# Fuel problem with 4.3 cfi gmc sonoma



## crankshaft (Apr 2, 2008)

I have a 1996 GMC Sonoma truck with a 4.3 liter that has been wrecked on the front passenger side. Truck was parked for over a year and recently I began to start repairing it. Engine will run temporarily when I pour gas in throttle body, I have 66 psi on the fuel pump pressure, but no fuel out of the injectors. Water pump was damaged in wreck and serpentine belt is not on engine. Could this be related to the injector problem? Any suggestions about what to check next? Thanks.


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## Raylo (Feb 12, 2006)

Is that 66 psi fuel pressure at the test connection on the fuel rail? I'm not sure which version of the 4.3 you have but that sounds like it is probably OK. Is your motor a CPI with the central injector or does it have individual injectors for each cylinder? If you have FP in the rail but nothing out of any of the injectors it would have to be a computer failure or perhaps a break in the wiring to the injectors from the crash. I guess it could also be a damaged sensor or wire such as the throttle position sensor which is a major input to the computer for how much fuel to flow, i.e. how much to open the injectors. Not a lot to go on here but if the motor was running OK before the crash it has to be crash related... and repairable.




crankshaft said:


> I have a 1996 GMC Sonoma truck with a 4.3 liter that has been wrecked on the front passenger side. Truck was parked for over a year and recently I began to start repairing it. Engine will run temporarily when I pour gas in throttle body, I have 66 psi on the fuel pump pressure, but no fuel out of the injectors. Water pump was damaged in wreck and serpentine belt is not on engine. Could this be related to the injector problem? Any suggestions about what to check next? Thanks.


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## BUDFAN8 (Apr 11, 2007)

if your fuel pressure is getting to the injectors i would lean to the wiring trouble. if you can get your hands on a noid light that would be a good start to figureing out if your injectors are getting signal to open.


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## mack1 (Nov 27, 2007)

Hi crankshaft and welcome to TSF:wave:

I'm not sure how you checked to know that the injectors were not working. They are hard to get to on your truck. I have a 96 S10 Blazer and according to the Haynes, should be the same as yours. Simple, I know, but have you checked the fuse? It is fuse #10 (ECM ignition) 20 amp on mine. You can't get a voltmeter probe onto the wires going into the large square plugin to the injectors. It's hard to unplug also. There was a hard to see holddown clip on mine. However, if you have it off, on all other engines and years (Haynes didn't show ours) the wire is pink and is 439 if you can see a number on it. With the ignition switch on, that wire should have 12 volts on it. That's the supply wire. The signal wires coming from the PCU (or ECM or Computer) should have 5 volt pulses when the engine cranks over. You might be able to track them back to the ECM and back probe them with a voltmeter. AC scale might be best.

There should be 5 volts across the Throttle Position Sensor(TPS) between the gray and black wires. Between the black and blue wires, the voltage should increase smoothly form 0 to 5(or near) volts when depressing the foot feed. The sensor is located on the side of the throttle body and attached to the throttle cable. Other sensors influence the amount of fuel, but the TPS is the main one. 

66 psi is the standard fuel pressure for that model. It will drop 3 to 10 lbs at idle, when you get there. 
Your ignition seems OK if it will start with fuel injected into the intake. 
I guess it is hard for me to believe that all 6 injectors went bad during the year of downtime. If you are not totally sure, check the gas tank for water. A lot of moisture can build up over time inside a gas tank if there was any way for air to get in. 

If you don't have a manual, I can post any data you might want, except the wiring diagram Haynes didn't include. They also didn't include the cable call out for the PCU.

Hope your problem is electrical and easy to find:smile:
Mack1


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