engine ground to firewall
 

On the back of the 4.0 engine block (97) is a tape-like ground 'cable' between engine block and firewall. Mine is somewhat smugged with old oil/grim etc and I'm currently cleaning up the grounds.What does this one ground for? (in other words, if I would refresh this one, what would that possibly do/improve/prevent from happening?)

That puppy there provides the ground path for the spark plugs back to the battery, among other things. It's pretty susceptible to corrosion. Very highly recommend replacing it. If it's bad it can cause misfires, stalls, hard starts, etc. You can replace it with a 4AWG cable or higher. I was lazy and bought a 1 AWG starter cable and drilled one end out so it would fit over the head bolt... the thinner cables I would have had to drill out the connectors on both ends. :cheers:

Mine isn't even connected and i have no problems at all.... Weird

You're talking about the one that goes from the driver's side rearmost head bolt up to the firewall correct? I actually just replaced this cable today with some 4AWG wire because mine was caked with oil. I saw no difference at all after replacing it.

This is the response I got from Jon at Kelley's Works in Progress (who makes some quality battery cables) about this wire: "The cable you're talking about runs from the rearmost stud on the cylinder head, driver's side, and goes up to a screw on the firewall above it just a bit. If you're missing this cable (read: it's been removed by a previous owner,) you'll want a 7/16"-14 nut for the head stud, and an M8-1.25x20m/m screw for the firewall.

I'm not sure if it can be reached forward to a different screw for your year yet - but I've also attached that lead to the rearmost fuel rail mounting screw on RENIX - which is much easier to access (this screw should be 5/16"-18x3/4", if you need one. But, I doubt it.)


While removal of this cable would be a significant problem for RENIX - as it's the only OEM chassis ground, and the ECU grounds to the chassis inside the cabin - the Chrysler-spec rigs have a dedicated chassis ground to the battery, and therefore a direct ground path. However, that cable should be maintained, as it provides a redundant ground connection between the engine and chassis (which improves the "zero reference" for the engine management sensors.)"

Check out his website: http://www.kelleyswip.com/index.html

Just for my reference, whats a 4AWG cable?
(and yes, I think we're talking about the same cable, but my driver side is on the other side, since in Oz ;)

4 gauge wire.

AWG = American Wire Gauge. Here in Canuckistan we're supposed to be metric but we import so much from the States its hard to keep things straight. The crossection is 21.2 square millimeters

Thanks for all this, gives me some idea for a replacement.

Canuckistan. That's funny!!!!!!!

You will eventually. Replace it; it is a CRITICAL ground point!!

I've been driving it like this for about 5 months now without a single problem pertaining to engine to body grounding.
Though. I did re bolt it on today i see no difference. Its the same tape-like metal grounding wire am i correct? I see you guys talking about 4 gauge wire, is it really important?

It is to us. It was an under-designed/under-engineered system to start with . Do what you feel is best for you.

And generally speaking, if both Cruiser AND Mr Walker advice on something (the same), it tends to be something to take their advice on (if you really have no idea).

X2

Roler,

In researching this ground strap on my '99 XJ, I've found that its purpose is to eliminate (reduce) radio noise.

Here's the text from the 1999 XJ FSM concerning radio noise suppression (same for '98 and '00-'01 and essentially the same for '97):

RADIO NOISE SUPPRESSION

DESCRIPTION

Radio Frequency Interference (RFI) and Electro-Magnetic Interference (EMI) noise suppression is accomplished primarily through circuitry internal to the radio receivers. These internal suppression devices are only serviced as part of the radio receiver. External suppression devices that are used on this vehicle to control RFI or EMI noise include the following:

· Radio antenna base ground

· Radio receiver chassis ground wire or strap

· Engine-to-body ground strap

· Resistor-type spark plugs

· Radio suppression-type secondary ignition wiring.


The above statement is essentially the same in the 1997 FSM but has the following statement concerning the Engine-to-body ground strap:


“Engine-to-body ground strap (if the vehicle is so equipped)”

The radio receiver chassis ground is located at a ground terminal designated G108, which is located on the instrument panel frame structure near the headlamp switch. The engine-to-body ground strap on the firewall provides a close proximity ground path to the radio recever chassis ground point.

Note that the '97 FSM description differs from the '99 FSM description only that it states "if the vehicle is so equipped". Not that it makes any difference here but apparently there is a posibility that the '97 XJ may not have this strap if there is no radio installed.

Earlier XJ's may not use this ground strap strictly for this purpose.

Braided ground straps sold at Advance Auto Parts, and elsewhere, are suitable for replacement if your ground strap is no good. I think a large gauge cable would be an overkill in this application.