Running poorly

  • 1996 FORD F-550
  • 7.5L
  • V8
  • 2WD
  • 83,310 MILES
Actually, this is a 1997 Rexhall Aerbus motorhome on a 1996 Ford F53 stripped chassis with a 7.5L gasoline engine. The engine is where the problem is, nothing with the motorhome. We were driving the motorhome to park it at what will be our "home away from home, which is about 185 miles. At about 140 miles I started noticing some very short hesitations, which quickly grew into popping through the carburetor, stuttering, and a general loss of power. By the time we got to our destination I was down to a max of about thirty five mph. If I tried for any more speed it would pretty well shut down completely - sounded like someone had completely covered the intake. But it made it to our lot and we got it all setup spending about a week doing it. Came back home for about a week and went back to stay another week, taking a new fuel filter with me. I installed it, started it and it would "goose" just as hard and long as I would hold it. Spent another week and came back home. Then here comes Harvey and we decided to evacuate it back home - the day before mandatory evacuation was put in place. Got about fifty to sixty miles back up the road and it started throwing its fits again. Luckily there was a small RV park where this happened and he let us park it just off beside another space. Continued home, Harvey came and finally went and went back down with an OBD-1 scan tool I purchased. When I started it it was as if it was all fixed - rev up as high and long as I wanted to. But went ahead and ran the scan tool with the following results.
Engine Off
172: HEGO HO2S sensor fault/lean
334: EGR Valve Voltage high
Engine On
412: cannot control RPM during KOER high RPM check
531: invalid cylinder balance test due to throttle movement during test
632: overdrive transmission cancel switch/no action during self engine run test
All of the "popping", jerking, jumping, loss of power seems to start at about 2200 rpm. And then when the problem starts the Tach goes crazy - jumping all over the place. But the engine is not doing what the tach says.
So since the engine seemed to be doing okay, and it might still be 1-2 weeks before they will allow us back into our property, we take the motorhome to a very nice park about 25 miles away. The nice folks at this park were giving RVer's that were evacuating their RV's half off until they could move them again.
Anyway, about a week later, we decide to bring the motorhome home. Got her up and running and on cruise at about sixty five. Fifty miles down the road it starts throwing its fit again. We pull off and wait for twenty minutes. Start it up everything okay again. Another twenty miles down the road, same thing, only this time we had only waited about five minutes. So we waited another ten minutes and made the next twenty miles home. Although, it did hesitate very slightly a couple of times just before we drove in our driveway. It did not appear whether we waited a few minutes or twenty minutes after shutting it off.
The fuel pump was replaced with a "new" style at about 70,000 miles. New high end plugs and wires at about that same time. Changed distributor cap and rotor just before we brought it home this last drive. There is a 1997 Ford truck owners manual in the motorhome, but since it is set up for OBDI, it is most likely a 1996. The book says it is OBDII, but the engine in the motorhome is not. This is about to drive me nuts!
Wednesday, September 20th, 2017 AT 2:55 PM

1 Reply

  • 44,374 POSTS

The key is when it gets hot and the tachometer jumping around. It sounds like you have an ignition coil that is going out. It would be difficult to test because it only breaks down under load.

Is the coil leaking by chance?

Please let us know what you find.

Cheers, Ken
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Thursday, September 21st, 2017 AT 2:50 PM

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