Question about 2002 Ford F150 Regular Cab
Batteries test fine
Alt test fine
Starter test fine
Relay's click in fuse box and vehical cannot be jumped but acts like very low batteries. After batteries are disconected vehical will start normal. suspect computer or some kind of security interference. only the factory security
I believe you may have a bad connection, probably a bad ground connection. There should be a ground wire that connects from the neg term of the battery to the engine block, unbolt the connection, clean it up, and reconnect it. Run a new ground wire to engine block if need be, size 4 wire.
If this does not resolve the problem, examine the pos term and wiring to the starter.
Did you pull the starter out of the vehicle and have it tested. When the bushings begin to go, the rotor will intermittantly drag on the field coils and it will act like low battery.
If your voltage is dropping to zero, more likely you have a bad connection
Posted on Sep 25, 2009
You mean by batteries act low,is when you try to start the vehicle it wont turn over normally,i dont understand the part that you say it starts fine after the batteries are disconnected,it sounds to me like the starter has a ''flat spot' on the inside of it, check the batteries for 12.8 volts at engine off, then turn on headlites and turn key as if to start engine and see if they dim during trying to start engine,either you have a very HIGH RESISTANCE connection(i.e. Corroded or rusred to the frame) somewhere in the start circuit, or a bad battery or starter motor possibly brushes inside starter
Posted on Sep 24, 2009
ENGINE CRANKS BUT WILL NOT START
When the engine cranks normally but won't start, you need to check ignition, fuel and"http://www.aa1car.com/library/compression.htm". Ignition is easy enough to check with a spark tester or by positioning a plug wire near a good ground. No spark? The most likely causes would be a failed ignition module, distributor pickup or "http://www.aa1car.com/library/crank_sensors.htm".
A tool such as an Ignition System Simulator can speed the diagnosis by quickly telling you if the ignition module and coil are capable of producing a spark with a simulated timing input signal. If the simulated signal generates a spark, the problem is a bad distributor pickup or crankshaft position sensor. No spark would point to a bad module or coil. Measuring ignition coil primary and secondary resistance can rule out that component as the culprit.
Module problems as well as pickup problems are often caused by loose, broken or corroded wiring terminals and connectors. Older GM HEI ignition modules are notorious for this. If you are working on a distributorless ignition system with a Hall effect crankshaft position sensor, check the sensor's reference voltage (VRef) and ground. The sensor must have 5 volts or it will remain permanently off and not generate a crank signal (which should set a fault code). Measure VRef between the sensor power supply wire and ground (use the engine block for a ground, not the sensor ground circuit wire). Don't see 5 volts? Then check the sensor wiring harness for loose or corroded connectors. A poor ground connection will have the same effect on the sensor operation as a bad VRef supply. Measure the voltage drop between the sensor ground wire and the engine block. More than a 0.1 voltage drop indicates a bad ground connection. Check the sensor mounting and wiring harness.
If a Hall effect crank sensor has power and ground, the next thing to check would be its output. With nothing in the sensor window, the sensor should be "on" and read 5 volts (VRef). Measure the sensor D.C. output voltage between the sensor signal output wire and ground (use the engine block again, not the ground wire). When the engine is cranked, the sensor output should drop to zero every time the shutter blade, notch, magnetic button or gear tooth passes through the sensor. No change in voltage would indicate a bad sensor that needs to be replaced.
If the primary side of the ignition system seems to be producing a trigger signal for the coil but the voltage is not reaching the plugs, a visual inspection of the coil tower, distributor cap, rotor and plug wires should be made to identify any defects that might be preventing the spark from reaching its intended destination.
ENGINE CRANKS AND HAS SPARK BUT WILL NOT START
If you see a good hot spark when you crank the engine, but it won't start, check for fuel. The problem might be a"http://www.aa1car.com/library/fuel_pump_diagnose.htm".
On an older engine with a "http://www.aa1car.com/library/carburetor.htm", pump the throttle linkage and look for fuel squirting into the carburetor throat. No fuel? Possible causes include a"http://www.aa1car.com/library/fuel_pump_mechanical.htm", stuck needle valve in the carburetor, a plugged fuel line or fuel filter.
On newer vehicles with electronic fuel injection, connect a pressure gauge to the fuel rail to see if there is any pressure in the line. No pressure when the key is on? Check for a failed fuel pump, pump relay, fuse or wiring problem. On Fords, don't forget to check the inertia safety switch which is usually hidden in the trunk or under a rear kick panel. The switch shuts off the fuel pump in an accident. So if the switch has been tripped, resetting it should restore the flow of fuel to the engine. Lack of fuel can also be caused by obstructions in the fuel line or pickup sock inside the tank. And don't forget to check the fuel gauge. It is amazing how many no starts are caused by an empty fuel tank.
There is also the possibility that the fuel in the tank may be heavily contaminated with water or overloaded with alcohol. If the tank was just filled, "http://www.aa1car.com/library/us10325.htm"might be causing the problem.
On EFI-equipped engines, fuel pressure in the line does not necessarily mean the fuel is being injected into the engine. Listen for clicking or buzzing that would indicate the injectors are working. No noise? Check for voltage and ground at the injectors. A defective ECM may not be driving the injectors, or the EFI power supply relay may have called it quits. Some EFI-systems rely on input from the camshaft position sensor to generate the injector pulses. Loss of this signal could prevent the system from functioning.
Even if there is fuel and it is being delivered to the engine, a massive"http://www.aa1car.com/library/vacleak.htm"could be preventing the engine from starting. A large enough vacuum leak will lean out the air/fuel ratio to such an extent that the mixture won't ignite. An EGR valve that is stuck wide open, a disconnected PCV hose, loose vacuum hose for the power brake booster, or similar leak could be the culprit. Check all vacuum connections and listen for unusual sucking noises while cranking.
This will help. Thanks please keep updated.please do rate the solution if helped.thank you for using fixya.
Posted on Sep 24, 2009
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Posted on Jan 02, 2017
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