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View Full Version : Innacurracy of 8V iginition coil lead!!!



glhs875
12-14-2006, 03:08 PM
I have noticed from using an MSD shift light and Digital 6 control box on two different cars now that there is a fluctuation on the (-) coil lead above 6000rpm. I suspected it on my Daytona, as I would have the shift connected to that lead, and it would somtimes flash on and off well before the 6200rpm I had it set to. I just confirmed this on my GLHS. I have the shift light hooked straight to the computer because of the problem. It seems to work flawlessly. But I was experiment with the rev limit on the MSD. My shift light is set @ 6400rpm (computer lead), I set the rev limit on the box @ 6500RPM to experiment with bouncing off the limit just long enough to make the tires hook before the 2nd gear shift. That idea seems to work. But the rev limit is kicking in and out in 2nd gear well before the shift light comes on @ 6400. It will eventually spin to 6400, but spit and sputtering, unlike the normal ignition cut out that the MSD box gives. I finally tried raising the rev limit bak up to 7500RPM after some other things. It then pulled smooth to the shift light @ 6400RPM. This has been causing me some problems for a while now. And I suspect it is limiting some upper RPM HP!!!

ShelGame
12-14-2006, 03:23 PM
Stupid question - did you dis-able the rev limiter in the ECU when you went to the MSD (assuming you're still using the Chrysler computer for fuel)? The stock rev limit is set to somewhere between 6000 and 6200 rpm. It cuts fuel as well as spark. So, if you didn't dis-able it, you're possibly still hitting the stock rev limit and cutting fuel...

turbovanmanČ
12-14-2006, 03:24 PM
What wires are you using? you need some Aurora's, :thumb:

glhs875
12-14-2006, 03:30 PM
Stupid question - did you dis-able the rev limiter in the ECU when you went to the MSD (assuming you're still using the Chrysler computer for fuel)? The stock rev limit is set to somewhere between 6000 and 6200 rpm. It cuts fuel as well as spark. So, if you didn't dis-able it, you're possibly still hitting the stock rev limit and cutting fuel...

The stock rev limiter has been raised to 8500RPM.

glhs875
12-14-2006, 03:34 PM
What wires are you using? you need some Aurora's, :thumb:

Accel spiral core. I may try some different/ better wires. I was using the same wires on the Daytona. But this problem has me worried and wondering just how good the stock type of ignition is, and could explain some of the hard time to making these engines make good power above 6000rpm. And it could explain some detonation problems as well.

glhs875
12-14-2006, 04:31 PM
I changed the coil lead to (-) negative. That's the one I have noticed a problem with in flucuation above 6000RPM. Not the 12V (+) source lead.

Frank
12-14-2006, 04:47 PM
Its not the coil wires Simon.
:ban:




It sounds like you maybe experiencing some form of ripple voltage across the top of the normal. We know there is 12volts going to the coil. When the computer wants to fire the coil, it pulses the (-) terminal to battery ground. When this happens (and only happens on the very first computer pulse of the start sequence)), you get voltage of around 2000volts out the secondary (aka spark side). Now when you interrupt the voltage, aka computer releases the ground path, the EM field collapses and now you see 125volts on the primary side of the coil, now during this huge collapse, you will see a pulse again by the computer providing ground path, and wham, you now have 20,000+ volts out the secondary!

Now there is multiple ripples caused from voltage reflections and such for lack of better words. I would suggest you go to the parts store and find youself the condensor they use on say a 94 Ford Bronco. It is the giant capacitor they attach to either the (-) or (+) terminal on the coil. This removes some of the really high ripples seen that piggy back onto the voltage lines. Without this suppression, you would get noise on like radios and such. Typically they are built in elsewhere and are no longer needed on the coil wire. However you are now needing a smooth single and dont have one. Just splice it in.

If it is indeed the problem, then no loss of HP was seen. However if it doesnt take care of it, back to square one. The reason I say that is because typically the RPM parameter the computer uses for fuel calculation is what it is telling the power transistor circuit to do. It typically doesnt read itself. If it did, then you would experience the same problem.


Frank

turbovanmanČ
12-14-2006, 05:05 PM
Its not the coil wires Simon.
:ban:






Frank

Hahha, your a funny guy, :lol:

Frank
12-14-2006, 05:09 PM
I was being funny?

Frank
12-14-2006, 05:09 PM
Oh.... I guess I was. ;)

glhs875
12-14-2006, 05:43 PM
That's one possibilty I was thinking of was some bleeding of voltage or signal pulse into the (-) neg coil lead. I will try a resistor/capactor and see what happens. Thanks, Frank.

PS. Do I need one that just basically Tee's in like normal on the neg or pos lead (which one do I to hook it to ?) or one that is hooked up in line. I think however it goes, it will need to be before the MSD box to correct things there, and not at the coil itself, I'm not sure on that either. That makes sense, because I wasn't running the factory capactor on either car. I removed them.

johnl
12-14-2006, 08:55 PM
Did you check the plastic rivets that hold the timing shutter wheel down?

If the shutter has ANY movement, the timing will be shaky. I used a soldering iron to tighten it up on both of my TDs.

Frank
12-14-2006, 09:08 PM
That's one possibilty I was thinking of was some bleeding of voltage or signal pulse into the (-) neg coil lead. I will try a resistor/capactor and see what happens. Thanks, Frank.

PS. Do I need one that just basically Tee's in like normal on the neg or pos lead (which one do I to hook it to ?) or one that is hooked up in line. I think however it goes, it will need to be before the MSD box to correct things there, and not at the coil itself, I'm not sure on that either. That makes sense, because I wasn't running the factory capactor on either car. I removed them.

The cap attaches to the line and the outside just grounds to the frame.



Frank

glhs875
12-14-2006, 11:23 PM
Did you check the plastic rivets that hold the timing shutter wheel down?

If the shutter has ANY movement, the timing will be shaky. I used a soldering iron to tighten it up on both of my TDs.

Yes, it's fine. I think it's like What Frank said. But that was a good idea!! :thumb:

glhs875
12-14-2006, 11:28 PM
This problem has been causing me a power loss! There are sometimes when the MSD rev limiter gets tripped as much as 500 to 1000RPM to soon! It's erractic. And it seems the higher the revs, the worse it gets. When I was spinning to 7200rpm (shift light) with the S3 cam, sometimes the rev limiter would get tripped before 7200 with it set @ 7800RPM!

Frank
12-14-2006, 11:56 PM
What I meant was, outside of the rev limiter, ripple voltage wont cause a loss of spark power.


Frank

TurboBuggy
12-15-2006, 04:07 AM
Hooking straight up to the coil ground is bad because its a dirty signal, I had issues with this when I was hooking up my wideband/datalogger.

There is a way to use that signal but you have to use a potentiometer or something like that.

edit:: Read up here, you should be able to adapt this to what you are doing
http://www.innovatemotorsports.com/forums/showthread.php?t=4888



Use a 10k Ohm potentiometer from Radio Shack (up to 50 kOhm will work). Connect one of the outer pins of that to the tach output, the other outer pin to ground and the center pin to the LMA-2/3. With that you can dial down the tach signal so the LMA-2/3 only reacts to the real ign. pulse. This will allow to only get the real ign. peaks to the RPM converter because its designed to work also with much lower signals than a tach is usually designed for. Once you got a 10 to 50kOhm pot from the nearest radio shack. Those have 3 pins in a row. Connect the middle one to the RPM converter. Connect one of the outer pins to coil negative, the other to ground. Turn the pot to the ground side with engine iding. Then slowly turn it up until RPM reads correct at idle. You can test that without a laptop by disconnecting the LM-1 from 12V. Pressing the record button then (LM-1 running on 9V battery) will show RPM on the LM-1 display.

Here's the link to that wiring diagram.
http://67.43.173.134/tachwire.gif

glhs875
12-15-2006, 08:41 AM
I will keep that in mind when I get a wide band. But I'm hoping the capacitor added to the coil ground will clean up the signal enough so the rev limiter on the MSD box will be more accurate. It's amazing how sometimes the cheapest parts can make such a big difference!

Frank
12-15-2006, 08:52 AM
Ya. On my Ford, which has the cap suggested, it is litterally called on the drawing 'Radio Capacitor (Supresses Igntion System Noise)'

glhs875
12-15-2006, 08:57 AM
Ya. On my Ford, which has the cap suggested, it is litterally called on the drawing 'Radio Capacitor (Supresses Igntion System Noise)'

When I go to the parts store, what year and what kind of Ford do I ask for one for?

Frank
12-15-2006, 09:08 AM
Its for a 1994 Ford Bronco with the 302. When you get it, you will need to cut the single wire connector off and splice it into the (-) wire of the coil at the coil. The cap body will need to be clamped to the grounded bracket that holds the coil.... the cap might come with the clamp mount, if not a good hose clamp might work.


Frank

glhs875
12-15-2006, 09:10 AM
Thanks Frank! YOU DA MAN!!! :thumb:

BTW -I actually run a Ford type of coil. Like on a 302 FI engine.

TurboBuggy
12-15-2006, 11:27 AM
I will keep that in mind when I get a wide band. But I'm hoping the capacitor added to the coil ground will clean up the signal enough so the rev limiter on the MSD box will be more accurate. It's amazing how sometimes the cheapest parts can make such a big difference!

Well even though that is a fix for a wideband issue, it should still work for what you are doing since the problem they had was spikes in the rpm signal frequency and the potentiometer suppresses them somehow. But I guess a capacitor set up as a filter should work also.

glhs875
12-15-2006, 02:20 PM
Well even though that is a fix for a wideband issue, it should still work for what you are doing since the problem they had was spikes in the rpm signal frequency and the potentiometer suppresses them somehow. But I guess a capacitor set up as a filter should work also.

We will find out!! :thumb:

Skibbe
12-15-2006, 02:58 PM
Ya. On my Ford, which has the cap suggested, it is litterally called on the drawing 'Radio Capacitor (Supresses Igntion System Noise)'

Correct me if I'm wrong, but don't our coils have this from the factory? Why do we need a Ford part?

Frank
12-15-2006, 05:37 PM
Didnt know it was in the coil, I thought it was elsewhere. Well he isnt running a stock coil. In addition, I just so happen to own a Ford, so I know the cap exists and how to hook it up.

Aries_Turbo
12-15-2006, 07:26 PM
yeah we have these on our cars stock.

Brian

Garret
12-15-2006, 09:10 PM
yeah I was going to say it's on my car as I just cleaned it today

GLHSKEN
12-15-2006, 09:42 PM
Yep, It's there...

WVRampage
12-15-2006, 10:42 PM
Yeah they have them.

Aries_Turbo
12-16-2006, 12:56 AM
Frank-N-Furter is FIRED!!! ;)

Brian

Frank
12-16-2006, 01:07 AM
Bite me. Its not always needed and in addition on our cars. Acceptable noise levels maybe achieved just with coil design. I know my TD doesnt have one... I say that loosely because it could be built into the coil or whatever.

Point being is he is having issues that are indicative of ripple voltages and noise. Adding a cap will help.


Frank

iTurbo
12-16-2006, 01:50 AM
Most every 8v car I've ever seen that used the oil filled coil also had the cap mounted adjacent or piggyback on the coil bracket. I've run without it for a long time with no issues or radio noise that I can tell. The only cars I haven't seen them on were the later TMs with the E-core (thermostat mounted) coil, and the TIII. I suppose they could be internal like Frank suggested.

GLHSKEN
12-16-2006, 10:29 AM
I suppose they could be internal like Frank suggested.

I suppose, BUT:


Frank-N-Furter is FIRED!!! ;)

Brian

I liked Brian's sentiment best

2.216VTurbo
12-16-2006, 11:03 AM
Yeah, Frank's been uncharacteristically testy throughout this thread:rolleyes: Dog run away or something Frank? Maybe one of these:grouphug: will help...

Frank
12-16-2006, 03:02 PM
Oh I am just giving Aries_Turbo crap.... me and him are buds, so ya. ;)

Aries_Turbo
12-16-2006, 03:59 PM
i have the distinct pleasure of being friends with Frank..... oh yeah, and pointing out the things that he misses or is mistaken on! its especially fun when it is something about our cars ;) hehehe

Brian