Engine and Gearbox

See the Maintenance overview for more information on when rebuilds are required.

We will collect various techniques and anecdotes for rebuilds in this section as we gather it from dealers.

For information on the GCU, see the Shift Harness and GCU page.

Limp Mode Diagnostics

Throttle Type	Diagnostic Steps
Gen II — Drive-by-Wire	Connect the Red OBD connector to run diagnostics. If no fault codes exist but throttle is limited to 40%, check the Speed Emulator first. Quick check: in Neutral, rev the engine — if it does not rev beyond 6,000 RPM, the Speed Emulator is NOT working.
Gen I — Throttle by Cable	Connect the White OBD connector to run diagnostics. Limp mode at full throttle only = throttle is over-extending past ECM limit. Peak throttle percentage should not exceed 95% when viewed through OBD. Dash setup: 92% max.

Note

Ignition Fuse: The 10A ignition fuse controls the ECM, Ignition Coils, O2 Sensor (not used in race configuration), and Pair Valve.

Throttle Rises on Its Own at Idle (Gen II Drive-by-Wire)

On a Gen II drive-by-wire car, the engine sometimes gains revs at idle as though the pedal were being pressed, with nobody touching it. A drifted calibration in the throttle position sensor (TPS) at the pedal box is one cause, and you can rule it in or out in a couple of minutes. Cycling the sensor resets the calibration.

The signature that points at the TPS is what the revs do when you take the engine out of neutral: they run high in neutral and drop back to a normal idle in first gear with the clutch pressed.

Danger

Do not chase this with fuel pressure. Lowering fuel pressure takes some of the edge off a high idle, so it looks like it is helping, but it leans the engine out and will cause detonation. 42.5 PSI is the absolute floor, and nothing should run below 45 PSI. If you have already dropped it, set it back to 45 PSI before going any further.

Danger

The engine is making its own throttle input during this fault. Before you start: put the car in neutral, chock the wheels, keep everyone clear of the front and rear of the car, and keep a hand on the ignition switch. Do this in the paddock with the car stationary.

1. Start the engine and let it idle. Confirm the revs climb on their own.
2. With the engine still running, unplug the TPS connector at the pedal box, next to the accelerator pedal.
3. Watch the idle. If the engine settles to a normal idle, TPS calibration was the problem.
4. Plug the connector back in, engine still running.
5. Shut the car down at the master switch, not just the ignition, then restart.
6. Blip the throttle. Response should be normal.

The pedal stays dead between steps 4 and 5 even though the connector is reconnected, so do not treat that as a second fault. The restart in step 5 is what restores throttle control, and it is not optional.

If the reset does not hold

A reset that works for one session and then comes back was never the calibration. Three causes produce the same symptom, and they are worth checking in this order, because that is cheapest first.

1. Pins seated wrong in the connector clip. Unplug the TPS connector and look at where the wires enter the clip. On one new car the clip itself was fine, but the pins had never been pushed home into the connector body. Reseating them fixed it. This costs nothing but a few minutes.
2. The subharness between the TPS and the main harness at the engine. Try the intermediate harness before you buy a sensor. It is much cheaper, and one owner’s car held throttle position at 5 to 12 % instead of dropping to zero and banged off the neutral soft limiter around 4,500 RPM because of it.
3. The TPS itself. Replace the sensor only after the first two come back clean. On a used car this has failed outright and been covered under warranty, so ask before you buy one.

If the idle never settles in step 3, skip the reset entirely and start at cause 1.

On a car with an AiM dash, a stuck reading next to Accelerator Pedal is the same fault seen from the cockpit: one car that would only idle showed 148.6 there and would not clear.

Watch throttle position on a scanner through the Red OBD connector while you work. A reading that never returns to zero with your foot off the pedal points at the sensor or its wiring; a reading that sits at zero while the revs climb points somewhere else, so continue with Limp Mode Diagnostics.

Recommended Engine Oil

Rush Auto Works currently recommends Klotz KV1560R (15W/60 racing oil). This replaced the previous recommendation following testing that showed meaningful improvements in wear protection.

Caution

Warm-up requirement: When using Klotz KV1560R, the engine must be fully warmed up before entering the track. This oil is thicker at cold temperatures. Skipping warm-up accelerates wear.

Amsoil Dominator 15W/50 is a well-regarded alternative used by a number of owners.

Oil change interval: Change at each event weekend, or per the service interval schedule.

Low oil pressure once the engine is hot

Older cars in particular can show low oil pressure at operating temperature while reading normally cold. Oil grade is the first thing to change, and it is the reason the recommendation above is a 15W/60: a thicker oil holds pressure at temperature where a thinner one drops off.

If you are running something lighter, move to Klotz KV1560R or the Amsoil 15W/50 before you look at the pump.

Caution

Owners used to fit a high-volume oil pump gear for this. Do not plan around it: it is no longer permitted for spec competition. Check the current Technical Regulations yourself before you consider one, and ask your dealer.

Read the pressure through the dash rather than by feel. The RPM OilP Ratio channel compares pressure against what the engine should be making at that RPM, which is what you want here, since a raw PSI number at idle tells you very little. Oil System Health alarms explains the thresholds.

See Fluids for the complete fluid specification list.

Clutch Replacement

An important note; when tightening and using blue loctite on the clutch, do not fill the motor with oil right away as it will cause the loctite to have trouble bonding. Leave the bolt torqued and the motor dry for some time (at least 24 hours) to allow the loctite to bond properly.

Failure to do this can cause the bolt to come loose, and will cause shift issues and failure of the clutch to fully engage.