In the process of finishing up a T2 trans/rear end swap on my S4 NA. I decided to make sure it cranks before I drop it back on the ground. I'm glad I did, because there is something WRONG.


When cranking, the starter engages, but the engine does not turn. It clicks rapidly, like when battery voltage is low.

After repeated crank attempts, the battery terminals get warm to the touch. Not hot, but definitely noticably warmer, so there is current draw for sure.

A few more crank attempts later, it will, on cue, pop a circuit breaker (battery relocated to rear driver's side. 150A breaker).



When I still had my NA trans in, the battery relocate never gave me an issue, so I'm positive I've wired that correctly. 2 150A breakers, one at the battery, and one in the engine bay. Have never had one of them pop.


When swapping the trans, my original power harness was GONE, so I unwrapped the harness, and replaced the starter positive and ground. Those were the only wires I touched in the harness. Factory uses 4ga wire for the starter, so I did the same. I am almost 100% certain the polarity on the starter is correct.


Only non-Mazda part of the drivetrain is the clutch, which is new to the car. It is an ACT clutch for an S4 T2 with a lightweight flywheel.



Have no idea what the hell could be wrong. Any help is much appreciated. Pics below for reference.





Starter ground, terminated to chassis. 12\" run from starter negative to chassis

Engine bay circuit breaker. Starter positive hooked up the right post. Left post is facing the firewall, and that side leads back toward the battery

Circuit breaker at battery. This is the one that will pop

Starter wiring

Another angle of starter wiring. Positive on the right, ground on the left. The ground is on the post that HAS the braided cable.

 

Update:

Swapped in a fresh battery, same issue.

Measured voltage at the S terminal on the starter while cranking. It measured 11.5V.

Checked resistance on the starter ground to where I grounded it to the chassis. Resistance was ~64ohms. From the starter ground to bare metal on the chassis, not where I grounded it, resistance was ~56ohms.


I'm starting to think perhaps my starter could be bad, but I don't want to throw a parts cannon at the thing. Also doesn't explain why the wires at the battery get hot, and pop the circuit breaker. Could it be the resistance in the ground??



Edit:
For reference, I measured resistance from end to end of the same gauge wire that goes to the starter (4awg). A 4' run of 4awg measures 50ohms.

 

so if you just put a wrench on the front pulley of the engine can you spin it by hand? does it matter if its in gear or not?

 

Why is there a “ground” on the left post of the starter?

doesn’t the starter just ground through the metal starter body.

doesn’t the starter have constant 12v on one post, and signal to the space connector. When it receives signal, the solenoid operates and passes current through the output post (braided starter cable) to the starter motor.

I think you’re grounding the starter motor power wire.
remove that ground you added to the braided starter motor cable.

you can put the ground cable to the starter mounting bolts.

Please correct me if I’m wrong.

 

Yes, engine turns over easily by hand. Only about 5-10 ft/lbs are required

 

I believe this is what's happening. Normally the ground in that area goes to one of the starter mounting bolts.

It's hard to tell because the wires aren't factory, but I'm wondering if the one side is ground and the other is the +12V supply. When OP is turning the key it completes the circuit and is causing a dead-short

 

You wrote;
Checked resistance on the starter ground to where I grounded it to the chassis. Resistance was ~64ohms. From the starter ground to bare metal on the chassis, not where I grounded it, resistance was ~56ohms.

That's very high resistance. Should only be a few ohms. This is the reason why your wires are getting hot. I would suggest itrying to lower the resistance of that starter ground connection.

 

If this is the case, is there no wire that goes to the post with the braided cable?

 

Even checking resistance of bare copper wire, a 4' run has resistance of 50 ohms end to end. What could be the reason for this?

 

Correct. IIRC one side (the side without the braided cable) gets 12V. The other side with the braided cable gets nothing (cable goes to the starter motor).

When you turn the key it powers the trigger wire, which pulls the solenoid and closes the contacts to provide 12V down the braided wire

Bad multimeter or probes. It should read zero or very near zero.

Test the probes to one another without the wire and see what you get

 

correct. Constant 12V goes to where you have the red wire, so that is correct. Signal from you turning the key to crank goes to the spade connector (smaller wire), so that is correct.

the only other cable that should be on the starter is the braided one which came with the starter.


when signal voltage is applied, the solenoid (basically an electromagnetic switch) closes the circuit between the two male posts so the constant 12v will travel in one post on the starter solenoid, and out the other post on the starter solenoid to the starter motor. The current is used by the motor and magnets to spin the engine, and grounds through the starter body, through the engine and car chassis. The “ground” cable you have incorrectly mounted is usually mounted to the starter mounting bolts to provide an easier path for the current to get back to the battery, aiding in crank speed.


Try disconnecting that ground cable you added to the starter and just bolt it to the starter mounting bolts. That’s what I believe to be the problem from the evidence provided to me. There’s still a chance there’s some other wonky wiring going on elsewhere, but start with checking this.

 

Let me run out to the car and give this a shot. That ground that I have running to the starter should go to the engine block or the top starter bolt, correct?


You're right on the bad multimeter part, lmao. Touching the probes directly together gives 60ohms lol. Time for a new one ig

 

Should be as this image on the left. You have an extra cable going from the starter solenoid to the negative battery terminal.

 

doesnt really matter exactly where you reposition the ground cable. Starter mounting bolt or engine are fine. Closer to the starter body is the most effective due to reduced resistance but will work fine either way.


looks like we’re all on lunch break lol.

 

Bad cable?
Bad terminals?
Bad connections?

 

Ok good news and bad news:

Good news is that was my issue. Relocated the ground and she cranks

Bad news is, it'll take a few hits of the ignition to crank. One hit, there's a whir, but starter doesn't go. 2 hits, same thing. Then on the third hit, it'll crank.

​​​​​​Sometimes it's more than 3, sometimes less. But rarely cranks on the first go.


Starter cut relay?

 

Hooray glad you got that part sorted.

Regarding the 2nd issue of requiring a few clicks to get it started:
It’s been my experience that the factory wiring is old and can’t supply enough voltage/current/whatever to engage the starter solenoid. I say this because I have had the same issue, then rewired up to a push start by totally bypassing the stock wiring while still incorporating the clutch switch for safety, and using a relay, and it fired right up everytime.

if keeping the stock system, I’d investigate replacing the wiring which is constant 12v into the starter relay, and 12v from relay to starter solenoid.

I appologize that is vague but the idea is to freshen the wiring in between voltage source to the starter solenoid.

could probably test that idea by getting some wire, connecting one end to the starter solenoid male spade connector, then attaching it to battery positive to act as a simulated low resistance circuit. Of course when in neutral.

I’ll let others chime in with their thoughts.

 

I guess this is kinda transforming into a "Problems with T2 trans swap" thread.


After installing the shifter, it's having some trouble going into certain gears. Some gears will take a lot of effort to go in, others will lock out completely. Clutch has not been bled. Not sure if having the clutch depressed would make a difference here. Should I be concerned?

 

To add to my previous post, the car is not running. Car is up in the air, drivetrain is in and filled with fluid.

 

It could be the starter cut relay, but I chased this same issue and I had a brand new starter. I installed an additional relay at the starter. There are several starting issues in these FCs. The starter cut relay is one and bypassing that may solve it, but often it can just be old wiring. The signal wire to the starter solenoid can't carry the current needed to engage the solenoid. You could rewire the engine harness (the true correct way) or install an additional relay at the starter (technically a bandage that does not fix the underlying issue, but it works). The signal wire will have enough juice to trigger the relay. I've done this and it cranks every time now, where it was very unreliable before.

 

A few questions for you:
What was the condition of the T2 transmission before you installed it?
Is the T2 transmission from an S4 or S5?
Did the T2 transmission come with the same shift lever that you show in the video?

 

i'm not totally convinced it should make a difference with neither the engine nor the transmission moving, but i suppose you could try jacking the rear up and turning the wheels a bit, then try the shifting through again and see if the rough spots get easier.

 

Transmission was good before install. Would go through all gears easily.

It's an S4

Different shift lever, but I test fit the shifter lever on the trans before installing on the car

 

I may give that a shot...I'm at a loss. Transmission shifted fine before install

 

Is that shift lever from an S4 or S5? I would suggest swapping shift levers using your original S4 NA shift lever and seeing if that leads to any improvement.