So I just bought a 1986 Ranger with a 2.9 engine in it and every time I fill up the tank It'll run but then once I stop and let it cool down it will fire up and then die after a couple of minutes. And I'm not sure where to start with it.

 

Welcome to the forum

It reads like TFI module issue, but nothing to do with full tank of gas, TFI module is on the distributor and they are notorious for not restarting spark when they get warm, then work again when they cool off a bit

Loosen the gas cap after filling up and see if still does it, could be a tank venting issue, you are getting an air lock so fuel can not be pumped from the tank

 

What's the tri? And would it shut down from an excess of pressure?

 

No, it would shut down from a lack of fuel

 

All right, so I open the gas cap and it still won't start, It'll crank all day, but it will Not start, I also replace the fuel pressure regulator last night

 

Did you do 50/50 test
Spray gasoline or quick start(ether) into the intake, try to start
If it starts and dies spark is OK but no fuel from injectors
If it doesn't fire/start, then spark is the probem
50/50 instant results

 

Okay, so I did that, got nothing. So I noticed a Schrader valve on the fuel rail. So I took the cap off and I hit the key a couple of times to make sure The truck was trying to Prime and when I hit the Schrader valve, there is no fuel coming out which tells me there's no pressure in the fuel system.

 

It didn't start when you added fuel manually into the intake?

Then you have a spark problem to deal with FIRST
You may not have fuel either but spark is first to get working

The IAC Valve gets 12volts on its red wire with key on, unplug the 2 wire connector and see if red wire has 12v with key on
This same red wire powers injectors, computer, fuel pump and most other engine systems except spark
If not then EEC relay is not being activated

The TFI module gets 12volts from ignition switch under steering column, info here: https://therangerstation.com/tech_li...agnostic.shtml
Scroll down to the bottom to see wiring, unplug TFI connector and see if you have 12volts on RUN wire with key on

repeat 50/50 test until it starts

 

Alright so i pulled a spark plug to double check if i was getting spark and i guess i didn't get gas into the intake good enough because the plugs fired just fine. So that was my bad. And now im back to thinking about the lack of fuel pressure

 

So engine starts when you add fuel to the intake?

testing a spark plug never tests timing so unless its a single cylinder lawn mower or motorcycle.....................


But lets says it does start when you add fuel to the intake, so spark is there and timed correctly, but then dies, so no fuel from injectors

Turn key on and listen for fuel pump(s) to run, they will run for 2 seconds only, so turn key off and on as much as you want to decide you do hear them or don't
They are loud, a HUMMMM
On an 1986 you will have 2 fuel pumps, a lift pump in the tank, and a high pressure pump in the frame rail, under drivers seat area
You can cycle key on and off a few times and then test for fuel at the schrader valve

In the engine bay will be the OBD1 test port, look here: https://therangerstation.com/tech_library/OBD_I.shtml

It should be near passenger side firewall on the larger wiring harness that goes into the cab to the computer
In the above drawing the Fuel Pump slot is labelled

If you GROUND that slot it will close the Fuel Pump relay full time, so no 2 second thing
So use a jumper from that slot to a ground, battery negative
Then turn on the key, fuel pump should now have 12volts all the time
Might be easier to test this way