1998 Chevy 2500 2WD truck

Tiny
JOHN WEATHER
  • MEMBER
  • 1998 CHEVROLET TRUCK
Just bought the truck, not running, the engine will not start. Fuel pump works and pressure is 60 to 64 psi. Engine will run when gas is put in the throttle body, but quits when gas runs out. I read the codes and got P0108 & P0122, then cleared codes, ran the engine for 1 minute with external gas supply and no codes re-appeared. The TPS seems to work, tested with a ohm meter, receiving voltage and the sensor does work as far as variable restinace with ohm meter. Fuses are all good. I'm stumped. Your wisdom is greatly appreciated.
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Monday, January 1st, 2007 AT 6:32 PM

6 Replies

Tiny
MIKEYBDMAN
  • MEMBER
Im wondering where you connected your external gas supply? I see an inline filter. Have you eliminated that? I know if it is partially clogged it might be limited flow vs. Limiting pressure. Also in reading your post, I started thinking about back pressure. I would check the fuel vent pipes at the tank. Kinks, cloggs, cracks. They shiould just be nylon pipes, and once kinked, they need to be replaced.

Good luck, and please let us know what you find out.
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Monday, January 1st, 2007 AT 7:04 PM
Tiny
JOHN WEATHER
  • MEMBER
The external fuel supply a can of gas poured into the throttle body. Yes, I changed the fuel filter and all of the lines from the tank to the throttle body are ok. I put a presser gauge on the fuel line, pressurized the line(60 - 64 psi.) And put 12v to each injector which resulted in no pressure drop. Could it be the fuel pressure regulator? How can I test the regulator?
Thanks for the reply,
John
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Tuesday, January 2nd, 2007 AT 3:01 PM
Tiny
MIKEYBDMAN
  • MEMBER
Ok, if it only works with fuel poured in and you have good pressure, I would rule out the regulator, and fuel pump. Need to know which engine you have.I think there are 5 different ones for that model.

It sounds to me like your injectors are not opening. In most of your type of vehicles power is pupplied to all injectors by the underhood fuse-relay center. Usually the fuse is a 20a ECM 1 fuse. Make sure that is getting power first.
That eliminates power to injectors as a problem, and just leaves control.
Control is done by the VCM (Vehicle Control Module).
In most vehicles, once the ignition signal is satified from the ignition switch, it tells the VCM to give fire and fuel. Since you have ignition, we can assume that signal is getting there. Now comes the tricky part.A timing signal is sent to the VCM from both the crankshaft sensor and the cam shaft sensor to time the fire and fuel. A lot of vehicles will use the crankshaft sensor for spark, and the cam shaft sensor for fuel injectors. Im trying to read up on your truck and see which your uses.
I think most injectors run on a 5v supply, so I wouldnt put too much voltage to them.
I did find these descriptions I will paste for you to read.
STARTING MODE
When the ignition switch is turned to the ON position, before engaging starter, the Control Module energizes the fuel pump relay for 2 seconds allowing the fuel pump to build up pressure. The Control Module then checks the Engine Coolant Temperature (ECT) sensor and Throttle Position (TP) sensor in order to determine the proper air and fuel ratio for starting. The Control Module controls the amount of fuel delivered in the starting mode by changing how long the injectors are energized. This is done by pulsing the injectors for very short times.
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Tuesday, January 2nd, 2007 AT 4:19 PM
Tiny
JOHN WEATHER
  • MEMBER
When the ignition switch is turned on the pump runs for 2 or 3 seconds. I jury rigged a light to the injector plug harness and turned the engine over, the light came on briefly when it seemed it was time to fire for that cylinder. It seem that the injectors are not letting gas thru, either their all clogged or the fuel regulator is not letting gas in to the injectors. Does the fuel go thru the regulator to the injectors? Or is it just in system to regulate the fuel pressure? So if the regulator is bad all that will happen will be low fuel pressure?
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Tuesday, January 2nd, 2007 AT 5:41 PM
Tiny
MIKEYBDMAN
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Well, if your injectors are getting power, and you have fuel to the Fuel meter body assembly, then it makes sense that something in the fuel meter body is obstructing the flow. Im not sure what you meant by Briefly lite up the light when that cylinder was supposed to fire.
Could the fuel regulator be blocking the flow.I doubt it. It should just be a spring loaded relief valve that opens to keep the pressure at or below 66 psi.
My gut felling so far is that the timing for your fuel injectors is not being signaled correctly, or at all. I cant see all the injectors being clogged at once.
Without being able to connect test equipment and see if the injectors are getting the proper signal, it is a little hard to trouble shoot.
I have had cars not firing at all and it be a crank or cam sensor, but I hate to steer you towards something without knowing for sure.
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Tuesday, January 2nd, 2007 AT 7:45 PM
Tiny
JOHN WEATHER
  • MEMBER
Just a short note to let you guys know what went on. As you know I don't know how long the truck has been setting. Everything was ok on the outside of the engine (fuel pressure, fuel filter, power to the injectors and injectors receiving pulse power at the time of injection). I removed the upper manifold and the injector assy. With a air hose applied 110 psi air pressure to the fuel inlet port and then to each of the injectors I applied 12v (I know it is too much voltage, but applied for.5 second) and each injector opened and passed air and the fuel regulator bypassed the excessive air. The truck runs fine now, I think by doing what I did I broke loose the injectors, which could have been done without removing the upper manifold. Anyway the engine is running fine now and thats all that counts.
Thank You for all of your input.
Thanks again'
John
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Sunday, January 7th, 2007 AT 5:58 PM

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