Volvo: 1991 volvo 740 didnt start, air filter oil, volvo 740

Question
QUESTION: Wow - for the first time in my experience of this car (owned since 79K miles), I was actually stranded.  I do the under-hood tune-up work myself and had recently changed the exhaust/cat/plugs/air filter/oil + added fuel-injector cleaner into fuel; then passed emissions even better than before.  Now 2 months later and 177K.  After a short 10mile drive, I parked the car and minutes later it wouldn't re-start - though the battery is good and starter turned fine.   Car sat for 2 days, then started up first attempt.  Drove home.  I haven't changed the fuel filter for 40K miles...could this be it or should I investigate further?  Much appreciated.

ANSWER: Lewis,
You can change the fuel filter, but I do not feel that will be the "fix" for the no start. What you needed to know is if when it was not starting, did the fuel pumps come on, both main and pre, is there injector pulse, was there spark? These are the things you need to prepare for in the event the car again will not start. Guessing and replacing parts now is just guess work, not a bad thing for those parts to be renewed, however. If you do want to throw some parts at it, replace the fuel pump and Injector (radio suppression) relays, power stage, flywheel pick up.

---------- FOLLOW-UP ----------

QUESTION: This is just a follow-up and thankyou:  I diagnosed the fuel pump and it was ok (but repl the filter along the way).  The issue was with the original fuel injector relay.  The internal solder joints were cracked.  When the car heated up, they expanded and no longer provide sufficient current.  Not surprising considering the relay is in the engine compartment and was subject to 17years and 177K miles of heat and vibration.  I resoldered the joints (and resealed the relay w/caulk) and it works fine now. Just an FYI - there is an identical relay (same part#) used for the fan.  It too was faulty...now both are working!  Thanks again!

Answer
Lewis,
Yes I know about the relay you speak of four prong #1323592. That is called a radio suppression relay and helps to shield and keep the voltage constant to the injectors. As I understand it the relay shields the "noise" from the injectors from interfering with the radio. It is like the ignition coils most are now transistorized, or have a built in suppressor.