Hi guys, to start, I have an 88 F350 with the 460 and zf5. Truck has been running fine until recently. Just yesterday it died and I couldn't get it to start.

Codes are good, only one I have that I know of is 81 for the air diverter which has nothing to do why it won't run. All 3 fuel pumps are working and all 3 are new. Fuel pressure at fuel rail KOEO is around 35. At HP fuel pump KOEO it's around 70 psi.

Just a few minutes ago I disconnected the battery and then the ecm connector at the firewall and reconnected it. Now I have it running. Pressure at rail is about 28 KOER. Disconnecting FPR and I get about 36-37. Sounds odd that pressure would be super low at the rail? Does not leak down so as far as I know the injectors are fine.

Normally I would think the HP fuel pump is weak but it is new, and it consistently got over 60 psi when connected right at the pump. What do you guys all think? The truck right now is stuck at a harbor freight

 

My first thought is poor electrical connections or bad relay. Heck even I have been through a bunch of pumps recently, most have died under 300 miles.

But it sounds like you have a fuel regulator issue. Unless you have a modified engine that needs 70psi of fuel you have way too much fuel pressure. Normally the pumps in the tank push 15psi (or so) of fuel to the pump on the rail. The rail pump bumps that pressure to about 38-41psi. Now your fuel pressure reg should be on the return side of the fuel rail and not the supply. IF your seeing 70psi at the pump and 35 at the valve on the fuel rail then you might have a issue. You should have 38-41psi of fuel from the front of the HP pump on the frame to the regulator.

 

It has a new FPR that seems to be working correctly though. I get a solid 28 when connected and 37 when disconnected. This would be like when you go WOT and get the 40 psi they say. When I do WOT test it is around that 37-40 mark so it is regulating down correctly imo. Hopefully is just the connections. It is running fine now...

 

That's enough pressure for the engine to start and idle.

Check your spark the next time it quits.

 

Spark appears to be fine. When it was sputtering it sounded like a loss of fuel. Guess I may have to chalk it up to a bad ECM ground. Once a reconnected it ran fine. Still going to get the pump replaced though. Also just now checked codes and I have a code 22 MAP sensor out of range. I know the MAP is important and integral to running correctly, but would it make the truck kill and not start?

 

I've seen the MAP cause both conditions in the past.
Check the Reference voltage to the MAP, should be 5 volts dc. Orange/White wire.
The ground is Black/White.
Signal is Dark Green/Light Green, you will need a Frequency setting to measure this.

 

Luckily The MAP sensor has a lifetime warranty. Going to just swap it out, I don't have a meter that measures Hertz. Also going to swap in the old FPR, as well as the old Dizzy cap. I guess it could have been ignition. Now that I have the truck at home I will check spark at each plug. Before I just tested it at the coil.

On my 460 the plastic air horn piece with the diverter for the IAC is broken. The result of trying to take off the air intake hoses in -10* weather. When it was stuck in the parking lot I noticed it was sucking air to the IAC even when unplugged. I heard they only failed in the closed position? Going to get a new one as well. I'm now sure that mine is bad. On cold start the idle isn't higher for the 30 seconds or so that is factory set. Hopefully with these new parts it will be running better than before it killed on me.