I've received some responses to this problem on my '87 740 Turbo (199k miles), but haven't isolated the problem yet.

When the car is warm-- 10 minutes at idle, taking 5 minute drive-- it won't start. I've changed the main fuel pump (got it cheap, so it seemed like a good idea), filter and pump relay, and there's no gas in the vacuum side of the fuel pressure regulator. Also cleaned the connectors at the radio suppression relay, and an unknown (brain?) relay in the trunk. (Not shown in Haynes, as I can find. But I've usually found Haynes basically useless aside from routine maintenance issues.) So now I'm thinking there is a sensor or other relay problem causing this.

However, the car always starts when cold (air temp under ~50 degrees F) AND has sat for a good 6-8 hours. But yesterday: car sat all night, temp around 50, but would not start when I went to work on it, around 65 degrees, balmy for this time of year. The passenger side of the car faced the morning/early afternoon sun, and even after nightfall and a 10 degree drop-- nothing. It's back up to 55 this morning, and it fired right up.

Though they look clean I'm re-plugging it today, and will check for leaks at the intake manifold (thanks FAQ). I'd like to check/replace the following, but I'm not sure where they are (again, either no useful pictures in Haynes of the issue was not addressed at all):
Cold start injector
Power stage
Hall sensor (found, but not easily accessible)
In-tank fuel pump (I can't disconnect the electrical-- suggestions?)

I've done basic maintanence and other small repairs in the past--rebuilt and reinstalled slave cylinder (works great), blew two belts and replaced them no problem-- so I'm confident of being able to do this work. This is my second Volvo (drove an '85 240 to 223k) and the first one I've worked on myself, thus I find the help from pics/schematics/etc a very useful tool.

Thanks for any help.
Tim

Does it try to crank at all or just sit there? If it just sits, it could be a bad starter relay (mine has the same problem.) Assuming the fuel pump clicks on, leave it on and try jumping the terminals on the relay itself with a screwdriver. I've been starting my car like this for months (yeah, I know...)

Tried the screwdriver as a temporary fix to no avail. The car cranks jut fine, but doesn't fire. Here's my last couple days (following procedures from the FAQ):
1. Took off the distributor and found some oil/grease-- not much. Cleaned it with some carb cleaner and dried it out. Checked the hall sensor connector for charge and it was fine. Q: Am I supposed to check the sensor *in* the distritubor for charge?
2. Checked charge at the coil-- just fine.
3. Tried to take the ignition control unit off to check for charge and couldn't get it off. It's "stuck" at the back of the unit near the firewall. Suggestions?
4. Put in new plugs (time to do that anyway). Old plugs looked fine.
5. Looked at the fuel pump relay under a magnifying glass-- saw no cracks. Q: Can I re-resolder a relay? It's been done once.
6. Had to jump-start the car yesterday; the battery was almost dead. The car idled for ~20 minutes, died, started back up again right away and ilded for another 20 minutes. I went out and started it 4 more times last night, about once every half hour-- no problems.
7. Started up twice this morning. Drove 1/2 mile (~5 minutes), let it sit for 2 hours and it WON'T START AGAIN!
I am hearing/feeling the fuel pump relay click twice, but I am not hearing the fuel pump (under the driver's side) come on. Am I getting any closer to solving the problem??
Sorry for the long thread...

while the car is NOT starting, check if:
A) Do you have spark at the plugs?
B)does the tailpipe smell of gas after cranking awhile?
this should give you a pretty good clue as to weather you have a spark or fuel problem.

If you have a spare ignition module, try it out. warm restart is a typical failure pattern.

Try cranking the warm engine with the acellerator floored to initiate clear flooding mode. If it starts, you problem is caused by excessive fuel(injector leak or mistriggered cold start injector). Unlikely, but easy to test.

why would you check or replace a cold start injector when you state that it will start cold? also an intake leak will not keep your car from starting! how does the car run after it starts? first thing you do when the car stalls is to check for spark at the spark plug or at the coil wire where it goes into the dist cap. stop changing parts because they were cheap or free. you may be causing additional problems.if you have no spark,it could be a pick up in the distributor or a bad module which is about the size of a match pack(sits on inner fender behind headlight)or a bad coil. if you h ave spark and it does not start,remove the ashtray,reach into the relay section behind fuses and put your hand on the fuel relay(white,on left side)and feel it when you try to start the car.it should click twice. if it does not,tap or wiggle it and try again. the radio suppression relay is the same as the cooling fan relay,switch them and see if it runs. the problem with this relay is never a bad connection,it is a bad solder joint and trying to repair is a temporary fix. what ever caused it to heat up enough to melt the solder,will most likely do it again. if you switch the 2 relays keep in mind that the cooling fan may not work when it gets hot

This may or may not help, I had a similar problem, I think ( you don't mention if the starter is turning over or not.) Sporatically mine would not turn over. Dead. Nothing even though the battery was charged. The positive terminal was found to be snug but not tight. That cured it mostly but I still had a not as sporatic problem. A new starting interlock/backup light switch for the auto tranny seems to have elimintated the last of it. Knocking wood.