Sudden onset.
About two weeks ago, she just suddenly started having trouble starting... most of the time.
It doesn't seem to matter if it's been sitting for 10 minutes or all night. Occasionally it will fire right up, but usually it takes a few tries. Sometimes a LOT of tries.
Sometimes when it catches, it does so definitively. Other times it kind of coughs and sputters until it kicks over. Once in a while it will die a second or two after starting.
Other than that, it runs like a top. No lights on the dash. OBD I shows all clear (1-1-1). Ran a confidence test and everything seems to be functioning correctly.
Found a couple of potential vacuum leaks and repaired them. No change.
Thought the distributor cap was cracked, but it turned out to be just the rubber cover. Nonetheless, it now has a new cap and rotor.
My son replaced the plugs a few of months ago. So that shouldn't be the problem.
Father-in-law (retired mechanic) suggested a test for a fuel pump pressure leak. That doesn't seem to be the problem either.
Any suggestions before I start chasing the wild geese with red herrings?

 

Did you check fuel pump relay and temp sensor?

 

Sure sounds an awful lot like fuel pressure. A tire gauge will fit that schrader valve, but obviously you're gonna get gas all over you if you measure it that way. But you can measure that if you want to. I can never get a real pressure gauge on there without taking the throttle linkage off. I don't know why they had to orient it the way they did.

My first response to a thing like this would likely be to jumper the fuel pump relay. You can do that for free in a couple of minutes.

 

+1. I'd test for fuel pressure. Autozone will rent/loan a guage and RobertDIY has a Youtube vid on the how to. For 850s/early V70s you should see around 39 PSI at the rail. Measure cold, then crank and see what happens as the pump engages, then with the engine running. Another option is to jumper the fuel pump relay prior to the first cold start (see https://www.matthewsvolvosite.com/fo...ic.php?t=18663 for some insights) turn the key to position 2 and give the pump a bit to build pressure then try starting. If this helps, you could have an issue with the pump, the relay or the fuel pressure regulator. Do you see a puff of smoke on first start up? That may indicate a leaky injector allowing pressure to slowly bleed off (possible but not the most likely scenario). There's also a fuel injector relay up on the cowling by the radiator. Usually when those fail you get no signal to the injectors. I don't think thats in play here since you noted the car will stumble as if it wants to start vs sounding like its totally out of fuel. At any rate, you can try rapping on that relay which will help unstick it...

 

Not the relay yet.
Temp sensor has been an ongoing problem since long before this. Son replace the engine temp (coolant) sensor. I replaced the EGR temp sensor about a month ago (OBD I code 4-1-3). Dash display still jumps around a lot, but guessing that's just either the gauge or the connection at the panel.
Unfortunately my daughter's dog ate (yes, I know) my service manual and I haven't been able to replace that yet.

 

Father-in-law (retired mechanic) suggested a similar pressure pre-load technique. That didn't help.
Haven't seen any smoke, even after it "stumbles" when trying to start.
I'll check the relay and the pressure.

 

I was having the same issue last week. If your temperature gauage moves before you start, it's the temperature sensor. I also changed the thermostat, it was the original one and still working. Car runs so much better now.