Bennitoapplebum

Not to complicate things further, but your spark plugs 1&2 are very lean. The +12v power for the INJECTORS are wired from the center. A heavy gauge wire splits into 4, feeding each injector. Meaning 2&4 gets dibs on power. When you plug in your CTS, the ISV reactivates and draws more current. Just something to think about.

You can adjust that all the way down to full continuity (0 ohms). By then, if you can't get the AFR's within a good range, it's safe to say the problem lies elsewhere.

Yes I remember. That is definitely a lean misfire. The next steps would be to: 1. Fully warm engine up. 2. Leave CTS plugged in. Adjust CO pot to obtain a decent idle AFR. 3. Go for a drive and record the driving AFR. 4. Report back with the results of changes. Ex. drive smoother, misfire, kicked ass, blew away a MK5, etc.

No apologies needed, this is all great info for others to read. The resistance readings for the CO pot and air temp sensor sounds reasonable. Pins 9 and 5 would be a combined resistance of the CO pot and air temp sensor together. For the ISV, the 12v is constant(ignition). The ground is a pulse modulated signal from the ECU. The voltage will always vary ~3-12volts, depending on how far off idle target is, engine on or off, etc. You say you had an idle mixture of 15-18. Was it idling decent at all? That doesn’t sound too bad of a mixture at idle.

It can be confusing at first. The sensor reads oxygen 02 content so a higher number means more oxygen (lean). I’m thinking your CO pot adjustment of ~80 ohms might be where you need it. It was giving you a decent idle and driving air/fuel ratio.

Did the idle raise when you plugged in the cts? Or drop? You might have to play more with the bypass screw to find a sweet spot, where the idle doesn’t change much from plugging back in the cts. With the cts plugged in and the engine fully warmed up, record the idle rpm(ECU target rpm). When you unplug the cts, the idle will raise, or drop. Play with the bypass screw in the direction needed to match the recorded target rpm. You need to find a good air/fuel ratio to reach this target. Plugging in the cts will turn on the idle stabilizer back on. And the afr will change a bit, but the idle stabilizer won’t be working too hard to reach the target rpm. If your CO pot is that far off I’m thinking the problem is elsewhere.

Was all this with the CO pot at ~500ohms? Your CTS sensor might be out of range, or your engine may have been still warming up, while unplugging the CTS. By any chance you have the factory thermostat in there?

This type of fuel injection system fires all injectors at once per engine cycle. It requires a slightly richer idle. 13.5-14.5 is probably the leanest it will idle smoothly. Anything leaner will surge and hunt for stability. 14.7 is ideal, but not realistic with this injection system.

Actually your #5 pic (ground bus) is not the correct one. It’s above the fuse box. I can see it in your other picture, after the aftermarket switch picture. It’s bolted right above, has around 10 “fast-on” type connections, with about 4 brown wires occupied. I also see a thin black wire connected to it (looks shaky) kinda burnt. Might wanna check out what that is.

I remember why the CTS needs to be unplugged while adjusting the CO. The ISV idle stabilizer is inactive while the CTS is unplugged. You get the idle speed close to ~800 using the bypass screw. And adjust the CO using a wideband. After the adjustments, you plug the CTS back in and the ISV will hold the idle speed closest to 800rpm with the varying load, power steering, fans, acc, etc. So in your video, your idle was too high. When you plugged your CTS back in, the ISV pulled the engine back to its target idle speed.

Also another thing to point out: The injector flow. I recall you had purchased a new set of injectors. If the flow rate deviates from factory, you may be having to compensate with the CO pot. I’d say wait for the wideband installation to help simplify some things.

Was the car fully warmed up while the CTS was unplugged? You could’ve bee adjusting the CO while the engine was warming up, or cooling down. I don’t know what function unplugging the CTS serves while adjusting CO. I do know that both CO pot and coolant sensors are important for fueling equations within the ECU. I kind of remember unplugging the CTS at one point, for adjusting CO. But eventually ended up leaving everything plugged in while making any adjustments. Does anyone here know why the procedure calls to unplug the coolant sensor?

Shutting down the engine after a drive causes an engine to go into “heat soak” mode. The entire engine heats up due to the cylinder’s heat not being transferred to the radiator, fuel cooling, etc. When you restart the car during this stage the ECU delivers an increased ASE(after start enrichment) for a period of time~30 sec. Judging from the symptoms you explain and from the color of your plugs, your issue seems to be fuel related. Any ignition system will have a hard time lighting a mixture as lean as yours, especially during increased load. A quick test would be to crank that CO pot up by a large amount and see if she drives better or worse. I’m betting it will run way smoother and consistent.

Would you say that your engine has reached a higher temperature while sitting? If so, then heat related intermittent problems are, guess what... ground related. When metal expands under heat it sometimes increases the current capacity in poor grounds. This may not be your case. Just something to think about.

Yes you can tune the idle that way, the mixture and idle speed go hand in hand so constant back and forth adjustment might be required. Yes getting a wideband will definitely help with tuning and diagnostics.

That’s better lighting to read the plugs. That’s too lean of a mixture for boost. It might be okay for short runs, but will be inconsistent due to knock and timing pull. For economy you’d want all your plugs looking like #2. Though that still looks too lean for my taste of tuning. For all out full throttle top speed fast and the furious runs, you want the plugs looking dark grey and sooty.

I think 500 ohm was the factory’s starting setting, but still needed adjustment before capping the pot off. Each G60 got its differences and the CO pot was a way to tune for the right air fuel mixture.

1/2 turn increments should be easier to tell if it’s getting better.

The only thing I can think of that relates them are the shared voltage. If the grounds are not good, you’ll get low voltages. Many components need full voltage to work properly. Have you fixed the main grounds?

Ah, I’ve assumed you had the cams in there already. Yeah that’s definitely a misfire. With that understood I’m thinking it’s still a fuel issue. Next step would be to try the CO pot adjustment. You want those plugs looking a little more sooty.

Sounds like she’s almost there! There could be a vacuum leak somewhere, but it’s sounding more like a tuning issue. When you say ‘missy’ or ‘burbly’ do you feel a hesitation? Or just slightly jerky with a steady throttle? From what I remember with the 268 cams there was always a light load/cruising misfire under 2000rpm that immediately went away upon throttle addition. If there’s hesitation upon any acceleration, then I’d worry. I’m not sure if that’s what you mean though. You can leave that spark plug gap for now. It should be good, but if you wanna add more boost then you should close the gap. Im assuming you just need a tad more fuel, but we’ll see after looking at those plugs.

Yes, about two degrees should be good. Be careful, with the power addition from the increased timing, you’ll want to keep advancing timing till the engine blows up😂it gets addicting. Try 2 degrees. See how she drives.

Looking a little better now, still a little on the lean side for these motors. But the 4th plug looks a little whiter than the rest. I’d look into that. Increasing the gap will be harder to ignite under boost, but may help with the cruising loads. The current plug conditions you show are safe for about 8-10 lbs of boost. If you’re running any higher boost you need more fuel. Are you comfortable with adjusting your timing? If you’re running low boost ~8 lbs I feel that advancing the timing slightly will help with the cruising misfire.

I’d say leave the CO pot where its at, and just turn up the fuel pressure for now. Then go for a drive and pull the plugs again to have another look. It sounds bothersome, but it’s tuning😂

Make sure those plugs are resistor type. You seem to be running lean, most definitely causing the misfires. The porcelain is white, lighter than tan. The color for these motors should be more sooty, darker grey. You’re almost there, after you sort out the fueling issue I’ll bet she’ll pull like a freight train. It would help to have a wideband 02 meter to squeeze the most out of your motor, but pulling the plugs for a reading isn’t bad on the 8 valve motors. You can address the fueling with one of three ways: 1. CO potentiometer adjustment 2. Higher fuel pressure regulator (4 bar) 3. Stand alone fuel management.