Hello.

I just purchased a used 97 F 150 6cyl, extended cab, with 78K miles, which passed smog with flying colors. Once I owned it, it started to run rough at stops, with rpm dropping to 500.
Had camshaft sensor and gear under it replaced, since person I bought it from indicated he had done some work on it, and this was his answer to the rough idle.
The other day, it started to buck, like fuel was not getting to the engine. Eventually it just shut off, and the truck came to a stop.

I have checked the fuel pump connector, and the black and orange and black show resistance from the vehicle. The pink has no voltage, and the yellow has 9.5v

The 20amp fuse #19 is good, and after switching relays from fuel pump and wiper, which are the same, nothing changed.

Inertia SW did not trip, and have power to those wires.

Checked voltage on relay pins, and several have 12 volts. The relay has 5 pins, but it appears the center one does not connect to voltage, as I don't see copper inside that housing.

I connected a newer obd2 reader, but it can't read the vehicle, so I can't see if any codes show.

No service engine light or engine light shows at any time, as it did before I disconnected the battery. I installed a new fuel pump, as others have done. They used to come on briefly when turning the key to start. Only ABS light comes on briefly now.

Have schematic, and trying to figure out what changed, but after many hours, I'm stuck.

Not sure if I should disconnect the ECM harness, but it appears solid.

Something is not allowing voltage to the pump, and that's the frustrating part.

Any suggestions would be greatly appreciated, and I hope everyone is having a wonderful holiday.

 

Did you test the fuel pump before changing it ?
- This would be jumpering the normally open contacts in the fuel pump relay slot with a wire. The fuel pump will run regardless with the jumper in place.



The other test is to check the fuel pressure at the fuel rail.
- gauge on the schrader valve

The fuel pump might not run if you have cycled the key enough times without starting the engine.
- Seem to recall it is either 3 or 6 key cycles without starting it, that it will not run the fuel pump anymore.

You might want to diagnose where things are at with fuel pressure at the rail before you change any other parts for the heck of it.
- Also, when was the last time the fuel filter was changed ?

 

Thanks for your reply SSCULLY.

I did not check the pump prior to replacing it, but the old one does work if 12 bolts is put to it.
Noticed the 30A PCM fuse by the left finder was blown, and when replaced, blew again, so possible short somewhere.
I cycled the engine several times after new pump, and then disconnected fuel lines, to see if anything was coming out, which it didn't.
Would the rail have pressure, if the truck coasted to a stop, after the engine shut off while driving?
I can jumper tomorrow and see if fuel comes out.
Not sure when filter was replaced, but was told engine had been rebuilt last year, and it did sit idle for some time, as it only has 78K on it

 

If your fuse for the PCM is blown, the pump will not operate since it's controlled by the PCM.

If a fuse blows, it is ALWAYS a short circuit.

 

I have an owners manual,which shows the fuse locations and what they are.
Today, I bought a 30a fuse/breaker, so when I turn the key the button pops up, and can be reset.

I started unplugging various sockets last night, as I had read other people were able to isolate what was causing the short, but no luck for me.

I don't see any wires that are burned from touching the manifold.

Is there any way to run the multi meter from ground and touch all the connectors inside the power dist box to find a problem, or is it time to get someone with a scanner?

I checked under the dash, and there is a device that must have been installed for an alarm. If I unplug the wire harness, the doors will still lock, and from what I found on the internet, it had a remote, but nothing was given to me.

 

What is the specific identifier for the blown fuse?

 

other than the fuse is position 24 for the pcm, I'm not sure how to answer

The tach while the engine was running, had on occasion dropped from 2000 to 0 for a split second, then return, without any noticeable engine change.
If that could have caused the 30a fuse to blow, I'll need to know where the wire comes off the engine.

Can I post pics to show what I'm talking about?

 

Started removing 02 connections at the trans and passenger side manifold.
Fuse 24 did not blow after pass side manifold disconnect.
Re connected trans, and then pass o2 W/o fuse blowing.
Started engine. shut off, and cleared--- P0344 Ford - Camshaft Position Sensor 'A' Circuit Intermittent Bank 1 or Single Sensor

After a few minutes, I turned engine off, but it blew same fuse on trying to restart. Not sure if heat affected the sensor, or if un connecting and re connecting was a fluke.

INspection on wire harness does not show any burnt or frayed wires.

Letting engine cool, and will try again. If it starts when cold, could it be one of the o2 sensors going bad under heat?

 

I found an area on the wire harness protective shield that had melted, and there was a wire showing thru to the copper, so I figure it must have been shorting to the manifold.
It was behind the passenger side of the engine, and could only be seen when I removed the mega fuse blocks, and then the connectors that hold the wire harness, so I could pull the harness up and forward. I have cleared the P0344 code which still shows, but the engine is still running after starting and stopping. If the code does not go away after 50 miles, I might have to take it in to see if the camshaft indicator is faulty, even tho it has been replaced completely. Perhaps the timing is off.

 

Tach still drops sporadically, but the engine does not change. Need to find where the tach wire originates, to see if it is loose or touching something. Not sure where schematic for that would be tho.