Absolutely Stumped

I own a 92 RV on an E350 chassis with a 460. I am having a drivability problem that even the Ford dealer has not been able to solve. First the outside tempature must be above 90 degrees. When I am pulling a grade in second gear around 25 to 35 mph. After a period of time I notice a loss of power and slight missfire. At the top of the grade, the engine will shut down. The engine temp is normal. The engine compartment is warm and it is always hot outside. If I let the unit cool for 30 minutes, It will start and run fine. Once again this only happens when pulling a grade at slower speeds when it is hot outside. Remembering some of the problems with ford ignition problems in the early years, I suspected this was the problem. After a breakdown I have been checking the module which sits in a heat sink on the fender well and it is pretty hot. I took the vehicle into the local ford dealer and he kinda agreed with me. Changed the module and the stator. I was out this weekend going up a 11 mile 7% grade and same problem. Hmmmm. The module is mounted on the left fender well behind one of the batteries. I am now thinking it is not getting enough airflow to cool properly. I think in 93 or so they moved the module to the distributor which would allow airflow from the fan. Maybe this was a fix. I am preparing to relocate the module. Has anyone seen this problem before or any other ideas?

Yes it could be a hot module but maybe it could be fuel pressure. Tape a fuel pressure guage to the windshield and try it the next time. Watch the pressure when you loose power. Also try some Top Tier Gas. You might be getting a vapor lock with the hot gas.

I know faulty plug wires will arc out and fail under a load on a hot day. If you haven't had new wires within 60,000 miles it would be good to replace them. But, if the problem is heat to the ignition module I agree with you. Mount it in an airflow someplace. If that can't be done because of the wiring you could run some fabric duct tubes like are used for the air flow under the dash from the outside air in front of the engine to the ignition module. I have used some of that type of material to run a cold air intake to the throttle body of my car. It works well.

Hi
You may aleady have solved it by now but I just found the site . If it helps any I had a similar problem. It would always start and go but a few miles into it the engine would start to misfire and gradually get worse to the point of being unreliable .I never loaded it up to where it would stall. After several Dealers, one of whom told me the engine was shot and there was hydrocarbons in the coolant I found a local shop who pinpointed it the PLATINUM plugs had reached their usable life. Apparently platinum plugs don't show the waer on the tips ( I looked) they break down internally from heat and load and start to misfire. I put a change of plugs in and haven't had a problem since.

Phil

Thanks for the info. Spark plugs are one of the easiest culprits to fix. I knew it was either the wires or the plugs. Did it have Motorcraft or Autolight plugs? The resistance of the plugs will increase until they misfire under a load. I'm glad you got it fixed.

Heh. I had the same problem with an old Windsor. It would heat up and die. Only when it was hot. Once it cooled down it would start right up.

Turned out to be the mechanical fuel pump. Changed that out and it ran like a champ.