1997 Volvo S90 crank but no start

1997 Volvo S 90 cranks but doesn't start. I have replaced the RPM sensor, I
have tried replacing the engine computer with a known good one but it still
would not start. I have no spark and no injector pulse. The car will start
after many long cranking tries. The car has about 75,000 miles. I am an
ASE master mechanic with many years experience and this once has me
stumped. Any suggestions what might be the problem. Could it be the
coolant sensor even though the one in there test fine? I have tried
replacing the coolant sensor and am still having the same problem, any
ideas, thoughts, spells that will make this car run???/

 

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?