Hey guys, I figure while I'm asking advice, may as well address cruise control as well. I have only had this car a couple of months, but am sorting through it, all the while nursing my 89 XJS convertible back to a clean bill of health. The cruise on this car didn't work from the first time I tried it. Drove it 800 miles home, tried it several times, but never got it to work. Any advice on where to start? Would drive it a couple of thousand miles on business this week, but not crazy about hitting the road with no cruise.

 

Hi superchargedtr6,

Sorry that I haven't seen your other posts so I don't know what year and model of the car with the cruise control malfunction - it's always a good idea to include that when starting any thread, and to also add the info for all your Jaguars in your signature line. It will also be helpful to know some more details about the cruise behavior. Does nothing happen when you try to engage the cruise control? Does the dash cruise indicator illuminate? Any other details may be helpful. Below is a link to the X300 cruise control system parts diagram (with identifying part names), and below that is the diagram itself:

Speed Control Equipment - Parts For XJ Series from (V)720125 to (V)812255 (X300) | Jaguar Classic Parts UK



On our '93 the dump valve stuck open (part 2 in the diagram), preventing the system from developing vacuum. The dump valve and pump are on the front left inner fender/wing near the air cleaner box. The purpose of the dump valve is to immediately release the vacuum from the cruise control system whenever the brake pedal is applied or the cruise control system is switched off. You can test the dump valve by removing it from the fender, blowing through it to see if it will pass air, the applying 12V to the electrical connector to see if it will block air (it should not pass air with 12V applied).

The vacuum diaphragm in the speed control actuator is known to sometimes fail (part 3). The actuator is near the throttle body and its linkage attaches to the throttle body. You can test the actuator with a hand-operated vacuum pump to confirm that it will move under vacuum and will hold vacuum when left for a while.

If the purge valve has failed, I don't think the system will turn on at all. If the actuator has failed, the system may turn on but will not control the speed.

Electrical problems are not unknown, but mechanical problems seem more common, so I'd check the dump valve and actuator first. Please let us know what you find.

Cheers,

Don

 

Thanks Don! I am leaving for a few days, but will check all of this next weekend. Not sure how to post my car info, as I tried in my profile, but this car is a 97 XJR, VIN#791541. The cruise does not activate at all. No light, no anything.

 

It may or may not be relevant, but I read somewhere that if your ABS isn't working, then as a consequence, your cruise won't work either. Might be worth considering.

 

Hi superchargedtr6,

In addition to a possible ABS fault mentioned by sogood, there is a brake pedal switch which disables the cruise system when the pedal is applied. It would be worth checking that switch for proper operation. If you don't have the X300 Electrical Guide, send me a private message with your email address and I'll send it to you in pdf form. Figure 08.1 of the manual shows the cruise control circuit ("Speed Control" in Jaguar terminology). Unfortunately, the link at Captain Jaguars where the manual was previously available for download has been down for a few months.

Cheers,

Don

 

I posted in another thread about finding two vacuum lines loose today. They both have a pinkish stripe on them. Now wondering if they might have something to do with my cruise, AND my anti knock codes/check engine light?

 

I'll have a look tomorrow but I'm pretty sure one of the pink stripe ones does go to the cruise control "vacuum" bulb thing usually found next to the throttle body on N/A motors

 

AlbBolivar,

Could the vacuum bulb thing you are describing be the "speed control actuator," Part 3 in the diagram that I posted on 6-22? Both the EPC and jaguarclassicparts.com show that the part number for the actuator is the same for the 3.2L and 4.0L engines but different for the 6.0L engines. They do not indicate whether the supercharged 4.0L uses the same part as the N/A 4.0L.


Superchargedtr6,

Can you check the components shown in the parts diagram to confirm that all their hoses are connected?

Don

 

I will do my best. When looking under it, very hard to figure out what goes where, until I "know" this car.