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I would first suspect the fuel pump. Do you hear it buzz on for a couple seconds with turning the key to ON, not start?
It should come on for 2 seconds to prime the line with pressure to the engine. Do you hear it? Stand by the gas tank and have someone cycle the key to on if you need to.
If you hear nothing from the tank, you need to investigate the fuel pump and it's circuit.
There will be a fuse for the fuel pump, it is under the hood in the power distribution box-the fuse/relay block. The power for the pump goes from that fuse to the fuel pump relay (also in that fuse/block) and when the engine computer signals that relay on, the power goes through the relay and then directly to the pump in the tank.
Try this test, if your pump doesn't work-test the FPR-to test if the relay is getting a signal from the computer: hold your finger lightly on the relay. now have a helper cycle the key again from off to on (not start). Every time the key is cycled you should feel the click of the relay energizing. If you feel it click and you checked the fuse and it is good, and you still have no pump coming on, then it is likely you need a new pump. Bang on the bottom of the tank, a couple of raps, then see if pump turns on. A failing pump can sometimes be turned on by jolting it like this, but it only works a time or two or three.
So now what? If the pump is working and putting fuel to the engine, then check for spark at a spark plug. Usually a sudden no start means the engine has lost either gas or spark.
You don't say if you have checked that the Fuel Pump is working.
1. You need to check that the fuel pump is operating and getting power.. Have someone turn on the ignition (but not start the engine) If you listen near the FP location you should hear the fuel pump run for 3 seconds and stop. If in doubt do this a couple of times until you can hear the pump run and stop.
2. If you cannot hear the pump running check the fuel system related fuses.
3. If the fuses are good check that the relay for the fuel pump you replaced is functioning. Have someone turn the ignition on and off a few times and listen for the click from the relay or put your finger on it.
4. As a final check have a simple fuel pressure test done on the fuel system if not done already. . If everything is running normally and you are getting good fuel pressure then the starting problem will be somewhere else.
I'd have to test when problem is ongoing. When you first turn on key, no crank, you should hear the pump run for a few seconds then stop. For initial prime, the computer doesn't need rpm signal. Engine cranking, the computer needs to see rpm signal or it won't ground the fuel pump relay. W/o rpm signal, no spark at the plugs and no fuel injector pulse. I know your talking about fuel, but, when problem is ongoing, check spark and fuel injector pulse, engine cranking.
Intermittent problems are a pain, have to test when problem is ongoing.
The only manufacturer that uses a fuel cut off switch or inertia switch is Ford. Your jeeps fuel pump power supply is ultimately controlled by the cars computer.
If you suspect there is a fuel pressure issue the first step would be to actually check fuel pressure with a fuel assure gauge. Or listen to see if you can hear the fuel pump run for a couple of seconds when you turn the key to the run position. If there is no fuel pressure or you can not hear the fuel pump run than the next step is to check for power to the fuel pump.
You should be able to find the fuel pump harness back by the fuel tank. There will be a connector where the fuel pump harness plugs into the vehicle harness. You'll want to check for power to the pump by back probing the wires at that connector. There should be power for a couple of seconds when the key is turned on and any time the engine is cranking. If there is power the fuel pump is bad.
If there is no power let me know and I'll be happy to help you with some further diagnosis.
Hi, your fuel pump may be failing. You can check the pump by removing the clamp from where the fuel line attaches to the fuel rail. Pull the hose off to see if there is fuel pressure there. If no pressure, check to see if you can hear the pump coming on when you turn the key on. If the pump is coming on, it's probably bad, but you may want to try cahanging the filter before getting a new pump. If the pump is not coming on, try checking the pump fuse first, then try swapping the fuel pump relay to see if it will come on. Please get back to me if you have any questions, and thanks for using FixYa.
I had the same problem and to my understanding blazers are known for their fuel pumps going out. You might hear the fuel pump engage but that doesn't mean it is putting out enough fuel pressure to keep the engine running. Your best bet is to have it towed to a local shop and let them run a pressure test to check and see if your getting enough fuel pressure or if your a big do it yourself type you can rent a pressure tester from auto zone or your local auto parts store. If you don't want to do that you can get a fuel pump for around 3 to 4 hundred dollars and replace it and see if that cures the problem.
Quick safe way to check fuel pump. Put key in and turn to ON position listen for the pump to buzz or hum. Don't hear it its either the relay, pump or circuitry.
There are other tests but too envolved and dangerous to do. Bring vehicle to repair shop if you don't hear pump buzz. If it Buzzes them problem is either with spark or air.
need spark tester to test for spark. Do visual inspection on air intake plentium (no wholes, leaks) make sure mass airflow sensor is a-ok.
Put a fuel pressure guage on the test port on fuel rail. With fuel injected engines if pressure is too high or low car wont start.
Cycle key off to run (not start) you should hear the pump run a few seconds and stop.
Fuses first. Then, disconnect the fuel line at the throttle body (unless there is a fuel pressure testing port) and see if there is fuel when you turn on the key. If not, fuel pump, probably in tank. (assuming there isn't one on the side of the engine..) If there IS fuel in the line, then the computer may not be engaging the injectors. Check for wiring issues on something that old. Maybe the main junction splice for power to the computer. (Not sure where on that one, sometimes it's in a dumb place, like near the battery and it gets corroded).
There should be a 2 second prime by the fuel pump. This prime by the fuel pump is standard for GM vehicles, and if it is not present a hard start is encountered. Turn the ignition to the run position and listen for the fuel pump operation. You may have to have an assistant listen at the fuel filler by installing a long slender funnel into the fuel inlet to the tank, remove the gas cap and insert the funnel, listen at the large end of the funnel to see if the pump can be heard running. Using the funnel acts like a megaphone and makes it easier to hear the pump. If the pump runs for 2 seconds after you turn the key to the run position (DO NOT attempt to start the engine during this test) and the engine doesn't start due to lack of fuel, check for an obstructed fuel filter. (Just change it, it's probably overdue for service anyway since everyone thinks it get changed during oil changes, but never really does.) If the pump doesn't run during prime interval, the computer may not be turning on the fuel pump relay, or the relay is defective. To check the relay, use another of the relays in the power distribution box to substitute for the suspect fuel pump relay and retest. Be sure to wait at least 30 seconds between key cycles since some systems have a delay timer built in to keep the pump from over running. Be sure the relay you sub into the fuel pump socket is identical to the one you remove and properly oriented in the socket. The engine will run following your manual prime because an additional set of contacts in the oil pressure switch will power up the fuel pump relay once proper oil pressure is achieved by an idling engine. If you find that the relay is not defective, but doesn't provide a priming impulse, the engine computer may have failed. DO NOT use a conventional test light with a filament type bulb to check any of the computer circuits that drive the fuel pump relay, or any other computer controlled circuits on an automobile ( or pickup) The driver circuits in a vehicle computer can be blow-out by over-current when using a conventional test light. You can use a high-impedance DVOM for testing safely.