Occasional no start on 94 850. Any Advice?

[Constantine8020]

I have been daily driving a 1994 Volvo 850 non-turbo for a year now and for the most part have experienced no issues. Occasionally though, the engine will fail to start. Sometimes it will hiccup while cranking like my timing is off, other times it will crank indefinitely and never once even try to start. This almost always happens once the car is up to temp but has once or twice happened on cold starts. I had the camshaft position sensor changed about 8 months ago which seemed to make it run a little better but the problem persisted, and I have taken the connectors off of both the cam and crank sensors and cleaned lots of corrosion out which seemingly helped until it recently died on me again. Once I let the car cool down fully (or more realistically get it towed home) it starts without a problem again, leaving me fully stumped. As time goes on the issue seems to happen more often, in the first few months of ownership this never happened.

My OBD1 codes are;

A3: 213 and 214 which I believe to be my rear wheel ABS sensors, unrelated but not sure what that's about

A6: 324 and 214 which are camshaft signal intermittent and VSS signal intermittent. The car is an automatic and has no trouble shifting so I think the VSS is a problem for future me, but the camshaft signal is the one that catches my eye

and B2: 122, which from what I have read online is a cruise control thing and can be safely ignored.

A nearby mechanic thinks there might be some fault in my ECM causing it to lose signal intermittently, but I'm not sure. Would a faulty cam sensor cause a no-start when the crank sensor is throwing no errors? Could it be an electrical issue between any of the sensors and the ECM? Some longshot forum posts suggest an engine coolant temp sensor, but it is throwing no codes and the bolts in my thermostat are stuck tight so I haven't been able to test its resistance.

I know this is a huge write-up but this issue has been beating my ass for months now and as this is my only car and I am a poor college student I really need it to start being reliable. Any advice would be appreciated.

[Simmy]

the fuel pump takes signals from the camshaft position sensor check or try a substitute one

[Luxobarge]

Originally Posted by Constantine8020

A nearby mechanic thinks there might be some fault in my ECM causing it to lose signal intermittently, but I'm not sure.

You're right to be not sure, it's extremely unlikely to be the ECU itself, these are supremely reliable on these cars and unless it's been abused or exposed to extreme heat or flooded or something. If it were me it would be the last thing I'd be looking at.

Your ABS codes are quite likely to be poor solder joints on the PCB on the ABS module, where the pins from the multiplug are soldered. Are you getting an ABS warning light? (assuming the bulb is working and not blown or removed). If you can solder reasonably well, it's an easy and pretty much free fix, just fiddly and a bit time consuming. Loads of threads on here about this very common problem.

Assuming that VSS = Vehicle Speed Sensor, then fixing the ABS will quite possibly fix this too, as it detects vehicle speed from the front left ABS sensor, which may well also be affected by the poor solder joints issue.

You are getting cam sensor codes, which is a big clue, so I'd be pursuing this. Standard practice is to note down the codes, then erase them, then run the car and see what comes back. If you still get cam sensor codes then this is an even bigger indicator. Fairly cheap and very easy to replace.

HTH

[Constantine8020]

Thank you both for the replies! I'll look into the ABS fix you mentioned. No light on the dash, though it comes on with the key in 2nd position so I know the bulbs not out.

I've been hesitant to blame the cam sensor because as I mentioned it was replaced recently. Is it possible there's another point of failure, or maybe that it was installed wrong? I suppose it's also possible that it's a dud, new parts aren't always the best quality. Whats a good way to test it?

I've tried erasing the codes a few times and I've been unable to, not sure if I'm getting the procedure wrong or what. I've disconnected the battery a few times, that should do it right?

Thanks in advance.