My 850 Turbo hasnt had any isaue thats kept it from running untill today. Drove it fine, though its had maybe 3 slightly longer starts than usual this month. Parked at a store, came back out and the car wont start. Occasionally it will, and it will run fine for around 10 seconds, then just shut off.

I have 2 others at home, so i used a known working fuel pump and fuel pressure regulator, as they are pretty quick and easy to replace, and no change. I tried jumping the relay, and no change. Checked all fuses and associated relays, they all look fine.

Ive no idea what else it could be. Do these cars have some antitheft devices or something?

It does have a code for the front O2 sensor, slow response, but its had that code since I got the car 3 years ago, and a certified volvo mechanic told me it wouldnt effect driveability, only fuel econ and emissions a bit.

 

start by seeing if you have spark. Next I'd checking fuel pressure at the rail - should be 40 PSI or so. You can also see if you are getting a pulse at the injector. These cars do have an immobilizer so you can try doing a reset by locking/unlocking the doors 5X with the key fob or key in the door. Did you look at system voltage to make sure you don't have a weak battery? What happens if you try to start with a jump?

 

Thanks for the reply. I double checked all my diag again, and found fuel pressure was perfect(as expected), compression is a bit low(very old and beat up engine, but runs fine anyway), no major air leaks(been chasing boost leaks since forever though), but there is now intermittent weak spark, like you suggested. When I tested before, spark looked plenty healthy and it still wouldnt start, but now I cant get more than a couple pops out of the coil when cranking.

The battery is tired, from all the cranking, but ive been putting a generators 12v 8a output on it to keep it able to turn over for testing. This car easily starts with a nearly dead battery though lol. Almost as if, as long as the engine can turn 3 times, it will start.(before all this anyway)

Ill check that immobilizer thing, I had no idea such a thing existed. Any idea what triggers it? I didnt do anything out of the ordinary...

Im not sure how to properly check for injector pulse, but I know fuel is getting into the cylinders from how wet the plugs get while cranking(found when doing compression testing)

I spose ill try a new coil from another car, though ive never seen intermittent weak spark like this. They usually just die, no spark at all.

 

Replaced coil, no change. I get spark now, but its weak still. Going to try the injector relay next I guess. About to give up on this car though...

Correction, after retesting, it appears I STILL dont have spark, even with a working coil. Ive no idea how this is refuses to work, its incredibly frustrating.

 

After buying, trying, and returning(like a douche) each sensor that controls spark signal to the coil, I found the culprit as a failed camshaft position sensor. No clue why it failed, the new and old units look identical, clean, no damage... replacing it worked though. /shrug

my poor wallet, the new one is $100. To return it and pullyard/rockauto, or na....

/thinkthink

Thanks for the help!