Ford Guy's Need Help

[fishseeker]

I have a 90 F53 M/H Chassis 460 F.I and its driving nuts. Bought in July last year. Only made it 1 mile before it quit. No bigie,had it towed( thank God for AAA RV). Replaced fuel pump in Dec. and it made it about 30 miles then went into limp mode. Pulled fuel tank and cleaned it. Made it about 20 miles and back into limp mode. Fuel peasure is at 40psi at fuel rail with key on. 30psi at idle. Drops to 20 when you give it throttle. Replaced fuel reg., TPS is working as should. ICM replaced. Bad Computer? Bad wiring in new pump? Replacement pump assembly is Motorcraft PFS 48 for 75 gallon tank. New gas. I'm at loose what to try next :bash:Voltage is good.

[hrd2fnd]

trade it in for a Chevy LOL. I'm sure someone here can help with ideas

[12Gauge]

Take it to a repair shop for diagnostic, should run you about $100. 

[fishseeker]

Take it to a repair shop for diagnostic, should run you about $100.

Kinda hard to take a 34' Motorhome that ain't running to a diagnostic shop.

[hrd2fnd]

is it throwing any check engine codes? are you able to read any stored codes

[Sunbkpk]

Sounds like you may have a restriction some where. Could be a kinked or smashed fuel line. Too long a fuel line with many bends can also drop pressure.

You could check the flow rate at the engine versus earlier in the fuel line to see if you are getting sufficient volume.

[Kowsrule30]

Fuel lines can collapse with age... Or could possibly be clogged... You didn't say you replaced the filter???

[gaddy]

pluged tank vent ?

[raydog]

might be vapor lock?

[coachcw]

you need at least 30-32 psi to make the injection work properly . just take the fuel cap off to see if tank vent is plugged but I doubt it , it would take a while to put that 75 gallon tank into a vaccum, i'd follow the fuel lines forward and look for a fuel filter inline , some fords had both  a sin on plastic filter and the standard fg800a steel filter . if it has the spin on filter just disgard the element the steel inline will be plenty but make sure its free.also look to see if a line is pinched when the tank went back in .

[fishseeker]

Has new filter,only 1 inline plus sock on pump. have 13' on top of tank clear no kink. Gas cap off. Think I'll drop the tank again and retrace the lines. Not fun. Maybe use the compresor and blow the line from fuel rails back. Do a test on wiring on fuel pump. Just don't make sence. May take the computer in for testing.

[coachcw]

you may also check your gauge I've seen the shrader on some testers not allowing for enough flow so you get a false low preasure reading . if your gauge has a dump valve dump it while running and see if it stays running if so your volume is good.

[coachcw]

you may be barking up the wrong tree , all early fords with the 60 pin cnoector at the pcm use pins 20 40 and 60 for grounds I use a 4651 head lamp bulb to test power and grounds on the pcm if it will light a head light bulb the grounds are fine . pull the coil wire and crank it over make sure you have a white hot spark not just orange . I've also seen guys put a 4/6 cylinder ignition rotor in the cap causing to big of a gap , s pop the cap and make sure the rotor says 8cyl on it .

[Heredoggydoggy]

If you drop the tank again, make sure the fuel pump intake isn't pressing against the bottom of the tank hard enough to cause a blockage.  Those 460's drink a lot of fuel, and any restriction could cause starvation.  same thing was happening to my '90 Bronco II, but the 2.9 V6 didn't mind it anyway.  The main problem was that water and grime were being thrown off the tire onto a crack in the filler hose and destroying the fuel pump.  When a mechanic listened to the pump, he said that he could hear the pump start up, then sat there and "growled".  Changed the pump and haven't had a problem since, once I put a new filler hose on.  That year the gas filler hose was a small tube inside the bigger outer hose that served as the vent for the tank.  the crack in the outer hose was letting crud into the tank.

[coachcw]

most those ford mhs have a moded tank and ad ons to the fuel lines . if the pump pick up is on the bottom it should be screaming . I've seen voltage drop across fuel pump relays and the roll over switch connectors . the roll over switch is often mount on the passanger side under the dash.

[philepe]

Does it have dual tanks?  Does it have dual fuel pumps, 1 in tank and 1 on the frame rail?  If dual pumps it sounds like one pump is dying.  I think the rollover switch he is referring to is the "inertia switch".  Check for voltage drop across it, super easy with a voltmeter, check you tube if your not sure how.