Why are my plugs fouling

[gavinc69]

Some of you my know the mods on my car but for those that don't a quick overview :

1980 3.0 SC engine (full rebuild)
Port and polish heads
993 Cams
RS Cut Valves
KKK 3LDZ turbo install
930 WUR - rebuilt to factory spec for a 930
Intercooler
Still running SC CIS (EURO)

The car has always been set to run a bit rich, I have always had the surging on a cold startup.

Since the turbo install and the 930 WUR install the surging has also been present on a warm start but seems ok once thoroughly warmed up and restarted.

My AFR's are typically Cold start 10.2 rising to once warm about 13.5 at idle, cruise about 14.2 and onboost about 11.6

From what I read thats all good, for 930's at least.

But if the car if left idling for say 10mins it fouls up the plugs, you getting missing which cause's a vibration through the car when rev'd and under acceleration.
If you go drive the car this will clear after say 300-400 metres and the car is fine again.

I have checked the plugs and they are dry but thick with black carbon dust.

I tried to lean the idle to get rid of the cold surging but it also affects the rest of the AFR range meaning I'm leaner on boost

The only modification the company could do that built the WUR and to tap the bottom giving access to the small 4mm adjuster. I was told this is for warm/boost adjustment.

I has since read some say this is actually for warm only!

I have also read some of you guys also get fouled plugs, so I changed from the W3DP0 which run cold to the 964 turbo recommended plugs, can't remember the name but they run a little hotter. This doesn't seem to have made any difference.

With just the idle mixture and warm/boost adjustments do you guys think thats enough to get things in shape. Wanted to ask before I go play?

I appears need to lean out the idle which should effect the idle and cruise, then dial back in some on boost.

I have leaned the idle a little so the AFR's are now warm idle 14.2, onboost 12+
It still fouls the plugs after a long idle though.

[Tippy]

If it were an old engine, I would have blamed the valve guides.

Any blowby?

You also changed to a hotter plug. So that sounds ruled out.

How's the health of your ignition system?

[dos531]

Leaning the idle mixture should have a very minimal effect on the a/f ratio under boost. You are correct that the adjustment on the bottom of the WUR is for warm pressure only.

I had an intermittent miss at idle on my car and it ended up being a bad ground on my CDI. Your idle mixtures seem perfectly fine, so I would check the ignition system.

[gavinc69]

Ignition has been updated with MSD Digital 6AL, MSD Boost Retard Module, MSD Blaster coil, Magnecor wires.
The Cap and rotor arm are both recent and the car run's perfectly when warmed up, no missing, hesitation, nice smooth acceleration and pulls smoothly from 1000rpm.
I removed the plugs and cleaned them a few weeks ago and the car went for 2 runs since, both aprox 30miles each and after each run left to idle for 10mins so the thermostat activated for the front oil cooler so I could check oil levels correctly.
Each time the missing and vibration appeared after idling for a short while when you rev'd the car but went away as I drove it down the road again.
Could incorrect engine timing have any effect on this?

The control pressures are obviously set in the WUR for a 930 but my car is an SC, so I'm thinking really the control pressures should be set for an SC but then enrich as boost comes on like a 930.

Just seems strange that my AFR's all seem good compared to the info I read in all others posts and I'm still getting this issue.

I may try to lean the idle a bit more and then richen the WUR warm setting to try and counter the idle lean for warm/boost as it appears all I need is a leaner idle situation and cold start if possible.

[gavinc69]

Would gapping the plugs help.
I originally had the plugs gapped to, i think, 0.50 to take advantage of the MSD.
Since the rebuild the plugs have been left as standard, would gapping them again help with a more fuller burn and be lease likely to cause fouling of the plugs?

[DSM]

Started with Bosch W3DPO non resistor type plugs and had issues right from the start. Changed to a resistor type plug (NGK BPR8ES ) which appears to be better suited for my TEC3r system. This got the car running well but then the plugs began fouling out… or so I thought?

Information from NGK website:
NGK "R" or resistor spark plugs use a 5k ohm ceramic resistor in the spark plug to suppress ignition noise generated during sparking. NGK strongly recommends using resistor spark plugs in any vehicle that uses on-board computer systems to monitor or control engine performance. This is because resistor spark plugs reduce electromagnetic interference with on-board electronics. They are also recommended on any vehicle that has other on-board electronic systems such as engine-management computers, two-way radios, GPS systems, depth finders or whenever recommended by the manufacturer. In fact, using a non-resistor plug in certain applications can actually cause the engine to suffer undesirable side effects such as an erratic idle, high-rpm misfire, engine run-on, power drop off at certain rpm levels and abnormal combustion.

This is my build experience… Brand new plugs (NGK BPR8ES) appeared to foul after only a few short drives. My build is a bit extreme, so I thought... I hope this is not yet another gremlin I'm going to have to live with or troubleshoot for who knows how long? Build (3.4 Turbo, Very aggressive cams, Tec3r Full Sequential, Twin Plug, blah blah blah, etc....... Put down 430hp thru wheels @ .9 bar.) All that aside I always like to start with the simple things. Sometimes they are overlooked. After changing out all plugs multiple times….. I felt its time to tackle this. First part checked, the plugs. Should read 5k+/- 500 ohms. I began checking resistance of new and used plugs. To my surprise even some new plugs read well below 4.5k ohms. I batched plugs with over 4.5k readings, then installed only in tolerance used plugs for a test. She immediately fired on all six and hasn’t been a problem since. Ran it all last summer nearly every day! When time to by new plugs. I’ll buy say 20(They are dirt cheap!) then simply check resistance and return any out of tolerance.

[Tippy]

Although 0.050" gap is good for idle and part throttle, that's way too wide for boost.

Flame out will easily occur.

IMO, I'd run no bigger than 0.030, but I personally run 0.025" and may go 0.020" so I run 1.4 bar.

[Tippy]

Started with Bosch W3DPO non resistor type plugs and had issues right from the start. Changed to a resistor type plug (NGK BPR8ES ) which appears to be better suited for my TEC3r system. This got the car running well but then the plugs began fouling out… or so I thought?



Information from NGK website:

NGK "R" or resistor spark plugs use a 5k ohm ceramic resistor in the spark plug to suppress ignition noise generated during sparking. NGK strongly recommends using resistor spark plugs in any vehicle that uses on-board computer systems to monitor or control engine performance. This is because resistor spark plugs reduce electromagnetic interference with on-board electronics. They are also recommended on any vehicle that has other on-board electronic systems such as engine-management computers, two-way radios, GPS systems, depth finders or whenever recommended by the manufacturer. In fact, using a non-resistor plug in certain applications can actually cause the engine to suffer undesirable side effects such as an erratic idle, high-rpm misfire, engine run-on, power drop off at certain rpm levels and abnormal combustion.



This is my build experience… Brand new plugs (NGK BPR8ES) appeared to foul after only a few short drives. My build is a bit extreme, so I thought... I hope this is not yet another gremlin I'm going to have to live with or troubleshoot for who knows how long? Build (3.4 Turbo, Very aggressive cams, Tec3r Full Sequential, Twin Plug, blah blah blah, etc....... Put down 430hp thru wheels @ .9 bar.) All that aside I always like to start with the simple things. Sometimes they are overlooked. After changing out all plugs multiple times….. I felt its time to tackle this. First part checked, the plugs. Should read 5k+/- 500 ohms. I began checking resistance of new and used plugs. To my surprise even some new plugs read well below 4.5k ohms. I batched plugs with over 4.5k readings, then installed only in tolerance used plugs for a test. She immediately fired on all six and hasn’t been a problem since. Ran it all last summer nearly every day! When time to by new plugs. I’ll buy say 20(They are dirt cheap!) then simply check resistance and return any out of tolerance.

That is interesting. I've never tested resistance in plugs. I have a misfire during take off that rears its ugly head every now and then. Wonder if the plugs are to blame.

[Black_Hat]

+1 for cheap NGK plugs

I'm using NGK "R" resistor FR5

Nothing but good things to say and the smaller size socket make R&R the plugs easy.

[gavinc69]

Cheers, I'll look at the plugs and try some out.

[Speedy Squirrel]

That's what I would do, buy the cheapest possible plugs for my $30K motor. What could go wrong?

+1 for cheap NGK plugs



I'm using NGK "R" resistor FR5



Nothing but good things to say and the smaller size socket make R&R the plugs easy.

[gavinc69]

Check tonight and currently installed Bosch WR6DP0 which do have a resistor.
I'll pull them and check the resistance just to see what the results are.
They all looked in an identical condition when checked before so I can't think there's issues with some and not others.

[fredmeister]

Originally Posted by gavinc69

Check tonight and currently installed Bosch WR6DP0 which do have a resistor.
I'll pull them and check the resistance just to see what the results are.
They all looked in an identical condition when checked before so I can't think there's issues with some and not others.

Did you have the MSD shielded signal cable installed from the green coax at the dizzy to the MSD box?

I ask because using this shielded cable should be enough to offset any EMF from non resistor plugs and other sources--that's the reason they sell it.

I just wonder if using non resistor plugs alone could really have that much effect on the MSD box.....just guessing but seems that MSD should have a better designed system to handle this.

I have had bad experiences with the MSD box in my 930. Never got it to run right. and I tried everything.