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I have a H23A Bluetop swap, and I'm using a TD60U distributor (internal coil, JDM H22A, OBD1). I'm starting to tune it and I'm noticing that sometimes power drops off a little after 5500rpm. On the datalogs, the rpm dips and seems almost like it is misfiring. For example, at 5500rpm the next couple data points show 5400 or 5300rpm, then after it shows 5500rpm. At 7000rpm, it is more prevalent. The engine speed increases steadily, it just seems like power is dropping off. Ignition timing changes have no affect. On the datalogs the actual and table ignition timing values are steady.

When I check the timing with a timing light at idle it doesn't hold at 16° it bounces around quite a bit. The engine speed or sound of the engine doesn't change at all. I checked the timing light on other engines and it was steady, so I know it isn't the light. The distributor is a new Autozone unit, but is a possible for the sensors internally to be failing and causing this?
 

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Is the distributor brand new? Coil? Igniter? Cap and rotor? Have you checked spark output, making sure you have good hot blue spark? Timing lights rely on a good surge of energy pulsing through the wire to generate enough of a magnetic field to induce a current into the timing light pickup, or you can have erratic operation. All of the above pieces in the distributor must be in good working order to run the engine and to allow a timing light to function. Also make sure the timing light pickup isn't too close to other wires.

Disable fuel by pulling injector plugs or killing injectors through your tuning solution.

Pull a plug wire, make sure the car is in neutral, then have a friend available to spin the car over or manually jump the starter solenoid with a jumper wire to get the car to spin over. Take an incandescent (NOT LED) test light and connect the clip to chassis ground, then move the tip of the test light towards the open end of the plug wire. While cranking, spark should easily jump a 1-1.5" gap and be bright blueish white.

If you can't jump a 1" gap and/or the spark is dull orange color, coil is weak, or power to the coil is not right or igniter transistor is weak/malfunctioning and not allowing coil to charge properly, or cap and rotor are crappy. Make sure you have good power supply to the coil, and make sure the ground supply pulse from the igniter module is OK by using a bigger lamp of some kind while spinning the engine over watching for pulse. It should be able to pulse a 3-5 amp load through with no issue.

Also make sure your plug gaps are right, too wide and it makes it hard for the coil to jump the gap properly.
 

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I had the same issue with my dizzy jumping around in towards the end-days of my B7/ZC build. I changed plugs, wires, etc... Turned out to be oil that was getting inside the dizzy through the seal and jacking stuff up.
 

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You can test the resistance of your dizzy to see if it's within spec using a multimeter. It's super easy to do, use the google-box to show you how. If it's outside spec than that's the problem. Also, I'd check the wires and plugs... How old are they? What are you using to tune? In my experience anything other than OEM is garbage when it comes to distributors.
 
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