1998 K1500 Starts and Dies- MAP Code

[bigj-dog]

The other day a friend of mine left the lights on in his '98 K1500 (5.7/Auto) and when he jumped it, it started and died after 2 seconds. We've verified the fuel pump is getting juice and is pumping (although for some reason it never reads on my gauge at the schrader valve, but I checked at the filter and it pegs the gauge). If you pour gas in the throttle body it'll keep running, if not it runs for 2 - 4 seconds and stops, no matter what you do with the throttle. I scanned it and the only code that came up had the description of Map/Barq Output High. I can't remember the actual number (sorry) and now I cleared it and it doesn't run long enough to come back on. I did unplug the MAP Sensor, but it didn't make any difference (I had a '94 Grand Caravan that started and died immediately and it ran if I unplugged the MAP (replaced it to solve problem)). Does anyone have any ideas? FYI, I did pinch off the return hose and the gauge still didn't read at the schrader valve, fresh tune up and no gas in the oil. Thanks for reading.

[2000CAYukon]

The fact that you can not read pressure at the schrader valve is not good. The fuel rail (or fuel line) could be clogged. It needs 60 - 65 in the fuel rail to start well.

//2000CAYukon

[bigj-dog]

That was my first thought, but it starts just fine, it just dies a couple of seconds later. It doesn't matter if you cycle the key a bunch of times to run the pump extra or if you bypass the relay and run it constantly for few seconds before starting it or if you open the throttle. I'm thinking that the injectors either aren't pulsing after that initial start or the computer is leaning the mix out so much it just won't run after the initial start. Also, there is no security light on the truck.

[bigj-dog]

Quick Update-
Checked Map Sensor and electrics per Haynes Manual and everything is fine. there is a security light on truck though, and it's on, but not flashing.

[J-Ri]

You may want to try removing the valve core and checking the pressure again. Nothing big enough to plug the line should get past the fuel filter.

[bigj-dog]

Good point, I will try that. I'm also going to try the 'key on for 10 minute' security relearn/reset thing 3 times. Will post back with results.

[bigj-dog]

Attempted security re-learn to no avail. Removed core and fuel pressure is 65 at the rail. I suppose I need to bypass the security system?

[J-Ri]

I don't believe the truck should start at all if the security system is at fault. If you have access to a scan tool, watch each sensor as the engine is running.

[bigj-dog]

I only have a code reader, no scan tool. I have seen in other forums that if the security system receives a bad input after the engine is started it'll shut down power to the injectors -vs- a bad reading before it starts, which will not allow it to start at all. This one just had the battery ran dead when they left the lights on and all of the sudden, start and stall. Tonight I'm going to verify that the security light is on all the time when the key is on, (instead of coming on for 5 seconds and shutting off) and make sure that the computer is disabling the power to the injectors after a few seconds of running. At which point I will most likely kick the tire and tell them to take it to the dealer, since I will recommend not bypassing the VATS.