'96 850 T5 (B5234T, M56H): Crank, no start

[abscate]

You basically can’t check a crank or cam position sensor with a resistance measurement to confirm operation. If it shows open, or “ infinite resistance “ it is dead but a wide range of resistances can show on working parts.

Another example of how looking for a spritz of fuel doesn’t give you enough information to troubleshoot.

[Cookeh]

You basically can’t check a crank or cam position sensor with a resistance measurement to confirm operation. If it shows open, or “ infinite resistance “ it is dead but a wide range of resistances can show on working parts.

I followed the Volvo workshop testing methods, and agree that resistance can be hit and miss. The fault from my testing of the CPM was a voltage error, and perhaps a smidge more reliable (albeit it a very slight smidge).

Another example of how looking for a spritz of fuel doesn’t give you enough information to troubleshoot.

Yes, certainly seems so, and will be one of the more prominent factors in a purchase of a pressure tester. Per your recommendation, of course, which would have made the diagnosis even easier.

[Cookeh]

Not entirely convinced my issues are solved as today the crank no start reared its ugly head again. This time it appeared to be a hot-start issues - I am not sure if this is linked to previous scenario or not.

I had spark, again, I had fuel at the rail (though still haven't tested pressure at the rail as I havent found a reasonably priced one as money is tight, sorry abscate!). After giving the engine an hour to cool it started up immediately.

The confusing part to me is that the engine had previously had two hot starts within the last hour - with no issue. I have since been unable to replicate the hot-start issue.

If it is a hot start problem relating to fueling, should I be looking at anything beyond the pump/coolant temp sensor? CTS was replaced 2 years ago with genuine Volvo item, for background.

If its not a hot-start, what should I be looking at?

[abscate]

Which fuel pump relay did you buy?

Hopefully not a kAE..... known for bad OBQ

[Cookeh]

It was a ProfessionalPartsSweden one. The only one I could find in the UK at the time.

[abscate]

Ouch. They don’t have a great reputation over here.

Rumor is that the Princess of proPsrts Sweden married Lucas, the Prince of Darkness

[Cookeh]

They're normally well recommended over here, but they wouldn't be my first choice. They're often stocked by some Volvo dealers who cant get NLA items. I definitely would have preferred a Volvo branded item but they're now a classic part in the UK so need ordering from Sweden with a 2-3 week lead time.

My CTS tested fine today, within Volvo specs, and I've still be unable to reproduce the hot start issue. I've rechecked all vac lines and aside from a degraded (but still intact) vac line from evap filter to manifold they're all fine. I've ordered hose to replace that. In theory I suppose an evap leak could cause the issue, though I have no codes. Will look into testing methods for the evap valve, just in case.

[abscate]

If it is not firing It’s a fuel or ignition issue. You can have a huge vacuum leak and will still get some fire going

[Cookeh]

My perhaps twisted logic was that if the evap isn't working properly it will essentially be vapour locking on hot-starts. I'm happy to drop that line of investigation of its nonsense though.

Is it possible for sensors to struggle under high temp scenarios? Yesterday's ambient temperatures were 27'c when the hot-start failure occured. Temperatures since have been approx 10'c lower. I'm still not entirely trusting of either that fuel pump relay or the CPM.

[abscate]

Go back to jumping the relay with wire if the problem reoccurs to nail it down.