Another hard start when hot thread

[Lornnn]

My stock 3.0 starts just fine when cold and runs great with 140k miles. When it is started hot, however, it takes maybe 3-5 seconds to fire. When I look at most of my search results for this issue, the ECT was the problem and the thread dies. I checked for codes, found that the ECT was bad or malfunctioning so I went ahead and replaced it. A week after replacing my ECT there no codes but the same issue is present. Thing is that if I'm out and about and the car is off for 5 minutes, it fires right back up. 10-15 minutes? Also fine, but starting to push it. After ~30 minutes, an hour, even a few hours (when the car isn't completely hot or completely cold) it'll have trouble again and take 3-5 seconds of cranking before it finally starts.

Spark plugs were replaced with OEM NGK's last year as regular maintenance.
The fuel pump was replaced with an OEM unit last year along with the fuel filter (was starting to groan while starting and didn't want to get stranded) and I use 92+ octane only.

The car performs great for her age and there are no other codes present so I'm really at a loss here...

Thanks for any insight

[Lornnn]

G28 Engine Speed Sensor, aka CPS?

Thanks, Spike. Still no fault codes on my end but I've found posts elsewhere in which a failed CPS didn't actually throw a stored code. Worth a shot; I'll see if I can swap one out from a local 3.0. Thanks again.

[diagnosticator]

Check the residual fuel pressure in the fuel rail after 10 miniutes after turning the engine OFF. If the residual fuel pressure is less than the specified 3 bar, that will cause delayed fuel delivery during hot engine starts with possible vapor lock in the fuel rail.

[Fast4esT]

I think it is the cam position sensor that also causes no start/hard start when hot?

[diagnosticator]

I think it is the cam position sensor that also causes no start/hard start when hot?

Yes, that is one of several possible causes for hard hot starts.

[Lornnn]

I don't have a fuel pressure gauge but will try to get my hands on one. What would poor fuel pressure point to other than my pump or filter (which were replaced last summer, less than a year ago)? Without any codes it'll be tough for me to try and figure out which, if any, cam position sensor is faulty. Thanks for the help.

[imnuts]

Check the residual fuel pressure in the fuel rail after 10 miniutes after turning the engine OFF. If the residual fuel pressure is less than the specified 3 bar, that will cause delayed fuel delivery during hot engine starts with possible vapor lock in the fuel rail.

Without installing a test port ahead of time, there is no way to test the system fuel pressure on the 3.0.

Sent from my DROID Turbo 2

[diagnosticator]

Without installing a test port ahead of time, there is no way to test the system fuel pressure on the 3.0.

Sent from my DROID Turbo 2

"Fuel pressure at idle speed Vacuum hose connected: 3.2 to 3.8 bar positive pressure, Vacuum hose disconnected : 3.8 to 4.2 bar positive pressure.



Residual pressure after 10 min, Cold engine: Approx 2.2 bar positive pressure; Warm engine: Approx 3.0 bar positive pressure".

Bentley shows a special inline pressure gauge used with the 3.0l.

[SJorge3442]

"Fuel pressure at idle speedVacuum hose connected: 3.2 to 3.8 bar positive pressure, Vacuum hose disconnected : 3.8 to 4.2 bar positive pressure.



Residual pressure after 10 min, Cold engine: Approx 2.2 bar positive pressure; Warm engine: Approx 3.0 bar positive pressure".

The 3.0 doesn't have any way to determine the pressure. We don't have a valve anywhere

Sent from my Nexus 6 using Tapatalk

[diagnosticator]

The 3.0 doesn't have any way to determine the pressure. We don't have a valve anywhere

Sent from my Nexus 6 using Tapatalk

See pic posted above.

[SJorge3442]

See pic posted above.

Well damn. Good post. Learn something new new on here every day

Sent from my Nexus 6 using Tapatalk