1997 Volvo S90 crank but no start

If there's no spark then you have an electrical problem somewhere. I'm not real familiar with this car, are there any relays that control power to the ignition control box or ECU?

To be quite honest, you are not a very good master mechanic if you cannot solve a basic ECU power / primary igntion problem.

Check and replace the main relay, and check the ECU is powered up and has good ground on the relevant pins.

If that is ok, which RPM sensor did you replace? There are two. Flywheel and cam sensor. You need both working.

A dud CTS or break in the wiring will not prevent the ecu from fueling- it will default to a fixed value. This is fundemental knowledge.

Tim..

Tim, I did replace the main relay, that is basic. The ECU is powered up and has a good ground to the relevant pins. I replace the RPM sensor and the cam sensor tested fine, I replaced it just to be sure.

What other suggestions would you have?!

Right, so we can assume:

a) The ECU is properly powered with +12v and 0v. b) There is a cranking voltage of at least 5v AC from both the CAS and the CPS. c) There is +12v present on the injector rail.

Given that you say there is NO injector action OR primary switching this could rule out the dual igntion amps.

Does the tacho needle jump at all during cranking? If not then its either possibly a dead ECU or a broken harness wire- the ECU is not aware the engine is turning.

If the tacho is jumping then you must have injection takign place in which case re-examine the primary feed to the amps and coil packs.

At this point i'd firstly use the jumper and set the ECU to manual actuator test mode and see if it is capable of firing the injectors and / or use a FCR to capture live data during cranking.

Any past history of problems with the car, or did this happen suddenly out of the blue?

Tim.

Could the chip in the key be acting up , or the antenna in the steering column isn't working?

ojm8183 wrote: