RF interference from igniton box?
 

Has anybody ever had a problem with the CAS getting interference from ignition boxes? I have 2 msd 6a boxes located on the cross bar behind the fans. I have been having some problems driving around 2500 rpms, with a light load on the car(cruising), rpms jump up 300 or so and right back down, just enough where you can feel it in the car. I was told that it usually indicates a lean spot, but it doesnt do all the time. I havent noticed any problem yet in boost, just at around 2500. I thought maybe the location of where my boxes were could possibly cause a interference. Just a thought.

well yeah,they could cause interference,but it's more likely your plug wires.I have no idea how rf interference would affect the cas

why do I keep getting logged in as george ohr,i dont even know who he is!

What type of plugs?

b10egv

Those are non-resistor plugs. I know many people run them with "no problems" but if you suspect interference I'd try swapping them out first, with a resistor plug.

I currently have the same problem and im searching for a fix. I did find a RF filter from radio shack that cleaned up alot of it but it still pops up now and then. Originally my taylor plug wires were causing much of it, i have switched to msd 8.5 but wondering if maybe the 10.0 would be better. Ill let you know if i find some combination that eliminates it all.

mike

wow, Im using taylor 8mm also. So tell me someone, what is it that gets the interference? The plugs , wires, CAS , Coils?

it could be anywhere that can pick up RF interference. The most important thing when it comes to RF frequency is to have a very good ground. Even grounding could introduce RF noise because it can potential use the ground plane as an antenna and radiate RF frequency to the surrounding areas. RF is simply an electromagnetic field. Any magnetic type pickup (CAS) could pick up the noise. Filters could help eliminate as long as you know what frequency (low pass filter) you want and what to cutoff. The only problem with using filter is that it'll introduce lag because it takes time to charge the capacitor before discharging it so your rise time will shift over a certain degrees (especially at higher frequency). Either way you look at it, The best way to isolate the problem is to relocate the ignition box and put it as far away as possible. You can also damper the radiation by putting the ignition box inside a seal (metal) box. That's what I would do if relocation is an issue.

thanks pluto, that makes more sence to me now.
So would locating the boxes inside the car effect anything, could the long wires be a problem?

Update on the interferance, orignally had taylor wires then swithced to msd, it was greatly improved but still intermittaly there. I cant believe this but this morning i installed the factory mazda wires and drove 30 miles to work with zero problems. Im not conviced its gone but i didnt feel anything this morning, ill drive it home and datalog this time.

mike

CAS problems tend to cause a tach needle twitch -
but not always. Is this a factory ECU?
Seconded on the resistor plugs - use them.
I have my ignition boxes inside the car - no problems.
Don't put any kind of filter in the thick red and black wires on an MSD - the "single pulse flyback" doesn't have much sense of humor there, and you'll lose spark energy big time (I don't think those wires are your problem anyway).

Im using Haltech ems, i guess my CAS are getting interference from the 2 msd box's that are mounted about 6-8 inches from them.
Heres another question sence my wires from the boxes have been shortened, what type of wire should I buy to extend them with?

Extend the wires with the same gauge wire or larger.
I'm guessing that it's not the boxes themselves that are causing a problem, but either the wires going to the coils, or the spark plugs/wires. Do you have resistor plugs yet?
Somewhere I saw an aircraft EMS that used coaxial cable for the ignition coils. Odd, but might actually help.

I was having this problem with th e BUR9EQ plugs before. Im start to get confused a bit on what this thread is about. Some of us are talking about spark arc and some talking about RFI, im getting confused.
The problem im having is the tach needle twiching. Sence my boxes are mounted so close the CAS I figured the were getting an interence from the boxes.

Spark arc/RFI/ etc - all related and potentially contributing to your problem.
If the boxes are close to the CAS, the coils wires sort of have to be close also.
There's a lot of current (and interference) when they fire. My timing light will trigger if the pickup is even next to those, and not clipped onto anything (that's why I mentioned the coaxial cable - haven't tried it myself). Make sure the CAS wires are far from all coil/power/spark plug wires in the ignition system. On the FC at least the "home" signal can be a little tricky - haven't seen the FD CAS. Also check the resistance of your spark plug wires. What brand/type are they?

Spark arc and RFI are not related by any means, ie cant see RFI but can see spark arc. anyway went back to the factory ngk plug wires and so far no problems at all. 93redFD, my tach was also twitching and sometimes dropping several hundred rpm. Im running a e6k and msd dis2, the msd is mounted in the back of the car and the wires are completely seperate from the haltech harness. Try going back to the factory wires, i was baffled that an expensive set of msd and taylor did more damage than good. Also im running B9EGV plugs so its not the plug resistance more like the secondary wires resistance. Be sure to change one thing at a time, rather than rewiring your car overnite.

mike

Im using two MSD single post coils for the leading and They have been relocated right under the fuse box on the drivers side, so I want be able to use the OEM plug wires.
If your having spark arc, are your wires touching each other, close by or what? Also can there be an arc from coil to coil?

Its not an arc issue, i believe its a low resistance in the aftermarket wires causing a electro field around them and dissrupting the cas. If you believe its arcing try getting a spray bottle with saltwater inside and spray the coil and wires down with it. This should induce a arc if you have any voltage leaking out.

mike

>>Spark arc and RFI are not related by any means

Arc causes RFI ,whether it's at the plug, or through a faulty wire, coil, etc. In the old days they used to make transmitters called "spark gap transmitters" that used just that principle. These have since been banned by the FCC because of the broad spectrum they create. Also I think Howard Stern was being broadcast on one.

update, I pulled the msd's, blaster coils, taylor wires, changed the CAS and also went with resistor plugs (BUR9EQ). This problme still exist in tach, i notice lately that sometimes it will drop a 1k to 1500 rpms and pop right back up.

What wires are you using since you dropped the taylors? Ive got an update as well, a friend of mine just pulled his msd wires off because of a roughrunning/misfiring condition. If you suspect the wires, try using a testlight. Attach one end to bat neg, then run the probe along all your secondary igniton components, keeping it very close but not touching. If theres a week spot it will jump to the test light and youll see the voltage. My next question is after youve done that, can you determine whether the engine is hot or cold when your problem arises? Possible a component is heating up then failing. Keep us posted.

mike

well I went back with the stock everything. After taking all that stuff off and replacing the cas, the problem is still there, what pisses me off the most is that its not as bad as it was. I dont think its interference anymore. The biggest pain in the ass is that it doesnt happen all the time. This problem is really starting to piss me off.
I dont know what else it could be. Im going to check the clearence on the teeth tonight, to make sure the pully isnt bent.