2Lucky2tha7

iTrader: (3)

What can I do to the wiring harness, etc. to avoid the possibility of misfiring? I know for a fact that I am definitely misfiring at higher rpms. I believe it was also the cause of my friend's s4 TII block cracking it's front iron last weekend. I'm also about to install an MS in my brother's 1st gen very soon and I want to make sure that I know what to do to avoid any possibility of misfiring before going ahead and buying one for his car.
So:
Should I shield the coil (-) trigger wires separately as well as the plug wires individually to prevent this as well as the possibility of (as crazy as this sounds) grounding BOTH sides of the CAS shielding wire? For a better explanation as to why I am stating these, check out this thread on nopistons, especially the last post from Maxt.
http://www.nopistons.com/forums/inde...howtopic=69260

I know for sure that I am getting nasty misfiring at higer rpms, but fortunately I'm not running a turbo like the guy up the street from me with his turbo'd vert. He told me months ago that it would stumble and backfire randomly at 7k rpms and up.

This thread is similar to what I'm talking about when I get near 7k rpms. It's pretty much stated in the 1st post:
http://www.nopistons.com/forums/inde...2&st=0&start=0
Although the topic of these threads deals with haltech ecu's, I wanted to post them up because the problem is extraordinarily similar to my (and 2 others) megasquirt misfiring problems at high rpms.

2Lucky2tha7

iTrader: (3)

Well, it's obviously RFI interference. I also forgot to note that the majority of the time when I'm cranking the engine, it will try to rotate in the opposite direction for a split second. Not only can you hear it, but you can feel it. It's obviously misfiring.
I think I will have to go up and over the top and pull apart the harness and re-route my CAS wires FAR AWAY from the coils, plug wires, alternator wires, etc. and possibly use some type of aluminum tubing to route it through from the MS to the CAS.

2Lucky2tha7

iTrader: (3)

Now I'm not sure if aluminum tubing will help with low frequencies. Whether it will keep the low frequency in and keep the high frequencies out......I have no idea. I'll keep searching and reading because I'm already using copper braiding for my wires for the CAS and it's not enough. The CAS signal is a low frequency (magnetc), but what is affecting it are all of the higher frequencies around it. Anyone know what I can use that will be the most effective?

2Lucky2tha7

iTrader: (3)

I'm looking into replacing my CAS wire(s) with a coaxial cable of some sort. Possibly a double braid or braid and foil type. Here's a question: when grounding the braided part of the wire/ cable, should it be grounded near the CAS, next to the ECU, away from the ECU at it's own separate source, or should it be grounded at my grounding "chain" that is directly intertwined with my ecu grounds and battery ground. The chain ends about 4" from my ECU.

2Lucky2tha7

iTrader: (3)

(I'll just keep adding to this....)
Part of my grounding chain is connected to the body of the alternator. Will having that one ground there create too much noise?

AlexG13B

iTrader: (7)

i had a prob when i had a ground cable leaving alternator housing to strut tower (went over CAS wires) and gave me alot of trouble. car wouldnt start and ran funny till i removed that ground all together. this was on a megasquirt btw.

muythaibxr

The way you ground is VERY important.

I've had the most success with keeping the stock grounds, and just cleaning them up.

RFI can be avoided with good CAS wiring. Twist the G+/G- wires together, and then Ne+/Ne- wires together, then wrap them in a good shield and ground it on one side.

You can also mess with the hysteresis potentiometer a bit to help remove noise.

Ken

Aaron Cake

iTrader: (1)

Yep, what he said.

It's key to bring all shielding grounding points to the ECU. Basically copy the stock configuration. Mazda brings and ECU ground out to the engine, then grounds the CAS shield (as well as O2 and knock) at the ECU. They don't run a million ground points around the car as this can cause other issues. Personally I don't like grounding my ECU only to the engine, but I do run a ground wire from the engine to the ECU ground panel (on the fuse box next to the ECU).

Quality shielded cable is the key, and keep it away from obvious noise sources. Just because Mazda runs the CAS pickup wire beside the spark plug wires doesn't mean you have it. Run it away from the alternator down that side of the engine and then up along the firewall.

Don't reuse the stock CAS connector if it is gunky, dried out and old. Replace it with something new to avoid voltage drop and intermittent connections (which will cause noise faster then anything).

You don't also have to test for noise at wide open throttle. Just free revving to reline will generally show noise easily enough.

Jobro

iTrader: (2)

Did you adjust the cas gap as close as possible without the teeth touching?

2Lucky2tha7

iTrader: (3)

I'll try and check that tomorrow (it's raining today). I'm pretty sure I did, but I'll go and make sure.

SCCA RX7 RACER

Hi There

In the past I have been fooled by what seams to be a miss fire on the electrical. Check your data log in that area to insure your not running to lean giving that chatter miss fire feel. Also the other extreme would be to rich and have it flood then clear it’s self. This feel is more a gurgle sound and the bucking feel.

Have a quick look it may save you some trouble shooting time.
Have fun
RX7 Racer

2Lucky2tha7

iTrader: (3)

I am going to change my leading coil out for another one I have laying around. After talking to my friend about it more and more, I realized that the problem got steadily worse (but very slowly) over the course of time that I have had the Mallory Hyfire ignition amplifier in my car. It's been doing it more often lately even at cruising speeds. Although it's more subtle, it's still there. I'll be disconnecting the amplifier as well and I'll see how it goes.
I wonder if I should worry about the trailing coils as well, even though they are not being "driven" by amplifiers.
(I'm also going to check the gap in my CAS)

muythaibxr

I've had problems with the ignition amps before with misfiring, etc... I usually just recommend using the stock coilpacks as they generate a pretty strong spark already.

Ken

2Lucky2tha7

iTrader: (3)

Well, I swapped out my leading and trailing coils with other used ones and it's definitely alot better, but I still get a little detonation above 7k from time to time. The way I figured that there was something wrong with one of the trailing coils (T1) is that I used my voltmeter on it while it was idling and the resistance on T1 was something like 12k+ ohms and T2 was in milliohms. The 2 trailing coils that I swapped in were in milliohms as well. The funny thing is that all the coils were registering between 0.6 - 0.9 ohms.