Spark plugs

[Eddyvdw]

See picture of plugs 2-6 (can't get 1 out, missing a tool...)
What do you guys think, #4 is not playing along right?
Ed

[James Brown]

# 5 is the best one, #4 and 6 if wet could be oil if dry could be running rich. But overall, not bad. How many miles on the plugs? What special tools do you need for #1?

[Eddyvdw]

Thanks.
They are definitely not oily, just a little black.

The tool to remove the plugs is too long and get's stuck between the block and the side.

Ed

[m1franck]

WR5DC plugs, those seem to be a little cold if the car has MFI or carbs. Your picture looks like a long hood 911, so I'm assuming it's not CIS or EFI. Yes, WR6DC is the stock heat range, but I believe the carb experts recommend 1 to 2 steps hotter such as WR7DC to WR8DC. Also, to read plugs correctly you need to do a "clean" chop on the throttle. If you idle around getting it to the garage, then your plug reading is compromised.

[Eddyvdw]

Thanks. I'll change them.
I pulled the plugs after a 30miles drive.
Cheers,
Ed

[Eddyvdw]

Let the car idle for a few minutes (while checking oil) before switching the engine off.
Btw, the car is a 911E (Mfi) from 1972.
Ed

[BSNMOE]

check air flow thru stacks at idle and around 2500/3000 RPM. See if your pulling equal air.

[hessel1974]

Originally Posted by m1franck

WR5DC plugs, those seem to be a little cold if the car has MFI or carbs. Your picture looks like a long hood 911, so I'm assuming it's not CIS or EFI. Yes, WR6DC is the stock heat range, but I believe the carb experts recommend 1 to 2 steps hotter such as WR7DC to WR8DC. Also, to read plugs correctly you need to do a "clean" chop on the throttle. If you idle around getting it to the garage, then your plug reading is compromised.

Interesting statement. Can someone elaborate why hotter plugs would be better for such an engine? Our host sells the standard 5 plugs for a T engine. What I know about plugs is that the hotter they are, the less heat they extract from the combustion chamber. So wouldn't hotter plugs affect the valves in a negative manner?

Thx Hessel

[Flieger]

You want the coldest plug you can run without fouling.

[scarceller]

+1

Originally Posted by flieger

you want the coldest plug you can run without fouling.

[scarceller]

#4 and #6 look like fuel rich. I know MFI runs tad rich but those 2 look a bit to much. I'd run the engine in mid to hi load in the 4000RPM range then shutdown as quick as possible and check them again.

I'm not sure how MFI calculates air/fuel for each cyl but I suspect maybe not enough air or to much fuel in cyl #4 and #6. If this where a EFI car I'd suspect injectors with bad spray pattern and/or to much fuel flow.

[Eddyvdw]

Finally pulled #1 as well

You touch on one of the key concerns of a MFI driver; a too rich set up!

The car is a 2.4E MFI with a calibrated pump. The pump nicely heats up via the HE and the thermostat is at full extend when warm.

The oil is not smelly and stays at same level. Only smokes a bit when cold but no smoke when warm. The tail pipe is black / dark grey.

What are the other symptoms of too rich?

Thanks,
Ed

[scarceller]

Few things to watch for:

1 fuel Economy
2 be sure you don't have a cyl mis-fire condition (cyl 4 & 6)

If you have access to a WideBandO2 meter it may help you pin point a rich condition. Like are you rich at idle, PartThrottle and/or WOT?

I'm not a MFI expert maybe others can help figure out what is considered to rich for a MFI car.

What are typical AFRs for these conditions in MFI?

Idle
PartThrottle
WOT

[Eddyvdw]

Installed the new hotter plugs and opened the airflow screw on 4 and 6 with half a turn. Drove for about 30 miles quite "spirited". The car feels strong at the entire rpm range and doesn't miss fire.

Let the engine rev at 4000rpm for 20 sec before turning off.

Pulled # 4 and #6 again. Number 4 and 6 plugs are a little less black but still not the desired brown.

Might open the airflow screw another half turn and give it another go.

Ed

[Eddyvdw]

Opened air screw to 2,5 turns on #4.
Changed spark plug gap to 0,7mm
No change

Must be cylinder leakage....

Still car drives really well, strong through the entire rpm range, great sound.

Ed

[Rot 911]

The "E" and "S" engines are really finicky and almost impossible to get the setting right with out a meter to measure exhaust gases while you are making adjustments. I would much rather have the plugs a bit rich, then a bit lean. On my '72 E, the engine was really happy with a hot plug. I ran NGK BPR6ES plugs.

[Miguel Antonett]

Not to steal the thread, but what about these plugs, 30K miles on them

[scarceller]

The top 3 look good but the bottom 3 seam lean, the one in the center at the bottom looks like it's missing material around the center electrode, if it is it may be indication of mild detonation in that cyl. what engine are these from?

[Zeke]

Don't open the air adjustment screw to lean out a cylinder. Those are there to balance out for a smooth idle at 950 RPM. You most likely have a couple of valves that are not seating well. Put new plugs in and run it hard after warming up properly. You can idle some before shutting it down, but keep it at a minimum to get down your street and into your work area. Shut it off without revving the the motor. There will be a minute layer on the plugs from the slower driving but the true color and condition will show through well enough to determine what the analysis is.

You could use a hotter plug in a cold cylinder, but don't take your car to the track or on a long trip in that condition.

[Miguel Antonett]

Originally Posted by scarceller

The top 3 look good but the bottom 3 seam lean, the one in the center at the bottom looks like it's missing material around the center electrode, if it is it may be indication of mild detonation in that cyl. what engine are these from?

They're coming from a 3.3L 78 930 with 100K on it. Those plugs have around 30K miles on. Last track event on those plugs was two weeks ago, pulling pretty good...