2000 K3500 5.7 Vortec hard start and rich condition

[etap_franklin]

Good Morning! I've seen a lot of posts on this topic but haven't found where it's been solved just yet.

Scenarios
Truck fires up just fine after sitting overnight
Truck fires up just fine after being off for 5 minutes or so
After a few hours I need to hold WOT to get her to fire up
Truck always runs rich

Brand new Delphi MPFI unit
New cap, rotor
Plug wires are on the way
New Coolant temperature sensor

I ran a test to eliminate heat from the equation by switching on the key in the morning and then not cranking it until a couple hours later. I had to hold WOT to get it to start up after doing that.

Any fresh thoughts would be appreciated.

 

[skylark]

The coolant sensor that you replaced, was it the one in the head or the one in the intake?

 

[etap_franklin]

The one in the intake that communicates with the PCM.

 

[skylark]

The most common cause would be a faulty cts. Using that logic I would check for resistance on the ground side of the connector for the cts. A quick and dirty check would be to jumper the cts connector with a paperclip and see if it still requires throttle to start. If it still does then I would be looking at the iac and throttle body passages.

 

[etap_franklin]

IAC is new I forgot about that one. Also, I stopped thinking anything to do with the CTS once I ran that last test that I mentioned where I just cycled the key a couple times and then had to hold WOT to crank it even though it was stone cold.

 

[redfishsc]

Correct me if I'm wrong, but I think this can also happen if the fuel injectors or the fuel pressure regulator or leaking badly. I know I've had friends with these that had very hard time getting their vehicle started because the fuel pressure regulator had leaked a lot of fuel into the intake while the truck was turned off.

 

[etap_franklin]

Yeah that's a typical issue. I just installed a Delphi MPFI unit though and it holds prime for at least 5 minutes so I ruled that out. I'll do a leak down test as soon as AutoZone decides to replace their busted kit that they rent out.

 

[etap_franklin]

Thanks for yall's help by the way. I ended up solving my hard start problem by rewiring the ground that's on my thermostat housing! Easy day!