1994 GMC Sierra SLE K2500 Intermitently Won't Start

[cc333]

HI,

 

I'm new here, and I'm hoping some of you can help me out.

 

Today, I've begun to have intermittent problems starting my truck.  As far as I can tell, everything's fine mechanically, and neither the ignition system nor the fuel system have issues as both work perfectly under ordinary conditions, but for reasons I've yet to ascertain, something is preventing the fuel system from engaging.

 

The symptom is basically when I turn the ignition switch to on, where I'd normally hear the fuel pump pressurizing the system, I only hear silence.  Curiously, the Service Engine Soon (SES) light is off as well.  When these two conditions occur, the engine won't start.

 

Eventually, the fuel pump will begin engaging and disengaging erratically, and the SES will flicker sometimes in time with the fuel pump's "spastications", but mostly it stays off until the system eventually stabilizes, at which point the engine will start and the fuel system functions normally.

 

It seems to me likely that the ECM relay is failing, but I can't figure out if this model even has an ECM relay, or where it would be if it does.  I managed to find the fuel pump relay, and unplugging it (predictably) disables the fuel pump. However, the SES stays lit when I do this, which would seem to indicate that the ECU is still receiving power, so I don't think this relay is the problem.

 

There's also the possibility that the ECU itself is failing, because the symptoms seem to superficially fit, but I don't know for certain because I'm relatively new to this truck (I bought it used a few years ago).

 

Since I'm in fire-prone California, I really need this truck working so I can get my horse out in case of an evacuation (I've already had to evacuate four times in two years... *sigh* ). Good thing it's only February, or I'd be panicking right now!

 

Thank you!

 

c

[CamGTP]

Don't rule out a failing ignition switch.

[cc333]

EDIT: Never mind, after thinking about it some, I realize the ignition switch must be OK, because all accessories come on as they should with no intermittent failures, and the engine consistently turns over like normal.

 

The only unusual things are the dark SES light and inoperative fuel pump.  I'm beginning to suspect ECM failure based on the symptoms I see, but I'd like it if someone can help me confirm.

 

c