360 Multiple Misfire Codes. We have tried everything!!!

Calling all mechanics and folks who might have had a similar problem. I have misfire code issue that we have been trying to solve for literal years. Smoke and leak down test pass with flying colors. I’m also getting a slow down light now in the dash. This is a very exhaustive list of things that have been done to the car in the last year to try and solve the issue. The list is in chronological order. Please let me know if you have any insight or suggestions. You’ll see at the bottom we were able to pass smog but that was a miracle considering the window without faults was extremely short. They all came back.
I’ll try to answer any questions as best as I can but I am not a mechanical type of guy.

Thank you!

Battery was replaced in the initial service.
- Complete repair of the battery covers mounting bar as a nut-cert had pulled out and the second one was loose.
- Reposition aftermarket stereo wiring.
- Supply and install a proper upper battery hold down as this was missing from the vehicle.
- Add a shim to the battery posts as the current terminals are not clamping down on the battery posts as well as desired.

- Mis-fire codes, test drive, check common sensors in the engine bay, quite a few sensors in disarray – routing, sheathing, securing clips broken.

- Remove spark plugs, change out the plugs as these can commonly foul and not look horrible

- Clean and inspect all the coil packs.
- Change all the coil packs out with a donor car to see if the fault is gone or possibly moved to another cylinder.

- Clean the main ground connections for the engine, on the lower motor mount, in the right rear fender, on the engine ECU’s, on the back of the 5/8-cylinder head.
- Fabricate and install a second ground wire on the engine.

- Check all related fuses and relays. Inspect the wiring harnesses behind the seats as aftermarket radio wiring is present.

- Supply and install a new camshaft position sensor as the 1-4 sensor was found to have bare and exposed portions of the wire harness.

- Measure and observe oxygen sensor voltage readings and fluctuations. Remove the rear oxygen sensors, found a debris chunk in the right rear sensor flute, both sensors were replaced.

- Measure fuel pressure on both cylinder banks, quick pressure drop was present when the engine was shut off.

- Send out all the fuel injectors for inspection and cleaning due to the possibility of an injector leaking which is common.
- Inspect the contact pins in the fuel injector harness, inspect wiring in the harness housing.

- Complete inspection of the knock sensors, swap sensors from bank to bank, run the vehicle with the sensors unplugged to verify a code would show up in the ECU directly related to the knock sensor.

- Complete inspection of the timing reference sensors, clean the magnetic pickups, then swap them from side to side to see if a fault moves to the other bank.

- Complete a smoke test of the intake manifold to identify any vacuum leaks.

- Inspect the vacuum operated throttle solenoid under the intake manifold as this linkage arm was noted to have been replaced during a recent service.

- Remove both throttle bodies for inspection of the intake manifold as the catalytic converters can break down and introduce debris into the engine through the intake manifold. A good amount of oil residue was present inside of the manifold. Whatever oil was accessible was cleaned out.

- Inspect both throttle bodies, opening and closing of the butterflies with the throttle pedal, clean the wiring harness and connectors, both connector locking clips are broken

- Complete inspection of the water temperature sensor, check the coolant level which was found to be low. Noted were the radiator fans to be running all the time opposed to at engine temperature, engine temperature was very slow to come up.
- Inspection of the fan switch found horrible and patched in wiring, a good used harness was fitted with a new switch to correct the radiator fan operation, now they come on at engine temperature.
- Complete replacement of the coolant thermostat which was found to be stuck open and a lot of silicone sealant was inside of the housing.

- Alternator charge light was illuminated on the dash. Alternator harness plug was showing an overheated terminal, this was cleaned but the light still was on, the alternator was sent out for rebuilding, the warning light was now off. In previous test drives the battery light did flash for a moment but never stayed on, a few times the engine did seem slow to turn over when warm.

- Complete inspection and evaluation of the 1-4 camshaft variator as well as the variator setting.
- Complete testing of the camshaft variator solenoid actuator as the engine oil is quite dirty and possibly faults were present with the O-ring seals on the solenoid.
- Adjust the variator timing due to this being incorrect.

- Complete inspection of the oil pressure relief valve as the oil pressure was fluctuating quite a bit.
- Change the engine oil and filter due to introduce clean oil in the variator solenoid, the lifters, and to see if the oil pressure readings become stable.

- Inspect both engine ECU wiring harness pins, verify the ECU is correct for the vehicle.
- Send out both ECUs to determine if they have an aftermarket tune or program in them.

- Complete removal of the top intake manifold to clean out all the engine oil residue. Upon doing this access was great so the complete manifold was removed from the engine / cylinder heads. Scaring was present on the base manifold flanges from aggressive surface cleaning with a tool. This created a surface that was no longer flat, the gaskets that were removed showed signs of air leaks and area’s that did not have crush on them. The previous gasket material on the cylinder head was not properly cleaned and some of the original gasket material was still present. The manifold flanges were fly cut to return them to flat and true surfaces for a proper connection and seal to the cylinder heads.

- Complete a leak down test on the 1–4-cylinder bank.

- Remove the rear end cap cover of the 1-4-cylinder bank to compare the camshaft reference scratches to the camshaft caps, in efforts of seeing if the camshaft were obviously out of time.

- Complete measuring and re-timing of the intake and exhaust camshaft on the 1-4-cylinder bank. This required the valve cover and the end cap to be removed. A new gasket was fit post setting the camshaft timing. The camshaft timing was more than 10 degrees off on both camshafts.

- Complete inspection of the spark plugs on the 1-4-cyilnder bank once again. Replace these spark plugs with the optional plug for this engine. Currently one bank of plugs is slightly different from the other.

- Remove all the oxygen sensors to visually inspect the catalytic converter cores, front and back.

- Swap the thermocouple sensors from bank to bank as a fault code was present for the catalytic converter temperature being too low. Clean the control boxes and the electrical connectors to the control box.

- Swap the throttle bodies from bank to bank in efforts of identifying if the misfire moves with the part.

- Sway the mass air flow sensors from bank to bank in efforts of identifying if the misfire moves with the part
- Supply and install a new set of sensors, reset the ECUs and run the vehicle through self-learning processes.

- Remove the left side fuel pump to evaluate fuel level readings versus what is in the tank. Inspect the pump for age and any faults with the feed hoses.
- Supply and install a new pump on the 1-4-cylinder bank as this was the common fault side of the engine.
- Move the new pump to the 5-8-cylinder bank to evaluate fuel level readings on the dash and to see if any change was present in the running conditions of the vehicle.

- Complete inspection and testing of the air injection valves to verify they are opening and closing in conjunction of the air pump cycle.
- Repair a small crack in a vacuum canister top fitting.
- Complete replacement of the canister with a metal canister opposed to the plastic one.

- Inspect and clean the wiring connector at the throttle pedal switch as the vehicle felt as if it was on four cylinders and an immediate fault code or slow down warning light was present. This happened a second time and a fault code was present for this switch.

- Install spacers on the rear oxygen sensors as fault codes were present due to the engine having aftermarket exhaust headers that do not have a pre-cat.
- Add a second spacer to push the sensor farther out.
- Add a ground wire to the oxygen sensor to assure they are working properly.
- Supply and install a “mini-cat” spacer as faults were still present.
- Clock the “mini-cats” to obtain different readings.

- Pressure wash the engine to remove dirt and overall residues.
- Paint the left and right-side engine bay panels black as they were previously painted white.
- Complete tidy up of the engine bay wiring as it was in disarray when the vehicle arrived.
- Smog test the car – Passed
- Change the engine oil and filter
- Secure the front under-tray and the right front bumper skid plate as it was loose.
- Gasoline......
- The third brake light does have some bad bulbs in it.
- Inspect the brake fluid reservoir for solid particles, signs of the reservoir breaking down.
- Secure the rearview mirror as it had fallen.
- Remove the upper battery cover mounting bar to secure the nut-cert that was loose and to replace the nut-cert that was missing.
-Swap out both fuel pumps
-Checked Cats (perfectly fine)