backfiring

[mooshie]

Well I finally got the car tuned today and got rid of the light throttle hesitation that has been plaguing me for ages. Now I have a new problem- at closed throttle, going down hills or just backing right off the car is popping and backfiring badly.

is it just a poor tune? or is there something else that could cause this?

Current AFR below and the old AFR in the attachment

18364

[Limbo]

sounds like its abit rich, backfiring is usually unburnt fuel in the exhaust, should ask your tuner

[Lukey]

it sounds cool

[trism]

Means that its running too rich under negative vacuum situations. Take it back to your tuner, there's a couple of parameters that can be changed to fix it.

Sent from my HTC Desire using Tapatalk

[mooshie]

I thought that it would be caused by a rich condition, I was hoping that there would be something that i could do myself without having to take it back there.

just worried that it could damage the turbo, cat or muffler.

[dougie_504]

Did it happen during the tune at all? I'd take it back and complain

[TODA AU]

Check you overun fuel cut value.

[mooshie]

Thanks Toda. This sounds exactly like my problem, if I press the accelerator even slightly the backfiring and popping stops.

just for those that are wondering what he is talking about-
Over-run fuel cut-off
The ECM implements over-run fuel cut-off when the engine speed is above 2000 rev/min with engine at normal operating temperature and the throttle position sensor in the closed position, i.e. the vehicle is "coasting" with the throttle pedal released. The ECM indexes the idle air control valve open slightly to increase the air flow through the engine to maintain a constant manifold depression to keep emissions low. Fuel is progressively reinstated as the throttle position sensor is opened.



I cant do this myself though right?
the really painful thing is, living in the hills, I am off-throttle all the way to the shop!

[DC2-PWR]

Thanks Toda. This sounds exactly like my problem, if I press the accelerator even slightly the backfiring and popping stops.

just for those that are wondering what he is talking about-
Over-run fuel cut-off
The ECM implements over-run fuel cut-off when the engine speed is above 2000 rev/min with engine at normal operating temperature and the throttle position sensor in the closed position, i.e. the vehicle is "coasting" with the throttle pedal released. The ECM indexes the idle air control valve open slightly to increase the air flow through the engine to maintain a constant manifold depression to keep emissions low. Fuel is progressively reinstated as the throttle position sensor is opened.



I cant do this myself though right?
the really painful thing is, living in the hills, I am off-throttle all the way to the shop!

Was wondering what Adrian meant too, so thanks heaps for the information.

Subscribed to see how people fix issue

[TODA AU]

I cant do this myself though right?
the really painful thing is, living in the hills, I am off-throttle all the way to the shop!

Maybe you can, what ECU is it?

[mooshie]

it is an Autronic SM4

[TODA AU]

it is an Autronic SM4

If the ECU isn't password protected, It's pretty straightforward.
Have you got the software?

[mooshie]

I had a look on the Autronic website and they have a download for the SM4 for Windows, unfortunately no laptop but I am sure I can use one of the 8 other computers floating around the house...

I will give the shop a call tomorrow to find out if it is password protected. This program looks pretty good though, could I have it hooked up all the time and be monitoring everything happening with the engine?

[mooshie]

Well I went to the shop today and he quickly showed me how I can do this myself.
Looks pretty easy, I just have to get it the right way around.

Adrian- is the cutout lower and then recovery higher? As in the injectors cut at say 1800 RPM off throttle and then recover at 2000 RPM?

I use these numbers just as an example, what would you recommend?

Apparently they didn't re set the fuel cut as they turn it off while tuning...

As I don't have a lot of spare time on my hands, it might be a couple of days before I get this all done. They bloke that does the tuning offered that I can email him the file and then he can send it back to me with the changes done even though he is on holidays this week. If I can I would rather try and learn something new myself though.

[mooshie]

ok, I checked the over run fuel cut values and they are set at about 2000-1800 rpm depending on the coolant temp. does this sound about right? I adjusted the figures down by about 200rpm and it made no difference at all.


Help....

[TODA AU]

ok, I ch
ecked the over run fuel cut values and they are set at about 2000-1800 rpm depending on the coolant temp. does this sound about right? I adjusted the figures down by about 200rpm and it made no difference at all.


Help....
Check your TPS values are correct.
Setting TPS is an automated function with autronic.
Also check TPS & MAP sensor values for ORFC.
Approx.1-1.5% TPS / 25-27kpa + rpm values given.
ORFC must be beyond idle control range both hot & cold.
Also for smother transition, you may need to add recovery fuel.
Lastly, reduce the ignition timing on overun to say 20-25deg.
(This will also help)