Eratic AFR and Poor Performance @ High MAP & TP

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portmod7
MS/Extra Newbie
Posts: 21
Joined: Fri Nov 30, 2012 10:00 am

Eratic AFR and Poor Performance @ High MAP & TP

Post by portmod7 »

Hi guys,

Still messing with this thing. I recently switched over to staging my injectors and I have a progressive linkage on my TB that starts opening the secondaries around 50% TP.

I really like the cruise and low RPM driveability with this setup, it seems to be working well. However, it seems like since I switched to staging the injectors, it runs really rough and the AFR is really erratic at high load and high TP. It seems right when the secondaries start opening, it starts sputtering and struggling to gain RPM. You can see it in the datalog from today pretty clearly.

Before I switched to staging, my cruise and low rpm driveability was not nearly as good, but if I opened up the throttle, it would pull hard and run really strong all the way to redline. The throttle plate linkage was 1:1, so the rear blades opened at the same time as the front.

At first I thought maybe it just needs to tune some more, but the erratic AFR threw me off, it's not like it's rich or lean, it's all over the place. It almost seems like it's the way the air flows into the intake as the secondaries open or something. I don't know, any ideas??????

Sorry the datalog is so short, that's the only way I could get it uploaded... Hopefully it's enough?
____________________________________________________________________________________________________________________
MS2 w/v3.0 Board; MS2/Extra Firmware v3.4.0; TunerStudio MS v2.6.14
- MAP on TBI, 3-bar Baro sensor on MS2 PCB

TBI: FAST EZ-EFI "1.0" Throttle body & associated injectors, sensors, etc. 43psi max fuel pressure.
- 1.5bar MAP Sensor
- (4)65lb/hr FAST High-Impedance Injectors
- 4-wire Stepper IAC
- IAT
- TPS
- Coolant temperature sensor in the cylinder head between cylinders 1&3.

Ford EDIS-8 Ignition
- 36-1trigger wheel custom made to match tooth width to VR Sensor
- Standard Motor Products PC19 VR Sensor
- (2)DIY Autotune IGN-4 4-Tower Coil Packs
- MSD 8.5mm Super Conductor Wires
- NGK Spark Plugs

14point7 wideband controller and O2 sensor

Engine/Trans: GM Fast Burn 385, 350ci V-8, Crate Motor/4-speed Saginaw Manual

Fuel: Aeromotive Stealth 340 In-Tank Pump, vacuum referenced pressure regulator with fuel return to tank
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Matt Cramer
Super MS/Extra'er
Posts: 17499
Joined: Thu Apr 16, 2009 8:08 pm

Re: Eratic AFR and Poor Performance @ High MAP & TP

Post by Matt Cramer »

This could be a misfire for a number of reasons, not just fueling. But the misfire or lean condition seems to start before the secondaries engage.

The primary pulse width is a lot higher than the secondary. Try bringing the staging up to 100% a bit earlier. I'm wondering if you have a fuel distribution issue when the secondary throttles are open but receiving less fuel.
Matt Cramer -1966 Dodge Dart slant six running on MS3X
portmod7
MS/Extra Newbie
Posts: 21
Joined: Fri Nov 30, 2012 10:00 am

Re: Eratic AFR and Poor Performance @ High MAP & TP

Post by portmod7 »

Matt Cramer wrote:This could be a misfire for a number of reasons, not just fueling. But the misfire or lean condition seems to start before the secondaries engage.

The primary pulse width is a lot higher than the secondary. Try bringing the staging up to 100% a bit earlier. I'm wondering if you have a fuel distribution issue when the secondary throttles are open but receiving less fuel.
Thank you Matt.

I will try that. The base staging table seemed to start off low(5%@2kRPM, to 10%@3kRPM, to 20%@4kRPM, etc.) and ramp up... Is that necessary, or can I wait until 4k RPM and stage in at 50% or higher all of a sudden? Is that what you had in mind?

I have also tried staging off TP as the primary parameter, and MAP as secondary with similar results.
portmod7
MS/Extra Newbie
Posts: 21
Joined: Fri Nov 30, 2012 10:00 am

Re: Eratic AFR and Poor Performance @ High MAP & TP

Post by portmod7 »

I think you were right Matt. I brought the staging in sooner in the rpm range and more aggressively, starting at 70%. It seems to like that way better so far. Hopefully it continues.

Thank you!
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