GM-GMC: 1993 GMC Suburban runs very rich, electronic fuel injection, gm website

Question
Dear Mr. Jacobson,

I am struggling with this issue.  About 2 weeks ago my Suburban simply would not start, I had just driven it 15 min. prior and have had no issues with it.  Talking to my car-buff friends the made some suggestions, this is what I have done.  Replaced the plugs, distributor cap, rotor.  Checked the EGR valve, retimed the vehicle and inspected for vacume leaks.  I can now start the vehicle but only if I hold the pedal to the floor, it starts very rough, blows much black smoke and finaly starts.  It accelerates well but the fuel injectors are dumping gas into the vehicle, running very rich.  The computer shows codes 12 & 54.  Any idea's?  It suprizes me this started so suddenly.  Thank you in advance for the help and recommendations.

Sincerely,

Larry Refior

Answer
Larry,

I drive diesels, and your problem is one reason why.

54- mixture control (m/c) solenoid or circuit (carbureted models) is what a GM website shows for your 54 code.  The 12 code is normal diagnostic mode.

I suspect that you have a stuck or malfunctioning mixture control solenoid (or whatever GM calls it).  I have no idea where it is or how to get to it and I do not have any tech manuals to help me.  It may be in, on, or near the fuel injector assembly, but that is only a guess on my part.

Electronic fuel injection is fine when it is working right but not so good when a component fails.  And, yes, thay can fail suddenly and without warning or symptoms.