Truck is my tool and it is broken NEED HELP

Help! I went out to start my truck last week and no spark.(94 F150 with 4.9L) So I have replaced the ignition module, coil, distributor and now the ignition switch. The symptoms: It will sometimes start now but then die after a few minutes, other times it will not start at all. When it wont start: no spark and now power to fuel pump. I have wiggled every wire I can find while it does run to try to make it die and no wires seem to be the problem. I have checked the relays and alternated the locations and no change. When it doesnt start the fuel relay doesn't sound like it is clicking but hard to be sure. Please give me some advice.

Thanks
Charlie

Sounds like the symptoms on my 2001 Ford Ranger, except I never checked for spark. Turned out to be the fuel pump.

Sounds like it could possibly be the inertia switch located by the passengers toes on the firewall if I remember right. I replace a fuel pump once because my stepdad knocked the plug loose to the switch on an Explorer.

Hello teachingscience,

When the engine is not starting, just squirt a little gas in the intake. If it starts
you'll know it is not getting gas. That is my guess.I don't know if you have checked the fuel filter, it may be that it is all of you starting problems. My guess is a bad contact in the fuel pump relay, or the pump itself is bad.
Try onother relay out of another circuit to try, you may get lucky.
Good luck!, and post back if you do..........




Guido.

Tried that already, when it doesn't start squirting gas doesn't work either

Checked the inertia switch also. Its like the signal from the computer is failing. I'm leaning toward either the computer itself or a short somewhere that stops the voltage from getting to the fuel and ignition circuit. Just now sure where to go next.

Check the wiring on the fuel tank where the harness plugs in . Had one go bad on an 87. The plug is plastic and it had disintegrated. Causing the fuel pump to work intermittently.

Hello teachingscience,

You did not mention what kind of weather you are in. Moisture in the computer chip will sometimes lose ignition. If it is very humid where you're at, it may be the problem. You can get an air drier and warm up the computer box a little at the time when it fails to start. If moisture is the problem the air dryer will evaporate the moisture and it may start up for you. You can also pull out the chip and reinstall it. It may make a better contact and solve the no start for you,

Guido.

Better check it again because spark and fuel failing at same time sure sounds like that's the problem.

For the no spark, you didn't mention anything about the stator in the distributor (aka ignition pick-up), its the sensor that recognizes the engine is turning to energize the fuel pump and control fire. The fuel pump should still prime for a couple seconds after turning the key to run though. I wouldn't say you have no fuel unless you did a pressure test and noid light/test light on at least one injector (fuel pressure should be around 50psi key on, 40psi running)

The EEC and fuel pump relays could be problematic too but sounds like you eliminated that already, I usually replaced those as a set.

(quoted from post at 06:42:35 06/17/15) Help! I went out to start my truck last week and no spark.(94 F150 with 4.9L) So I have replaced the ignition module, coil, distributor and now the ignition switch. The symptoms: It will sometimes start now but then die after a few minutes, other times it will not start at all. When it wont start: no spark and now power to fuel pump. I have wiggled every wire I can find while it does run to try to make it die and no wires seem to be the problem. I have checked the relays and alternated the locations and no change. When it doesnt start the fuel relay doesn't sound like it is clicking but hard to be sure. Please give me some advice.

Thanks
Charlie

Click to expand...

When you have this issue does the check engine light turn on. If not you have a electrical issue... If it does the main relay is working that's the first hurdle to jump...

Its always good to clean grounds. The main relay ground is on the upper radiator support near the battery make sure the ground cable and the ground lead off the ground battery terminal to the rad support ground are clean and in good condition...

It showe's the fuel pump ground to be on the right front fender apron.

Buggerd up battery terminal cable ends will bite you especially the ground side...

If you are having no spark and no fuel pump at the same time, it would point to a problem with power to the computer. You may also have a multi-function relay box or power distribution box out near the battery somewhere on the radiator support or inner fender. At the risk of repeating myself, I once again suggest that you DIAGNOSE before you start throwing parts at it. You may also want to invest in some repair manuals. They can make things a lot easier.

A few questions:
1) How are you verifying that you have no spark?
2) Are you sure that the distributor is timed right?
3) The parts you say that you replaced (distributor, module, etc.) are new or used?
4) Have you checked out the ignition switch connector to see that there are no burned or melted wires?

Now a few suggestions:
I would take a look at the ignition switch connector. They do handle a lot of current and tend to darken, melt, or corrode after 20 years of use.
Also note that Ford computers have been VERY RELIABLE over the years. I have only had to replace ONE for a failure in my entire career as a Ford technician. All others (very few) were for programming updates.
Being a 1994, you would have the 60-pin computer. I can also post you the pinouts for the power and ground connections.

Note to guido: Ford computers do not have removable/replaceable PROM chips like GM vehicles. They are sealed units and are potted in some sort of protective medium and not easily serviceable except by the remanufacturing plant.

Note to ALL: Blaming these problems on weather conditions, temperature variations, and the like is usually not a good starting place to diagnose a problem. As was explained to me many years ago by older and more experienced people, the same car or truck was designed to run equally well in desert, arctic, humid, hot, tropical, cold, and any other weather condition that may be encountered within the expected operating area of the vehicle.

Thanks for your help, I used new parts. I have determined that its not the fuel side. I bypaseed the relay and it was still pumping as it died. I have narrowed it down to the 5 volt reference voltage at the throttle position sensor disappears when it dies. I have checked the ground going into the computer to make sure it is staying grounded and it is. I have not tried to check any other wires that go into the computer. The plug on the ignition looked like new, nothing has been hot. While running, I also wiggled the plug and wires with no effect along with every wire and plug under the dash and under the hood I could get to with no change. It may run for 1 minute or 20 and out of the blue, the 5volts goes away and its like I turned the key off. I would be very appreciative of any advice you can give.

Charlie

A post above reminded me to mention something else, which may not be the track you are on but its a good thing to remember for future. The check engine lamp needs to be on (unless bulb is out) anytime the key is on, the check engine lamp should go out during cranking, if the light does not go out when cranking engine that means the PCM is not seeing a PIP. The PIP is basically the crank signal to the PCM.

If you are losing the Ref voltage it could be a problem with one of the many sensors that use the 5v Ref. I would try unlugging them one at a time while measuring the circuit to see if the 5v comes back. Its kind of rare that a sensor shorts out on the reference voltage side but it happens. Seems like I have seen EGR, MAP and maybe a TP sensor do that before. Reference voltage is supplied by the PCM through an internal regulator, hope you don't have a PCM problem. Also check for codes, even though it might be something insignicant, it might lead you to the direction of the Ref voltage problem.

Whats the fuel pressure. (pump running does not confirm you have enough fuel pressure)

How do you know the grounds are good. Can you tell me the pin numbers you checked to confirm a good ground and how did you confirm it.

Check the pickup sensor in the distributor. The computer won't energize the fuel pump, injectors, or the coil if it's not seeing a signal from that.

If the 5-volt goes away, it will shut down the whole system. That reference voltage is what the computer lives on. This voltage comes from ignition power when the key is in the "ON" position.
You should have a 60-pin processor in your truck, so the following pins are important:
Pin 1 is keep alive memory. This is a yellow wire, and should be hot at all times.
Pin 16 is ignition ground. This is a black wire with an orange stripe.
Pins 20, 40, and 60 are all grounds. Black on pin 20, black with light green stripe on pins 40 and 60.
Pin 26 is reference voltage. Orange wire with white stripe.
pins 57 and 37 are vehicle power. Both are RED wires, and both should be hot with the ignition switch ON.

Reference voltage is generated by a voltage dropping and regulating circuit within the processor. This voltage is vital for the operation of the system. It powers ALL sensors and provides control voltage to relays. Basically all sensors operate on the 5-volt reference voltage. Relays, solenoids, and injectors are operated by 12 volts directly from the battery. Control is achieved by grounding the circuit to activate.

With the introduction of the OBD-II system, the processors added another 60 pins, becoming 120-pin units. Your vehicle being a 1994 is right near the changeover, and could actually have either processor in it.

First thing to diagnose is if you have power on the RED wires when you lose reference voltage. If you have power on the red wires, and you have verified that you have ignition power going to the processor, that would indicate a failed processor. This is a rare condition, but cannot be completely ruled out.

Also, check the wiring harness for any spots that it may have rubbed through - like in a support bracket or near any metal components. This happens surprisingly often.

I might also suggest that you take a look on eBay for an EVTM manual. This is Ford's Electrical and Vacuum Troubleshooting manual. It gives you color codes of wires, wiring diagrams, connector identifications and locations, pinouts, and a wealth of electrical information.

Sorry to be so long, but there is a lot of ground to cover here.

Finally got the ruck going. It turned out to be the computer. Sure wish I had tried that 1st. I had checked early into the diagnosing but there were none in any local salvage yard but after I replaced the coil, ignition module and ignition switch, the local place got in a truck like mine with a matching computer, I picked it up the same day they got it in and it purred better than it had in years.

Thanks so much for all your great advice.

Charlie