Hey

So I've been troubleshooting an issue with my seven for the past couple weeks. After I completed the battery relocation and my vmount, the car cranked fine like it had a full size battery and was perfect. One day I took it to the store, came back out, and it wouldn't start. Just click. A few tries and it finally turned over. Just really slowly. Looking at the voltage on the PFC I always get low readings, 10.8v, 11.0v, 11.8v. One time it read 12.5v and it started perfectly! I've checked all my connections and they're sound and tight. My positive and negative are high quality 4AWG with high quality terminals. Connection goes to the chassis for ground near the battery and to the starter for my positive. I've moved the positive to the fuse box and had the same low voltage. I purchased a trickle charger and even after that indicates a full charge, I only get 11.5v on the PFC. Cranking is slow. I haven't been stranded yet but it's sketchy. I got the battery load tested and it tested fine. I've added a large ground from the starter body bolt to the frame and that also did not help. I've considered a "starter booster relay" but I think my issue is relevant to the displayed voltage on the PFC. I think if I can fix that indication, the cranking issue will fall in line. Anyone else have a similar issue to this with a relocated battery? Battery is a Braille b2015 425CCA

Matt

 

Battery relocations are a real pain, this is actually not an uncommon problem. I would do some reading up, I've heard that the ground actually needs to go to the factory ground point up front.

Stock, the negative battery cable goes from the battery to the bracket that holds the fuse/relay block on the driver's shock tower, then down to the engine. Is there still a good ground from the engine to the frame?

Dale

 

11.5V is low, I get 12.0V even with the fans running before cranking. If the battery is healthy then something is causing this voltage drop, assuming this started after the relocation, I would start probing with a DMM to see where the drop is. Ohm test from the battery - to the OEM battery Ground, mine is less than 1ohm IIRC. Same as the positive, but test it to the end of the cable without it connecting to the fuse block. If you see any resistance then start tracing backward to different connection point, like where the ground is mount, kill switch etc.

Couple other things came to mind, might not relate to your issue since you are not even getting the proper voltage, but how long is the negative cable from battery to the chassis? The shorter the better but should definitely be less than 3ft. And you said 4AWG wire, is that 4 or 4/0? I think Copper 4AWG wire support less than 100A current draw, so I would try to find out what your wire support.

 

For what it's worth, I half-assed it with 2-gauge welding wire and cheap terminals and it worked fine. I also grounded it straight to the body.

I would think 4-gauge wire is asking for problems, even if the wire and terminals are high quality.

 

I don't think 4awg is my issue. There are plenty of others using 4awg with no issues. I do think Dale is onto something with the ground though. I originally had the main engine ground only going to the bracket. I grounded that to the frame and my starts are noticeably better, however not like it was. I think there is too much resistance in the chassis to the main engine area. I read that XLR8 had better results when he grounded his trans to the passenger side of the car. I think this would help provide a more direct ground for my starting circuit. I'll report back on results.

I don't believe my wiring size to be at fault because the car originally cranked like a champ for the first month I had the v mount and the battery relocation. But I think grounding could be a relevant issue.

Matt

 

Do you see low voltage during cranking or when the key is just on (but not cranking)?
Also if you have the key on and check the voltage at the alternator with a multimeter...?

 

If it worked then, but not now, something has changed.

Clean and tighten your connections?

 

I see 14.3v with my alternator running and 10.8-11.0v with just battery power (not cranking). When I crank it obviously goes lower but I had the battery load tested and it passed. If I get a chance today I'll make a ground using some spare parts and ground the trans to the passenger side and report back on changes.

Matt

 

How old is the battery?

Charge it using a battery charger and see what happens.

 

^ His battery is new.

Did you get a chance to Ohm test the + and GND? 11V at the battery is no good for a new battery, can you charge it back to 12.5V? Voltage at the battery + vs starter +?

14.3V is on your commander correct? Are you getting the same or similar voltage at the battery the same time? A voltage drop test between the battery + and - to the starter will tell you where the problem is, I too suspect it is the ground as Dale suggested. FWIW, few years ago I had a similar issue with my daily with battery at stock location, one day out of the blue I just get 10.5-11.0V at the turbo timer and the car wouldn't start. Did a lot of probing with a DMM, turned out the car decided the OEM ground between the starter and battery is no good and started to use my SS clutch line as the prefer path to complete the circuit. I had to swap out the fried clutch line and add a big ground cable from the starter straight to the battery. Because of that I was extra cautious with the relocation on the FD, Ohm test and voltage drop test every section and component in the circuit.

 

Definitely onto something with grounds.

Added a 2awg ground from the transmission tailshaft to the body and cranking is way better. Voltage still doesn't show 12.5v, but cranking is more reliable and faster. I looked at my ground from under the car (where the bolts pass through) and they didn't seem to like the bonded sealing washers on them. I only used sealing washers on the underbody side as the ground touches bare metal inside the cabin. This weekend I'm going to pull the bins (FML) and upgrade my battery ground from 4awg to 2awg (what the rest of my main engine/chassis grounds are). I'm also going to double check my ground at the chassis for the battery under the bins is as good as I thought it was. I might add star washers under the ground mount for a little extra oomph into the chassis but I'm gonna check voltage and cranking before I put it all back together so I don't screw myself.

Getting closer to fixing this! I have been checking things with my DVM as well. I see 12.7v at the starter with it. I think my ground for my battery just isn't as happy as it should be.

Matt

 

I had some intermittent issues with cranking voltage on my car, which has a bin mounted battery from a previous owner. The main battery ground was attached to the battery at a body point on the passenger side rear bin (a good, clean connection), I added a hyperground-style wire directly onto that connection point and ran this cable forward to connect to the back of the intake manifold, taking the chassis out of the equation for the grounding to the engine (although there still are other chassis to engine grounds in the engine compartment). This resolved the problem.

 

FML is an understatement lol, especially with the bolts through the chassis (mine is the same).

For my battery ground, I used one of those 0 gauge terminal (Stinger SPT5212) and mounted it right behind the bin on a flat surface, I did use sealing washer on the backside. It's a good idea to bump the wire size on your ground, I prefer bigger ground than +, my + is 2AWG and ground is 1/0AWG.

Hopefully a bigger ground wire can fix your issue.

 

Good info here.

Ze Power Mx6:

Thats the exact part im using for my ground. Only with 4 gauge. I think bumping it up to 2 ga and making sure it's really solid will fix this problem. No click starts all day today, but I think the 2 ga bump will make her act like I want her too.

Matt

 

Pulled the bins and I double failed.

So I looked at my sealing washers on the bottom and one has burned up. This allowed the grounding block to get a bit looser. Pulled the grounding block and I only brought it down to primer and not down to metal. Guess I got tunnel vision towards the end of rebuilding my car for the v mount, relocation, etc.

Double fail.

Sooooo. I def got it to bare metal for this time and I'm grabbing new locking hardware.

Will post results.

Matt

 

Well, there's your problem.

 

Yup

Scraped the paint to bare metal, tightened the bolts back up with new sealing washers, PFC shows 12V and cranks like a new battery. Close this baby out!

Thanks for the help guys.

Matt

 

If your battery is relocated, you will experience massive voltage drop and current drain through the wiring.

I use triple 000, 3/0 gauge wiring from Battery to Starter, then starter to alternator. No voltage drop. And with RX-8 upgraded starter internals, the engine spins over 360rpms.

Upgrade quite literally to the largest possible ground and positive wires you can fit. you will not be disappointed.

 

3/0 is overkill big time.

The 4awg power wire I used is a BC-5W2 spec oxygen free copper silver-tinned magic cable or some nonsense. I really only found this out after I used it, however some searching has yielded me with my cable has an amperage rating of a little over 160amps. This is more than enough to start our engines which, per FSM, only takes 90amps. 4awg standard stranded copper wire from like an auto parts store would barely be sufficient as the amperage rating for the lower quality stuff is, surprise surprise, lower. In fact, the 2awg stranded copper stuff I used to replace my other 4awg wire actually has less of an amperage rating. Bigger isn't necessarily better. Your resistance might be lower getting up to your starter/alternator, but it's def overkill big time.

Attached is a video of starting my seven with 4awg wire to quantify my claims.


https://youtu.be/Bswvwlt0UVs

Matt

 

Your video honestly doesn't sound bad at all

The 3/0 is definitely overkill, but I've picked up over 100rpms in cranking moving to this size over a 2ga wire, so to me its worth it. Originally seeing over a 2v+ drop to all the accessories during a cranking with a similar sized battery in similar location using copper-clad 2ga wiring to fuse box and down to starter. Recorded rpm was a round 150pm. After moving up to a 2/0 gauge and routing directly to the starter, seperate from fuse box, ecu recorded over 340rpm. However that was on a 20b which likely had a greater amperage draw.

On this current car, we're using a 3/0ga direct to starter, and voltage drop is less than .6 during cranking, with rpms over 360rpm.

In the end all that matters is the car starts correctly, and 360rpm might be way more than necessary for everyone. But, I like to have the most possible cranking RPM to help out, especially when the engine and wires hot. So if you can fit it, every bit helps. IIRC correctly it was turblown who originally suggested the 2/0 wire.