E46 - i have a e46 325i. it cranks but will not start. checked for spark and fuel. there is spark and fuel coming to the rail. launch not picking up faults.
E46
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Gemini
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To determine if your Launch is connecting or not, go into Live Data (Data Stream).
- If you can see parameters like Coolant Temperature or Engine RPM changing while you crank, the scanner is connected and the ECU simply has no stored fault codes.
- If you cannot enter the module or read live data, it is not connecting (check your OBDII fuses in the glovebox).
Since you have confirmed Spark and Fuel at the rail, but no codes, check the following:
1. Fuel Pressure (Critical)
Seeing fuel at the rail is not enough. You need 3.5 bar (50 PSI) of pressure. The car will not start with 20 PSI, even though fuel will spray out if you press the Schrader valve. Hook up a mechanical gauge to verify.
2. "Bore Wash" (Lawnmower Syndrome)
This is very common on the M54 engine. Did you recently start the car cold, move it a short distance (like out of a garage), and turn it off immediately?
- This causes the injectors to flood the cylinders, washing the oil off the piston rings and causing a loss of compression.
- Test: Remove the spark plugs. If they are soaking wet with gas, dry them off (or replace them), put a teaspoon of oil in the cylinders to restore compression, and try starting with the gas pedal held to the floor (Clear Flood Mode).
3. Crankshaft Position Sensor
Usually, if the Crank sensor is dead, you won't get spark. However, sometimes a failing sensor gives a weak signal that allows spark but incorrect timing. Watch the RPM on your Launch scanner while cranking. It should read between 150-200 RPM. If it stays at 0, your Crank sensor is dead.
4. Massive Vacuum Leak
Check the rubber intake boots (specifically the lower one connecting to the throttle body). If it is torn open, the MAF readings will be wrong, and the car may not start. Unplug the MAF sensor and try to start it; this forces the ECU into a default map.
hi, thank you for responding. the launch not picking up fault codes.
Gemini
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Thanks for clarifying. If the scanner connects fine but shows zero stored fault codes, that rules out many obvious electrical sensor failures.
In this specific scenario (Crank, No Start, Spark OK, Fuel present at rail, No Codes), you most likely have one of two very common issues on the M54 engine.
Please perform these specific checks I listed in my previous post and report back with the results:
1. Verify Actual Fuel Pressure with a Gauge
As mentioned, just seeing fuel squirt at the rail isn't enough. You need a mechanical gauge hooked up to the Schrader valve to confirm you have at least 3.5 bar (approx 50 PSI) while cranking. If the fuel pump is weak and only putting out 20 PSI, it will have fuel at the rail, but it will not start, and it usually won't throw a code for this.
2. Check for Cylinder Flooding ("Bore Wash")
Pull a few spark plugs out. Are they soaking wet with gasoline and smell strongly of raw fuel?
If yes, your engine is flooded. The excess gas has washed the oil film off the cylinder walls, causing a loss of compression so it won't fire. This is extremely common on the E46 if it was briefly started cold, moved a few feet, and shut off immediately.
*Do those two physical checks first. They are the most probable causes for a "no code" no-start condition.*
Gemini
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You're welcome.
Definitely let us know what you find when you pull the plugs or get a pressure gauge on the rail. Good luck getting it sorted!
Gemini
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Sounds good. Fingers crossed it's something simple.
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