Need Some Help With Required Fuel

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Need Some Help With Required Fuel

Postby Scottie-GNZ » Sat Mar 31, 2012 8:20 am

Having a problem with the engine running lean under load and could really use some help understanding what's going on.

Little background: Engine is a 2JZ-GTE, 1680cc low-impedance injectors (currently on pump gas but plan is for big HP on E85), D585 coils in a COP arrangement, MS3/MS3X/relay board. Everything is wired for sequential but after chasing noise issues on the sensor for a while, I decided to get the car going with semi-sequential/Wasted-COP and come back to full sequential at a later time. The OEM VR sensors have been changed with the cam sensor disabled and the crank sensor replaced with a 36-1 wheel and hall sensor.

After weeks of fighting the VR noise issue, the engine fired up on the first crank with the hall sensor. The calculated Required Fuel is 2.0 but it was way too lean so I bumped it up to get the engine to opertaing temp and with some tweaks on the dead tme, I was able to get the Required Fuel down to 2.9. Engine idles at 875 and .94 Lambda and I can live with that considering the injector size and cams. Did some low-speed driving and that tune is coming along fine but have an issue with trying to apply load to the engine. As load increases is gets increasingly leaner with misfiring around 4500 and 5psi boost. While reviewing the datalog and msq, I noticed something odd with the required fuel. It is my understanding that the top required fuel value is what is calculated and the bottom is what is downloaded to the MS. My msq as last used has 2.9 on top and .48 on the bottom. If .48 is what was downloaded, that should explain the lack of fuel under load. Took me a while to understand the .48 but the Squirts percycle value is 6 and 2.9/6 is ~.48. The squirts value is a 6 because one advice I got was to try and see what works, then another said that setting is ignored with seq and semi-seq and to set it at 1 for seq and 2 for alternating. Guess I only saw the part about the setting is ignored, and just left it at 6 :?

It seems obvious that the calculated req fuel is being divided by the squirts/cycle value and that is what is downloaded to the MS. Before I go back out and try this again, I wanted to get some feedback on what others thought/have experienced.

Thanks
Scottie
Turbo LS Mustang
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Re: Need Some Help With Required Fuel

Postby racingmini_mtl » Sat Mar 31, 2012 9:05 am

You mention that you have low impedance injectors but you don't mention how they are connected to the MS. Do you have inline resistors or external peak&hold drivers? You do know you can't connect low impedance injectors directly to the MS3X, right?

Jean
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Re: Need Some Help With Required Fuel

Postby Scottie-GNZ » Sat Mar 31, 2012 12:25 pm

Oops, sorry. I meant hi-impedance. They are FIC hi-impedance injectors.
Scottie
Turbo LS Mustang
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Scottie-GNZ
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Re: Need Some Help With Required Fuel

Postby xrattiracer » Sun Apr 01, 2012 11:04 am

injector dead times really come into play with larger injectors like this too. if you "fudge" the required fuel numbers to make up for an incorrect dead time setting to make it run correctly at idle, the fueling will have an error in other parts of the map.
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