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I have read where people have had problems with dual IPRs. I'm reading here that duty cycles are halved or doubled with dual IPRs. I asked the question if voltage drop was taken into consideration when running IPRs in series. The answer I got was that the PCM didn't care about voltage. It only cared about ICP. Well that is true, however, the IPR cares and it is the part that controls the ICP.

Now correct me if I'm out in left field here.

Looking at Ford schematics, it appears the IPR has a resistance of 10-20 ohms. At 12 volts 20 ohms consumes 7.2 watts of power. In case you didn't get 5 years of electrical engineering, watt is a measurement of energy and we refer to Ohm's Law to calculate it.

If we hook two IPRs in series, we get 40 ohms. At 12 volts we get 3.6 watts.

If we hook two IPRs in parallel, we get 10 ohms. At 12 volts we get 14.4 watts.

At first blush, it seems that running 2 IPRs in series makes little sense. We've doubled the IPRs and halved the power with the same duty cycle. I would doubt that the results are linear, but it would seem that we are closing the valve half of what we normally would. We've doubled the valves so we have twice the leak rate. You would almost expect four times the normal duty cycle in order to keep up.

Parallel IPRs seem to make more sense. This setup allows the valves to position themselves to the same as the single IPR with the same duty cycle. Thing is we have two valves dumping oil. Under stock conditions, we would need to increase duty cycles to maintain pressure. Maybe by twice normal.

I think Charles tried pointing this out. We are doubling the spigets so we need to up the duty cycles to get back to where we were. Of course these systems are running higher flow rates than stock and that will negate some of the extra flow from the double IPRs.

I don't know... If you need two IPRs, parallel seems the more logical way to go. I would think you only need two if one can't dump enough oil and even then I think there are better ways of regulating that before screwing in a second IPR.

I do want to thank Charles. I understand most of what he was saying and learned a bit. I've included his earlier post to keep folks up to speed. :bowfast:

Charles said:Just a refresher on the IPR and what the duty cycle means...

It's ~440ish hz PWM signal to the IPR. The duty cycle is % of closure.

If the signal frequency is 440hz for instance, the PCM would ground the wire to the IPR 440 times every second for a varying percentage of time on each of the 440 events.

So that means that we have 440 events with a duration of ~2.27ms each. Now the PWM comes into play in the relative on vs off time for each of these events. If for instance, you were running a 30% duty cycle, that would mean that for each of the 2.27ms events the PCM would pull it to ground for ~.68ms and release it for ~1.59ms. Then imediately pull it to ground for ~.68ms and release it for ~1.59ms again 440 times every second.

Now if it were a 50% duty cycle the relative on vs off would be ~1.36ms each, or grounded half the time and open the other half of each event.

The effect on the resistor, in this case the IPR is not actual movement from totally open to totally closed. Physical objects do not react this fast so the net effect is the same as if you'd actually applied an analog current to it even though it was actually digital (On vs Off).

So a duty cycle of 20% means the IPR is 20% closed and a duty cycle of 40% means it is 40% closed.

If you doubled the flowable area to drain the pump volume, you would then have to close it down twice as far to still maintain the orifice size you originally had at half the flowable area. Meaning going to two IPRs should double your duty cycle.

Just thought everyone could use a refresher on what the duty cycle was and what it meant.