Hard to start when weather is cold 35 degrees or lower

[byron townsend]

09 GMC Sierra Denali 291K struggles to start only when cold. When attempting to start it will try but dies, once started it idles rough and the exhaust has a strong smell. After running for a few minutes, it levels out. It appears to be firing but something is causing it not to start. The truck cranks fine after it warms up, at times after driving when starting it will crank but not a strong start, it barely catches and soon idles fine. I have replaced the fuel pump with new wires and plugs.

[Maria Medina]

First, check your oil...if consistently below freezing check into 5/30 or 0/30 oil. Check with your dealer and vehicle manual for more info.

 

Also, check the age of your battery. Most batteries optimum operating cranking amps are around 24-36 months. Especially in consistently cold weather. Then batteries start lagging power. 

Edited January 17 by Maria Medina

[byron townsend]

My oil was changed Saturday and the battery is fine. 

[davester]

Oil put in was 5w30?

 

Installed ACDelco plugs from a reliable source (ie, not amazon/ebay)?

How did the old spark plugs look?  Much of a variance from hole to hole?

 

Assuming you bought good plugs and 5w30 oil, then I would be checking fuel pressure, and using a bi-di computer setup to be checking what the ecm is doing when starting the engine, like what temp it's reading, and what the other sensors are doing.

 

As well, checking for any codes, as there can be some even if the CEL is off.

Edited January 17 by davester

[richard wysong]

an errant intake air temp or coolant temp sensor could be the culprit and not set a code. You need to hook it up to a scan tool that does live data to figure it out