Hot start issue on VR6

[JaysBlueR36]

Hi folks,

My R36 has an intermittent "hot start" issue whereby if you drive it for say 3-4 miles and then leave it for over 30 minutes it seems to crank but not fire up first time. If you then put the key back in the ignition and try to start the engine again it starts straight away... Weird.

More weirdly if you start the engine again immediately after turning it off having done that short journey the engine starts up fine. It's only if it's left for 30-45 minutes.

Cold starts are not a problem. First time from cold it will crank up and then fire into life as normal. It does crank a little bit but then that might completely normal. They are noisy engines after all!!

It's had its new genuine ignition coils and spark plugs in September last year and a new coolant temp sensor done this year. I'm about to have my PCV Diaphragm done (old ones perished and causing a vacuum leak) also thr rocker cover and intake manifold gaskets are being replaced as well as the injectors flow tested/cleaned and the intake valves walnut blasted. It's done over 100k so needs these.

Thing is what could be causing this intermittent issue?



Thank you

[kamold]

Any fault codes logged?
Does anything show in the cluster when it's cranking but not starting?
Sounds like it could either be a fuelling issue or an immobilizer issue.

[MIG]

Did you manage to fix your misfire?
I had a similar thing when I pinched an o-ring putting the high-pressure fuel rail back on; the pressure on the rail would leak down overnight and cause a long crank in the morning. Check out the measuring block for the high-pressure fuel rail. It should sit near ~5 bar at idle and go up to ~8 bar when stopped due to the heat when the engine stops.

[HaydEn]

Sounds like the crank angle sensor is on the way out.

Next time it doesn’t start, reach in and give the harness a wiggle.


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[JaysBlueR36]

Thanks to everyone for their responses.

So the car doesn't do this from cold start or if you've done a decent journey only if the trip was really short and then it's left.

It may well be a fueling issue. Thats why my mechanic suggested focusing on the injectors next. Having the injectors serviced is about 1/5 the cost of a new set of OEM ones. The car I've noticed has started puffing out a cloud of noxious smelling visible gas on cold start that goes away quite quickly but it doesn't smell good. When you rev it once you're moving it doesn't out gas at all. I will ask my mechanic to check the high pressure fuel regulator to make sure its all good

The car seems like it has the softest of misfires still. The idle is rough but through a process of pain staking testing I've found the PCV diaphragm is perished. If you cover the little hole at the back of the valve cover it will make the idle rougher, as soon as you uncover the same hole it will hiss like anything. I've got the RKX kit to replace it. I will be doing the EVAP (purge valve at the same time as all the other gaskets.) Im wondering if the PCV is bad enough that it's causing a rough idle and for some oil burn on start up.

If it was the cam angle sensor would it not do it all the time? It cranks and starts fine 99.9% of the time.