1990 F250 7.5/460 EFI Dual Tanks.

First of all, I don't know much. But want to learn as I go so will much appreciate any and all help. Can you help me get this thing back to operational? Willing to buy/try whatever needed.

This truck used to run like a top. A guy who was using it did a "tune up" (details to follow) and at some point after that (this is now a couple years ago) it started running very rough. Or really, hardly running. Starting cold it would barely keep idling, sort of surging, engine shaking... if I let it warm up long enough say 30-40 min it would become drivable and keep running. Without that warmup it would not drive, it would stall. With the warmup it wasn't quite normal, but it was close. At some point a nasty rattle sound started, which seemed to be the Cat. Based on a youtube I saw, I tried at one point to change the MAP sensor but it made no difference. Eventually, I cut off the Cat to see if it was blocked, it obviously wasn't working by the sound but I did check it with a laser thermometer and it wasn't working. The internals of the Cat were all shattered (the rattle sound). There is at least one connection on top of the Cat that is of course now disconnected. I have verified the plug wires were done correctly* including considering routing of #7 #8 so they're not parallel but do cross at 90-deg.

*firing order found online as: 1-5-4-2-6-3-7-8; as to location of #1 on the distributor cap, I saw diff pics online showing #5 & #1 on right side of nearby clip and another source with the clip between them. So, I stuck paper towel in #1 spark plug hole and rotated engine until it blew out... twice... first time rotor pointed to #6? I think, second time I assigned location it was pointed at to #1. So, relative to the clip for the cap clip is between #4 & #5 with #1 next over clockwise from that. Sound correct? (I'm attaching an image I found online that I believe shows the correct orientation for the wires and is what I've implemented.)

>> So, my first question is what will be the result of having cut out the Cat? What issues will that cause (other than the sound!)?
>> PCV valve connector is fine...I originally posted here there was an issue, but was incorrect.
>> Next step will be to test the fuel rail pressure. I'll update here with results.


Things that were done during tune up:
New plugs, plug wires, distributor rotor, fuel filter, air filter, pcv valve, adjustment of distributor by ear.

 

Most Ford distributor caps have the #1 cylinder marked with a big "1".

 

Check for key on engine off fault codes.

 

So it seemed like #1 & #4 spark wires were not setting off my induction timing light. Closer inspection revealed that they are getting a signal, but maybe weaker than others? What I found is that if I give it more throttle then there's enough energy in the wires to trigger the induction light. The other cylinders wires are able to trigger it at the idle, such as it is, which itself is very weak.

I used the Innova OBD reader to find EOKO had no codes. But CM had code 95, "fuel pump secondary circuit failure". I bench tested the fuel pump relay and it seems to work ok. I bench tested the inertial switch and it works correctly. However, I am only finding 6-7v on the switch wires. When I applied 12v to the other switch wire, I can hear the fuel pump running. I switched the tank selector and both pumps can be heard. I started truck and ran it with 12v on that fuel pump line and truck ran much better. However, it shortly conked out. Why would I only see 6-7v on the switch wire? I've seen others say this is normal? When I started it and tested the voltage I saw about 10.5v,v which again I don't understand. Help?

What I've seen using the induction light is that after a while it stops lighting. Someone suggested maybe coil is bad? Thoughts?

 

The fuel pump relay is energized for 1-2 seconds when you cycle the key from the Off to Run position. After that time period the fuel pump relay is dropped out. The 6-7 volts you are seeing on your meter is back feed from the fuel pump monitor circuit in the computer. When the engine is cranking and/or running the computer sees the PIP pulses from the distributor. The PIP signal is used to trigger when to fire the coil and injectors but it also keeps the fuel pump relay energized. 10.5 VDC at the fuel pump when running is on the low side.

 

Today I had the inertial switch out and I directly supplied battery positive to the wire running from switch to the fuel pump in the front tank. Could hear it running. I fired it up and was able to get a fuel pressure reading on the rail. (Do to my error, any previous pressure reading listed before/above was invalid and sb ignored.) Today I got a good reading of 34psi. While it was still running I managed to pull out the vacuum to the pressure regulator and could see pressure to rise to 40psi. So, the pressure looks good. Remember, however, we got a Continuous Memory code of 95, which is a failure in secondary fuel pump circuit. While supplying power to the switch leg (via a Power probe III) I was seeing 11.5v. My understanding is that this is just showing how much power the battery has. I'm assuming the alternator isn't making good power given how it's running. (Or should I be looking at the alternator?) Truck runs for a couple minutes at a time then halts. It starts more strong then quickly degrades into hesitation at idle and eventually dies at idle. I also put the inertial switch back in place and ran it just the same as when I supplied power directly, seemingly giving same fuel pressure (I didn't release pressure between times, but gauge did move around.)

That's all I got. What's next??

 

If the voltage is below ~12.5 VDC with the engine running you have an alternator problem. I still do not understand why you are supplying voltage to the fuel pump circuit. As I stated before power is applied for 1-2 seconds when cycling the key from the Off to Run position. When you turn the key to the Start position the engine will crank over which triggers PIP pulses from the distributor. Those pulses tell the computer to fire the coil and injectors. Those same pulses also tell the computer to energize the fuel pump relay. Opening the fuel pump circuit will trigger Code 95 (Fuel pump secondary circuit failure. The EEC senses infinite resistance to ground from the fuel pump on the Fuel Pump Monitor circuit.).

Low voltage can also cause driveability issues so I would have the battery and alternator tested.

 

​​​​​​This was because I got a false reading of no fuel pressure on the fuel rail. I had supplied 12v to fuel pump circuit just to see if pump ran and if it made a difference in pressure, it did not. The pressure reading was because of my error in over tightening the gauge to the shrader valve. After I corrected that I did get good pressure. I've cleared the code 95 and it hasn't come back, so far.

 

Today I checked into the ignition coil. I discovered that the connector to the high voltage cable out to distributor was deformed, possibly from arcing or corrosion. The coil resistance across the low voltage terminals was 0.7 ohms, so in spec. I'll attach pic of the coil connector.

I removed the SPOUT connector and it ran longer than it had been. It seems the computer is shutting it down either deliberately or by adjusting timing and killing it. When it first starts it runs better, stronger, but after 30 secs or so it starts to really struggle and eventually dies. With the SPOUT out it kept running, tho poorly. While running I verified again #1 & #4 spark wires do not power in induction timing light. I also used a spark plug tester and saw no spark on #1. I tested the input wire to distributor and saw what my inexperienced eyes thought was a weak spark. Not sure how bright it should be. I attached video of it, not sure if you can see it well enough.


Ignition coil high voltage connector.

 

<deleted w/o knowing how to delete> 😁

 

Installed new Motorcaft ignition coil, no change in operation. Even with SPOUT removed, truck starts strong from cold then quickly degrades to conking out. Based on previous tests, it seems #1 & #4 fire at first and then quickly quit sparking. What could explain no initial spark on two cylinders then no spark on those cylinders?

 

Have you looked at all of your plugs to make sure none of them were accidently hit against the engine,closing the gap of the plug when installed. I dod this once on a cavalier and it ran like crap till I figured it out.

 

Also if you haven't done it yet, get a timing light and time it with the spout removed. I assume you replaced the distributor cap along with the rotor.

 

I will do this. I am going to check compression anyway.

 

With no spark on #1 how can I check the timing with the light? Is there any spark wire I can safely swap with #1 to see if I can get a spark on #1 from a different terminal? Still couldn't check timing like that but it'd tell me if it's the distributor or not.