Help me diagnose my miss over 4500rpm.

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89on35s said:
74 Plymouth Duster, 360, A-500, 8 ¼ w 3.23 sg. Running at 185 degrees (confirmed with good IR heat gun). 3/8” pick up in tank with -6 AN braided line between tank and fuel pump. New Carter HV fuel pump with Performance World regulator set to 6 psi. Fuel filter is perfectly clean. Holley 670 Street Avenger on an Edelbrock Performer 318/360 intake. Stock 1.88/160 J heads and unknown pistons (100PSI compression even on all cylinders when cold). Unknown cam, but definitely more duration than stock. Stock electronic ignition with cheap parts store ign. box with external ground jumper to case. I adjusted the reluctor gap to factory spec. Timing at 22 deg. btdc @ idle with total 34 deg. in at 2500 rpm. I messed with it for a quite a while and it runs best there. I just redid my intake gasket due to a bad vacuum leak and it seems perfect, no more vacuum leaks. ? I put new MSD wires on it, a new parts store cap and rotor, I will put new plugs in it as soon as I have time, but I did pull them when doing the compression test and they looked fine.

No hint of ping and runs smooth and sweet up to 4500 rpm then sputters badly (even free revving it in park). It recovers immediately when I shift. I used to shift at 5300 no problem, and accidentally let her spin up over 6000 once unintentionally.

The season is almost done here and I’ll be putting it in the garage for the winter with the intent of doing some work on it to be ready for spring. My question is this, where should I spend my time looking for this miss?

What spec does everyone use to set the reluctor gap to? Did my cheap shitty ignition box partially fail? I am leaning toward it being an ignition problem but I really don’t know.

Any thoughts would be greatly appreciated.


Cley
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Just had the same problem
Your fuel pump is laying down
Replaced mine with a Edelbrock pump
No more problem
 
As to the reluctor gap;
The spec is .008 with a non-metallic gauge
The actual working range I have seen is from zero to .035.
The vanes on the reluctor just disturb the magnetic field which triggers the ECU to fire the coil. I have seen very few pick-up failures; even with the pole piece machined down a fair ways by the reluctor. The size of the gap didn't affect anything on my engines, but when the gap gets to be too big,I guess the signal gets erratic, and the ECU reports on that right away.On mine that started happening after .035.
We use a non-metallic feeler because the magnetic pole piece attracts the feeler, and the vane thru the feeler, and then it gets difficult to figure out if the gap is too tight because the feeler is dragging,or just dragging magnetically. You can put anything in there you want, as long as you bear that in mind. IMO, the gap ain't nearly as critical as one might think.
One thing that probably is important is the condition of the top bearing/bushing, cuz if the reluctor vanes are moving closer and further from the pole piece, I suppose that could create spark scatter. But to that I gotta add, my factory smogger-teen D is from 1973, and has plenty of wear in it. I'm pretty sure if it was a point-type D the engine wouldda quit running maybe decades ago.lol
BTW, the ECU has to be well-grounded. If you insulate it from the apron,the engine will not start. I'm gonna guess that more than a few ECUs have been thrown away because when the new one got installed, it got it's ground back, and in fact, the old one might have just needed it's ground restored.
 
In my attempts to make this work, I installed a separate ground to the battery from the case of the ECU. It's all working now!

Cley
 
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