If I drive my V-6 780 and then cut it off for about 10-15 minutes it won't start again until it has sat for 30 minutes or so. The starter turns the engine well but it won't start. I have had it checked by two mechanics. Any ideas?

I agree with Herb's assessment, the RPM/Flywheel speed sensor is the most likely culprit in this case. The first symptoms of a failing impulse pickup sensor (RPM sensor) is a no-start after it's had a heat soak. It isn't a problem when the engine is running since the fan and the vehicle speed keeps fresh air moving through the engine bay and keeps it reasonably cool. After shutting down, it gets pretty warm under there...

If you run into other no-start issues, I put together a rough list awhile back on troubleshooting a no-start condition for the B280F and B280E engines. Feel free to print it out or bookmark it for future reference, and please pass it along to anybody that has a no-start in a B280.
http://www.brickboard.com/RWD/index.htm?id=937949

FYI, the B280F and B280E both use LH Jetronic 2.2 fuel injection systems and they look identical when sitting side by side. The component locations are the same, and only a few minor differences exist (ECU firmware, emissions spec'd limits, etc).

God bless,
Fitz Fitzgerald.
--
'87 Blue 240 Wagon, 255k miles.
'88 Black 780, PRV-6, 147k miles.

Hello:

My first suspicion would be the impulse sender on the top of the bellousing. Other candidates are the fuel system relays-- resolder the fuel injection relay in the console and the radio suppression relay. I've never wrenched on a 780 before, but if it is similar to a 760 of similar vintage there will be two identical relays clipped to the coolant recovery tank-- one is the radio suppression relay, the other is for the auxillary fan in front of the rad. Swap those relays to see if the car will start afterwards. If so, resolder or replace them. These intermittent type problems can be a challenge to solve and it can be frustrating and expensive to fix if you just throw parts at them. In my mind, though, the impulse sender is effectively a wear part like a radiator-- 10 years and you are on borrowed time. Don't buy them at the dealer-- go aftermarket like fcpgroton.com or the like. Resoldering relays in these cars is a minor cottage industry in itself...

Good luck!
--
Herb Goltz, London, Ontario, Canada '92 245 w/109K mi