This page shows the areas you should ensure are well grounded. A =LOT= of wierd engine behavior is caused by poor grounds, especially on early XJ's!
This first diagram shows some of the major ground points to ensure are making good contact. Note that some of these are 'add-on' ground points! The factory wimped out and only used the harness and a braided ground strap located on the rear, driver's side of the head that then attaches to the firewall. If someone removes this ground strap (or it goes bad) then you will end up with all kinds of bizarre electrical and engine issues! Having wierd behavior you can't figure out?... Check your engine grounds and add more ground straps if necessary! (ESPECIALLY check out the TPS harness!)
The big kahuna of ground straps is the one running from the engine head to the firewall on the driver's side. If this one is gone... count on wierd engine behavior! On RENIX (Non-HO) 4.0L engines you should be on extra alert regarding your TPS ground wire! Check for leakage / high-resistance and if necessary install a jumper ground wire direct from the TPS side of the connector direct to the firewall ground.
Note 1 - The Throttle Position Sensor is VERY sensitive to poor grounds and the connector to the TPS often gets oxidized by moisture infiltration.
Go down to your local auto parts store and pick up a generic, pre-made battery ground cable that has an 'eye' on both ends. Attach this at the shown mounting bolt for the dipstick tube and then connect it directly to the frame / front chassis. (There are a couple of good locations - you'll have to crawl under and see for yourself!)
If you have pics of your own repairs or can suggest other methods - please contribute your ideas (and pictures) to this article!
February 7th, 2007