Rev Limiter Testing

[jrcotner]

Is there a method to test the 4500 rpm rev limiter?

[spandit]

Find a hill....

If you could turn the alternator at 4500rpm with a drill or something, you might be able to test it. You'd obviously have to take the fan belt off (and fan too, I think). If I recall, it's not actually a limiter, just a warning light. In top gear I've never got close due to the aerodynamic efficiency of the truck!

I have, however, installed MegaJolt ignition which comes with a rev limiter built in which you can set at any level. That works (the basic version just puts the ignition timing to zero but you can install an add-on that cuts it completely)

[stiffler4444]

I can get mine to turn on with sufficient flat or downhill highway use (if I'm not paying attention, my truck slowly, very slowly gains speed under the right circumstances).....

You can also get it to blip if you put her in low gear and rev it up. I was in 4 lo this summer in some sand and had my RPM high enough to get a flicker....

[Jim LaGuardia]

The rev limiter grounds out the voltage to the coil keep the engine from over speeding, this is to keep military personel from speeding or damaging the engine. The engine can actually go up to 5000 rpm for short periods without damage if the module is bypassed.
If the light on the panel flashes as you turn on the key, the module is working.
Most module failures result in early grounding(Light comes on below 4500rpm), this type of module failure usually limits top speed to around 57mph.
All this information is in the repair and operators manuals that every Pinz owner should have, you just have to take the time to read it.

[spandit]

Interesting, I didn't realise it actually functioned as a limiter

[Jimm391730]

Most module failures result in early grounding(Light comes on below 4500rpm), this type of module failure usually limits top speed to around 57mph.

Mine failed so that it was partially grounding across all rpm ranges, including idle. From my experience the average DC voltage at the + side of the coil should be about 17 volts; with my bad RPM module I was only getting about 8 volts at the coil. Removing the module and jumpering the middle two terminals from each row together gave me back 17 volts at the coil, with an amazing difference in performance.

I would suggest checking the coil voltage while the engine is running (not the points/Pertronix side of the coil) and if you don't have at least 14-15 volts I'd suspect the module was failing. I don't have any realistic way to determine if it limits the RPMs, or what RPMs light the indicator. The module actually measures the rate of ignition pulses and has no idea or care what speed the alternator is going.

[Winter Beater]

I have Jim L's 2.7L kit and regularily bounce the light on between shifts. Normally it lights and then I shift, but once while pre-occupied with a merging vehicle doing silly things the engine shut down. Probably hit 5000 rpm, so yes it is a rev limiter.

[jrcotner]

Jimm had the answer I was looking for. Thanks.