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Thread: Soften deceleration fuel cut on low RPMs

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Posts: 31-40 of 44
2013-08-04 22:58:57
We were just getting confused with the simple "fuel cut" wording. Since there is other tables to do with decel fuel.

Think of it as decel fuel cut. The other decel fuel tables must be "how much fuel is cut"?

I have played with the fuel cut tables once and only once. What I did was use the values coldest value and make the whole table the same. Now it has certainly stopped the insane bucking but does have some adverse side effects lol. fun thought! hehe

If anyone else is going to try this maybe you should try lower values than I did. Copying the middle value and using across the whole table should work good.

The biggest thing to remember is use values above were your having the issue! Mine was under 2,000rpm mainly, around 1,500rpm. So keep the RPM values in the table above that.

The biggest thing is since these tables were not modified before why does it buck so bad when you have mods?
Same goes with another small issue im having with the timing staying static under 3K and until 65c. Why does it hesitate once you have modded your engine lol. The "idle timing" table has not changed! ugh
Last edited by Haulin200sx on 2013-08-04 at 23-01-57.
2013-08-05 01:25:45
Overrun fuel cut cuts fuel when the throttle is CLOSED.
Decel fuel reduces the IPW when the throttle is CLOSING above a certain rate.

Hope that helps.
2013-08-28 22:06:49
Well after many many drives and playing with the fuel cut and doing data logs I can now say for sure! this overrun fuel cut has nothing to do with the low speed off throttle bucking issue.. For me it happens off throttle around 1,500rpm when cold or hot. Its not activating the fuel cut flag when this happens. Could be something to do with the timing jumping from high to low???

Back to the drawing board.............
2013-08-29 02:12:55
Did you log TPS voltage and the TPS closed flag as John recommended??

The fuel cut flag will NOT be activated if the TPSclosed flag is not initiated.

I have a sneaky feeling it is something mechanical and not anything to do with John's software. Upload a base map and do a few logs as mentioned above and report back
Last edited by Boostlee on 2013-08-29 at 15-18-04.
2013-08-29 03:39:39
My car was terrible for this issue for a long time. Log your battery voltage and see if its constant, i had a dud alternator, replacing it didnt make the problem go away entirely, but it has helped a lot.

Look at TPS Closed timing table under idle too, ive got mostly 20deg up to 2400 rpm atm, higher idle timing rpm seems to help keep the revs up a bit and deadens the bucking i found. Also try raise your Initial Idle Duty numbers, it makes the idle stay higher than ideal, but means when you back off the gas its keeps the idle up rather than dropping it into full vacuum..
2013-08-29 14:54:20
Have you tried increasing accel enrichment? A larger TB will allow more air for each degree of throttle opening.
2013-08-29 23:30:41
Originally Posted by OnTheChip
Have you tried increasing accel enrichment? A larger TB will allow more air for each degree of throttle opening.

I don't really think this will help Dave.

The TPS closed flag does light when I'm off the gas pedal, so all is good there. Everything is within specs that I can see. Overall the tune is really good.

It happens when I'm coasting across a parking lot in first gear at around 1,500rpm, when im OFF the gas BUCK BUCK BUCK.

When I first seen this tread I though Nicoxis wanted to remove all his decal fuel haha but after a few of his posts it seemed like his issue is close to mine.

Now I haven't been paying much attention to my voltage, it never drops below 13V but the battery light does flicker/dim light sometimes. Evlnxr might be on to something here though. Will have to get out again and datalog the shit out of it
2013-08-29 23:46:26
Yea, 1500 is well below the overrun fuel cut limit. Sounds like an idle control issue. Are you RT or SA?
2013-08-30 12:12:53
Originally Posted by OnTheChip
Yea, 1500 is well below the overrun fuel cut limit. Sounds like an idle control issue. Are you RT or SA?

I always took it to be a idle control issue with my car too, the alternator problem was causing a fault, then the idle control issue would raise its head. Idle control issue can still be made to happen at times, but its not as bad. Also adding some fuel in the far left row of fuel table helped a little, but im not sure this was a cure.

Raising the idle duty initial value just keeps the idle high, which means you cant coast off throttle in 1st under 1500 as it wants to keep rolling, but at least it stops the bucking.
2013-08-30 16:06:50
My battery is a rock solid 14v, so I don't think my issue is related to this.

What I found is that my throttle closed flag stays activated not only on 0.45v but also up until 0.49v, is this normal?

Other things I've tried with no success,

- Raise Min TP (10)

- Raise Idle Ignition timing (20)

- Lower RPM TPS Enrich Factor on low RPMs.
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