Mechanics

CHEVY STARTING PROBLEMS DUE TO FUEL PRESSURE LEA

2003 Chevrolet Tahoe

Engine Performance problem
2003 Chevy Tahoe V8 Four Wheel Drive Automatic 170000 miles

Our 2003 Chevy Tahoe Flex Fuel system doesn't maintain pressure on the fuel line over time and has trouble starting. It rarely starts on first turn of key. We replaced the fuel pump, the fuel filter, the fuel regulator, the throttle body, the crank shaft positioning sensor and still had problems starting the truck. So we decided to check the fuel pressure. We found that after turning the key several times that our fuel pressure was normal and the truck would start but after sitting for an hour or more the pressure would leak down. When we put a gauge on it by the fuel filter the pressure stays consistent over time but when we put the gauge on the fuel rail it goes to zero over time. Is it supposed to do that? If not, what could be causing it? Remember we have already replaced the fuel pump and fuel regulator. The only thing we haven't replaced or checked is the fuel injectors.
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Dbrummett
October 16, 2010.




At the fuel rail, does the pressure drop more than 5 psi in a minute? If so, after seeing everything you replaced, if it isn't an injector leak, I don't know what it is?

JDL
Oct 16, 2010.
Today we tested the pressure at the fuel rail and it is about 40 psi right after starting it and turning it off which we think is within normal limits for a Flex Fuel system. Then after a couple of minutes of turning it off the pressure went to 45 psi without us doing anything. It is holding steady pressure even after a couple of hours. But now has a new issue, when we start it, it starts running rough and dies. So it seems like the issue is intermittent. It is very frustrating because when it starts running rough it gives a code that there is a communication failure with the crankshaft positioning sensor which we have replaced twice. Also, there is a second code that says ATC failure. What is that about? We are beginning to wonder if this is a PCM problem. Any ideas?

Tiny
Dbrummett
Oct 16, 2010.
One day the Tahoe will have trouble starting and maintaining fuel pressure then on a different day it will start right up no problem and maintain pressure but then start idling rough and die. When we finally get it started and it doesn't die and if we hold the gas down and put it in gear we can drive it without any problems. But then it will have the little engine light on the dash. When we check the code it says that error in communication with the crankshaft positioning sensor and a second code that says ATC error. Any ideas?

Tiny
Dbrummett
Oct 16, 2010.
What is the engine vin? What were the actual codes? You may need to check if cam and crank sensors are in sync?

JDL
Oct 16, 2010.
The code is: P0336B with our OBDII Scanner.

Tiny
Dbrummett
Oct 16, 2010.
I found P0336, crank sensor code. I'd check ref voltage--ground and signal circuits. There other possible issues?


http://www.2carpros.com/forum/automotive_pictures/170934_tahoe_crank_sensor_1.jpg


JDL
Oct 16, 2010.
The vin# is: 1GNEK13Z13R308608. How do we check to see if the crank shift positioning sensor & Cam sensor are in sync? Also how do we check the voltage ground & signal?
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Tiny
Dbrummett
Oct 16, 2010.
You would have to use a scan tool that shows live engine data. The info below is for p0336.


http://www.2carpros.com/forum/automotive_pictures/170934_po336_1_1.jpg



http://www.2carpros.com/forum/automotive_pictures/170934_p0336_2_1.jpg


JDL
Oct 17, 2010.

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