1993 Ranger XLT 4.0 AT. Initially replaced ECM for other problems and then noticed Cruise w/n disengage when brake depressed unless pedal is pushed several times and with more pressure. Put in another ECM and have same problem. Have replaced the brake switch and lights come on as they should. When pedal is pushed the vacuum dump valve on the pedal will dump the vacuum to the servo but when you release the brake pedal the cruise control kicks back in and speeds truck back to set speed. So this tells me that the dump valve is only a fail-safe feature for when pedal is depressed and does not actually deactivate the servo. Everything else with the cruise works fine: On/Off switch, Set/Accelerate, Resume, Coast. Can anyone tell me how to proceed next? Like where to find speed control module and how to test it? How to check servo to see if it is getting or dropping voltage that will electrically disengage it, etc? Don't want just throw parts at it. The new ECU's that I used came from ECU Exchange in Florida and there still remains the possibility that they are still the problem. Any help or suggestions will be appreciated.
Look at your brake master cylinder. If there is a switch located on the end of the cylinder casting, that is also a cruise control cut off. Someone may come along here and advise you how to test it without actually having to throw good parts at unknown parts.
When you say you replaced the brake switch are you talking about the one on the brake pedal that has five wire going to it? This exact switch may only be on newer models than 93, but one of the 5 wires goes to the cruise control cutoff when the pedal is pushed in.
Hi ranger pat, there are no switches on my master cylinder. The only wiring there is to resevoir low level switch. The brake switch I replaced is the brake pedal switch that turns on the brake lights and has only 2wires. I found a site last night, "www.thorssell.net/hbook/ccexpl.html" that explains how it works. It says that the brake light switch wiring goes to both the brake lights and to the speed control amp. Guess my next step is to find this amp and put the meter to it and see if I am getting the input and output signal going to servo. The brake lights come on like they should. Thanks for your response.
Found possible cause today. Hooked up voltmeter to brake switch wire at the speed control amp and monitored it while on a trip. I found that while in cruise that when brake pedal is depressed to slow down, that the vacuum dump valve kills cruise when pedal is lightly pushed, but when pedal is released the speed goes back to set speed. Watching meter, the amp gets no 12 volts under this condition. Doing the same action but pressing harder (further down) on pedal the amp gets the 12 volts and shuts off cruise as it should. This tells me that the dump vavle is activating before the brake switch. Now I need to see how to adjust these two items so that cruise is controlled by the switch before the dump valve as the dump valve is supposed to be a fail-safe device to make sure servo has no vacuum while braking. I did replace the brake switch after this problem showed up but only checked to make sure brake lights came on. I did not look to see if there is an adjustment mechanism at that time as lights worked, so something got out of kilter before replacing switch. I did try another amplifier before actually seeing what was happening.
If anyone can tell me how to adjust the brake switch and dump valve to get this right it will save me some research and that is a tough area to get to (being a big guy)
trying to see what you don't know what you are looking for :-) :-)
I don't think mine is adjustable either by just looking at old switch and knowing how it is installed. Nothing mentioned about adjustment in Haynes manual. Maybe I can do something with vacuum dump valve. Nothing in Haynes manual on this valve. Will ask mechanic friend at local Ford dealer. Will check that out later.