throttle release/fuel control

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mikerobison
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throttle release/fuel control

Post by mikerobison » Tue May 27, 2008 3:23 pm

When you release the the throttle pedal which sensor notifies the injectors to cut fuel?

The reason I ask is when I accelerate then slowly release the pedal to a cruise speed my air fuel meter fluxuates between rich and lean and causes a violent jerking through the drive train. (the fluxuation and the jerking happen at the same time) If I accelerate then release quickly the reaction is deminished greatly.

This could also be a vacuum issue but I am curious of the injector control. Thanks
Mike

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Post by hEaT » Tue May 27, 2008 3:28 pm

I'm guessing the TPS.

Do you have a narrowband or wideband? Narrowband will fluctuate like that. They are good for seeing the transition between open loop and closed loop, when the injectors shut off on decel and that's it.
Joe
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Post by mikerobison » Tue May 27, 2008 3:32 pm

narrow

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Post by MerkXRTurbo » Tue May 27, 2008 3:35 pm

It's mostly the VAM. When the TB closes, the airflow diminishes so the VAM closes too. It also, however, gets some input from the TPS (it tells the EEC that the engine is now at low load), and the O2 sensor.
3" mandrel bent exhaust, Ported/Polished head, 1.89/1.57 valves, Gutted uppper/Knife edge lower intake, T3/T4, LA3, Big VAM, Cold air intake, 40bob header, Gillis valve, Forge BOV, Mustang SVO T5, Conquest intercooler, 20psi.

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Post by BeefFajitas » Tue May 27, 2008 3:38 pm

Do you have an IC? Some people report that problem with an IC. The VAM is too far away from the TB to really report an accurate amount of air in the system.
-Nate
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anglin
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Re: throttle release/fuel control

Post by anglin » Tue May 27, 2008 3:38 pm

mikerobison wrote:When you release the the throttle pedal which sensor notifies the injectors to cut fuel?
Mike, like Joe said, it sounds like your TPS. Don't associate the mixture fluctuation on your air-fuel ratio gauge with the jerking of the car. It sounds like you are just seeing it transition between open and closed loop (the fluctuation occurs in closed loop because the computer is paying attention to the oxygen sensor and adjusting the mixture accordingly).

You can check for good sweep of the voltage output on the TPS with an analog voltmeter (described in the shop manual) or you can just replace it. The TPS isn't an expensive part.

Of course, we are diagnosing this problem with nothing more than your short description. If you didn't mention that your car has an intercooler with 45 feet of plumbing and no BOV/BPV, you could just be experiencing trailer hitching. :dunno We need more info, but I'm gonna guess it's your TPS.

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Post by mikerobison » Tue May 27, 2008 4:26 pm

I do have a IC rs500 with stock intake, and I have a BOV that appears to operate perfectly. It is a dual stage diaphagm style.

The transition between open and closed loop should take longer than 1-2 seconds. I thought the computer stayed in open loop untill 10 seconds of contant thottle position before going to closed loop...Assuming you have reached operating temp. Almost instantainously to when I apply throttle the AF Meter Reads a rich signal showing I am no longer in closed loop.

I have another VAM I'll stick in.
I'll also check the TPS

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Post by hEaT » Tue May 27, 2008 5:21 pm

Doesn't take that long at all. I can roll on the throttle and watch it switch almost instantly.
Joe
1985 Nimbus Grey XR
2017 Ford Focus RS

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