leading spark vs trailing spark

[speedjunkie]

I've been having issues with starting my car for a while now. Myself and some buddies have been troubleshooting every so often over the past few months and we've tried quite a few different things. However, we've noticed that the spark on the leading plugs is not as big or strong as the trailing spark. I've swapped a few parts with my roommate...leading coil, spark plug wires, coil harness...still no change. This is using stock coils and stock NGK plug wires, and I've been using 9s for all four plugs for quite a while, along with a Twin Power, but we don't have the TP hooked up at the moment for troubleshooting (it's been disconnected since a few weeks ago when we last worked on it). So, is the trailing spark supposed to be larger and stronger than the leading spark, or vice versa?

We took some video and I'm trying to get them off my phone and onto the computer at the moment, but I figured I'd ask first. If I can ever get the videos on here, you'll also notice that sometimes it cranks faster than other times. I'm thinking that might be another problem and I'm trying to track that down too, but I want to check on this first. It cranks faster a lot more often since we've been messing with the ignition system, so we thought that might be an indicator.

[chibikougan]

I would speculate that leading is for preignition and waste spark trailing fires seperatly where leading fires both at the same time.

So trailing gets better charge as its firing one plug instead of 2 at the same time for the pre-ignition and waste spark...:o11:

Then again I am a crazy mountain person....

[speedjunkie]

Does that go along with what Pettit said at the bottom of this page?

http://www.pettitracing.com/rx-7-recommendations/

I would think if the leading plugs do most of the work, that they would be the hottest. But I'm a crazy mountain man too lol

[chibikougan]

I would think yes that would be the first to deteriorate as they explain.


Here is this too.

http://www.tmp.rotaryengineillustrated.com/re101/ingition.php

[88turboii]

the trailing plugs do get more energy than the leading, since the leading plugs share a single coil. if you can see spark at the plugs, i highly doubt weak spark is the problem

[t_g_farrell]

Use a coil per leading plug, that will fix your problems. DLIDFIS or whatever. Look it up. Huge
win on the ignition and won't break the bank. Would have to go full CDI to get better.

[Garfinkles Motor Works]

Try a second gen leading coil they are not to expensive. You be able to find one for $ 40- $80 .My car runs two single lead 65 k volt coils so there are four total mounted on the side of the fender .The longest 40 Ohm MSD spark plug wire is about 6-7 inches long.

[Monkman33]

I have a second gen leading coil. $75 shipped in the US.

[speedjunkie]

Thanks guys! I already picked up a set of new AEM smart coils and a harness from LMS-EFI, and I just finished a mount for them in the stock location. I wanted to see if I could get the car running first to make troubleshooting easier if I had put the new coils in and it still didn't start, but I'm thinking more now that I just have low compression. I'm going to pull start it again today though and let it warm up and check compression before I pull the engine. If I have decent compression I might try installing the new coils first. My only problem is I've never had luck getting accurate results with the piston compression testers (although I'm not sure why) and I've been told it will register less because we live at high altitude, but I'm not sure if that's true or how far it's off if that is true.

I have an 87 Turbo II also so I could try the coil from that I guess.

[88turboii]

sounds more like a vacuum leak to me

[speedjunkie]

Vacuum leak on what? I've never had good results with them on ANYONE'S car if that's what you're talking about. And the one I used Saturday is brand new and wouldn't hold pressure, even with the Schraeder valve in there. I was trying to find my tool to make sure the valve was tight but I couldn't find it.

[88turboii]

actually i get the same low readings with my comp reader. good compression is about 30psi on mine, holding the button

but i meant intake vacuum leak could be causing your problems.. LIM to engine and UIM to LIM gaskets, lower injector o-rings, blockoff plate gaskets, any of those leaking can cause no-start or hard to start

[speedjunkie]

Well they're not always low readings, but they're always inconsistent. And it was about 30 or 40 the other night on the rear rotor, which was the only one we checked. But I wasn't holding the button and it acted as though I was.

I've never heard of those things causing that much of a problem. But I'll check that stuff when I take it apart. Thanks!

[chibikougan]

Well they're not always low readings, but they're always inconsistent. And it was about 30 or 40 the other night on the rear rotor, which was the only one we checked. But I wasn't holding the button and it acted as though I was.

I've never heard of those things causing that much of a problem. But I'll check that stuff when I take it apart. Thanks!

An easy way to find vac leaks is get a squirter bottle spray around suspected area and the water should plug the vac leak and pick the idle up.

[Prodigy]

An easy way to find vac leaks is get a aerosol can spray around suspected area and the brake clean/carb clesner should plug the vac leak and pick the idle up.


I've heard this before a few times...


wouldnt water make it hesitate and stall out? I guess still achieving the same same effect..

Either way... :P


J.

[chibikougan]

I've heard this before a few times...


wouldnt water make it hesitate and stall out? I guess still achieving the same same effect..

Either way... :P


J.


Nah it picks up the idle for a short time while it gets sucked in. Super fast and easy.