I have a 2004 sierra 1500 with a Vortex it doesn't want to start on rainy or damp mornings.. new cap coil wires and plugs..sometimes after many tries it will.. either dry or below frezzing it starts

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Asked by Dec 25, 2014 at 11:48 AM about the 2004 GMC Sierra 1500 2 Dr SLE 4WD Standard Cab LB

Question type: General

Once running it seems ok  but on a cold morning I drive 2 my coffee stop then 5 minutes later it starts or a little hard  but misses for about 1-2 miles then fine the rest of the day ( now this only happens  after it's been damp outside,, Good fuel pressure no codes
please any ideas thinking a odd crank senor above starter or in the distributor driving me nuts..  but if I park inside everything is fine (haven t parked from a rainy day and have it sit over night yet) Thanks Frank

2 Answers

68,695

Sounds like carburetor icing. Or in this case it would be throttle body icing. Very rare these days but it can happen. In cool damp weather ice can form on the throttle plates and unset the apple cart. To combat this, vehicle manufacturers either pre-heat the air going to the throttle body or, as I believe is the case with your GMC, a small coolant system passage runs around the throttle body. This directs hot coolant around the throttle body and keeps it warm enough so frost won't form on the throttle plates. To check this, when you have the drivability issues, keep the engine running and remove the air intake pipe to the throttle body. Look for white frost covering the inside of the throttle body assembly. If it's there, look at the air intake system. If it's supposed to be pre-heating the air and it's not, there's your problem. If there's no provision for this, a good cooling system flush should fix you right up. HTH. -Jim

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well this doesn't answer the no start or hard to start question even today it was in upper 40's after cranking smelling gas almost wanting to run.. usually when it is like this it will start this is the second it didn't.. i'm leaning towards crank sensor because I had a leaking clutch slave cylinder unit.. thinking the brake fluid might have done something to the crank sensor.. this is just a wild guess.. thinking the start issue is might be cause a little out of time..just a real odd thing going on.. sure is a moisture problem.. only when damp or all out wet.. Open hood let sun dry everything out and everthing acts normal... once ran for a few mile runs good all day even if it rains....

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