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weschaney's avatar
weschaney
Explorer
May 11, 2017

Ford 7.5L 460 loss of power when hot

Hi guys, i just acquired a 1991 27' fleetwood class c rv. It sat for about 8 years before i bought it. I've since drained the old gas, new fuel filter, trans flush, motor flush and new battery. It fired up and ran like a champ for about 300 miles. Now I'm having a issue where after driving for about 5 miles and reaching running temperature it bogs down so bad it won't down shift and will eventually stall if you try to accelerate at all. After it sits over night it runs strong, for about 15 min.. then gradually bogs down till i have to pull over. revs fine in natural, so this is a issue under load. I took it to a trans shop, they said not a trans issue in their opinion, feels like a clogged cat to them. i removed the cat, still has has the same problem. any ideas?

THANKS FOR ANY HELP!!
  • Jerrybo66's avatar
    Jerrybo66
    Explorer
    Aug 21, 2017
    Thank you so much..
    So many times folks ask for help, many members take time to give their advice then if it works, that's the last of the OP. There were so many options here that made sense that we needed the final result. You're a good poster.. Thank you..
    Jerry
  • weschaney's avatar
    weschaney
    Explorer
    Aug 02, 2017
    Sorry for such a late update to this, but my assumption was right. Pulled the tank out and the pump was so rusted I can't believe it even ran. Installed a new tank/pump and now runs good as new!
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    May 15, 2017
    Back in the late 80's when folks begged me to cure repeated failures in the distributor mounted version of this nightmare I found Ford in their infinite ignorance of things electrical decided to use silicone GREASE as an interface between the aluminum module base and distributor. I replaced with TRANSPO manufactured modules and white zinc oxide thermal compound and that was the end of the issue. I was around 5 additional years to witness no further failures. Ford also used wires with crummy insulation INSIDE the distributor. have doubts? Look at the wiring insulation of the 2/0 diesel battery cables.
  • Horsedoc's avatar
    Horsedoc
    Explorer II
    May 15, 2017
    Fuel line getting too hot and vaporizing fuel before it gets to the EFI maybe? Is the insulation still on the line?
  • Gdetrailer's avatar
    Gdetrailer
    Explorer III
    May 14, 2017
    weschaney wrote:
    Hi guys, i just acquired a 1991 27' fleetwood class c rv. It sat for about 8 years before i bought it. I've since drained the old gas, new fuel filter, trans flush, motor flush and new battery. It fired up and ran like a champ for about 300 miles. Now I'm having a issue where after driving for about 5 miles and reaching running temperature it bogs down so bad it won't down shift and will eventually stall if you try to accelerate at all. After it sits over night it runs strong, for about 15 min.. then gradually bogs down till i have to pull over. revs fine in natural, so this is a issue under load. I took it to a trans shop, they said not a trans issue in their opinion, feels like a clogged cat to them. i removed the cat, still has has the same problem. any ideas?

    THANKS FOR ANY HELP!!


    Your engine most likely has the notorious Ford TFI (Thick Film) ignition system which is well known for STALLING, DIEING AND SPUTTERING and other drive ability issues WHEN HOT..

    Also well known for wiring randomly grounding out..

    HERE is some helpful info on the TFI ignition systems..
  • time2roll's avatar
    time2roll
    Nomad
    May 14, 2017
    Ignition will usually cause rough running or stumble pretty harsh.
    Smooth loss of power still sounds like fuel.
  • allbrandauto's avatar
    allbrandauto
    Explorer
    May 14, 2017
    if fuel pressure and volume is good next step is looking at computer system do you have a cheak engine light on with ign. on engine not running does it go out when running if yes you don't have computer problem
  • Gjac's avatar
    Gjac
    Explorer III
    May 14, 2017
    Wes this may be a long shot but some times coils fail when they get hot. What temp is your eng at when you lose power. Also when I first got my MH and was losing power I started the engine at night at saw that the ing wires were leaking to ground, there were sparks all over. These 460's and 454's generate a lot of heat, I end up going to 10.4 MM wires and headers to fix the problem.
  • bigfootford's avatar
    bigfootford
    Nomad II
    May 13, 2017
    weschaney wrote:
    Jim, it bogs and bucks, in neutral i can control the rpm fine, only when under load (in drive) it starts to buck and bog. The more research i do I'm finding a difference between fuel pressure and fuel volume. in some instances you can have good pressure, but the pump can be so clogged the volume is compensated thus starving the engine of fuel. kinda weird and hurts my head. I plan on testing the pressure while driving today. Thank you for the info.


    Do you have 2 tanks or just 1? 2 tanks has a pump in each tank. Two tanks two pumps it is easy to evaluate.

    Both my trucks have the 2 tank thing... My 89 had 1 pump for both tanks and my 04 has 2, one in each tank.

    Yes it does sound like it is intermittently encountering a fuel delivery problem...

    Measuring the fuel pressure will not separate a failure between the regulator and pump.
    Well there is more, it could be electrical but I rather doubt it because as soon as you relieve the demand for flow, back to idle the engine does not die.

    So if you were to power brake the rig upon failure and you are sitting the engine will bog there too? Power brake= in gear, depress the brakes and give it the gas not floor it but like you are going to take off.


    UGGGG.

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