I've relocated my battery to the rear of the hatch and ran 2 gauge wires for the power wires, and 0 gauge for the short ground which is at the most 2' and it grounds right to the hatch floor through one of the bolts that was already there. Ever since I've done this I'm getting ignition breakup at anything above 22-24psi. Battery voltage doesn't drop bellow 13.5v and its a new alternator. I'm running the stock ignition setup with Magnecore wires and BPR 8's gapped at .028....never had a problem before even at 28psi. Also does the coil pack need grounding through its mounting brackets as I just have it ziptied in place now due to my SMIM. Any input is appreciated, thanks.

Check for corrosion on the bolt/threads that you used for your ground. Also you must realize that with length increase so does resistance. The the same amount of resistance per foot, but now theres just more ft. of cable, so some of the power is used by the wires.
The ECU grounds it's side of the primary with the PTM(Power Transistor Module). It grounds the coil to charge it, and disconnects it when it fires the coil. A 90 coil pack has 4 pins, 1 for 12v, 2 to the PTM, and 1 for the tach gate. A 91+ coil pack has 3 pins since the tach gate is part of the PTM. The 2Gs act like the 91+ 1Gs but physical mounting location differs. The two pins to the PTM are the "grounds" for the coils.

So to awnser your question quickly about mounting of the coil pack...its fine the way you have it.

Run better grounds. I had this on a supra i was building. PUt he battery in the trunk and put a motec on it. the ignition would break up badly at higher RPM's and sometimes even at idle. IT was solved by running a better ground strap from teh engine to the body ( grind the contact area clean of corrsion till you see bare metal) Then for an extra measure, Just run some 8 or 6 guage wire from teh motor to the same mount as the battery is ussing for ground. Ohm's law really comes into play with a relocated battery. And A good ignition ground is a MUST for any hi power application.

You need to run a few more grounds, especially on a fuel injected car. I see some of the NMRA guys run the battery ground back to the engine in addition to several other grounds located thru out the car. You would also see that all power points are run directly to the battery.

Zex4g63 said:

You need to run a few more grounds, especially on a fuel injected car. I see some of the NMRA guys run the battery ground back to the engine in addition to several other grounds located thru out the car. You would also see that all power points are run directly to the battery.

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I don't think that going this crazy is warrented, but like I said. Clean up the mounting point for the ground that is used in the truck. Add some di-electric grease to the bolt.

fourreGsixty3 said:

I don't think that going this crazy is warrented, but like I said. Clean up the mounting point for the ground that is used in the truck. Add some di-electric grease to the bolt.

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Oh absolutely he needs to check what you said. But there is a reason why fuel injected race cars run all power and ground straight to the battery whether they are running an alternator or not.

Small article by Mike Browne(rest in peace)
Don't Just Go Fast - Go Fast Consistently!!!

turboglenn said:

Run better grounds. I had this on a supra i was building. PUt he battery in the trunk and put a motec on it. the ignition would break up badly at higher RPM's and sometimes even at idle. IT was solved by running a better ground strap from teh engine to the body ( grind the contact area clean of corrsion till you see bare metal) Then for an extra measure, Just run some 8 or 6 guage wire from teh motor to the same mount as the battery is ussing for ground. Ohm's law really comes into play with a relocated battery. And A good ignition ground is a MUST for any hi power application.

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Yeah you need to do this i just relocated my battery to the trunk and i just grounded the battery to the back of the car and then i had problems whit the car ..
make sure you run a ground wire to the engine bay i used one of the mounting holes for the battery tray to ground it then to the tranny bolt and remember i also have a grounding point in the trunk..
It works great now i could swear that my car starts way easier..

Thanks for the suggestions, I will run a few more grounds then and hopefully the problem is solved!

Well I ran 5 grounds from the engine to the frame/firewall/strut tower including one 6 gauge wire from the block to the rear grounding point for the battery. Seems to crank better but it still breaks up, although not as bad as before I think...definitely helped a bit. My voltage under load at the ECU as logged doesn't drop bellow 12.9v, from its regular 13.8v. I have my plugs gapped at .028" but seems like the spark is not strong enough. I really don't know what else to do now except for buying an ignition amplifier such as an MSD DIS or AEM CDI box or just go to COP(setup for direct fire via AEM EMS).

Did you check that the ground point son the body were clan and free of any rust or corrosion? Usually what you fixed helps when i've seen similar issues on cars with trunk mount batteries. On that supra, we actually had to grind the paint off the uni-body where we had all the grounds come together in order to ge a suitable ground. Might try that as well.

What turboglenn said is 100% true. Even with adding additional grounds if they are not free of rust or corrosion then it will help youyr break-up but would fix it, due to there still being some resistance.

I moved my optima to the trunk and it did make my car harder to start, that along with neededing a kill switch to race at the dragstrip with a relocated battery caused me to change my mind. I stuck it back under the hood and she fires up & runs just fine now.

Why am I saying this, seeing as it is not helpfull to you since you want it in the back. Well I will explain. You most likely relocated it for better weight distrobution, or at least I know thats why I did. Now doing this ADD's weight! because of all the heavy gauge wire. And the effect of it is not really noticeable.

SO, with that said here is what I am going to do. I am going to get a light weight racing battery and just mount it low in the engine bay around the stock location. This way I should not have the issues of a relocated battery. I do not have to install a kill switch if I want to go to the track. And my car will start easier. (So long as I don't let the little battery die) AND I will be reducing weight!

That really is the only down side to a racing battery. less CCA. And it will die faster, but so long as you drive it often I do not think it will a problem.

A red top race battery, with the JMFab small battery mounting kit, and attach those to the K-member directly below the stock location. Thats what Im doing...well sort of, but the rest of my plans are a secret.

All the grounds are nice and clean and corrosion/paint free. I relocated my battery to make room for the SMIM as the piping leading up to it interfered with the stock battery location. Thanks for the suggestions.

fourreGsixty3 said:

So to awnser your question quickly about mounting of the coil pack...its fine the way you have it.

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I disagree. My ignition breakup problem was caused by loose bolts holding the coilpack to its bracket. Mine is a '97, but still, you might as well mount the coilpack properly and see if it helps.

Most will say that the coilpack is a self-contained system, but remember that the mounting bracket itself acts as part of the core of the inductors. If that core is isolated, the coil may act like a transformer at times, transferring magnetic energy from one coilpack to another, causing cross-firing. This is my theory as to why the improperly grounded bracket caused my ignition problems.

Maybe if it were case grounded...BUT its grounded through the ECU. Also you will want to ask your self why people with SMIMs can just zip-tie their coil packs to a line or strut bar, and run perfectly fine.

To the OP: Check coil resistance. Factory states that resistance should be .70-.86 ohms @ 68*F for the primary, and 11,300-15,300 ohms @68*F for the secondary. If resistance is above those specs. by a enough it could be causing too much electrical drain on the system, and with the increased distance of the source voltage (battery) it is breaking up now, and not before, because restance is increased slightly with increase in wiring length.

How do you define or label primary and secondary? Is one across the 2 poles and one at the wire terminals? Or are you talking about the coil for 1-4 and 2-3, But i would think they would have the same resistance? I wish i had my FSM!!!!!!!! I'm lost on some things (terms mainly ) like i call a power transistor and ignitor. THere's other parts like that too, i just call things by their general names..I.e. coil pack = coil

turboglenn...the primary side is the "low"side (battery supply). To test it you back probe the connector. I'm not sure which 2 wires you have to back probe, but the resistance should be around .77-.86 ohms (but up to .95 ohms is acceptable) @ 68*F. Then test 1&4 & 2&3 on the secondary side (ignition side). Since coil packs that we have are step-up that .xx ohms turns to xx,xxx ohms. Resistance on the secondary side should be 11,300-15,300 ohms @ 68*F.




Just for anyone wondering how the ohms (voltage) is stepped up...

The Ignition Coil contains two windings of copper wire around a soft iron core. The primary winding is made of a hundred or so turns of wire. It is connected to the battery through the ignition switch. Current flows through it creating a magnetic field. When current flow in the primary winding is stopped (by the power transistor breaking the circuit ground), the collapse of the magnetic field causes a voltage to be induced in the secondary windings. The ratio of turns in the primary windings to the number of turns in the secondary windings determines the voltage step up. The reason for this HUGE step-up is because the hardest thing for voltage to do is jump an air gap, and it has to do so at the spark plug. If it can't jump the gap, then no ignition will occur, so the voltage MUST me very high for it to jump that .028" gap that we have

I'll jump in here - 'cause I'm having the exact same problem.

I've switched coil packs, transistors, plugs, plug wires, etc. double and triple checked everything it all leads back to the same thing. I have a BRAND NEW alternator and still have the same problems. I've tried two different ones.

We have a WEAK alternator that's producing some crappy economy car amperage for our race cars.

Honestly, I've added grounds, tried bigger wire (bad idea), everything has been done properly, however the voltage/amperage is just not there.

Our alternators are just to small to support a 15 foot run back to the battery.

I had 2ga, then 0ga, and I'll be switching back to 4ga and if that still doesn't work, I'll be buying a high current alternator from Alterstart.

The only think I might try is adding a capacitor as well... the quick discharge of a cap might help with the high RPM break up... right where I'm having it. It'll also support voltage regulation.