My challenger has a 440 in it, and I have a orange ECU with an electronic 440 distributor. The ECU is commanding the coil to fire twice on most every cylinder when the motor is idling. If I rev up the motor a little bit, around 2000 RPM then the unit stops doing the double firing. The 2nd pulse is very narrow compared to the first main pulse, and the 2nd pulse is about 2.5MS after the first pulse. I have looked at other engines running the orange ECU and electronic distributors, and they don't do this. I have heard of at least one other person who has a car that does this same double firing thing.

The reason this is important to me is that it makes any tachometer that is connected to the engine read high at idle, but then over 2000 RPM the tach reads normal.



Has anyone else out there seen this problem?

Does anyone have any idea what could cause this? Is this some kind of problem with my distributor pickup? Is this considered normal or abnormal behavour?

Thanks in advance.

GregGarner
Real Time Engineering
Greg@rt-eng.com

Dont know if this is the reason.But ARE engineering made a different reluctor wheel for the chrysler electronic ignition.To resolve some kinda of a problem like a miss.Could be the problem is with the older made units.As Mallory make the new chrysler electronic ignitions.Maybe these mallory ones are better then the older chrysler electronic ignition units

Greg, we have been emailing each other on this subject lately. As I stated, my conversion to orange MP unit on small block gives a high reading all the time. I show idle at about 1800 rpm and shift at almost 7500 rpm. I did my MP conversion about 1994-1995, which would I have Mallory or ARE?

Thanks for the info on the two different kinds of pickups. Does anyone know how to recognize which one is which?

This is the first I have heard of two different pickups, so I don't know which one you have. Later tonight I am going to dig through my pile of distributors and see if I have two different kinds.

Does anyone know more about the theory of the pickup in the distributor (reluctor) or what kind of electronics are inside the ECU? Has anyone every dug the potting compound out of the ECU? Any links to web sites that discuss any of this?

GregGarner
Real Time Engineering
Greg@RT-Eng.com

I was told a long time ago that Rick Eherenburg (sp) had an article dealing with this situation. I have personally emailed Rick with no response and asked him in this forum to respond to which he hasn't. Rick if you are reading this I would purchase a reprint if that is needed. It seems a lot of folks are having this problem.

I found a little more info on the web.

http://www.allpar.com/mopar/nopoints.html

This article states this:

"Check the distributor (1) Rock the center shaft back and forth. if there is any perceptible movement,get another distributor. <... deleted> (4) Check the air gap (the distance between the pickup and the reluctor). It should be .008 and must be checked with a non-magnetic feeler gauge. Make sure that the reluctor has not been contacting the pickup

From:

http://www.allpar.com/mopar/318.html

"Examine the reluctor teeth in the distributor for possible damage, nicks etc. which can happen if the gap gets too small. If there is damage to the teeth, replace the reluctor."

from (this link has some cool pictures of what a reluctor and pickup coil look like):

http://www.potentialtech.com/pmoran/LeanDelete08-04-04.pdf

Reluctor: an internal part of non-points distributors. The 6 high spots create a signal as they pass a pickup. The signal is then amplified by the Ignition box to activate the ignition coil.
Pickup Coil: an interanal part of non-points distributors. As the points of the reluctor pass the pickup coil, a small current is created. The pickup coil is fixed in a lean burn distributor, but vacuum advanced in standard electronic distributors.

If (when) we eventually find out what it going on here, I think this would be an excellent thread to put into the permanent tech archive.

GregGarner
www.rt-eng.com

I agree Greg, it's been going on 10 years for me. I know I can buy an aftermarket tachometer that would more than likely do the job better but I want and am willing to pay to get my original tach to read near right with the electronic conversion.

Rick Ehrenberg just responded to this question in Email. He says that he would suspect either a pickup coil problem in the distributor or worn distributor shaft bushings. He suggested that looking at the signals out of the pickup coil with a scope would help narrow down the problem.

I plan on getting some waveforms from my car tonight or tomorrow night to see if the pickup coil is actually commanding the ECU to fire twice.

He also says that the previous tach discussion you were mentioning above was related to a bad zener diode in the old tachometer boards that originally came with the cars.

GregGarner
www.rt-eng.com

PLEASE keep in touch!!!

Ive seen GM distributers with too much end play do that at cetain rpms,Buick even made a wave washer to correct it. Maybe the pulsations of the oil pump drive or the loose fit in the drive slot is causing it. Its been years since I looked at a scope pattern but I remember my orange box looking different than anything else,more up and down spikes than normal even through the area where the coil was charging. Wpould adding a condeser smooth out the pattern?

You would have to buy the AREngineering reluctor to have it in the distributor, it never came as part of a package as far as I know (which ain't far). All of the ARE parts I've had my hands on are top notch, though.

The old MP race electronic distributors had a modified reluctor. Basically a stock reluctor that was machined to create distinct, spikes for each reluctor point... visualize an end mill or giant drill bit used to drill out the center portion of the top 2/3 of the reluctor, leaving just a small base with 8 tall, sharp points remaining on the ends of the reluctor. A good, strong signal with nothing in the middle to create a false signal. I don't know if you can, or ever could, buy just that reluctor. Might be nice to have.

Clair

Lol Now I know why my tack has been doing that for the past ten years

Is this a problem with all Orange boxes?

I have one and I have not noticed a problem with my tach.

Ok, I went out and hooked up the digital scope to the reluctor pickup. What I found is that the reluctor is commanding the orange box to fire twice. Therefore the problem is not in the Orange box, and it is in the distributor.

I then started messing around with my distributor, and I found that it is completely worn out. I can move the reluctor itself back and forth more than the .008 inch clearance. I took the distributor apart, and I also found that the big spring on the mechanical advance is completely missing!

I have another distributor that is not worn out, but the coil pickup is missing. On this good distributor, I can't feel any play at all when I push on the reluctor from side to side.

I tore down both distributors and hopefully I can get a good one back together tomorrow night. I will post more if that fixes the problem. I expect that it will fix the problem.

I think maybe the magnet in the coil pickup was moving the reluctor somehow when the vane on the reluctor got close. I was able to see the double firing happen when I rotated the reluctor manually (using the mechanical advance). I also noticed that if I pushed the reluctor closer to the pickup as I rotated it, then the coil would tell the Orange box to fire 2, 3 or even 4 times as the vane on the reluctor swept past the pickup. If I pushed the reluctor away from the pickup, then it would tell it to fire only 1 time. I tried making the clearance I a little larger, but this seemed to have no effect on the problem.

I have pictures of the digital scope waveforms if anyone wants to see them.

GregGarner
www.rt-eng.com

This may explain one other minor problem I had noticed with my car. Sometimes it would miss just once in a great while. I am thinking now with this worn out distributor that it could definately cause a miss from time to time.

What would be the effect of not having the big spring? I am thinking that the mechanical advance would come on too soon, at too low of an engine RPM. I guess this might make it knock at low to mid RPM? I did not notice any knock at low to mid engine RPM. This engine does not have high compression, so maybe it would just show up as a slight loss of power at low to mid rpm.

My current thinking is that I should not modify my reproduction tach boards to fix this problem with worn out distributors. Previously I had modified one to avoid this problem on this particular car, but then the tach won't work over about 6000 RPM. I think the best fix is to repair the defective distributor, then the Orange box will put out only 1 pulse per cylinder.

What do you all think?

GregGarner
www.rt-eng.com
Greg@rt-eng.com

Greg, what kind of scope are you using?

I'd be interested in seeing the results of scoping the pickup, either here or in a PM. I also think it makes much more sense to fix the broken part than to modify a good part to work with it...

Makes me wonder just what shape my distributor is in. It WAS new or nearly new when I got it. I guess maybe 80K miles can do that to a part. Hmmm...

Clair

I have one of those 383 cast iron tach drive electronic distributors out in my garage I looked it over.And it has the reluctor with the seperated areas.The wheel is held on with a allen screw.Not press fitted with the roll pin