Hello,

91 F250 351W 5.8

A few months ago I had an overheating incident and have been having some issues since. It overheated, then I couldn't turn the motor back on until it cooled down, so it was probably pretty bad.

Caused intermittent rough idle and engine dying once or twice a month. Usually when getting off the highway.

I just changed my fuel filter, distributor, cap, rotor, ignition coil, plugs, and wires in an attempt to fix this.

My idle is smoother, but the problem actually got worse.

No error codes on either key in or engine running tests.

Before doing all of this, occasionally the car would turn off after getting off the highway. It also occasionally got a rough idle. Now after changing everything, the idle feels better when it's not having the issue, but still gets rough and it turns off much more frequently. Before it turned off maybe once or twice a month. Now it turns off every drive. I also feel loss of power intermittently when driving on the highway. Like it wants to die on my, but it doesn't. Probably because it's getting gas and can't die.

It also occasionally takes a long crank to start, but not always. Usually it starts right up. Also, if it dies it will turn right back on.

I also tried to look for vacuum leaks by using carb cleaner. I sprayed every connection I could see, but nothing.

I'm out of ideas on where to look.

 

Connect a fuel pressure gauge and verify you have 30-45 psi at all times.

 

There is a lot of hidden meaning in Raski's suggestion that states " At all times".

If for instance the fuel pump pick up screen in the tank becomes clogged for whatever reason,the engine runs out of gas or until you shut it off or it stalls and the suction drops and some of the foreign matter clogging the filter drops off and the engine will immediately restart until it clogs again.

You have to be watching the pressure gauge at that time to be sure if you have lost pressure.
The other option is to drop the tank and verify there is no "junk" in the bottom of the tank, not an easy job, but until you verify it is clean , the possibility will always be there.

 

Pressure stays at constant 30PSI. 40PSI if I take the vacuum off the regulator.

Stays at 30 even when the motor stutters.

 

Since you have said "Caused intermittent rough idle and engine dying once or twice a month. Usually when getting off the highway", I would look very closely at the EGR valve possibly hanging up in the open position. You could try unplugging the vacuum line off the valve, plugging it with a golf tee and see if the problem re-occurs.

 

Something you can try;
Go to any auto supply store and purchase an EGR Valve gasket, they are special.
Remove the EGR valve ,and with a mallet tap the pintle to allow it to fully seat and remove accumulated carbon. Reinstall the valve assy with the new gasket, but as suggested plug the disconnected hose and see what you get.

 

I will take a look at the egr.

Also. Today I tested the wires.

Ignition coil wire was 2.2k ohms, while all other wires were 0.4-0.5k ohms. Massive difference.

Could it be my ignition coil wire is going bad?

 

If those are the original wires the vehicle was built with , they are overdue for replacement. The same goes for the ign coil, do it right and do it once.

An ignition wire set is an easy item to replace as long as you do them one at a time.
There were problems with the original coils.
Also there were problems with the ign module mounted on the distributor. replace that also , and I believe your problems will go away.
Make sure you apply the heat sink grease supplied with a new module. You just about ruled out a fuel problem, and the parts that I suggest you replace were all problematic and the only way to know is to replace them. There are tests, but the cost to do them is more than the price of the new parts. Give it some serious thought.

 

This is what is new at this time: Distributor, ignition coil, plugs. cap, rotor

Not changed yet: Plug wires

I'm going to change out the plug wires today since I got that strange ohm reading on one of them.

If this doesn't work, I'm going to take a look at the EGR. It was replaced about 2 years ago, but something might have happened to it.

 

Get some dielectric "tune up" grease and as you change the wires, use a very small screw driver to smear a thin coating of the grease on the inside of the boots on both ends of each wire.