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ptharris

Over run fuel cut problem

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Hi guys Evo 9 plugin firmware 4.7.1.804 I have disabled over run fuel cut and have a lean condition on the over run which causes the car to buck. Not sure whats up as i have increased the fuel table numbers on the over run quite a bit, but my wideband still show lean pegged at 16.99AFR Does the same with over run fuel cut enabled Seems to happen around 2500 - 1300 rpm Attached is log showing this, any help would be great Phil

over-run-fuel-cut.problem.llg

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Hi Phil,

Overrun fuel cut is there to stop the bucking you experience when you turn it off. Any particular reason you've turned it off? It gives you engine braking, if you give it fuel it probably would try to accelerate downhill when you take your foot off the throttle etc.

Looking at your log your injector pulse width is still dropping dramatically suggesting that the area of the fuel table you are going into under overrun is lacking the fuel to keep your AFR's where you want them.

-Cameron

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Hi Cameron With the over run fuel cut turned on, i still experience the bucking at around 2000 - 1500 rpm on the over run. Over run fuel cut is set at 1600 rpm on warm engine Any ideas? It is going on a hub dyno tomorrow for fine tuning of the timing and afr's. But tuner isnt sure he will have time to look at this issue on the road after (he is very busy and doing me a favor getting me in tomorrow) Attached my map

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Hi Phil,

Is the bucking occurring when you put your foot back on the throttle? (I can't see anything that would constitute as bucking while in overrun).

The fact that it happens with or without the FC suggests it is some other issue like ignition timing.

Another thing to check would be MAP delay, if the MAP hose is too long or has fuel blocking it, that can cause bucking. If you are using cheap silicon hose then it can collapse under hard vacuum as well.

-Cameron

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Hi Phil,

Looks like the bucking is happening when you're coming out of the fuel cut at 1600rpm.

In your ignition table at 1500 it seems to be alternating between the 20 and 40 kpa zones, the 40 zone will create more power and increase the vacuum dropping it into the 20kpa zone where it makes less power and the vacuum drops away. It should probably be tuned on a dyno to hold it in those areas and get fueling and ignition correct.

-Cameron

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