Cruise Control Operation

[fester]

I not a ZJ person either but as stated if like the WJ then there is only the cruise on light and no other set light so it is possible the set switch could actually not be working either. You really need to start from scratch and work through all the system. Someone has mentioned codes, have you checked or have the ability to check. If the on light is working it makes sense the system is ready to accept input but make sure it is getting power where it should. Have you tested the cruise unit. If it is vacuum operated can you test it for vacuum, before you simply throw it out for a new one.

I am assuming the cruise has not worked since you purchased the car and not a recent incident. If recent has anything at all been done to the car that could have upset the system. You need to get your hands on a manual for it. Is it the same system as an XJ, if so maybe they can help you more. there's not a lot of ZJ guys left lurking around here.

[Nickw]

Originally Posted by fester

I not a ZJ person either but as stated if like the WJ then there is only the cruise on light and no other set light so it is possible the set switch could actually not be working either. You really need to start from scratch and work through all the system. Someone has mentioned codes, have you checked or have the ability to check. If the on light is working it makes sense the system is ready to accept input but make sure it is getting power where it should. Have you tested the cruise unit. If it is vacuum operated can you test it for vacuum, before you simply throw it out for a new one.

I am assuming the cruise has not worked since you purchased the car and not a recent incident. If recent has anything at all been done to the car that could have upset the system. You need to get your hands on a manual for it. Is it the same system as an XJ, if so maybe they can help you more. there's not a lot of ZJ guys left lurking around here.

I will buy a 'code tester' to plug in and see if i get any relevant error messages. I am not sure how i check the vacuum but u guess it will be easy enough to put the replacement unit about to arrive from the USA. The Jeep has dual fuel and yesterday i went over to Yorke Peninsula and returned about 16 litres for 100 km. Switching to petrol showed 18+ litres to 100km at twice the price!

[Nickw]

Originally Posted by fester

I not a ZJ person either but as stated if like the WJ then there is only the cruise on light and no other set light so it is possible the set switch could actually not be working either. You really need to start from scratch and work through all the system. Someone has mentioned codes, have you checked or have the ability to check. If the on light is working it makes sense the system is ready to accept input but make sure it is getting power where it should. Have you tested the cruise unit. If it is vacuum operated can you test it for vacuum, before you simply throw it out for a new one.

I am assuming the cruise has not worked since you purchased the car and not a recent incident. If recent has anything at all been done to the car that could have upset the system. You need to get your hands on a manual for it. Is it the same system as an XJ, if so maybe they can help you more. there's not a lot of ZJ guys left lurking around here.

I have a manual but it stops with advice telling me it needs specialist testing!

[Nickw]

The light comes on with the cruise button. As it never worked in my time i am not sure but there could be a fault in the set button. I guess i may need to get a Jeep garage to check it out. I think i have downloaded a full workshop manual so i will check that one out as well. Thanks for your advice.

[loggy1968]

the brake pedal switch has 3 seperate contacts inside it. 1 contact to operate brake lights . 1 contact to tell brake pedal up to be able to set cruise. 1 contact to to cancel cruise when you press brake pedal.the only way to test is to remove and test with multimeter. so your brake lights can be working but switch could still be at fault to stop setting cruise.

[Nickw]

Thanks for this suggested solution - I will locate and rmove the brake pedal switch or try to test it in location with the multimeter. I have a servo on back order and a diagnostic scanner to read the codes in the Jeep. I will progressively solve the problem and get the cruise working. Cheers N

[Doctor W]

Nick, are you aware that after turning on the Cruise Control, you then need to bring the vehicle up to speed (using accelerator) or close to the desired speed then press SET button and sometimes fine-tune speed using the RHS Accel/Resume button to go faster (about 3/4 kph each click or lower speed via holding down Coast button. You can go back a step by pressing Cancel once.

Have you got the Owner's Handbook to refer to as to how to operate the Cruise Control System?

Also are you aware that many installers do a pretty standard job on every model they do and that many MPI Jeep engines suffers damaging explosive backfires because of gas installations that are not liquid gas to the injectors with a separate control computer.