My 93 GMC pickup (5.0L engine) has been running great until the other morning when I went to start it and it runs really rough. I have a feeling the choke is stuck. I'm no car expert but I think when the flaps on the carb are down it means the choke is enabled, correct?
Should I be able to manually move the flaps to the open position without the throttle linkage moving? When I open the flaps with my finger the whole throttle linkage moves. I am not sure if this is what is supposed to happen.
Perhaps someone could be so kind as to tips for trouble shooting and fixing a stuck choke on this truck.
I used to have a 79 Malibu with the 5.0 l engine (305 CID)
I experienced the exact same problem.
My engine had a 4 barrel carb on it. From my experience:
When you depress the gas pedal prior to starting the car, the choke mechanism slams the choke buterflies closed. The choke butterflies are NOT to be confused with the throttle buterflies.
When you start the car, all is fine - for a few seconds. Once the engine starts to warm up, having the choke buterflies fully closed creates a condition where there is not enough air - the result is you start to run very rich, get black smoke out the tailpipe, and in short order the engine stalls.
This happens UNLESS! a device called the Choke Unloader is working properly! :)
The Choke Unloader is a vacuum activated diaphram which has a mechanical arm attached to it. As the manifold vacuum rises in the first few seconds of operation, the Choke Unloader, via its mechanical arm, pulls back physically on the choke buterflies, and opens - or unloads - them. The movent is slight, but just enough to allow enough air in to keep the engine running. Once the engine is warmed up enough that kicking the gas pedal will allow the choke cam follower to drop down to the lower idle, the problem "goes away" as the buterflies open up considerably more than the Choke Unloader is capable of doing.
The Choke Unloader is a small innocous little piece of hardware, also fairly inexpensive IIRC. However, if the Choke Unloader is not working properly, it can cause you no end of headache!
And the problem appears exactly as you have stated. Everything is fine, and then one morning - POOF! It does not work worth a damn.
I suspect that the diaphram eventually weakens with age, and finally ruptures.
Not sure if your engine is configured like mine, but there HAS to be either a choke unloader, or some equivalent way of controlling the fuel mixture, otherwise things just wont work.
If your mixture is controlled electronically, then I might suspect an Oxygen Sensor on its way out.
Just curious (if its not too much trouble) if you could tell me what exists instead of a choke for cold weather staring? I am always looking to learn something new :-)
Computer looks at several different temperature sensors, determines the engine is cold and the ambient temperature is cold, and increases the pulse width of the fuel injectors.
The main thing you'll need to learn is that the age of separate, discrete, single-task components in the fuel induction system to cope with varying operational conditions (cold start, hot start, cold idle, hot idle, etc.) are gone.
Can anyone tell me if there is a way to diagnose the problem on this Truck? I have had Chevys in the past where you could use a jumper to show a diagnostic code.
Is this doable on the 93 GMC Sierra? If so, where can I find instructions and the meaning of each code?
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