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Fuel VE Higher at Idle

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1989 Merkur XR4Ti (US Ford 2.3L Turbo), Garrett T3 turbo (stock), Deka 80 injectors, distributor batch fire ignition (stock), Walbro 255 fuel pump, AEM Wideband O2 controller/gauge

Running on MS2 with Tuner Studio.

While getting the setup running on the standalone (running through a Stinger Performance "PIMP" Plug n Play computer using MS2 internals), The car seemingly wanted a LOT of fuel while starting off with the idle tuning. This initiated a lot of investigation and fixing/uprating the fueling system, including a new fuel pressure regulator (stock, boost referenced), changing the in tank pump to a Walbro 255, and wiring modifications to reduce voltage drop to the pump, to no avail.

Then a LARGE exhaust leak was discovered and fixed, which corrected a lot of the problem. The gauge was indicating lean, but the exhaust smell and look of the spark plugs was pointing to a highly rich condition.

Once the car was stable enough to drive around, the rest of the VE table seems to be more in line with what is expected (magnitude-wise), but the transition from the idle area out to other parts of the table seems to make the car run into an overly rich condition and stumbles when the car is given wide open throttle from low RPM.

I'm not sure what is causing this difference only in the idle area, or what can be done to smooth the transition from the higher VE idle area to the surrounding area in the table. Attached is a photo of an older VE table (before working on tuning the surrounding cells for smoothness), for reference.

I am fairly new to tuning but learn quick and have started the EFI Tuning Fundamentals course to better help myself in the future. Feel free to ask any questions which may help you understand better about the setup or the tune.

Thanks in advance!

Attached Files

From my understanding your trouble is only with transitioning out of idle, and seeing as it is a new build there could be many variables. How rich are we talking?

This is heavily dependent on what you are using as your base map, but one possible oversight is applying acceleration enrichment aka transient fueling in excessive amounts.

Typically when you start a new tune, you want to disable compensations like acceleration enrichment and tune the base fuel map without making any abrupt changes in your acceleration (TPS).

I'll definitely take a look and make sure that the acceleration enrichment isn't overpowering things.

It was so rich that it was stumbling and had gone to max indicated rich (10 AFR) on the gauge.

Do you have appropriate injector dead time settings? It sounds like your dead times are too low requiring more mapped fuel at low demand?

Is injection sequential, semi or batch?

I am using the recommended injector dead time setting of 0.7ms, with the jumpers for high impedance injectors installed. The same issue existed on the stock low impedance injectors using the recommended settings (~1.1ms).

It's using the stock batch fire setup, 2 squirts per cycle.