Ground strap location, Firewall to .....?

OK, I have been trying to figure out a speratic low idle issue with my XJ when a member to me to test the ground on the TPS. Sure it enough its bad and reading at over 4.8ohms. while doing that I noticed a funny looking un-used threaded hole in the fire wall right next to the MAP sensor. I looked at it and thought hmmm, thats odd, I wonder what went in there. Then I started thinking about it and remembered that the previous owner recently had the top end done when all of a sudden it hit me. Theres supposed to be a ground strap there going to the back of the head. So my question is:

Where exactly does it connect to on the head? Its really tight back there and I cant really see where it would go.

There are several head bolts that have a stud sticking up. The braided ground runs from one of these to the firewall. Make sure and clean the mounting place on the firewall to get a good connection.

Originally the braided strap ran from the firewall to the rear most head bolt/stud near the coolant temp sender. It's common practice to run a #4 gauge cable from the firewall, after scraping it down to bare metal, to the rearmost mounting bolt of the fuel injection rail where it mounts on the intake manifold..

Another thing to consider ... 5-90 makes an awesome set of replacement cables from 1-gauge welding cable. That includes battery cables, rear grounding strap, alternator cable, etc.

I read his website and made some for myself and am very happy with the design. If I were going to do it over again, I would probably just buy them from him.

What year is your XJ? The ground strap needs to be addressed first, but if you still have resistance to ground on your TPS circuit there is a fairly simple way to fix it. Does the resistance change if you wiggle the harness between the MAP sensor and TPS?

montanaman said:

Another thing to consider ... 5-90 makes an awesome set of replacement cables from 1-gauge welding cable. That includes battery cables, rear grounding strap, alternator cable, etc.

I read his website and made some for myself and am very happy with the design. If I were going to do it over again, I would probably just buy them from him.

Click to expand...

5-90 is one of the best assets this website has, and i mean his buisness no ill will however you could also just buy the cables at just about any auto parts store, they may not be exactly how long you want them, but it works all the same.

cruiser54 said:

What year is your XJ? The ground strap needs to be addressed first, but if you still have resistance to ground on your TPS circuit there is a fairly simple way to fix it. Does the resistance change if you wiggle the harness between the MAP sensor and TPS?

Click to expand...

My XJ is an '89 without the C101 connector. I didn't think to wiggle around the harness but any info you can give me will help

First off, make sure you refresh the grounds at the firewall to cylinder head and the dipstick tube stud. Everything must be clean and shiny with no paint or oil at the terminations. Then, check the sensor resistance. And yes, have your meter on the sensor ground wire, the brown with white tracer, and wiggle the harness between the rear of the valve cover and the TPS.