I pulled the plugs on my eg33 conversion and cannot for the life of me decipher what is wrong. As you can see the 3 plugs on the left look fine. These were from one side of the engine. The 2 from the other side look to be carbon fouled with whitish tips? I was thinking weak ignition coils so I switched them around but nothing changed. I then swapped the o2 sensors with no change. Could oil cause dry carbon build up? The oil on the threads of the bad two plugs is from external leakage.

I did put new plugs in and only after 5 miles the plugs from the same two cylinders already had carbon build up while the other plugs are clean.

The engine does have hesitation and surging but still feels pretty strong.

I am thinking valve guide seals but would like another opinion.

Another pic

Not,sure how to diagnose this but if the system monitors a lean condition, like a vacuum leak, it will richer up the mixture.

If those two plugs are the farthest away from the vacuum leak, it's possible they would foul quicker than the others that are burning hotter.

I have checked and repaired all vacuum leaks. I have an attachment so I can plug an air compressor into the intake hose and pressurize it to about 10 lbs. Right now it has no problem holding the pressure.

The idle is a bit rough and when I accelerate the car surges and then pulls back. Feels like the engine is being choked to a certain degree.

Running too rich.
Do you have a way to monitor the mixture?
If no gauge, read up on your 02 sensor to see what it's sending out, typically between o.5-1.5 volts.

The thing that gets me though is of the three plugs from that bank only two are fouling.

You may need to tap into the ECU to see if it locked into limp mode.

If you cannot, remove both battery cables and zip tie them together for an hour, this will drain the memory of the ECU and take it out of that mode....then try again.

You may want to pull the injectors from the offending cylinders, and make sure they are clean, and have the correct spray pattern. Something is causing incomplete combustion in the pair.

Check the compression on all cylinders, report back if the two dark plugs have low compression.

I don't think these ECUs have limp mode. The OBD2's might but definitely not OBD1. The transmission controller does. Andrew, what you are describing sounds a lot like what I had....any backfiring/popping? Maybe you want to check your crank and cam sensors. If any of those are bad your timing will be totally jacked up. Just use a multimeter and measure the ohms...should have 2400 minimum when you touch the terminals with the + and - probes. Could also be something as easy as frayed or cut wires or a bad ground.

Ignition 100%? ,plug leads ok and tested for resistance? and yes injectors cleaned and then hope you have even compression,good luck.

I have not tested compression yet. I am in the process of swapping the injectors. The ignition is coil on plug type and swapping coils around did not change anything on those two cylinders. Maybe swapping the injectors will. I did replace the crank sensor and the other two cam sensors tested good.

So one of the sensors was bad or you had already done that?

I agree with MATHEPCAT. Test the compression.
Is it smoking when it is in high compression?
Is it burning oil?
If it is, I believe u have a problem with valve seals, and hopefully that's about it.

I did have a bad sensor but it was replaced a couple of months ago. The issue is still there. I know this because two of the new plugs I put in started fouling right away. I do believe the valve seals need to be replaced although I see no smoking. But would that cause dry carbon build up? I would expect it to be wet.

I would lean towards dirty injectors. I haven't looked at my fuel rail in awhile but if they terminate near those units you could build up some crap that eventually makes its way into the injectors. If not, it still sounds like they're hanging up a bit. That would account for no smoke but a stumble and surge scenario. Swap em out if there's nothing obvious and look for the same symptoms on those new cylinders. Happy Wrenching!

I would think electrical or injectors before valve seals or some other serious engine problem. You can send the injectors out and get them tested and resealed for like $10 each. I'm planning to do that soon.