B58 E9x Swap Cranks but Will Not Start
Short answer: do not start by replacing random sensors. A B58 E9x crank-no-start diagnosis should move in order from battery voltage and grounds, to DME power, immobilizer/security authorization, CAN communication, fuel pressure, ignition, and crank/cam synchronization. The goal is to identify which layer is missing.
A starter turning the engine proves only that the starter circuit works. It does not prove that the DME is awake, authorized, communicating with the chassis, seeing engine speed, or commanding fuel and spark.
First: make the symptom precise
Write down exactly what happens:
- Does the engine crank at normal speed?
- Does the scan tool communicate with the DME?
- Are there DME, CAS/EWS, FEM/body, or transmission communication codes?
- Is engine RPM visible during cranking?
- Is low-side fuel pressure present?
- Is high-pressure fuel pressure building?
- Are plugs wet, dry, or unknown?
- Does the engine briefly fire on starting fluid? Use extreme caution and follow proper shop safety.
“Cranks but will not start” is too broad to guide wiring work. These observations divide the problem quickly.
The six-layer diagnostic order
| Layer | What to verify | Typical clue when missing |
|---|---|---|
| Power | Battery, main feeds, relays, fuses | No DME communication |
| Grounds | Engine, chassis, DME grounds | Intermittent or multiple unrelated codes |
| Security | DME authorization, key/ISN pairing | Crank allowed but injection disabled |
| CAN | PT-CAN wiring, termination, polarity | Communication and torque-request faults |
| Fuel | LPFP, HPFP, injector supply | Dry plugs, low rail pressure |
| Timing/sync | Crank and cam signals | RPM missing or sync fault |
Check power and grounds under load
A visual ground connection is not enough. Measure voltage drop while cranking between the engine block and battery negative, and between the DME ground reference and the battery negative. Inspect the original E9x ground straps and any new engine-to-chassis strap.
Verify that the DME receives the correct switched and constant feeds. A relay that clicks can still deliver poor voltage under load. Confirm fuse locations against the donor wiring diagram, not a forum photograph from a different model year.
Confirm DME communication before chasing fuel
If the diagnostic tool cannot communicate with the DME, stop. Do not continue replacing pumps and injectors. Check DME power, ground, wake-up, CAN-H/CAN-L polarity, connector seating, and whether the selected DME is compatible with the programming/security plan.
CAN-H and CAN-L should not be casually swapped because the network may appear dead or produce a large group of communication faults. Use the wiring diagrams and a meter or scope appropriate to the circuit. Disconnect power before performing continuity work where required by the service procedure.
Security and ISN are not the same as a bad starter
A DME can communicate and the engine can crank while security authorization still prevents start. Confirm that the DME, key/security modules, and chosen integration method belong together. If the build uses a standalone controller or a modified OEM strategy, document exactly which module is responsible for authorization and which module is responsible for engine control.
Do not publish or share immobilizer secrets in a public build thread. Record them privately and keep the final configuration documented for future service.
Fuel and synchronization checks
Once DME communication and authorization are established, verify engine speed while cranking. No RPM usually points toward crank-sensor power, ground, signal, wiring, or DME interpretation. A valid RPM signal does not automatically prove cam synchronization.
Measure low-side pressure first. The HPFP cannot create stable rail pressure if the low-side supply is missing. Then verify rail pressure behavior during cranking and look for injector enable faults. Inspect fuel contamination and confirm that the pump control module and wiring are compatible with the selected system.
Common mistakes
- Testing fuel pressure before confirming DME communication.
- Leaving a donor ground strap off after painting or powder coating.
- Mixing an engine harness and DME from different strategies without a wiring map.
- Assuming the E9x chassis will automatically understand B58 torque and gear messages.
- Using a forum pinout without confirming connector orientation and revision.
- Clearing codes repeatedly instead of saving the first diagnostic scan.
A printable first-start log
Record battery voltage at rest and while cranking, DME communication status, engine RPM, security status, low-side pressure, rail pressure, and the exact DTC list. Repeat the scan after each change. This turns troubleshooting into evidence instead of memory.
The B58 Swap Bible's wiring and first-start sections are designed around this sequence: prove the network and control system first, then move outward to fuel, spark, cooling, and drivetrain.
When should I stop and get professional help?
Stop when wiring colors do not match diagrams, fuel pressure is uncontrolled, high-voltage or pyrotechnic systems are involved, or the car has repeated module damage. A qualified BMW technician with ISTA-capable diagnostics can save time when the problem is security or network architecture rather than a mechanical fault.