Mopar electronic conversion fires 4 cylinder only

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CdnValiant

CdnValiant

1969 451-S
Joined
Sep 14, 2014
Messages
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Location
Cochrane Alberta Canada
I have assembled and run a 451 in my 69 Barracuda. I retained the mopar electronic ignition I ran on the original 383 and it was working well the few times I have run the 451 in my shop. Today the car was hard to start and when it did start appeared to run on 1,3,5,7 only. Header stayed cold on 2,4,6,8 side and plugs were wet. Anyone run into this before?
 
have you pulled a wire on the even bank to see if they are sparking?

if the whole bank is not firing .....are the valve too tight?....

check the compression ....
 
Prior to installing in the car, it was set up and run and tuned on a test stand, same distributor and timing using test stand wiring, and ran great. I have about an hour or more of run time on the car in the shop and it was running fine, so firing order is OK. Nothing else was changed. The car has a Holley electric pump and Speed Demon 850 on a Street Dominator intake. I checked cylinder #2 and no spark. When the car did start and ran poorly the 2,4,6,8,side header stayed cold to touch. 1,3,5,7 all hot.
 
First thing I'd do is to check the reluctor gap.
Then mayba a different ECU. (but I wouldn't expect it to change anything.)

1,3,5 and 7 huh?
That's odd. :D

it would have to be doing this.

1. fires
8. no
4. no
3. fires
6. no
5. fires
7. fires
2. no

That seems to have to be a mechanical problem to me, as electrical components can't decide to fire only the even numbered cylinders.
 
I'm going out on a weak limb here, but OP do you have the passenger head grounded?
 
I can think of a few mechanical reasons. Are you certain there is no spark on the affected bank?
 
We had a 70 383 cuda here at the shop doing that and believe it or not ended up being the dist cap. It was only firing on one side of the engine
 
TrailBeast said:
First thing I'd do is to check the reluctor gap.
Then mayba a different ECU. (but I wouldn't expect it to change anything.)

1,3,5 and 7 huh?
That's odd. :D

it would have to be doing this.

1. fires
8. no
4. no
3. fires
6. no
5. fires
7. fires
2. no

That seems to have to be a mechanical problem to me, as electrical components can't decide to fire only the even numbered cylinders.
Click to expand...



^^^^^^^^^^^^^^^^^ This is not likely an ignition prob..

The Op says the the headers are cold ,, assuming no spark.. verify it..

Single plane manifold?? carb flooding one side

As stated check rockers,,
 
Thanks for the input. I will check out the issue cylinder by cylinder and confirm it is firing on all 1,3,5,7 and not 2,4,6,8 and get better information. The firing order is correct but I am baffled by the selective bank issue, as it doesn't seem to make sense. I will also check voltages at the ballast, coil, ecu etc and grounds and see if I can add more to consider. On cranking, it seems to crank evenly on all cylinders. This is my first post item in the forum and I appreciate the input.
 
There should be a ground strap from the rear of the passenger head to firewall.

I doubt that's the issue, but you never know.
 
A dual plane intake and a carb issue would do it though. :D

The only other thing I could think of is if the rocker shaft hold down hardware backed off.
 
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.
 
eh? I wouldnt plug the vent. Its there for a reason, it keeps the distributor dry (believe it or not) it vents moisture that gets in there from the crankcase. Plugging will gum it up with corrosion. 18436572 and the rule...rotor ALWAYS moves away from #8 when pointing to that banks end: big or small....see?
rota.jpg
 
I kind of thought the rocker shaft worked its self loose, but if there is truly no spark then it wouldn't matter. You say it turns over smoothly, and a shaft that worked loose may not allow that. There aren't a whole lot of things that the cylinders of one bank have in common. Crank, head, rocker shaft, cam, and rocker cover is about it. Unless an ignition problem is clearly obvious, I start with cap and rotor always. I did have a Demon that fired very strangely,but it had a bent dizzy shaft. Maybe the dizzy has a bad bearing.
 
I just had a thought. What if none of the hydraulic lifters on that side were getting oil pressure? No thats not it. You didnt mention the racket that would make.
- They have the exhaust/header in common too,
 
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