It's funny that you should mention this, my 780 just died on me yesterday while driving it. I opened the hood, swapped the Radio Suppression Relay and the Fan relay, and tried cranking. -and it started! I was definately blessed, as it was less than a minute before I was back on the road again.

Regarding your no start situation, I would suggest the following:

1. Swap the AC Fan Relay and the Radio Supression Relay (as I did). While you may have just resoldered it, it still can fail due to other reasons, moisture, carbon on the contacts, etc.

2. Swap your Main Fuel System Relay with a spare unit (the big white one in the relay box, second row, all the way on the left side).

3. Check your Fuel Pressure Regulator. Make sure she can hold vacuum for 30 seconds. (use about 25 Hg" on a vaccum pump rather than your mouth) Also, remove the return fuel line from the front of the Fuel Pressure Regulator and attach a short length of hose and run it into a cup or other container. With the engine cranking (and both pumps running), you should have a steady stream of fuel from the return port of the FPR. If you don't have a stream of fuel, it means that either your FPR is locked up tight (flooding the engine or a rich mixture), or that your pumps are unable to deliver more than 40 psi of fuel (insufficient fuel or a lean mixture). Attach an AMP meter to the wiring going to each pump and if one of them is lower than the spec'd values, change that one first. Off the top of my head, I believe the main pump draws about 5 to 7 amps, and the intank pump is 1 to 2 amps, but don't quote me on those numbers. Also, a clogged fuel filter will restrict fuel flow so it's a good idea to change it every 30,000 miles as spec'd by Volvo (located next to the main fuel pump).

4. Check the Flywheel/RPM sensor that's mounted on the top of the transmission, just behind the engine block. It is not uncommon for these to die from fatigue or have solder connections break. This is a common Hot-Start issue when they get old. Swap it with a spare unit.

5. Check your Air Mass Meter. Verify that the Platinum wire isn't broken (visual inspection when looking through it). Swap it with a spare if you have one, and make sure that the Air Filter Box Thermostat isn't the reason for killing your old AMM if it's dead. At 60 degrees farenheit, it should be drawing air from the Cold Air Intake (in front of the radiator) only, and nothing should be coming from the pre-heated inlet on the exhaust manifold.

6. Pull your distributor cap and clean the carbon off the contacts where the spark transfer occurs. Scrap them with a screwdriver until it's back to a shiny copper surface and the black carbon buildup is gone. Also clean the rotor in the same manner.

7. Swap your Ignition Amplifier with a spare unit. On the B280 equipped vehicles, it's burried between the Air Filter Box and the fender (you'll have to remove the Air Filter unit to access the Amplifier). The Amplifier is mounted to a ceramic pad for heat dissipation (with a thermally conductive grease between the two). This device supplies the ignition coil with a constant voltage and eliminates fluctuations from cranking or a week battery. I originaly though I didn't have one on my 780, but I just had to look harder.

8. Check and clean your ground connections (remove and scrub with a steel wire brush). The negative battery cable splits and grounds to both the engine and the chassis by the right side cylinder bank. The engine ground is only a few inches behind it and on the engine, but can be very difficult to get at (advise aproaching from below with the car up on jack stands). Also, clean the ground connections behind each headlight. You'll find multi-connection spade terminals there and this serves a plethora of vehicle functions (including a few critical ones).

The above list should get you started and covers the most likely no-start issues on a B280 engine. I personally advise keeping a kit of the following spare parts in your vehicle (taken from a salvage yard donor vehicle): Fuel Pressure Regulator, Main Fuel System Relay, Radio Supression Relay, Air Mass Meter, RPM/Flywheel sensor, and the Ignition Amplifier. The upfront cost of $50 to $100 for these parts is worth their weight in gold when trying to diagnose a no-start condition.

God bless,
Fitz Fitzgerald.
--
'87 Blue 240 Wagon, 253k miles.
'88 Black 780, PRV-6, 146k miles. (B280F engine)