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Old 11-18-2018, 10:11 PM   #51
lummert
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Starting to notice that these injectors work better at 2.7 Bar fuel pressure. Engine idles rough until it warms up at 3 Bar fuel pressure. Duty cycle is nearly the same at either fuel pressure. Idle: 60% compared to 58%. Engine off : 82% compared to 79%. So I take it that the fuel pressure difference has little effect on the duty cycle. So go with the fuel pressure that works best for the injectors?

Info that I found on Mustang Cobra site about running injectors that are too big:
* Lower fuel pressure and increase injector openings.
* Run richer at idle.
* Run a less aggressive injector if ECU allows it.
* Raise the idle speed.
* A combination of a few above...
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Old 11-19-2018, 01:04 PM   #52
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Swapped to a second BMW 2.5 Bar FPR because car was hard to start this morning (35* F) with the Buick 3.0 Bar FPR. Now to wait for it to warm up a bit outside to do a pressure test with this other BMW FPR.

Looking through my FPR's to see if I have a good OE Volvo type FPR.
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Old 11-22-2018, 02:54 PM   #53
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Today I found a different dwell to duty cycle conversion chart. I retested with the dwell meter on a warm engine and got 36 degrees on 6 cyl scale. According to this chart 36 degrees on 6 cylinder scale = 40% duty cycle. 40% duty cycle at idle in closed loop makes much more sense.

Ground controlled circuit @ 36 degrees on 6 cylinder scale = 40% duty cycle
Feed controlled circuit @ 36 degrees on 6 cylinder scale = 60% duty cycle

Not sure about the voltage reading that I was getting. With dwell meter at voltmeter connected at same time between test point and battery positive showed 5.95 VDC. 5.80 VDC corresponds to 60% duty cycle on same chart.

Last edited by lummert; 11-22-2018 at 04:10 PM..
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Old Yesterday, 02:59 PM   #54
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Found specs for 36 lbs/hr injectors when running at 39.15 psi (2.7 Bars).

34.0 lbs/hr @ 39.15 psi
357.3 cc/min @ 2.7 Bars
257 grams/min @ 2.7 Bars

35.84 lbs/hr @ 43.5 psi
376.7 cc/min @ 3 Bars
.52 BSFC - Estimated HP @ duty cycle
52.3 @ 80%
62.1 @ 95%
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Old Yesterday, 03:28 PM   #55
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Duty cycle is calculated by comparing the injector pulsewidth to the time it takes to complete an engine cycle.

For example, an engine idling at 800 rpm takes 150ms to complete one full engine cycle of 720 degrees crank rotation.

If your idle injector pulsewidth is 3ms then your injector duty cycle is 2%. Simple as that.

You’re trying to look far to into this.
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Old Yesterday, 03:33 PM   #56
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Quote:
Originally Posted by gross polluter View Post
Duty cycle is calculated by comparing the injector pulsewidth to the time it takes to complete an engine cycle.

For example, an engine idling at 800 rpm takes 150ms to complete one full engine cycle of 720 degrees crank rotation.

If your idle injector pulsewidth is 3ms then your injector duty cycle is 2%. Simple as that.

You’re trying to look far to into this.
One thing I know for sure is that these injectors (Bosch 0 280 155 811) work best at 39.15 psi (2.7 Bars), same as when running these on a Ford Mustang.
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Old Yesterday, 06:36 PM   #57
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When you’re trying to patch it into a different application such as this, maybe. When properly controlled they’ll operate just fine with any other common fuel pressure.
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