Greetings. Being a volvo driver for some 25+ years, I secured the Chiltons and Haynes 850 manuals before the first tank of gas. The car is a tight,clean turbo with 250k and I expect another 200k, just as soon as I get over a little funk the car decided to go into.
Car was running fine. Next day, car turns over but will not start. Up goes the hood to full up position. Rats. I knew I'd crack the books, but not this soon. Determined no spark at cap. Fuel is there. Coil is good (primary side .7 ohms,secondary side 8.26k/ohms between cap wire and one of the primary posts) Can force a spark going direct to bat. and gnd. on primaries. Note all tests done with battery connected. Using the Chiltons (the Haynes fell flat on its face here),checked the leads going to the power stage . With ign on, blu/rd(through to coil)=11.93vdc,y/w(signal from motronic 4.3 control module)=.131vdc,blk(gnd)is good. Note. when cranking, signal jumps to .238vdc figure this may aid initial start. Studying Chiltons schematic, the powerstage is essentially a switch that opens and closes the return (blue wire) from the other primary post to ground to cause the field collapse and initiating the spark in the secondary.The elctronic switch or gate is controlled by the module. This signal must, in my mind,be a controlled pulse. While cranking, my digital multimeter cannot see any pulsing probably- going to fast. Took wheel off passeger front, pulled back flap on inner well to expose nut on crank, removed spark plugs, disconnected leads to injectors.(when engine cranked, can hear gas going back to tank on bypass) Now, I can slowly advance engine using 1/2 drive socket on nut. With ign. on my assistant(my wife/ceo/boss)slowly cranked the engine, I watched the meter on the y/w lead (module signal) going to
the power stage looking for break in the signal. no break, steady on.
Checked the CKP(crank position sensor) for resistance OK at 263ohms.Removed same looks ok wiggled wires, ok. All values good on the CMP (cam position sensor)Removed same, looks ok

Pursuing the crank sensor. leads going to it: one carries 1.8vdc ign.on. (red/blk) the other(blue) must be the return to module this signal must be,in my mind,pulsed to reflect firing references on flywheel. Connect leads into each other and cut into the blue return and put meter between it. Trusty assistant cranks engine with wrench, ign.on .I'm getting a steady 1.8vdc through the meter, no gaps. This doesn't fit. I'm prepared to replace the crank sensor even though its resistance checks out.

Also, does the module need all inputs functioning to start engine. Is my rationale sound about pulsing at the powerstage input and crank sensor output? Reluctant to purchase an OBD reader just yet as I don't think this fault will show, judging by the fault code references. Not into towing to a Volvo shop.

Please Advise