joshuaho96

Oil change does not trigger code 21. Code 21 is for coilpacks primary side connection. You can try to clear the code with a battery disconnect, hold down the brake pedal to drain capacitors through the brake lights with the ignition on for 10-15 seconds before you reconnect the battery. I have seen R35 coil conversion permanently cause this code with no ill effects so it might be the resistance it wants to see isn't quite right on one or more coilpacks. Could be inside the ECU, could be the harness, could be a coil. You can test it all if you want or just ignore until the car actually starts misfiring.

I forgot you have a Nistune ECU. Use Nistune to do all the tests I mentioned instead of faffing with 30+ year old electrical connectors. You can read MAF volts off that too, there are reference values in the service manual to tell you roughly what it should be in different conditions.

As MBS suggested if this is happening when the engine is cold you're going to want to remove the intake air regulator and verify resistance + that the shutter is physically opening and closing. At -20C should be fully open, 20C half open, over 60C fully closed. At 20C should be 70-80 ohms. For AAC valve testing using a Consult cable see if you can raise and lower the idle by commanding more or less AAC duty cycle. Hopefully it's pretty linear as well, shouldn't be like 30% AAC valve is barely idling and 40% is 1500 rpm.

Reading through the engine service manual their advice is do a cylinder balance test. Unplug one injector at a time and see if the idle drops a consistent RPM. You can also do this using a Consult cable which is easier. They also call for unplugging the power transistor, then with the engine off and the fuel rail unhooked from the manifold verifying that you have good fuel flow (even injection, no dripping/leaks, etc) when you twist the CAS by hand. Also verify the spark by pulling the spark plugs and allowing the plugs to ground and turning the CAS by hand. I would also start doing the sensor checks and idle valve checks in service manual. Make sure the MAF tests reasonably, the intake air regulator is sane, etc. You may have to get new spark plugs.

Isn't there a PAR engineering gearset that has closer to stock ratios? And they claim they'll do whatever ratios you want.

From the factory on RB26s there's a fitting on the intake manifold collector/"plenum" that provides pre-throttle boost signal. That's how they did it back in the day, I figure it's fine to replicate it.

This is just a dumb way of keeping the wastegate closed to make more boost. Undo it and either follow the factory setup or redo it properly. Manual boost controllers just use a spring preload to determine when to close in response to boost pressure so it no longer vents to atmosphere.

I would put a fuel pressure gauge between the filter and the fuel rail, see if it's maintaining good fuel pressure at idle going up to the point when it stalls. Do you see any strange behavior in commanded fuel leading up to the point when it stalls? You might have to start going through the service manual and doing a long list of sensor tests if it's not the fuel system for whatever reason.

Nothing cheap, but I have seen the AC Hydraulic DK13HLQ which is pretty close to what you're asking for. The problem is the hydraulic cylinder mandates that the back of the jack be a certain height and Skylines have fairly deep inset floor jack points. A more certain and cheap option is to get some nominal 2x10 inch lumber boards and have one board be 1.5 feet, the other board 3 feet. Glue it all together with lots of clamps to maintain pressure. Make two of these. The ramp suggested above is a good idea, it takes quite a bit of clutch slip to get over each of the boards. I only need the first ~1.5 inches for my low profile jack on a standard ride height car but a lowered car you want to go up to the full ~3-3.5 inches. Paint it or store indoors if you want it to last.

Pull codes via the self-diagnosis procedure. As far as I can tell this is just a sign of transmission issues but not a code unto itself.

Sounds like a misfire. Check fuel pressure and don't even think about going into boost while it's like this unless you enjoy engine rebuilds.

The average previous owner for these cars were basically S-chassis owners in the US. Teenagers or teenager-adjacent. I often tell people that neglect is easier to fix than something that was actively "repaired" by previous owners.

I've heard the Tomei USA head gaskets are decent if you want to o-ring the heads but otherwise not recommended.

Drain it. I got official Matic D but you can get whatever is listed as Matic D compatible.

The incentives are mostly the same, yes. Ethanol is cheap compared to the cost of doing 98-100 RON with crude oil alone. 87 to 93-94 AKI all with E10. In 2020 Canada mandated E10 as a part of their "renewable fuel standard" and is supposedly going to go to E15 in 2030. In California where there are only 8 refineries with two threatening to shut down next year it's been over 20 years now of E10 and 91 AKI maximum because there's just not enough refinery capacity or crude oil supply relative to the demand for premium unleaded fuel. And CARB's low carbon fuel standard means functionally none of the diesel available at the pump is made from crude oil anymore. It's almost all entirely 20% biodiesel blended with 80% renewable diesel (hydrotreated vegetable oil) now. The number of gasoline vehicles that support E15 or higher ethanol concentrations is surprisingly low, I can't imagine it being wise to play tricks like this without flex fuel sensors in most of the fleet.

In the US almost everything is E10. It can't exceed 10% by much or fuel systems have trouble adapting. At the same time because MTBE, MMT, and TEL are all banned they need as much ethanol in it as possible to boost octane.

E10 is pretty tightly regulated in percentage. Too much and engines can't adapt. Every incentive is against them to have too little ethanol though. The more ethanol the higher the octane.

The other reason why I say this is because if you lose the motivation to mess with this stuff, at least if you can get the car back together and fixed up better than it came to you usually you can sell it for more than you paid. Skylines in that regard it's pretty rare for anyone to actually come out ahead.

My recommendation is start with maintenance. Find a ~15 year old car that is cheap for a reason and fix it up. For example, in my area F30 328i with N20/N26 are dirt cheap because everyone knows that the timing chain loves to stretch and take out the cylinder head around 80k miles. Buy one, do all the maintenance on it, if you're still motivated after that an N20/N26 can be easily modified for more power.

It's sodium citrate, I misspoke earlier. It's a citrate buffer solution. And yes, depending on how thin the metal in the tank is this may or may not be a wise decision but if it's just mild rust it should clean off and it should be fine.

You can probably scrub the rust with a toothbrush or something. After you get the rust off flush well with water to neutralize and you will probably want to also use a fuel tank sealer to keep it from rusting again.

The sodium citrate solution is designed to buffer the citric acid to keep it from attacking metal quite so much, the guy that came up with that recipe did a ton of testing on how much metal loss occurs over time and it's nothing crazy unless you forget about it for months:

Yes, it will take a fair amount of solution but the sodium citrate + citric acid + detergent is cheap stuff. Use laundry detergent instead of dish soap if you want to reduce the bubbles, also you could just buy sodium citrate and add some citric acid to the mix until you get to a weakly acidic solution if you don't feel like dealing with all the bubbling generated by adding everything together. For a fuel tank you need quite a lot of distilled water but it's probably worth the effort.

Take the fuel pump out of the hanger, purge the fuel tank of gasoline, try cleaning it with a soaking of this sodium acetate and dish soap solution. If there's no rust holes this should get the tank and hanger clean.

Not only should you be testing compression with a strong battery, you should be putting a charger on it. These cars have pretty small batteries and it's possible to discharge them enough that by the last cylinder the starter isn't turning as fast.