broman99

I started a thread a few weeks ago about an issue where turning on the headlights, pressing the brake pedal, and basically using any electrical accessories would cause my gauges to drop. Most notably was my oil pressure gauges (my stock one and my aftermarket one). My rpm would also drop a little too, and it would get a little too low for comfort (sometimes dropping down to 450-500rpm). I redid all my wiring on my gauges and got new alternators and nothing would fix it. So fast forward to now. I just finished swapping an S6 Alternator into my S4 and while I definitely notice a difference in the voltage consistency, it did not fix my issue. In fact, it doesn't seem to have had any effect. Even if I hold the rpm at 3000rpm, the gauges drop the same amount. So the alternator charging the car is not the issue.

Honestly I am at the end of my rope lol. I am a very particular person when it comes to my cars, and this has been driving me crazy. I have taken the car in to my usual mechanic and he and his guys could not figure out the issue. My only hunches now, are either the battery, or MAYBE something with the braking system although I doubt that. I am especially suspicious of the battery because this issue started IMMEDIATELY after I replaced the battery (as in the first time I drove the car after replacing it). A cell went bad on the old one and it wouldn't hold a charge. So I got a new one from Oreillys. I got the Super Start Premium battery, and it has 550 CCA and a reserve capacity of 100. If you guys wanted to look at it the part number is 35PRMJ. I don't know what the battery was before. It didn't have much writing on it so I didn't catch the brand or the specs of it. But yeah right after I replaced that battery I started having this issue. If anyone has any ideas I would love to hear them. I am on the verge of ripping my hair out at this point.

Akagis_white_comet

iTrader: (4)

Step 1. Take a deep breath
Step 2. Ax the parts cannon approach. Too many variables being added.

If adding a load (stepping on brakes, turning lights on, etc) affects the entire vehicle to such a drastic degree, your alternator is NOT the issue. Well, Series 4 alternators are a problem but that's another story for another day.

Ask yourself one question. What ties together all of the affected circuits and systems?
Answer: Grounds, you are experiencing Ohm's Law.

Detailed Explanation:
Trying to push more power (watts, or volts x amps) increases heat. Heat increases electrical resistance (Ohms). Gauge senders all work by varying their resistance with pressure/temperature/etc. So if you're adding resistance via a bad ground, your readings get skewed as you are seeing right now. Per the S4 FSM, Stock sender at 0psi reads Infinite Ohms. Resistance drops with pressure, showing 102.6 ohms at 110psi. Fuel level works the same way. 7 ohms at "full" and 95 ohms at "empty". Temperature gauge too, 12.4 ohms at "H" which is 130 degrees celsius and 153.9 Ohms at "C" (50 celsius). Don't ask me to math the conversion to Fahrenheit, I've been doing that on the 20B Cosmo for far too long...

Anyway, do you see a pattern now?
The extra resistance from a failing ground will pull them down like clockwork every time.

It also has the effect of "pulling power away" from any other circuit it is tied to. Think of trying to fill a bucket with a hole in it. The more you put in, the faster it leaks out.

A prime example is the ignition coils. Their grounds come from being directly bolted to the body.

Now the big question: What item, common to both the ignition coils AND both stock and aftermarket gauges, would produce this "skewing" effect on both systems simultaneously?
Main Ground Cable

The stock Oil Pressure sender is grounded through the engine shortblock (along with the ECU...). Shortblock goes through the Main Ground cable, connecting Starter body (shortblock) to Body (strut tower) and Battery Negative Terminal. I will bet you $50 that yours is failing because of the Middle terminal on the strut tower, making anything and everything sensitive to grounding drop like flies, one after another.

To solve the issue, follow it to the letter.
https://www.aaroncake.net/RX-7/grounding.htm

broman99

thanks for the in depth reply man. I spent last night following the instructions from the linked website on how to clean the main ground connection and got it back together before i went to bed. This morning I will check the car and see if theres a difference. Thanks a bunch!

broman99

So assuming that when you said Main Battery Geound you meant the one towards the bottom of the shock tower and not the one that is on a spade connector toward the top of the shock tower. I cleaned off the one st the bottom and it didnt fix the issue. Although I haven't check the one mounted to the starter.

Akagis_white_comet

iTrader: (4)

The Negative battery cable most likely needs replaced them, due to corrosion spreading from the middle terminal (Strut tower, the one you cleaned up) outward. Any weakness in it between battery and strut tower affect the entire car. Weakness between Strut tower and starter affects anything grounded to the engine. Stuff like gauge senders, ECU, etc are here.

The most straightforward solution is to pull the cable out and replace it with two 24" cables. One from Battery to strut tower, then the other one from Strut Tower to the starter mounting bolt. Since it's the same amount of work, replacing the positive cable (48") is a smart idea too. Simplest way to do it is to start at the battery and unwind the tape from the harness, working your way down. Find the end, start unwrapping it. It's 100x easier this way than trying to cut through it. Pull the cables aside and wrap some fresh tape around the remaining harness every few inches as you go. The goal is to have the harness bundled up without the battery cables in it.

This is a tedious, boring, dirty job. You will hate it and want to cut corners. Don't try that, or you will be doing the whole job again, without the luxury of being able to easily unwind the tape on the harness. Keep unwinding the tape until the cables can be remove with a simple pull by hand. Then add fresh tape so the old stuff doesn't unravel.

Also, one thing that I found really helpful is to get a stainless steel m6x1.0 bolt, 25mm long and thread it in from the wheel well side for the Strut Tower ground point. It acts as a stud for the cables to hook onto during installation, then just throw a nut on there.

Save your sanity. Work smarter, not harder.

broman99

Will do. I was dreading having to deal with the UIM tomorrow morning but honestly I would rather crimp and cut wires than remove all those hoses and lines again lmaoo. I just finished testing the car after redoing the starter ground and it definitely is better although not nearly fixed. Although it shouldn't have been hard making a difference when THE FREAKING LUG WAS MOUNTED IN THE WRONG SPOT. Before I got the car the previous owner put in a fresh 13b and who ever wired the car didn't put the ground wire on the starter bolt that goes through the bell housing. They put it higher up in a spot under the filler neck that was covered and dirt and oil and was also a nightmare to get to. I will surely be on that tomorrow though.

broman99

I will ask though, what gauge cable should I use for the wires?

Akagis_white_comet

iTrader: (4)

Now you see why I am so picky about wiring.

Read it again:
https://www.aaroncake.net/RX-7/grounding.htm
4awg is fine. You can use 2awg, but it'll be a bit more annoying to feed through.

To quote the author of the article, Aaron Cake: A properly done crimp is fine. A properly done solder is fine.

I've done both crimped and soldered cables before. My preference is to crimp due to the annoyance of having to heat the terminal with a torch. To get enough heat into the terminal to melt the solder properly with a common butane torch, it took around 4-5 minutes. And if you get impatient and don't heat it sufficiently as I apparently did once, heat and vibration will make an iffy solder joint fail. Generally not a fun thing when there's an unfused 12v+ 4awg cable flopping around underneath a vehicle, surrounded by all sorts of conductive things to short out on. And of course, trying to remove the loose terminal from the starter in question resulted in the stud spinning freely after snapping off inside the starter...

That was on my Expedition and it was the original starter from January 1997 with 316k on it. It was also after 5 years and 30k miles, and was the first time I had ever soldered cables. Such was the result after having a welding supply shop "crimp" terminals on with a hammer, my cat getting ahold of it and swatting the terminal across the living room. So I ended up redoing all of them, teaching myself to solder with a torch.

Next time I had to deal with cables, I invested in a hydraulic crimper that does 10-00awg and exerts somewhere over 16,000 pounds of force on each crimp. Add a selection of lug terminals from Ebay and you're ready to rock. First time I used it was underneath a V12 BMW 750IL to put a new terminal on one of the EKAT power cables (10awg I think). Probably the worst place to try and solder, lots of plastic covers, flammable padding and carpet plus the main fuse box (!) on the other side of the floor pan, and a cable that kept springing back every time you move wrong. Best $30 I ever spent.

broman99

Alright after a long day of work I got it all in there and took the car for a test drive. Huge improvement! Not perfect but much much better. I did notice that the dash lights momentarily dim whenever I press the brakes but I don't know if that is a problem or not. All my connections are good, greased and tight. I think its as good as I can make it unless there is something I missed haha. Thanks for the help man!

broman99

I read another forum thread about the bac not working properly. I tested it by turning on the ac and headlights and the bac idled up the car but after a second it went back down again and the car idled out.

Akagis_white_comet

iTrader: (4)

BAC is working correctly then. As for the lights dimming slightly when the brake pedal is pressed, that is also normal. 4 brake light bulbs, 27 watts each, plus the 3rd brake light (can't remember so I'm omitting for this) is another 9 amps of load that the alternator has to do with no warning. On a "70 amp" alternator, that's 13% of it's maximum output (burns out in minutes...). FD alternators (Also from Mitsubishi) fare slightly better, but still have the same flaw in how they work as it's just a slightly upgraded version of the same design specs.

Meanwhile, a Ford 3G alternator such as from a 92-95 Taurus will laugh at 70A, doing that or more at idle. Go to 2000rpm and you're at 90+ amps and it will do it all day long.

Mitsubishi added power at the top, like a peaky N/A 4-banger. Ford built up the base, similar to a torque-happy V8. Which do you think works better here?

broman99

Ah so thats the benefit of the taurus alt upgrade. Would swapping to LED light have less pull then? In reality I don't mind any of that, I am more worried by the car stalling when the ac is on and i press brakes. I will go check and make sure all my alternator wires are connected properly but I am pretty sure they are.

Edit: Well I think the issue was that I had put a hook connector between the new positive battery terminal and the hook connector that comes from the alternator so it didn't have a great connection. I will keep driving the car throughout the week and see if anything strange happens.

Akagis_white_comet

iTrader: (4)

LEDs would certainly lighten the load and it almost always makes sense to retrofit them whenever realistically possible. However, for something like this, it would be treating the symptoms but not the core of the problem. Did you re-use the stock alternator cable when upgrading to the FD Alt? If you did, that's the problem. It is 8awg, too small for the output from a FD Alt. Plus, where it is spliced into the Main Fuse cable, it was done in the worst possible way I can imagine. A staple, under a mountain of tape. Now you see why Series 4s have charging issues. Anyway, hit me up later. I'm overdue for a nap and later, a week's worth of system maintenance. While looking for a Series 7 ECU for a guy in the UK, and the 20B Cosmo Navigation discs from another guy somewhere in central Europe.

broman99

Sure thing thanks man (I made my own cable from 2 awg wire btw haha) good luck with your work