I have a 1994 Ford Explorer that won't start... I have replaced the fuel pump and descending unit and it still won't start. The only other option I have found was the inertia switch, but i can not find it. Where would it be located?

You have a descending unit? Why does your new part not fix the truck ? you ask? First we need to know if the pump can be heard to run. Then does it have spark ? spark loss could cancell fuel. if you look up above the carpet and kick panels by the firewall your inertia switch could be there. the power must flow through it. it is often found passenger side front on ford trucks. But do you get a fuel reading on the fuel gauge with the key in run?

You can hear the pump when I try to start it. It does have a spark, and I found the inertia switch but it was pushed down... What could be the problem?

Do you have a good battery and cables? The pos. cable can often have trouble where a few wires come together at the battery. They could get corroded inside the clamp at the battery and have connection trouble. If all the pos. cables show good power being sent, also inspect your power distribution box. one of the cables goes there. If it is all good, tell me if you hear the pump start when you key up

Next you must test the fuel pressure and injectors for functioning. For spark, you need to remove a plug and with its wire connected, ground its ground electrode, crank the engine. does the spark plug still work? With a fuel pressure gauge, attach to the service port on the injector rail. Key it up and attempt to start, is there a fuel pressure reading you can tell me ? bleed the gauge. is the system full of air bubbles ? try again, cycle the key off, on, attempt to start. bleed the gauge.

Earlier I checked the battery and it had a strong connection. I just started it and you can still hear the pump turn on when i turn the key over

What were the spark plugs condition and what kind are they and what is their gap?

Do you have a test light? back probe one of the injector connectors and crank it. ground the tester. ......Next I need a fuel volume test. with a suitable container catch the fuel from the rail as you press the schrader valve. key up and shut down a few times. in the interest of fire safety. restore the ignition system. what were the plugs like ? and another question, does it have a new fuel filter, (FG800)

How many ounces of fuel would you say you collected it 3 key-ups. And did your test light show power in use at the injector connector(s)?

If present fuel over 30+ pounds is not seen on the gauge, and you cannot collect an 8 oz glass of fuel, pull your filter off, hold it to blow the contents the reverse of its arrow direction into a suitable visible container. I use a white antifreeze jug cut in half. Blow the fuel back into the container. when it empties, it should be as easy to blo thru as whistling. Ok, what came out of it?

Be sure you have adequate ventilation and a fire extinguisher at the ready, or suitable water supply. return all clean unused fuel to a funnel at the fuel tank. clean the funnel and be cognizant of your doings around fuel and spark. excuse the obvious warning but I dont know for sure, your aptitude.

If all your pos. cables light a test light, and pulling and wiggling them is not affecting the applied voltage reading, the plugs are new, set to the gap specified on the CAFE regulation (tune-up) sticker, they must be shiny at the center electrode and the ground electrode, (where the spark occurs.) If they are an off brand, try Motorcraft, autolite, or a/c delco. If they work they work, and I will shut-up. If your filter is blocked ? hard to pass breath thru ? you need new. If you need a test light or a fuel pressure gauge ? you can get one from the parts manager and perhaps return it after ? I do.......The injectors can also be checked for power supply and switching with a little tester light part stores sell. it is specific for this but a standard 12v light will tell if you have function there.

A cheap DVOM can be useful because it can be more accurate for the power tests than a light. if you recognize a dimmer light ? you wouldn't need it. if you were unsure ? The DVOM lets you do a quick arithmetic to tell you volts you drop. Comprende ?

If you have relay troubles or fuse troubles, their function would be noted as inop. An eec relay can shut down the brain function and there would be no injector test light happenning. Vacuum leaks that may exist could lean out your fuel mixture, and weak compression readings can be found during a compression test. Troubles at your EDIS module would affect your spark tests. Crank sensor trouble can be tested with a DVOM. There was a bulletin about EDIS connector inspection. Trucks with battery leakage could have trouble there. it is in front below the top of the upper radiator support. might have to move the battery back away from it........................see what you can accomplish and I will check back in a 1/2 hr

Excuse me, that fuel filter is an fg872, Not a fg800, and that means you need special release tool for removal. Since you said you started it, i dont know for sure if you need further help. please report what fixes it in case this completes a thread that helps people. Let me know and they email me.

Its crankshaft position sensor or ICM. Usually CPS.