ls swap engine grounds
ls swap engine grounds i have a 4.8 turbo in my fox just changed over from a n/a 5.3 to the turbo 4.8 any ways now im having crank sensor cam sensor codes I think it is a ground problem, it does run just floods out the plugs with fuel I do have my battery in the trunk was looking to see were the swap guys are running engine grounds
My trunk mounted battery is properly grounded in the trunk. The two grounds that were a part of the engine wiring harness I attached to the back of the head. I have a 4 gauge cable grounding the chassis to the block near the driver's side alternator mount.
On The Tree
Joined: Sep 2015
Posts: 145
Likes: 0
I was also wondering about this after finishing my swap. I am going to add a 1 gauge ground from motor to frame (I have a 14 gauge wire currently installed) and the only other ground is the Speartech ground on the back of the head.
Don't just run a bolt through a random hole in the frame and call it good. At a minimum clean all the gunk, crud and rust off the spot you're going to place the ground. Even better, do all your cleaning then weld a stud to the frame and secure your ground to that stud with a nut.
No matter what never use self tapping screws as a ground. I can't tell you how many times I've repaired this when troubleshooting random electrical issues.
No matter what never use self tapping screws as a ground. I can't tell you how many times I've repaired this when troubleshooting random electrical issues.
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Always get flack for this but I'll post it again about battery in the trunk and using the frame for a ground. Copper is the best conductor used in automotive wiring. Lets give that a value of 100 percent. Compare that to brass and brass is only 22 percent and steel is 16 percent! Run the proper size ground cable from the battery to the starter mounting bolt and branch from there to body and frame. By all means use star washers and dielectric grease.
Use your DVM/ohm meter and check your grounds -- that is the best counsel. Notwithstanding 33willys counsel above, based on my measurements, there is zero difference (0.00 ohms) between my ground at the battery terminal in the trunk and my chassis grounds under the hood and in the passenger compartment. I've checked them -- standard procedure any time a new ground is created. Copper may conduct better than steel --- but you've not accounted for HOW MUCH steel you have in between the trunk and the front of the car. WAY more metal for the electrons to use than you can achieve with a copper cable. I've owned a number of cars with OEM rear seat and trunk mounted batteries. 100% of them have the battery grounded to the chassis within a foot of the battery location. None of them had a separate ground cable from the ground terminal of the battery to the engine/compartment. There's a reason....and it's not because they're trying to save a $.
On The Tree
Joined: Apr 2014
Posts: 192
Likes: 1
Always get flack for this but I'll post it again about battery in the trunk and using the frame for a ground. Copper is the best conductor used in automotive wiring. Lets give that a value of 100 percent. Compare that to brass and brass is only 22 percent and steel is 16 percent! Run the proper size ground cable from the battery to the starter mounting bolt and branch from there to body and frame. By all means use star washers and dielectric grease.
Launching!
Joined: Aug 2015
Posts: 206
Likes: 11
From: Duvall, WA
There's a huge difference in resistivity between aluminum, copper, and steel, but it's important, as Michael Yount points out, to note that there is a LOT of steel in a car body. Resistance is inversely proportional to cross-sectional area.
Here's an example, using some rough numbers:
Let's say you've got a 1/0 gauge copper wire. That is a nominal 8.25246 mm diameter, and has a cross-sectional area of 53.488 mm^2.
OK, now let's assume that we have a car chassis, made entirely of steel, and we want to consider grounding through the chassis. Let's assume that the car is about 2m wide, on average, down the entire length of the chassis, and the average thickness is comparable to 16 gauge steel. So, that's 1.5875 mm thick, by 2000 mm. Our steel car has a cross sectional area of 3,175 mm^2.
For the steel body of the car to be a worse conductor than our theoretical 1/0 copper wire, steel would need to have 59.36 times the resistance of copper. It seems like typical carbon steels have a resistivity of 1.5 to 1.6 x 10^-7 ohm-meter. Pure copper is 1.72 x 10^-8 ohm-meter, so steel is around 9-10x higher resistance. Thus, unless we have other reasons to do otherwise, we should probably just ground through the chassis.
Disclaimer: I am not an engineer, and my math could be wrong.
Here's an example, using some rough numbers:
Let's say you've got a 1/0 gauge copper wire. That is a nominal 8.25246 mm diameter, and has a cross-sectional area of 53.488 mm^2.
OK, now let's assume that we have a car chassis, made entirely of steel, and we want to consider grounding through the chassis. Let's assume that the car is about 2m wide, on average, down the entire length of the chassis, and the average thickness is comparable to 16 gauge steel. So, that's 1.5875 mm thick, by 2000 mm. Our steel car has a cross sectional area of 3,175 mm^2.
For the steel body of the car to be a worse conductor than our theoretical 1/0 copper wire, steel would need to have 59.36 times the resistance of copper. It seems like typical carbon steels have a resistivity of 1.5 to 1.6 x 10^-7 ohm-meter. Pure copper is 1.72 x 10^-8 ohm-meter, so steel is around 9-10x higher resistance. Thus, unless we have other reasons to do otherwise, we should probably just ground through the chassis.
Disclaimer: I am not an engineer, and my math could be wrong.
Anyone who actually measures will confirm your findings, provided, of course, that the grounding to the chassis near the battery is done correctly.
Additionally, if you run one (or more) ground cables/wires to the front and ground them up there -- you now have the chassis grounded in addition to the cable. On more than one occasion I've seen that arrangement be the source of stray currents that can and often do wreak havoc with ECU and CAN functions - weird symptoms that are very difficult to pin down. This shows up most often when someone convinces themselves that their rear mount ground isn't sufficient, and runs their ECU or CAN or other complex electrical component ground back to the battery with a separate wire, rather than grounding into the chassis near the component. Sure enough - remove the 'separate' ground, and ground to the chassis right by the component, and normal functionality is restored. Parallel ground paths and ground loops can cause some real challenges, plain and simple.
https://www.w8ji.com/negative_lead_to_battery.htm --- applicable paragraphs below.....
"Warning Read This!
Battery path current can be hundreds of amperes during starting, and battery path current is easily 25 amperes or more when charging the battery. Additionally, the alternator supplies all running current for all accessories, with the battery supplying current when an alternator cannot "keep up" with load. With high currents like that, the battery post should be exclusively dedicated to the battery-to-block ground lead, and the battery negative always must have a good solid connection to the vehicle chassis.
Sharing the negative battery lead to engine bolt with anything else or connecting directly to the battery negative post with anything except the block and chassis grounds is a terrible idea. (Connecting electrical devices or hardware directly to a battery negative post is a bad idea (no matter who tells you to do it) unless the negative connection is 100% ground isolated at the electrical device.) When an electrical device is directly connected to the negative post, if the negative post to block or chassis connection opens up or develops excessive resistance, the battery negative post will divert alternator or starter current through whatever is attached to the negative post. This can be hundreds of amperes! Very few devices and wiring will suffer a fault like this without permanent damage. It is also a fire risk.
Grounding directly to the negative post is a fire hazard at worse, and an unnecessary risk to your equipment at best. Battery post connections also increase likelihood of ground loops and ground conducted noise.
On a personal note, I'm not sure why USA and Japanese manufacturers instruct people to connect things to the negative terminal. I suspect it is because they have not thought through the safety problems negative post connections create, and they somehow think a battery post provides a "cleaner" voltage or a more reliable ground because of battery impedance. Accessory or ancillary equipment battery post negative connections are banned in many countries. As a general rule, vehicle manufacturers never make a negative post connection other than block or chassis. Professional or commercial grade accessory manufacturers also do not use negative post connections. The sole exception is when a device has 100% assurance the negative bus can never contact chassis ground in any manner through any path.
The only proper and safe way to connect accessories of any type (this includes ignition and stereo systems) to the negative post is via a path through the vehicle chassis. This is not only the safest path, the chassis is the lowest noise ground path. This is why every vehicle manufacturer has a lead from negative post to chassis, and all devices other than engine block mounted devices obtain negative via the chassis or a designated ground lug referenced to chassis. This is the only safe way to do things, unless the equipment supplier and installer can 100% guarantee there will never be a negative to chassis path through the equipment."
Additionally, if you run one (or more) ground cables/wires to the front and ground them up there -- you now have the chassis grounded in addition to the cable. On more than one occasion I've seen that arrangement be the source of stray currents that can and often do wreak havoc with ECU and CAN functions - weird symptoms that are very difficult to pin down. This shows up most often when someone convinces themselves that their rear mount ground isn't sufficient, and runs their ECU or CAN or other complex electrical component ground back to the battery with a separate wire, rather than grounding into the chassis near the component. Sure enough - remove the 'separate' ground, and ground to the chassis right by the component, and normal functionality is restored. Parallel ground paths and ground loops can cause some real challenges, plain and simple.
https://www.w8ji.com/negative_lead_to_battery.htm --- applicable paragraphs below.....
"Warning Read This!
Battery path current can be hundreds of amperes during starting, and battery path current is easily 25 amperes or more when charging the battery. Additionally, the alternator supplies all running current for all accessories, with the battery supplying current when an alternator cannot "keep up" with load. With high currents like that, the battery post should be exclusively dedicated to the battery-to-block ground lead, and the battery negative always must have a good solid connection to the vehicle chassis.
Sharing the negative battery lead to engine bolt with anything else or connecting directly to the battery negative post with anything except the block and chassis grounds is a terrible idea. (Connecting electrical devices or hardware directly to a battery negative post is a bad idea (no matter who tells you to do it) unless the negative connection is 100% ground isolated at the electrical device.) When an electrical device is directly connected to the negative post, if the negative post to block or chassis connection opens up or develops excessive resistance, the battery negative post will divert alternator or starter current through whatever is attached to the negative post. This can be hundreds of amperes! Very few devices and wiring will suffer a fault like this without permanent damage. It is also a fire risk.
Grounding directly to the negative post is a fire hazard at worse, and an unnecessary risk to your equipment at best. Battery post connections also increase likelihood of ground loops and ground conducted noise.
On a personal note, I'm not sure why USA and Japanese manufacturers instruct people to connect things to the negative terminal. I suspect it is because they have not thought through the safety problems negative post connections create, and they somehow think a battery post provides a "cleaner" voltage or a more reliable ground because of battery impedance. Accessory or ancillary equipment battery post negative connections are banned in many countries. As a general rule, vehicle manufacturers never make a negative post connection other than block or chassis. Professional or commercial grade accessory manufacturers also do not use negative post connections. The sole exception is when a device has 100% assurance the negative bus can never contact chassis ground in any manner through any path.
The only proper and safe way to connect accessories of any type (this includes ignition and stereo systems) to the negative post is via a path through the vehicle chassis. This is not only the safest path, the chassis is the lowest noise ground path. This is why every vehicle manufacturer has a lead from negative post to chassis, and all devices other than engine block mounted devices obtain negative via the chassis or a designated ground lug referenced to chassis. This is the only safe way to do things, unless the equipment supplier and installer can 100% guarantee there will never be a negative to chassis path through the equipment."
On The Tree
Joined: Apr 2014
Posts: 192
Likes: 1
When I was a kid I had grounded a rear trunk battery to a piece of stamped oem bracing steel in behind the rear seat. Don't confuse this as solid cause the entire structure only acts as big as the smallest cross sectional area between your ground and the load. Big body will have no effect if not into a large cross section like a multilayer frame area. Dad had me move it to a thru bolt on the rear sub frame rail and the car cranked like a night and day difference.. lesson learned.
Use your DVM/ohm meter and check your grounds -- that is the best counsel. Notwithstanding 33willys counsel above, based on my measurements, there is zero difference (0.00 ohms) between my ground at the battery terminal in the trunk and my chassis grounds under the hood and in the passenger compartment. I've checked them -- standard procedure any time a new ground is created. Copper may conduct better than steel --- but you've not accounted for HOW MUCH steel you have in between the trunk and the front of the car. WAY more metal for the electrons to use than you can achieve with a copper cable. I've owned a number of cars with OEM rear seat and trunk mounted batteries. 100% of them have the battery grounded to the chassis within a foot of the battery location. None of them had a separate ground cable from the ground terminal of the battery to the engine/compartment. There's a reason....and it's not because they're trying to save a $.
Launching!
Joined: Aug 2015
Posts: 206
Likes: 11
From: Duvall, WA
https://www.w8ji.com/negative_lead_to_battery.htm --- applicable paragraphs below.....
...
On a personal note, I'm not sure why USA and Japanese manufacturers instruct people to connect things to the negative terminal. I suspect it is because they have not thought through the safety problems negative post connections create, and they somehow think a battery post provides a "cleaner" voltage or a more reliable ground because of battery impedance. Accessory or ancillary equipment battery post negative connections are banned in many countries. As a general rule, vehicle manufacturers never make a negative post connection other than block or chassis. Professional or commercial grade accessory manufacturers also do not use negative post connections. The sole exception is when a device has 100% assurance the negative bus can never contact chassis ground in any manner through any path.
The only proper and safe way to connect accessories of any type (this includes ignition and stereo systems) to the negative post is via a path through the vehicle chassis. This is not only the safest path, the chassis is the lowest noise ground path. This is why every vehicle manufacturer has a lead from negative post to chassis, and all devices other than engine block mounted devices obtain negative via the chassis or a designated ground lug referenced to chassis. This is the only safe way to do things, unless the equipment supplier and installer can 100% guarantee there will never be a negative to chassis path through the equipment."
...
On a personal note, I'm not sure why USA and Japanese manufacturers instruct people to connect things to the negative terminal. I suspect it is because they have not thought through the safety problems negative post connections create, and they somehow think a battery post provides a "cleaner" voltage or a more reliable ground because of battery impedance. Accessory or ancillary equipment battery post negative connections are banned in many countries. As a general rule, vehicle manufacturers never make a negative post connection other than block or chassis. Professional or commercial grade accessory manufacturers also do not use negative post connections. The sole exception is when a device has 100% assurance the negative bus can never contact chassis ground in any manner through any path.
The only proper and safe way to connect accessories of any type (this includes ignition and stereo systems) to the negative post is via a path through the vehicle chassis. This is not only the safest path, the chassis is the lowest noise ground path. This is why every vehicle manufacturer has a lead from negative post to chassis, and all devices other than engine block mounted devices obtain negative via the chassis or a designated ground lug referenced to chassis. This is the only safe way to do things, unless the equipment supplier and installer can 100% guarantee there will never be a negative to chassis path through the equipment."
the problem I most often see with body grounding on race cars, is that on say a fox body race car, it's made up of over 200 pieces spot welded together. some of those are then cut out and patched back in with self tappers and panel epoxy. and while when the car is at rest you can use a VOM and see resistance is very low, apply 800 hp and the car does a pretzel impersonation and thats when **** starts acting funny.
go to any serious race event, and look how the cars are wired. battery 12v B+ goes to a shut off switch, then to the starter and from there to a distribution block. battery 12v B- goes to the engine block via a 4ga or better cable. It's simple, it's cheap, it's damn near fool proof and it's easy to inspect if you suspect an issue.
In the end though, I don't think mitch's problem is in the wiring. we're narrowing it down and I more and more I think it's a tune issue.
go to any serious race event, and look how the cars are wired. battery 12v B+ goes to a shut off switch, then to the starter and from there to a distribution block. battery 12v B- goes to the engine block via a 4ga or better cable. It's simple, it's cheap, it's damn near fool proof and it's easy to inspect if you suspect an issue.
In the end though, I don't think mitch's problem is in the wiring. we're narrowing it down and I more and more I think it's a tune issue.
TECH Fanatic
Joined: Sep 2008
Posts: 1,643
Likes: 526
So I don't know if you all remember Click and Clack on PBS but they had a great tutorial on battery and how it works. The take way is that all amps/volts need to find a way from the positive terminal back to the negative terminal of the battery. That happens thru clean positive connections and clean negative connections. Wire sizes on both sides that can handle the voltage draw with little or no drop.
My E36 LS swap has the battery in the trunk. Negative cable grounded to the chassis. Positive cable all the way to the front. I added two grounds from the engine to the subframe on both sides of the engine. May of been a bit over kill but what the heck.
My E36 LS swap has the battery in the trunk. Negative cable grounded to the chassis. Positive cable all the way to the front. I added two grounds from the engine to the subframe on both sides of the engine. May of been a bit over kill but what the heck.
My dad was an industrial mechanic. Lots of memorable sayings when I'd work on the car with him....the relevant one here -- "Son, if it moves, lube it. If it doesn't move, ground it. Twice."