P38A Cruise control

Andy_J · Aug 8, 2023

Hi All

Before I go on a wild goose chase, just wanted to check the operation of the cruise control.

I have 4.6 petrol and have already replaced the cruise vacuum pipe across the back of the engine.

When my cruise is set it doesn't hold speed probably. It will set and hold the speed for about a minute or 2 then start to slow off, once the speed has dropped by about 2-4 mph it will accelerate back up to the cruise speed.

Is this normal operation or do I still have vacuum leak somewhere.

Thanks
Andrew

kermit_rr · Aug 8, 2023

Mine never held its speed spot on like a modern car, i assumed because it was mechanical and not electrical.
Check it's adjusted to the right feyw play and it's on the correct cam. The cruise is a steady curve, the accelerator pedal is not, you can easily spot the difference

pwood999 · Aug 8, 2023

Unlikely to be a leak, but worth checking the small pipes inside the vacuum control box attached to the bellows.

aj1954 · Aug 8, 2023

I found on mine it held steady at higher speeds, never used it under motorway speeds.

Andy_J · Aug 8, 2023

Thanks for the replies, I will give the other pipe work the once over and test the control box.
Still better than no cruise at all

pwood999 · Aug 9, 2023

Also check the cruise cable & throttle cable are the correct way round, and adjust them if the gap is wrong.

Assuming your P38 is the 2000 Thor in your sig:

P38A Cruise control

Andy_J

Active Member

kermit_rr

Very

pwood999

Well-Known Member

aj1954

Well-Known Member

Andy_J

Active Member

pwood999

Well-Known Member

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