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Old 02-18-2010, 04:32 AM   #1
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Default Injector duty cycle way high

Savington pointed out in another thread the injector duty cycle of my friends car we've been tuning is out of hand, something I honestly hadn't really noticed before.

Went out tonight for a few hours doing more work on it and to check everything out, all the settings in megasquirt look legit.. The AFR targets for high boost are 11.4 and it holds pretty well around that area until the manifold pressure starts to pass 16psi or so then it starts going into the *******. It was real bad the first time it really started to climb in boost, but after a little work I managed to get it down from what I first saw (13:1 @ 20psi!!) to 12.5, but yeah it needs more work.

Required fuel is set correctly, I checked all the other injector settings vs. the DIY PNP stock MSQ and it all matches up. Not sure whats wrong, but we're seeing 120+% injector duty cycle, not able to supply enough fuel for higher boost areas in RPM and I can't figure out why.

The turbo shouldn't really be making that much boost, its supposedly a 14psi actuator and is running off the outlet of the compressor. Guess we need to get it ported or switch to an EWG?

I know the spark map might be a little over the top. We have no knock sensor aside the OEM oil pressure gauge but have yet to see it dance. Granted thats not guarantee there is no knock, so I'd like to consider a less aggressive spark map. Thing is, when we first installed the FM2 kit I loaded up a pretty tame spark map and the car didn't pull for ****.. Like, my supercharged car could easily walk away from the turbo car. After swapping over to the map I was running it seriously came to life.. Our plans were to change that before weather got warm anyway, but now is good time as any.

Here's the setup:

GT28 Chinacharger
RC 550cc Injectors (Low-Z with inline resistors) <-- is that the problem??
OEM Fuel pump & Regulator
Jim B's dual feed rail (Yeah, John Hunter was one of the five lucky enough to actually squeeze one out of Jim...)
Infamous 18x12 Chinacooler
I think Paul's Spark map?

A Known issue, might not be related but worth mentioning. We discovered there is a very small vacuum / boost leak around where the fuel injectors seat into the manifold. We'll be checking that out this afternoon, along with testing the fuel pressure. What am I forgetting?

-Humble Monkey trying to learn!
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Old 02-18-2010, 05:00 AM   #2
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OEM fuel pump is your issue. The good ones are done at 240-250whp. Bad ones won't make 200whp. Stick a Walbro 255 in there.

As far as the timing map, double and triple check the base timing. Wouldn't surprise me at all if the base timing is 10 degrees retarded. Take 10 degrees off your timing map and it becomes quite a bit more reasonable - 7 degrees at 19psi is pretty low but in the ballpark on pump gas. Build a set of mechanical det cans and use them.

You should also run LESS timing at torque peak, and MORE timing near redline. IIRC your log showed the opposite. RPM is a natural detonation deterrent. You can run huge timing at redline and really extend the torque curve and pick up power - I can usually find MBT on pump gas in stock motors over 6000rpm.

You also need to get the boost under control. 19psi on a 14psi spring is no good. Port the IWG or switch it to an EWG. It's also best to reference the can post-intercooler, but that's done to solve boost drop at redline - you have the opposite issue.

Last edited by Savington; 02-18-2010 at 05:26 AM.
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Old 02-18-2010, 06:44 AM   #3
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Originally Posted by Savington View Post
OEM fuel pump is your issue. The good ones are done at 240-250whp. Bad ones won't make 200whp. Stick a Walbro 255 in there.
If you're cheap, (like me) Give the OEM FuelPump it's own clean direct 12v feed from the battery (obviously via a relay).

SlowMX5 did a writeup on his website

Stops the pump running out of steam at higher rpms. With appropriately sized injectors the OEM pump is capeable of flowing enough fuel for 300bhp - apparently.
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