How many ground strap connections do I need, anyway?

[ostrich]

My BBC-swapped 1980 Grand Prix has only two ground connections (not counting the interior). One is the negative battery cable connected to the passenger cylinder head (with no smaller wire going to the body), and the second is a small flat braided ground strap connecting the firewall to the intake manifold. That's it.

Problem: my TCI EZ-TCU controller occasionally loses the output speed signal from my 4L80E. When this happens, the controller assumes I am not moving... so it puts the transmission in 1st gear and it will not upshift. Fortunately, moving the shifter to '2' forces the transmission into 2nd gear, so if the controller gives up I can at least have two out of four gears and limp my way along. The only way to correct the problem is to completely shut down the car, wait for the electronics to 'go to sleep,' and then re-start it.

At first, I thought this was an obviously bad speed sensor so I replaced it with a new Delco one. No change. Now I'm wondering: what if there is a weak ground that sometimes interrupts the sensor's output signal? It is a running joke with some of my car friends that any electrical problem is always the fault of insufficient ground straps. Could that possibly be my problem?

I'll stop by O'Reilly and buy an upgraded negative battery cable which also has the integrated small line to connect to the body. (I've actually wanted to do this for a while.) That will give me one more ground connection. But could/should I somehow also add one between the transmission housing and... something? Maybe I can connect one of the transmission bell housing bolts to the firewall, for example?

Thoughts?

I have an idea about your issue. I was having intermittent speedo issue with my T56 sensor with my EFI connection LS upgrade electronics in my 85 Camaro with my Autometer speedo. From the factory your speed sensor wiring is braided. I made a new harness for mine (2 wires), put them in a drill to twist them together. Basically like twisted pair Ethernet cable (signal loss). Since then no issues. May help??

 

[timo22]

I remember asking Jared about that ground strap when I removed the body of my Bonneville. On my car, it went from the frame to the middle bolt on trans bellhousing.

timo22

 

[64nailhead]

My buddy has a '55 Chevy hot rod. He had lighting issues and kept blowing the $100 infra-red MSD module. I took a look and the only ground was by accident through his clutch linkage. We ran braided mesh grounds from the engine to the frame, from the engine to the body, from the frame to the body, and a dedicated ground from the battery to the MSD distributor. End of problems. You can't have too many grounds.

This 🙂

I don’t know if your issue is a ground issue, but you really can’t have too many. A ground from from the body to the frame in the front and rear
Of the car is great. 2 from the frame to the engine, and one large gauge wire from engine to battery is adequate imo. Electronic systems CANNOT have feedback through a ground.
I just referenced 5 grounds, and that is the minimum I would run with an EFI system or electronic sensors.

 

[565bbchevy]

More grounds never hurt, I am going to say I have no less than six 1/0 grounds throughout my Monte and a couple slightly smaller braided ones plus having a trunk mounted battery I didn't want any issues.

 

[Injectedcutty]

I have a 1/0 ground from the battery to the frame, a 1/0 from frame to engine, at least two from wiring to engine, firewall to engine, firewall to frame.

 

[Northernregal]

This 🙂

I don’t know if your issue is a ground issue, but you really can’t have too many. A ground from from the body to the frame in the front and rear
Of the car is great. 2 from the frame to the engine, and one large gauge wire from engine to battery is adequate imo. Electronic systems CANNOT have feedback through a ground.
I just referenced 5 grounds, and that is the minimum I would run with an EFI system or electronic sensors.

Agreed. I have 6. EFI and computer controlled stuff is a different game. Think of the whine of a bad radio ground and imagine its what your computer hears from the sensors. Same idea.

 

[Clone TIE Pilot]

I have the neg battery cable going right to a starter mounting bolt, the little memory saver ground cable from the neg battery clamp to the body, a ground cable from one starter mounting bolt to the frame, and the factory ground cable from the engine to the firewall. One of the upgrades police package cars have is additional ground cables.

 

[pontiacgp]

and to test a ground use a multimeter set on ohms which will tell you how good a ground is.....a test light will only tell you there is a ground.....

 

[454GrandPrix]

LOL. So the consensus says I need numerous more ground straps. I'll start working on that. Thanks, everyone.

My 82 GP was a diesel car originally. It had a ground cable that ran from the lower firewall, near the body mount on the driver's side, up to the engine.
You can see it dangling by the driver's side frame rail in the pic below.

Hmm, I don't recall seeing that cable on my car... but I'll double check.

 

[Tony1968]

I don't think anyone mentioned a ground from frame to core support. I think it's important. The more the merrier