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Old 03-08-2015, 08:59 PM   #1
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Default RX8 yellow injector duty cycle.

So I've been doing some research and now I'm starting to question if I have an underlying problem or if I'm just at the point of new injectors. I have RX8 yellow injectors (the 420cc ones) and looking over my logs I'm hitting 120% duty cycle at redline making 14 psi on a tiny BEGI chingacharger. I've heard these injectors are good for about 240hp so just curious if anyone has some experience with these injectors and have found high duty cycles or if maybe some wise folks think it's time for new fuel pump or fpr. I'm currently down to 10psi since that's the lowest my wastegate will go but I'm still hitting 9x% duty cycle. Car is a 91 with stock fuel system beside injectors obviously
Haven't been on a dyno yet to see my numbers because the high duty cycle makes me not want to waste cash if I need to buy other things. I don't really think I should be this high on duty cycle with such a small turbo.
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Old 03-08-2015, 10:02 PM   #2
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You are not the first to report a Duty Cycle greater than 100%. By definition there is not duty cycle above 100%. Injectors can only be open all the time, which is 100% DC. They cannot be more open. Nevertheless, it would appear that the EMS is asking the injectors to be open more than all the time, and is therefore reporting a number greater than 100%.

If the EMS is correct, then you need bigger injectors, but your AFR's should be reading lean, very lean. However, if your AFR shows too rich, then you may not need bigger injectors, you may only need to tune correctly.

1) What was the RPM and what was the pulse width in mS?
2) What was the AFR under said condition?
3) What EMS are you using?
4) Can you post a log that shows what you are talking about?
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Old 03-08-2015, 11:00 PM   #3
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Sorry, I'm on megasquirt 2.
1. 6485 rpm and 19.275 ms at 10.4 pounds at 11.9 afr which is pretty much what I am targeting at 102% dc
2. 11.9
3. megasquirt
4. my file is too big so I'll try and figure out how to compress it.

Thanks for any input

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Old 03-08-2015, 11:16 PM   #4
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I added the log in a Zipped folder hopefully that works.
Attached Files
File Type: zip 2015-02-17_21.46.54.zip (612.5 KB, 15 views)
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Old 03-08-2015, 11:43 PM   #5
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From your data, you are indeed open all the time, and at your target AFR; so no room for error.

Higher pressure FPR is another option to larger injectors. Injectors seem the most straightforward. Or stay at this power level / max RPM.

It does seem that you are at higher DC than I would expect at that boost / RPM; so you may be correct to suspect pump or regulator.
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Old 03-09-2015, 12:23 AM   #6
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yeah, I thought I was a little high for such low boost, just wanted the opinion of others before I started to toss more money at it. I'm certainly happy with whatever power I'm at currently compared to the stock 100hp, but what more for sure.
Thanks a lot for your input DNMakinson.
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Old 03-09-2015, 06:26 AM   #7
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Stock fuel pump or aftermarket?
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Old 03-09-2015, 10:21 AM   #8
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Quote:
Originally Posted by Savington View Post
Stock fuel pump or aftermarket?
running on stock. Just ordered a dw200 pump and a new oem fuel pressure regulator(which probably wasn't needed but doesn't hurt to replace a 24 year old one). So hopefully this will help. If not, its off to the dyno and seeing how far away I am from my 230whp goal
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Old 03-09-2015, 11:09 AM   #9
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Virtualdyno.net is a nice alternative to paying to dyno time if you're just looking for a number. It's been really accurate for me.

I've run several different injectors in multiple cars and megasquirt has always shown higher duty cycles than I would have expected. I've run around 100% dc in several instances without the car showing any signs of leaning out, never had the ***** to push it beyond that. FWIW my yellows were around showing 100% at ~210whp even though I've seen a lot of people get considerably more power out of them at stock fuel pressure.
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Old 03-09-2015, 11:14 AM   #10
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Quote:
Originally Posted by pdexta View Post
Virtualdyno.net is a nice alternative to paying to dyno time if you're just looking for a number. It's been really accurate for me.
Yeah I downloaded that a little while ago have yet to try and play with it however. And yeah iver heard people range from like 200-250 on these injectors. When I was running 14 pounds and having like 120% duty I was still at my target afr of 11.5 so certainly wasn't tunning lean. Just scary having numbers like that in the chance that inhector could fail and I run lean in boost and blow my dang motor.
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