HELP! All Mechanical Eliminated- Wont rev past 4K

[Arne]

I realize that the original poster hasn't been on the site in a while, but since I've seen references to a few others with similar issues I thought that I'd report some recent changes on my similar issue.

Interestingly enough, I have been experiencing the same issue on mine. Felt like a 4000 RPM rev limiter. Just today I finally got a change in symptom by advancing the timing more. My current theory is that the timing pointer is not correct, and that I was running it very much retarded. Try advancing the timing about 10 degrees more than what it is now and see if that helps.

FWIW - I cured my similar problem this morning. This may or may not apply to your car, but might be worth a try.

With the electronic ignition on my car I had been using wider gap NGKs as specified for 280ZX - BPR6EY-11 V-Power, to be precise. This morning, after reading in an old generic troubleshooting guide from the '70s that a miss under acceleration is often plug gap too wide, I installed a set of stock BP6ES-8 instead. Both sets of plugs were nearly new, and the wide gap plugs looked beautiful coming out.

But with the narrow gap plugs, the car runs perfectly. Pulls smoothly and strongly past 6000 RPM. No issues at all.

If you review my earlier posts, you'll see that I claim to have fixed it with a plug change a while back. Turns out that fix was not permanent, the problem returned after some time.

To recap, my car would rev great in neutral, but under load (accelerating through the gears) it would reach a point where it would simply stop revving, much like it had hit a rev limiter. The point at which this would happen varied depending on my ignition config. At stock timing (5° BTDC) it would hit the wall at about 4000 RPM. If I advanced the timing to 15-17° BTDC I could get over 5000 RPM before it started to sputter and then stop revving.

Here's what I was running up until yesterday:

Stock late '71 L24 w/E88 head and all emissions equipment intact
Original 240Z distributor w/vacuum advance (cleaned, lubed and tested)
Mechanical advance curve quickened by removing one of the two governor springs
Matching Bosch cap and rotor
NGK plug wires
NGK BP6ES-8 (normal .032" gap)
Pertronix Ignitor
Pertronix 3Ω Flamethrower coil
Ballast resistor by-passed
Timing set to 15° BTDC (timing marker verified manually)

With this setup, I could rev cleanly to 5000-5300 or so, but the car was prone to ping under moderate load, even on what the oil companies are pleased to sell as "91 octane" fuel these days.

Since the car did not do this in the past, I decided yesterday to revert to the way it was when I bought it. I didn't re-install the original cap, rotor and wires, but did reinstall the points, original coil and re-connect the ballast resistor, and set the timing to 10° BTDC as it was when I bought the car.

Test drive showed it ran properly this way—pulls clean and hard to 6500 if I want. So now it was a simple matter of parts substitution to find out where the issue is/was.

My first move was to install the Pertronix coil with the points. And that immediately brought the problem back. With the newer 3Ω coil in combination with the points, the car would pull up to a touch over 5000 RPM if the ballast resistor was bypassed, or only about 4000 RPM with the ballast in place. So it was back to the original 38 year old coil.

Next I installed the Pertronix ignitor, but retained the original coil and left the resistor connected. This also caused the problem to return, this time at ~4800 RPM. By-passing the resistor while using the original coil and the Ignitor again allows the engine to rev clear through to 6500 RPM.

So this is where I am today:

Stock late '71 L24 w/E88 head and all emissions equipment intact
Original 240Z distributor w/vacuum advance
Mechanical advance curve quickened by removing one of the two governor springs
Matching Bosch cap and rotor
NGK plug wires
NGK BP6ES-8 (normal .032" gap)
Pertronix Ignitor
Original Nissan 1.5Ω coil
Ballast resistor by-passed
Timing set to 8° BTDC

The car runs great in this config.

My conclusion is that the Pertronix Ignitor changes the spark in such a way that a coil in the normal 3Ω range can't keep up for some reason. The stock coil is rated at about 1.5Ω, and the resistor is rated at about 1.6Ω, for a combination of 3.1Ω.

The points ignition works fine with the original 3.1Ω coil/resistor combo, but the Pertonix will not, it needs the 1.5Ω coil alone to keep up. This is despite the recommendation in the Pertronix documentation calling for a 3Ω coil with no resistor for 6 cylinder engines for street use. It may be related to the fact that the dwell angle of the Pertronix (which is non-adjustable) is borderline low, compared to factory specs for the points.

Worse, the Pertronix 3Ω coil doesn't appear to truly be 3Ω, since it won't quite keep up with the points ignition even with the ballast by-passed. And since the Ignitor appears to require less than 3Ω to run well, the combo flat doesn't work.

My ignition package was purchased from MSA about 8 months ago. I will contact MSA about this, and see if they can take the 3Ω coil back, hopefully exchanging for a 1.5Ω instead. But that might not be possible, considering that we're talking electrical parts here.

So that's where I stand right now. The car is running great on the Ignitor and original coil (no resistor).