Ran rough for two weeks. Now does not start. Fuel pump OK. Tested at fuel filter cranking. Replaced ignition control module. Engine will run if I pour gas into carb. Injectors do not spray. Is it pressure regulator or ECM?
2007-06-29 04:04:44 · 3 answers · asked by Anonymous in Cars & Transportation ➔ Car Makes ➔ GMC
I own a shop, and have seen this a few times. What it turned out to be was the oil (sending unit) pressure switch. This is a safety feature wired into your vehicle in case you turn the car over, it shuts the fuel supply off. If you jump out the sending unit it ought to start up. If not, then you have a bad regulator, or the vacuum hose is off, split where it plugs on, or for some reason has no vacuum on it. You should check the pressure at the rail. There is a valve that should have pressure on it. You could even have a plugged return line to the tank causing this. Try to attach a vacuum pump to the regulator to see if it holds vacuum, if not its bad. The computer is the last thing that would go bad, but it may very well be the culprit. Check to see that the grounding strap that runs from the engine to the fire wall is intact, making a good connection, and the battery cables are clean. Any less than 12.0 volts, and the computer doesn't work properly. The signal wire from the igniton module to the computer could be bad, thus not letting it fire the injectors. Use a noid light on the injectors to see if the signal is there. This has bad fuel pump written all over it, and it could be bad. I have seen them act like they were good, but wouldn't keep the pressure up enough for the engine to run. The pressure at the rail is what tells if the regulator is doing its job or not. You can have pressure at the filter, but not enough at the rail. The injector supply is from the rail pressure.
Glad to help out, Good luck!!!
2007-06-30 03:41:49 · answer #1 · answered by Anonymous · 1⤊ 0⤋
If you are sure you have enough fuel pressure and flow and you say the ignition system is okay as you state it will start if you pour gas into the top, you have a problem with the injectors being fired. These systems use the pulse from the ignition module to the PCM to signal when to fire the two injectors. What you should do is remove both of the connectors at the TBI unit. Check the resistance of both of the injectors and compare. They both should have very little resistance as you are just checking coils of wire. Next turn the ignition on and check for a power supply to both injectors. If all this is good, crank the motor while checking for pulses across the injector connector. If you have power but no pulses, you have a wiring problem, an ignition module problem, or a PCM problem. You would have to obtain a wiring diagram to test the wires for being open between the dist. to the PCM and the PCM to the injectors. I have personally never seen a PCM cause this. It is usually a bad module or a broken wire somewhere. Broken wires are not that easy to find. Good luck.
2007-06-29 14:33:51 · answer #2 · answered by Deano 7 · 0⤊ 1⤋
Replace fuel filter,Check for good connection at oil pressure sensor,and water temp.sensor.Check distributor cap for defects like the carbon spring loaded contact in the top of the distributor being broken.Could be a pressure side hose split inside fuel tank.Check engine codes and ask another question.
2007-06-29 11:36:13 · answer #3 · answered by (A) 7 · 0⤊ 1⤋