Mopar electronic conversion fires 4 cylinder only

-
moe7404 said:
this may not help. but its what my dad came up with to reduce the confusion of wiring single fire V8s.
Mopar single fire V8 dist cap wiring
My dad made this saying about small and big block dist cap wireing. To reduce wiring confuseion. “the small block has the dist in the wrong place, in the back of the engine. BUT the shaft rotates the right way clockwise. The big block has the dist in the right place, in the front of the engine BUT the shaft rotates the wrong direction counterclockwise. Both wire #5 and #7 on both ALL ways have #5 before #7 on the cap AND block. And most / some stock V8s have the fireing order cast in to the intake manifold. And more info: if the cap has a vent hole next to the center tower. Plug it with JB-weld.
Click to expand...
No don't plug it at all... ever. One other function of the distributor vent hole is to let out excess ozone that forms; that will cause shorts and arcs inside of the cap if it builds up.

And the complaint about Ford small block with the distributor located up front was that in deep water, the water would blow on the distirbutor and short the spark....and that indeed was a common problem. So pick your location and it will have issues LOL.
 
By the way, if the plugs are wet fouled they may not fire. Just wondering how you tested for spark. With a dual plane too much fuel could be finding its way over there.Dry the plugs, open the choke, don't pump the throttle, and try it. Maybe someone could look down the carb for you. I would be carefull doing this. If you checked for spark by trying to jump the spark from the cap to the plug wire this would be a fail if the plugs are soaked.
 
Do you have another box or another ignition to test?

I've had nothing but issues with the MPP ignition items, boxes, ballast resistors, distributers.
 
when working alone I use my timing light by moving it to different wires
 
try a different distributor cap, could be cracked.

or move the wires one position on the cap and rotate the distributor to compensate.
 
Ok, lets think about stuff
-Post29. good idea.
-Post28. In my experience the ECU isnt that sensitive to reluctor gap.I have pulled them off shafts with less than zero clearance to around .020 gap. I have seen them with 1/2 a tooth gone.And with bent shafts. All were from good running engines.Whats your thinking?
-Post32. If you "move the wires one position and then rotate the distributor to compensate", That gets you back to square one, only with the V-can rotated 1/8th turn. So whats your thinking on that? And as to the cracked cap; The cap would have to be really messed up, with multiple ground paths all around the cap.
-As to post33. Im sure you probably know this, but the one offset slot in the reluctor is there to help in rotor phasing.I dont know if Chrysler designed it for that,but thats what I have used it for. I have never seen an out of phase rotor be able to choose which cylinders not to fire. It doesnt usually manifest until somewhere in the advance curve. So school me; whats your thinking?
-Man, this is a toughie!
-We are still waiting for the no-spark on left bank verification, right?
-I have seen reverse polarity on the mag.trigger do strange things.However it was still possible to set the initial timing and have it firing on all 8.The problem didnt manifest until the rpms started to climb.Thats just FYI.
 
AJ/FormS said:
Ok, lets think about stuff
-Post28. In my experience the ECU isnt that sensitive to reluctor gap.I have pulled them off shafts with less than zero clearance to around .020 gap. I have seen them with 1/2 a tooth gone.And with bent shafts. All were from good running engines.Whats your thinking?


-Post32. If you "move the wires one position and then rotate the distributor to compensate", That gets you back to square one, only with the V-can rotated 1/8th turn. So whats your thinking on that?
Click to expand...

I think 28 was referring to the plugs and not the reluctor. (I have seen it before but you would think the OP would have seen that when seeing the plugs were wet.)

On post 32, that was the point right? (his advance can was hitting the intake before he could get the advance needed.)
 
AJ/FormS said:
Ok, lets think about stuff
-As to post33. Im sure you probably know this, but the one offset slot in the reluctor is there to help in rotor phasing.I dont know if Chrysler designed it for that,but thats what I have used it for. I have never seen an out of phase rotor be able to choose which cylinders not to fire. It doesnt usually manifest until somewhere in the advance curve. So school me; whats your thinking?
-Man, this is a toughie!
Click to expand...

What Im thinking about is the slots that are 180* from each other. One side is used for BB engines (CW) the other for SB engines (CCW). Although now looking at the pic of it I see what your saying about using it for phasing. I didnt realize that the slots where so close to the paddles. I was thinking they were further offset and just tossed it out there as a possibility. Now viewing the pic of it I dont think that would cause the issue the OP is having.

View attachment Reluctor.jpg
 
So...just about everything is covered here. The answer may lie in the improbable. This situation occuring is almost impossible on its own. However, given the human factor it could easily be duplicated. That would mean you would have to cause it on purpose. Do you maybe have some friends (or fiends) who could have say altered the cap by maybe taking the contacts out for one side. Anyone with a little knowledge and some imagination could pull this off.

And now that I have concieved of this, I know just the victim i will try it on. Then I will refer him to this thread if he can't figure it out.
 
Thanks guys.
-Special thx to Speed. Ive seen those arrows on the reluctors.Ive never owned a BB,rarely tuned em. Never made the connection.
-But TB the can to intake was a different thread I think. Guy had an HEI clocked wrong. Is that correct or is my head getting fuzzy?
 
I have heard that if you take a pencil and draw a line in the distributor cap from one of the contact points to the base of the cap, then that cylinder will not get a spark.

Moving the wires by one position and then rotating the distributor to compensate will tell you one of two things.
1) If the same plugs still misfire then the problem is not the distributor. bad plugs or bad wires, or some combination of that and a weak coil.
2) If 4 different plugs misfire then it is the distributor or the cap. maybe a worn out distributor shaft of bearing causing it to wobble internally.
 
To Trapster, thanks also. That makes perfect sense. Guess Im too used to swapping parts. Ill try and remember that for my next roadtrip.
-And to Magnum, that is wicked devious,lol.
-Hey I just thought of a quick-test. Pull the coil wire out of the cap to perform a spark test there. while cranking the engine with a good battery, observe the spark stream. If it looks and sounds normal with a steady stream of sparks, well you know, the problem is post coil. If its spitting and sounding crappy, well, there you have it.Back up the bus,Gus. It almost has to be the ECU or the trigger or the reluctor is fubarred with all the left bank "paddles" gone.Gee wouldnt it be swell if it was the reluctor?
 
AJ/FormS said:
Thanks guys.
-Special thx to Speed. Ive seen those arrows on the reluctors.Ive never owned a BB,rarely tuned em. Never made the connection.
-But TB the can to intake was a different thread I think. Guy had an HEI clocked wrong. Is that correct or is my head getting fuzzy?
Click to expand...

Nope it was me, sorry. :)

trapster said:
I have heard that if you take a pencil and draw a line in the distributor cap from one of the contact points to the base of the cap, then that cylinder will not get a spark.

Moving the wires by one position and then rotating the distributor to compensate will tell you one of two things.
1) If the same plugs still misfire then the problem is not the distributor. bad plugs or bad wires, or some combination of that and a weak coil.
2) If 4 different plugs misfire then it is the distributor or the cap. maybe a worn out distributor shaft of bearing causing it to wobble internally.
Click to expand...

The problem I have with that theory is that if it was the cap or rotor it would take out random cylinders, or even a firing order of cylinders not the entire even numbered bank of them.

It is possible however that if there is something inside the ECU that fires the odd cylinders and another part that handles the even numbered cylinders it still could be the ECU.
It's a far fetched theory, but it's possible I guess, since I don't know exactly how they are designed.

Potato in the exhaust on that one bank would do it, but I sure can't think of a mechanical or electrical reason that we have not covered so far here.

Got a pissed neighbor (from Idaho maybe) :D
 
Grip the nose of the hood firmly with one hand. Hold the plug end of the four questionable wires in the other. Have assistant crank engine. Measure distance from vehicle to landing area and compute voltage.
 
I'm going to go out to left field a bit, everything was good til you put it in car. Is it possible when installing the header that you maybe bumped those four plugs and cracked the insulators? If you had the plugs out to install forget my thought. Like I said left field.
 
I haven't read every word of these 2 pages but there is absolutely no spark on one bank? If so it has nothing to do with carb or intake. No spark remember? If the rotor was bad or the cap was carbon tracked it is highly unlikely that just one bank doesn't spark. The firing order doesn't fire every other bank in the order, or in the case of a bad rotor or bent shaft not firing on one side of the cap. Like (1843) (6547). Change the cap and rotor just because but I bet you will find the problem in the control box. The whole block should be grounded as a unit. The negative cable to the drivers head and a strap from the firewall to the passengers head at the rear should be sufficient. New engines with fresh paint can provide a bad ground path. Clean the paint off all grounds. Hook a jumper up to be sure if you want to test. Just my take. This will be a fun one when you find out why. It doesn't make any sense. tmm
 
toolmanmike said:
I haven't read every word of these 2 pages but there is absolutely no spark on one bank? If so it has nothing to do with carb or intake. No spark remember? If the rotor was bad or the cap was carbon tracked it is highly unlikely that just one bank doesn't spark. The firing order doesn't fire every other bank in the order, or in the case of a bad rotor or bent shaft not firing on one side of the cap. Like (1843) (6547). Change the cap and rotor just because but I bet you will find the problem in the control box. The whole block should be grounded as a unit. The negative cable to the drivers head and a strap from the firewall to the passengers head at the rear should be sufficient. New engines with fresh paint can provide a bad ground path. Clean the paint off all grounds. Hook a jumper up to be sure if you want to test. Just my take. This will be a fun one when you find out why. It doesn't make any sense. tmm
Click to expand...

You too huh? :D
I didn't even bother trying to mention the firing order part of it (as in half the cap missing for example, does not mean you loose cylinders 2345, but 1843 or whatever) :D
Not all even numbered cylinders, or even all on one side could be anything but a loose rocker shaft, or malfunctioning ECU.
There is nothing else mechanical or electrical either one that can cause it to only run on one bank, well besides a plugged exhaust on a dual setup with no crossover.

I'm tellin ya, look for that potato. :D
 
TrailBeast said:
You too huh? :D
I didn't even bother trying to mention the firing order part of it (as in half the cap missing for example, does not mean you loose cylinders 2345, but 1843 or whatever) :D
Not all even numbered cylinders, or even all on one side could be anything but a loose rocker shaft, or malfunctioning ECU.
There is nothing else mechanical or electrical either one that can cause it to only run on one bank, well besides a plugged exhaust on a dual setup with no crossover.

I'm tellin ya, look for that potato. :D
Click to expand...

Ah yes. The old potato up the tailpipe trick. It won't run on those 4 but it will still have spark. Are we sure those 4 have spark or did I miss that in 2 pages of dialog?
 
toolmanmike said:
Ah yes. The old potato up the tailpipe trick. It won't run on those 4 but it will still have spark. Are we sure those 4 have spark or did I miss that in 2 pages of dialog?
Click to expand...

I'm not positive about the spark Mike, but was assuming he hadn't got to verify that yet.
Bet it doesn't :D
At this point I'll also bet the ECU is why.

Either that or it'll fire right up and run fine next time he tries it. :D
I hate those.
 
The ECU merely picks up a weak signal from the pickup coil generated by the reluctor passing close by. It amplifies the signal and sends it along to the ignition coil which opperates the same as a contact point system. The ECU and coil have no idea where the spark will ultimately go, the distrubutor distributes it to the proper plug wire. The reluctor would have to be damaged exactly right to missfire only on one bank. I was under the impression that the car and engine were both in the shop, assembled, and opperating correctly. Then at a particular restart the trouble began. Ouch. I hope that wasn't my leg getting pulled. How come I get the feeling some are watching this thread, saying nothing, and laughing a lot?
 
There is one way to solve the MP ignition problems... pull out the distributor, coil, control box, and ballast resistor. Place them in a garbage can. Purchase all new matched MSD components and install on engine. Follow MSD's wring diagram and get rid of the resistor. This is what I did after going through 3 MP boxes, 2 coils, 2 resistors, and a crappy running car for 2 entire summer driving seasons. Hate to say it, but the MP ignition stuff they are selling today is pure garbage.
 
You must log in or register to reply here.
-

Back
Top