Grounding through throttle cable, Return spring burned the crap outta me! - SOLVED Options

[clapeza]

Got the FI back in my car (1970 1.7L) and working recently. The PO had cut the throttle cable for the carb conversion, so I installed a new TerryCable.
I noticed that the throttle cable got hot. I figured that the ground strap was corroded or broken (I can see it, but can't get to it now.)

I installed a new ground from the rearmost engine case bolt to the battery ground stud on the passenger side of the engine compartment. I used a generic 4 ga battery ground cable from my FLAPS. One end is on top of the battery ground cable. The other is on the bolt that holds the oil bath air cleaner "shelf". This end of the cable is sandwiched between 2 washers on top of the shelf arm that the bolt goes through, with the nut holding it all down tight.

I cranked the car and it ran easily, and the throttle cable was no longer hot, or even warm. Success? Not so fast...

I then replaced the bushings in the accelerator pedal bracket, so it's nice and smooth now.

Didn't get a chance to crank it because I ran out of time that day.

I cranked it today, and blipped the throttle by hand on the throttle body. I thought I saw a tiny spark at the throttle return spring where it attaches to the rear wall. I touched the spring lightly with my finger and burned the crap out of it! The engine had been running only about 10 seconds at this point.

What gives?

Theory: The new accelerator pedal bushings improved the electrical connection to the body. The new grounding cable isn't making good enough contact to the engine case, so the engine is still preferring to ground through the throttle cable.

Assumption: A 4ga cable connected from the engine case straight to the body where the battery connects is an equal (if not superior) ground compared to the transmission ground strap.

I still plan on inspecting and possibly replacing the transmission ground strap, but I'm curious as to why I burned my finger...

Ideas? Advice?

[Spoke]

When you started your car, did the starter strain to start the car or did it turn over nicely?

If it turned over nicely, likely your transmission ground strap is ok.

If the spring heats up while running, then your alternator is grounding through the spring. Did you have the engine out and do some painting on the fan shroud? If you add a ground strap to the alternator, attach the other end to the engine case, not the fan shroud. The alternator already is grounded to the fan shroud.

BTW, for a transmission ground strap, I picked up a standard starter cable like this one at my FLAPS. I think the one I picked up was either 2ga or 4ga 12 inches long. It was longer than the original so I looped it once.

Starter Cable

[clapeza]

When you started your car, did the starter strain to start the car or did it turn over nicely?

If it turned over nicely, likely your transmission ground strap is ok.

If the spring heats up while running, then your alternator is grounding through the spring. Did you have the engine out and do some painting on the fan shroud? If you add a ground strap to the alternator, attach the other end to the engine case, not the fan shroud. The alternator already is grounded to the fan shroud.

BTW, for a transmission ground strap, I picked up a standard starter cable like this one at my FLAPS. I think the one I picked up was either 2ga or 4ga 12 inches long. It was longer than the original so I looped it once.

Starter Cable

The starter has always sounded and run strong. That's kinda why all the discussion around the transmission ground strap always seems to come back to talk about how well the starter pulls - this puzzled me. Mine seems fine. That's what led to the idea of the extra ground for the engine and not straight to the transmission.

I have not had the engine out of the car.

The new ground cable I bought looks exactly like the one you pictured. It's the one from the rearmost case bolt in the engine compartment going straight to the battery's ground post.

I'll look at the transmission ground and also look into a supplemental ground for the alternator. I finally got her off the jack stands. I guess she missed them!!

Thanks, Spoke!

[Spoke]

It's the one from the rearmost case bolt in the engine compartment going straight to the battery's ground post.

This is the cable you attached, correct? There should only be one grounding cable from the battery to the chassis. All other ground straps for components should connect to the chassis at some point including the engine/transmission/starter/alternator. If this cable does go from the engine rearmost case bolt to the battery negative terminal, it should be removed.

The only ground strap for the engine should go from the end of the transmission to the grounding lug on the bottom of the trunk floor. The starter is also grounded to the transmission to complete the starter current loop.

After you make any changes to the grounding, start the car and see if the wire gets hot. If it does, get your voltmeter and measure the voltage from one side of the spring to the other. Measure as well the voltage from the vehicle chassis to the spring. Need to know if there's a voltage between the spring and chassis. The alternator should be grounded to the engine but weird things do seem to be happening here.

[clapeza]

It's the one from the rearmost case bolt in the engine compartment going straight to the battery's ground post.

This is the cable you attached, correct? There should only be one grounding cable from the battery to the chassis. All other ground straps for components should connect to the chassis at some point including the engine/transmission/starter/alternator. If this cable does go from the engine rearmost case bolt to the battery negative terminal, it should be removed.

I'm sorry, I wasn't clear. The new ground cable connects the engine case to the chassis. It's connected to the same stud on the passenger side of the engine compartment that the negative terminal from the battery connects to. It is not connected only to the negative terminal of the battery, if that makes a difference.

But I'm going to disconnect it, and get back to basics and move forward.

As soon as I refresh/refurb/replace the transmission ground strap, I'll do the voltage tests you suggest. With any luck, I'll be able to get to this Friday afternoon.

Again, thanks everyone for the helpful and constructive comments. (...and not calling me an idiot!)