow and really only blows out when boosting hard.
 

dbsupra90

toonar
Apr 1, 2005
2,374
0
0
indiucky
ive seen #6 cyl build up with carbon due to the egr system. thats what it looks like to me. a comp test is def a good idea, and id suspect #6 to be a little higher than the others if carbon is an issue.
 

bwest

Drafting, not tailgating
May 18, 2005
502
0
0
HippieTown, CA
Please explain. Are you getting at how the egr inlet at the manifold is closest to the #6 runner and if malfunctioning, #6 will suck up a higher proportion of exhaust gas? I'm curious at what pressure the ex gas enters the manifold, because that would have an obvious affect on cyl distribution
 

dbsupra90

toonar
Apr 1, 2005
2,374
0
0
indiucky
i couldnt tell you the pressure differential. its just that several supra motors ive seen apart have had noticeable carbon buildup on #6 compared to other cyl. perhaps its a malfunctioning egr, egr design, or something completely unrelated. but its def a trend ive seen with the motors, and had thought the egr was the cause due to the proximity to #6.

regardless, carbon buildup will show up on a comp test.
 

sneakypete

Regular Member
Jul 18, 2007
1,129
0
0
Central NJ
i have the same problem with my car.
when i tore down my last motor, i noticed very excessive buildup on the #6 piston. was having the same issue with #6 plug. after blowing a bearing, i decided to go with a new motor.
about 3 years later, with a re manufactured motor, new sp61gt turbo, and maftpro, i am having the same problem with #6. all gapped to 0.032 with ngk platinum. i have the egr blocked off and pretty new coil packs. use royal purple (pricey) and run 93 octane from exxon, lukoil, or bp. only get 15-16 mpg. also burning a lot of oil (i think its my turbo seals) cant seem to figure it out either