Ford Repair Questions? Ask a Mechanic for Answers ASAP
Hello, my name is ***** ***** I am a professional here at Justanswer. Thank you for your question and I will assist you with your concern.What size engine do you have please?Have you checked to see if you have injector pulse at the injectors when it will not start?Have you installed a fuel pressure gauge and monitored the fuel pressure when it will not start?
V8 5.0 engine. fuel pressure has been checked. Have not checked injector pulse. Also notice that fuel pump doesn't seem to cycle when 1st trying to start. Once the van is started it will continue to start all day
If the pump is not cycling then how where you able to measure the pressure on the first turn of the key?
Been a while since we checked the pressure. We have no way of checking the injector pulse
when we turn the key the fuel pump runs continuously, it doesn't cycle. Could the problem be he computer module?
Okay there is one common cause for this type of problem providing the fuel pressure is okay that can be caused by a sticking Throttle position sensor. The computer system is designed to shut the injectors off to clear a flooded condition when you hold the throttle to the floor . If by chance the TP sensor is stuck in the wide open position it will not let the injector fire on a cold start. Start with removing the TP from the throttle body and see if it will rotate freely and let me know the results.
how do I get hold of tomorrow after we try this?
All you need to do is post back on this post. In here all day tomorrow as well. Let me know and we can work from there.
How can the sensor stick? I thought that is mechanical & tied directly to the gas pedal for this year & model?
The TP is rotated by the blade on the throttle body and the TP sensor is spring loaded and its very possible for the TP to stick. It mounts to the TB but is not connected other wise. Have you removed it and check to see if it returns to closed throttle position when you rotate it by hand?
Removed the TP Sensor.....it rotates freely
Okay then the next step is to double check your fuel pressure while the problem is occurring and if it checks okay the check and see if you have injector pulse at the injector when it dose not want to start.
Ok...will check the fuel pressure in the morning...that's when the van usually will not start on its own. We may need help in determining injector pulse when we get to that point.
Why is it that when the van won't start on it's own that the fuel pump isn't cycling on and off.....it just runs continuously. If it cycles properly the van always starts.
Then when we start the van with ether, it seems we have to wait about 10 minutes before something releases and we have full power?
In most cases if the pumps stays running with the key on this usually means the PCM is failing. You can check this fairly easy by disconnecting the PCM while the pump is running. If the pump then shuts off then that means the PCM is keeping the fuel pump relay grounded when it should and If that is the case I suspect your going to also find you are lacking injector pulse.
Will unplugging the PCM with the ignition on cause any damage to anything?
No it will not. Your 1986 is a plug and play PCM and no programming is required as well.
Unplugged the PCM. That shut off the fuel pump....what next?
If unplugging the PCM stops the pump then that means the PCM is the cause and will need to be replaced.
Is there any way to have the PCM checked before buying a new one? Once you purchase one it can't be returned
You can send it out to a builder in some cases.
Why does it work properly on some days and not on others?
The common cause is usually due to some loose on the circuit board.
Replaced the PCM....fuel pump still does not cycle....van still does not start.....absolutely no change
Okay are you getting the key on ground from the new PCM at the fuel pump relay when you cycle the key?
I don't understand this sentence
The fuel pump relay is controlled by the ground switching signal from the PCM . Can you check it at the fuel pump relay and see if the relay is getting a ground when you cycle the key.
The fuel pump comes on when we turn the ignition on.....it doesn't cycle on and off like it should. It comes on & stays on....the van therefore will not start unless ethered
Okay are you sure the new PCM is not defective. Does it turn off if you disconnect the PCM?
We just replaced the PCM this morning (at your suggestion) with a new one....problem is the same.
Yes, the fuel pump shuts off when we disconnect the PCM
Okay then you can recheck it and the system with the steps in the link below.https://dl.dropboxusercontent.com/u/104923897/Fuel%20pump%20test%20Aug%2026.pdf