Mark V Cartier - 400 engine - Cruise Control accelerate slowly instead of constant speed

PIFOUBMW

Junior Member
74
14
8
France
Hello from France,

When I bought my MARK V 400cid, the cruise control was not working at all. After some checks, I saw that the speed sensor D4AF-9E731 was out of order, (no 40 ohms resistor) , then I replaced it with a NOS from Ebay.

Now my cruise control is working but when I choose a speed, I see that slowly the speed increase instead of be a constant speed. I just received today another cruise control vacuum servo D6SA-9C735 and the little valve but problem still the same then I don't know what could be the problem.

My carburetor is not the original Motorcraft 2150 but a HOLLEY 5925-3 80500-1 2438 500 CFM STREET AVENGER Holley 0-80500 500 CFM Street Avenger Carburetor But vacuum comes from the intake manifold then it shouldn't be a cause.

Does anyone already had this trouble and have an idea of what to repair or replace ? may be could the electronic module D7AF-9D844-AA be defective because it is the only part not replaced but It seems working fine. Could the second vacuum servo be defective too ?

Any help ?

Thanks,
 

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michaelt62

New member
12
3
3
PA
Check to make sure that the servo chain is adjusted correctly(too much slack will cause slow reaction time). Also make sure to check for vacuum leaks(or just replace vacuum hoses).
 

michaelt62

New member
12
3
3
PA
Hoses always look good, but the best way is to use a Mighty Vac vacuum tester to check the whole system (hoses, valves and reservoir). The reservoir is inside the driver's side fender near the vent louvers and is actually a coffee can with a vacuum nipple. They tend to rust out where the mounting bracket is attached. The chain adjustment is listed on page 37-01-21 in the shop manual volume 3 Electrical
______________________________
 

PIFOUBMW

Junior Member
74
14
8
France
All hoses seems OK with no rust and I just received a new cruise control module from rockauto which is different of my original and problem is SOLVED ! 🙃

When opening the cruise control module, we can see capacitors which could be replaced, I will attempt to repair my original cruise control module.

There is a variable resistor, may be it permits to adjust the up/down speed for the cruise.
 

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PIFOUBMW

Junior Member
74
14
8
France
Good news, after the replacement of the 5 condensators, it's perfectly working then problem came from the condensator as expected.
 

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