Hello All,



I got the 'new' XJS ('85 US Spec V12) home and cleaned up (awesome car very low mileage, last painted in late 80's under warranty!), and have been tending to a few things, however I have a question pertaining to partial throttle.

Once the car is warmed up, she pulses while under 1/4 throttle. Once you give it the Welly, there are no issues.

Is this a function of the EFI (design) not liking partial throttle, or do I need to check for more air / vacuum leaks? Or??

Job one was to pull the distributor cap and re-glue in the vent ports (cap was otherwise brand new), as one decided to roll around in there (ack) when I pulled into the drive! Thank goodness for good timing!

Love the car, the suspension is a bit tired, but otherwise, she is sweet!

Cheers and thanks for the help.

Jeff

 

The 'could be' list might get a bit long.

But, ya gotta start somewhere so I'd make sure that the throttle bores are clean, the throttle blades gapped at the proper .002", the linkages synchronized, and the throttle bushings are intact. These are the bushings at the bellcrank part of throttle linkages where they bolt to the back of each inlet manifold.

Post back with any questions

Cheers
DD

 

Throttle potentiometer? Perhaps it's losing signal at the 1/4 mark? But then it would do that when the engine is cold too.

Shouldn't be a vacuum leak, not at that speed.

 

Just a follow-up and thanks to Doug, the throttle plates were not opening in sync, a quick adjust seemingly cured 75% of the issue, and I suspect the second issue I just discovered on the test drive is the cure for the balance, namely the pool of gas I now have in my trunk..

The bottom of the fuel pump is leaking through the plastic base (cracked). Also appears the original fuel filter is in the car, so click to buy both!

Am I ignoring another issue if I don't crack open the tank sump and check for nastiness??

Thanks again.

Jeff

 

Fluttering under light load could be the distributor cap (assuming your car does not have coil-on-plug engine) arcing; easy way to check is to run the engine in the dark and watch the distributor, the blue flashes will show if there is a problem.