1999 Gmc Slow To Start When Engine Warm

[delyle]

1999 GMC slow to start when engine warm It starts fine when cold (after sitting overnight) or after driving and then sitting for a couple of hours - basically cooling down - and it'll also start if I immediately restart it only after being off for a few mintes. But, if it sits for about 5 minutes or so then it's slow to start. It turns over (at the normal cranking speed) for about 3-5 seconds and then it'll fire. After firing up, it's a little sluggish but that goes away after 10-15 seconds and then it idles normally. Fuel pump replaced about three years ago.

 

Fuel Pressure Regulator looks good - no gas when i remove the vacuum line.

Comments or suggestions appreciated.

thanks to all,

D

[rodram]

... you should state which engine you have... but in general, a faulty CTS (Coolant Temperature Sensor) will cause poor starting and sluggish performance when the engine is warm

 

.. when failing, the CTS will tell the PCM that the engine is cold (no matter what temp the engine is) so the injectors will push the rich fuel mixture to it

 

.. CTS is located on the top front of the engine somewhere near the thermostat housing.

[nickvrebel]

in addition to the above, leaky fuel injectors have been known to cause the same issue on some early Gen III V8

[delyle]

Sorry, I should have known. It's a 5.3L Vortec.

David

--

 

... you should state which engine you have... but in general, a faulty CTS (Coolant Temperature Sensor) will cause poor starting and sluggish performance when the engine is warm

 

.. when failing, the CTS will tell the PCM that the engine is cold (no matter what temp the engine is) so the injectors will push the rich fuel mixture to it

 

.. CTS is located on the top front of the engine somewhere near the thermostat housing.

[zedbear]

Sticky idle air control valve??

[ColoradoSkiCountry]

It is either your fuel sending unit and or your your fuel pressure regulator. Very common problems with the 99-03 models. Had that problem on my old 99. Eventually it would not start at all. Replaced my fuel sending unit (fuel pump) which is a module in the gas tank, and she never had a problem after. (not to mention the fuel guage module which is in the same area in the tank was replaced and my fuel level was accurate again!)