Right after it dies remove your fuel pump and see if the " sock " on the pump is plugged up. I have had one get all plugged up from the trash on the bottom of the tank, then after sitting so long it all kind of fell off and let it start and run some more. Looks like your dropping pressure / supply to fuel rail. Pump could be puking even if new, of somethings getting clogged up. Frame pump is a low Volume high pressure. It pulls out of the switching unit next to it. I have had the valves in the switching unit get stuck and truck would die but that happened pretty quick.

 

Spent some time on truck today.
Here are results of some testing.
Pulled power off main pump and hooked main pump direct to a battery.
Pump buzzed away and fuel pressure crawled up to about 40lbs.
Started truck and pressure reduced to about low 30's
Observed that when fuel rail was pressured up and you relieved pressure with button on fuel guage, not a steady stream coming out , lots of bubbles etc.
When I removed fuel lines off diverter valve it was observed that what I thought was lots of fuel coming from lines.
As it turns out I believe neither of the tank pumps are pumping.
I do not think it is a case of them not working, but not coming on.
I think the old main pump what somewhat siphoning fuel out as best it could.
The new pump I put in the other day has only enhanced the problem.
Tommororo I will start a new search as to what the hell is causing the pumps to not operate.
Fuel tank switch.
will check voltage everywhere.
Im going to Hotwire pumps to check operation.

 

TAB/TAD are thermactor air bypass/diverter respectively. I believe the Hanes recommends using a vacuum pump/gauge and run power through and pump vaccuum , break the voltage and observe, then pump vacuum without voltage and run power again. I don’t have the book in front of me but I recall reading one is supposed to hold vacuum and break with voltage and the other is supposed to do the reverse. Don’t quote me here though, and do a bit of research to verify. I payed $7 for the hanes that covers all 1980-1990 bronco and f-series as well as the first few years of the 90s.
Keep us posted!!

 

Just saw the thread, not sure how I missed it. But, I would see if you have power to tank pumps before hot wiring them then check power at the tank selector switch. Maybe it's bad and not powering the tank pumps.

 

I did this today, powered the pumps through the whatchamacallit terminal for the code reader.
only the high pressure pump turned on.
I had changed the fuel pressure relay and am wondering what is the other relay beside it ? EEC?
Will do some reading of manual tonight to learn more.
I would have to guess no power at in tank pumps.

 

Check power at the selector switch. If it's not getting to the switch the problem is a relay or fuse. If there is power to the switch but not out then the switch is bad. If you have power in and out of the switch look between the switch and tanks.

 

And another day on the Ford.




Today I determined there is power out of dashboard selector switch to each of the fuel tanks.

I confirmed there is power to the terminals that attach to the tank pumps.

I ran a lead to the pumps direct to try to energize. Connected to 12v battery.

I was unable to confirm the the pumps are running, cannot be heard or felt.




With testing the power to dash switch and also trying to see if pumps were working I had to jump and ground a wire from port on computer plug in.

So several times I had the pumps going for a brief period in doing this.




I tried starting the truck once I found power at selector switch, I thought I may have wiggled the connection and perhaps things would now work?

The truck fired right up and is now running really bad, filled shop with smoke, black come in from tailpipe onto ground,shuddering and the odd backfire.




I shut the truck down and check timing, at first it dropped down to like 4 or 6 . I played with timing bringing it back to about 10 or 11 deg.

No change .

Pulled all spark plugs and they were black. Cleaned all and reinstalled.

Checked everything else I could but truck is still running the same.

With me running the pumps so much did I load it up with fuel it couldn't burn ?

Feels like a bunch of steps backwards for sure...still don't know if pumps works and I have fuel, and engine is in a bad way.


Just to get myself in deeper I've got a 88 Lariet showing up my yard in the am for a parts truck .
Its got buckets and console I will rob.

Appreciate any and all the input this far.

 

Since last post I have replaced both in tank pumps.
i now have fuel and can start the truck.
timing is rock solid.

BIG PROBLEM, I have gone from not enough fuel too now way too much fuel.
Spark plugs are fouled black, exhaust smell is extreme. Smoke everywhere.
Truck was running so well before and something has changed .
I have a parts truck now and can try parts from it, will do TPS, coil pack and that one left side of throttle body.

in diagnosing my previous fuel problem I have only done 3 things just before truck went bad.
I did a cleaning of TPS, again that one on left of throttle body, vertical guy with sensor on top, and I had the fuel pumps in continuous run mode.
All along any time I managed to start and run leading up to this point it has always sounded great and has never run with its now currant symptoms.

I read a 2 year long thread with a similar problem with hundreds of posts, th OP never solved the problem.

This Model of truck has a long history of ghost problems which is not sounding too positive.

 

if truck starts, and runs check your new fuel pressure regulator, by removing vacuum line and plug/cover with your finger, did fuel pressure go up, down, no change, what was reading before removing vacuum, then just to quick check your injectors, leave gauge hooked up and see how long it takes to loose pressure, if it drops fairly quick after turning engine off, maybe injector or 2 or 3 bad, my regulator(6 month old) went bad and fuel pressure shot up to 47 psi, (son said looked like rolling coal) he thought it was hilarious....not

 

I was looking at pressure tester and it held around 30 lbs after truck was turned off.
Vacume line off reg had suction on the end.
Because my supposed "fun" truck has become such an unreliable problem I bought another complete parts truck.
Today I changed coil pack, different relays, egr valve, inspected o2 sensor( brand new)
i really have no idea where to go at this point.

 

Problem may not be fuel. That ignition module on the side of the distributor is known to fail. Typically acts up when it gets hot when it begins failing. Just something to check. Sounds to me like a possibility. Ask anyone with an old 5.0 mustang, same deal on them. I hope this helps; Keep us posted.

 

Update, I managed to get the truck idling back to 90% of its original form.
Cleaned every ground I could find on truck.
Swapped map sensor from donor truck.
Unplugged ECT sensor.
It ran well enough to run codes, a 51 for the ECT being unplugged, a 90 something for a system failure and a 30? Which isn't in the book.
Started and restarted truck several times, felt to have good throttle, ran it for 10 min.
Was quietly optimistic that I may have made some progress with the map swap out.
Took truck round yard and it took about a hundred feet for it to start chugging and puking and running rich again.
Barely got it inside, it died and couldn't start it again.
The symptoms I've read about with a bad map sensor seemed to apply to my trucks condition.
It would seem I've got some other component telling my map to run rich.

 

Might want to check the MAP sensor vacuum line. Cheek to see if the vacuum lines (in general) haven't begun to crack. Common problem on these older vehicles. Also, check the EGR valve to ensure its not stuck open or remaining open. The EGR solenoid is supposed to vent the vacuum when its in the "OFF" state. A bad solenoid can hold the vacuum to the EGR in the OFF state.

 

Thanks, I've check all vacuum lines multiple times. Having the parts truck I had changed map, erg TPS , ECT sensors.
You know I'll have to rule out that the erg is actually working, have has it of several times and it is in the closed position.
So when I've got the truck completely cold it will start up and run really well...for 3 minutes.
i changed the ECT sensors the other day, I did not check resistance on then so can verify they are within range.
voltage gave me just under 5 volts.
Found out there is 2 ECT 1 to computer which is my new suspect and 1 to the dash guage.
Plan and hope to find resistance is out of range after work today.
My nieghbor remarked the other day that this truck is an enigma ...had to look up meaning in dictionary...and you know what ?it sure is. If the Basterd ever runs that's it new name! Enigma !!

 

I tested ECT sensor and determined proper voltage to it and ohms within specs.
That was a bummer since my code 21 I've been able to pull on occasion when the truck will run long enough to do so.
If the truck is stone cold it will occasionally start and run well for about 3 minutes.
Heats up adds more fuel and chokes it out.
Will not start again after this.
Could it be anything to do with my cooling system??
Top rad hose is rock hard and hot, new small leaks coming from rad.
Blew the heater core and waterpump failed.
Changed thermostat.
A blockage?
Rad cap?
Ford experts out there please chime in if there is anything you suggest I try out.
I want to drive this truck .

thanks .