3.2 Spark plug difference between banks

[turboquattro]

Decided to change plugs in my RoW car. PO installed wrong (used North American spec plugs). But, I noticed a big difference between banks, the light coloured plugs (normal as far as I can see) are from the right side bank, the dry fouled are from the left side.
Any suggestions on what might be the cause? Was not expecting this.

[dtxscott]

Check the grounds for the injectors on the side with the rich plugs.

[wazzz]

There are no grounds as such for the injectors, since the injectors get their "ground" as the signal that is pulsed from the ECU. The other terminal of each injector gets a permanent +12V power whenever ignition is on.

Since one bank looks much leaner than the other one, it may be worth checking the signal line that carries this pulsed "ground" between the ECU and the connector pin for this bank. Do the same for the other bank as a comparison. You need to do ohm tests while the ignition is switched off. Even a small stray resistance is significant, as these lines carry high currents.

Easier way to do these checks would be to disconnect the big connector at the ECU under driver seat and ohm between pin 14 and pin 5 on the injector loom connector. Do the same between pin 15 (ECU harness connector) and pin 6 (injector loom connector).
Injector loom connector is on the cross member near the left shock tower. It is a six-pin connector, but only four of them are used. Two for power, two for pulsed ground signals.

As a side note, both signal lines are tied together inside the ECU, so the six injectors are actually driven in parallel. In your case, it appears that one signal line is weaker than the other one.

[mysocal911]

Originally Posted by wazzz

There are no grounds as such for the injectors, since the injectors get their "ground" as the signal that is pulsed from the ECU. The other terminal of each injector gets a permanent +12V power whenever ignition is on.

Since one bank looks much leaner than the other one, it may be worth checking the signal line that carries this pulsed "ground" between the ECU and the connector pin for this bank. Do the same for the other bank as a comparison. You need to do ohm tests while the ignition is switched off. Even a small stray resistance is significant, as these lines carry high currents.

Easier way to do these checks would be to disconnect the big connector at the ECU under driver seat and ohm between pin 14 and pin 5 on the injector loom connector. Do the same between pin 15 (ECU harness connector) and pin 6 (injector loom connector).
Injector loom connector is on the cross member near the left shock tower. It is a six-pin connector, but only four of them are used. Two for power, two for pulsed ground signals.

As a side note, both signal lines are tied together inside the ECU, so the six injectors are actually driven in parallel. In your case, it appears that one signal line is weaker than the other one.

Or there's an intake air leak on that bank.

[brighton911]

I'm with Dave on intake leaks. In my experience, a fairly common occurrence and easy to check. And with a little effort, doable with the engine in place. And I wouldn't call them dry fouled, more like a correct mixture on them. The white ones are on the lean side, indicating a possible air leak.

[wazzz]

Air leak makes sense. Since the three "lean" plugs look the same, if it is due to an air leak, it has to be at the junction between the two half intakes. The rubber boot with the two clamps is a suspect here.

[turboquattro]

Thank you for suggestions. Will have a chance to look at it this week and will report.

[David]

A likely candidate is the cam timing not being the same left to right. BTDT.