Normally I would be talking about my 71 GTO 455HO 4sp but this time I need help with my Ford 460 in my 34' Motorhome...........just think of it as a big hot rod!!

Last spring I installed a Gale Banks Power exhaust System/ram air. The increase in power was unbelievable. When I parked the Motorhome for the winter last fall it was running good. I started it at least once a month during the winter as usual. I have 44.000 mi on the motorhome. 8700 mi ago I installed a new rotor/distributor cap, spark plugs (Bosh Plat 4) and Accel hi performance ignition cables. The coil was not touched.

This spring I found it was still running as good as ever until the engine reaches normal operating temperature. Then even under light acceleration the engine runs very rough, shudders and lacks power. If it is stopped and cools down for about 10-15 min it will almost burn rubber when compared to when it is hot.

I have been a “back yard mechanic” all my life but I gave up and brought it to my local garage mostly due to the lack of the needed analyzers etc. I will summarize:

1. On their portable analyzer there were no codes to read but the EGR voltage was not according to spec so it was changed along with its sensor and then gave the right readings but did nothing for the problem.
2. Again on the analyzer the oxygen sensor kept switching in and out of a closed loop which could cause the motor to run lean – that was changed – still same problem.
3. I greed to try a “Motorvac CarbonClean Fuel System Service” (www.snapon.com) to cleanout the Injectors and any carbon deposits from the valves and piston rings. Still the same problem.
4. Since I have recently changed the fuel pump, I suggested to check it and its pressure checked out good and we tried it with their external fuel pump (RV pump bypassed) and the problem was still there so it is not in my installation of the new pump. Running the engine both ways the 460’s regulator provided 30 lbs pressure and the specs say 30-40 lbs is normal. I am a little bothered that the reg is at the lower end of the scale.

The next thing on the list this week is to do a complete engine analysis to check out the electrical system and see if the spark is breaking down, bad coil / sensor when hot etc etc. This takes about 2 1/2 hours. The garage lets me stay right with them as they troubleshoot so I know exactly what is being done. What has us baffled is that on their portable analyzer a lean condition shows up when acceleration lightly under load………..but why. Both a bad EGR and oxygen sensor could have caused this – since they are now new, we know that it has to be something else. The one thing they mentioned as they were not familiar with the Gale Banks exhaust is that the oxygen sensor is moved from the exhaust manifold (extension cable provided by Gale Banks) to much further down the exhaust pipe.. They were wondering if the oxygen sensor gets hot enough in this new location to give the correct readings to the computer – I think that Gale Banks would have thought of that. (I have called the Gale Banks Corp. and they said they have hundreds and hundreds of the system sold for 460's and this has never reported to cause a problem)

Has anyone ever had this problem with a hot engine? Please remember that it has unbelievable power until it gets to operating temperature. To be exact the problem happens precisely when the temp gauge gets to the letter “r” on “normal”!! (does not read out the exact temp but their analyzer showed the water temp to be 193f) Any suggestions would be appreciated before I have to re-mortgage the house to pay for the bill when I get it!