Since fitting my homebrew ITBs I have been doing a lot of miles while tweaking the map. I have got things running quite nicely now except I get a fair bit of popping and banging when slowing down. Now I don't mind a bit of 'character noise' but I freaked out a horse today and the rider was lucky to stay on the beastie so I need to quieten things down a bit.

I have tried cutting all fuel above 2500rpm on 0% throttle but with no real improvement - is there a trick to this?

Do you have any air leeks in your exhaust ? that will make it back fire

If the ignition is over advanced it too can cause popping on overrun

its actually caused by being under fuelled at low throttle openings. There is not enough air velocity so the fuel puddles, doesn't ignite and ends up burning in the exhaust. increase the fuelling as you come off the throttle a little before fuel cut comes in and it should cure it. theory is that a little bit more fuel will cause it to ignite in the cylinder rather than the exhaust.

My car pops a little bit on over-run when it's hot - I like it!

If I have to pass a horse (there are a few riding schools near me) I usually floor the clutch and coast past nice and slowly. The engine's just on tick-over instead of over-run, so barely audible.

My Emerald map has fueling till cut off, which is at RPM below 1500 with 0% opening, so agree perhaps a little fuel might help.

I want pops and bangs, some flames would be nice as well. Singe the hairs off the horses legs

+1

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Originally posted by coozer
I want pops and bangs, some flames would be nice as well. Singe the hairs off the horses legs

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I want more 'character noises' as well. Count yourself lucky!!!

Was scaring the horse related to the noise of the car or are the car noise and scaring the horse two seperate episodes?? ooerr missus

whilst i agree horses should be confined to fields and bridle paths, breaking somones neck for being foolish enough to ride one of the fly ridden immense turd producing beasts seems a bit harsh.

Raz, great to hear that you are putting some miles on your new TBI's.

I have had a similar thing from time to time. Actually I have never really got to the bottom of how to manage fuel cut.

I can get pops and bangs if I lower the fueling on the over-run.
If I use a fuel cut, then it isn't very nice when I come back on the power.

The solution (in my case), is to run about 15-16 on the over-run and disable fuel cut. This isn't ideal from a fuel consumption perspective.
I have read that you can tune these problems out, but it wasn't easy when I tried.


Matt

Thanks for all the ideas guys - I live in a fairly rural part of Essex so horses are a part of life round these parts. I have to agree that the roads are not the place for the beasties but I guess they have to get from A to B like the rest of us.

I tried a little more fuel on the over run and presto! - all is quiet and well mannered now.
I knew you lot wouldn't let me down

You should be using a Wideband AFR meter to tune and one of the result of doing it this way would be it this should reduce this type of thing to an expectable level. What ecu are you using? as most can take a wideband feed directly and have some sort of Auto-tune feature these days which produce good safe starting points.
Using Wideband will help you maximise your engines capabilities while reducing the likelihood to damage due to running too lean etc.


[Edited on 29/3/11 by atomic]

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The solution (in my case), is to run about 15-16 on the over-run and disable fuel cut.

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On mine, I've found that if you go rich on overrun (13-13.5ish) you get a burble noise rather than the lean bangs and pops. May be worth a try Obviously you will use a touch more fuel.

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Originally posted by fatbaldbloke

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The solution (in my case), is to run about 15-16 on the over-run and disable fuel cut.

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Spot on, this is the correct way to do it.

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Originally posted by atomic
You should be using a Wideband AFR meter to tune and one of the result of doing it this way would be it this should reduce this type of thing to an expectable level. What ecu are you using? as most can take a wideband feed directly and have some sort of Auto-tune feature these days which produce good safe starting points.
Using Wideband will help you maximise your engines capabilities while reducing the likelihood to damage due to running too lean etc.

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Originally posted by RazMan

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Originally posted by atomic
You should be using a Wideband AFR meter to tune and one of the result of doing it this way would be it this should reduce this type of thing to an expectable level. What ecu are you using? as most can take a wideband feed directly and have some sort of Auto-tune feature these days which produce good safe starting points.
Using Wideband will help you maximise your engines capabilities while reducing the likelihood to damage due to running too lean etc.

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I have indeed been using my Innovate Wideband sensor and gauge to good effect - I have used 3 tankfuls to get the fine tuning done and its now running beautifully. The popping stopped when I increased the fuel on the overrun slightly and I have noticed the AFR has gone up to around 13.5 so not lean any more.

I would love to plumb the sensor into the ECU but have been told it is not very straight forward to do this on an MBE 970. I just keep an eye on the AFR under various throttle positions and at the moment it is running on the safer side of the ideal 14.7. If anyone can offer advice on getting the sensor to talk to the ECU I am all ears

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Originally posted by coozer
I want pops and bangs, some flames would be nice as well. Singe the hairs off the horses legs

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Originally posted by RazMan

quote:

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Originally posted by atomic
You should be using a Wideband AFR meter to tune and one of the result of doing it this way would be it this should reduce this type of thing to an expectable level. What ecu are you using? as most can take a wideband feed directly and have some sort of Auto-tune feature these days which produce good safe starting points.
Using Wideband will help you maximise your engines capabilities while reducing the likelihood to damage due to running too lean etc.

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I have indeed been using my Innovate Wideband sensor and gauge to good effect - I have used 3 tankfuls to get the fine tuning done and its now running beautifully. The popping stopped when I increased the fuel on the overrun slightly and I have noticed the AFR has gone up to around 13.5 so not lean any more.

I would love to plumb the sensor into the ECU but have been told it is not very straight forward to do this on an MBE 970. I just keep an eye on the AFR under various throttle positions and at the moment it is running on the safer side of the ideal 14.7. If anyone can offer advice on getting the sensor to talk to the ECU I am all ears

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Originally posted by mikemph
Normally you use the 0-5v analogue output of the wb controller onto the ecu... And then you have to make sure the ecu is configured to accept 0-5v as a wide band on which every input you are using. Im not familiar with mbe so can't tell you how exactly.

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Originally posted by ashg
always use afr as a guide. never think yo have to make the engine work at an afr value, always give it what it wants to run well.the 13.5 afr isnt that critical on overrun when you think in volumetric efficiency. with the throttle closed there is very little air going into the cylindermeaning it would only take a very small amount of fuel to make it look rich. so in reality it wont make a lot of difference to your fuel economy. the place you can make real fuel economy gains on cruse and idle which is where you should be concentrating on if its running well

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i dont know the ins and outs of your ecu but if you connect to the innovate via serial and open up the software you can tell it what voltage it should be pumping out at a particular afr. all you need to do then i find out what input your ecu is expecting. if i remember correctly you could set both analogue outputs to wideband using the innovate software meaning you have one for the ecu and another for the gauge both outputting different voltage ranges but still in wideband mode.

once its setup properly the map wont really change so technically you dont even need a lambda. the only real benefit of having one after its been properly mapped is for safety should you get an unexpected lean situation e.g something on the inlet side fails allowing it run out of spec.

2 degrees isnt really a good thing to be doing i hope you are keeping an eye on your exhaust temps as you could kill your exhaust valves if your not careful



[Edited on 30/3/2011 by ashg]

After speaking Colin @ atspeed, I am now convince that lambda control should not be neccessary if the map is set up well to start with - besides the ar$e of a job it is to set up.

First you need to first tell the ecu the type of Lambda system you're using, along with a number of settings, (temperature to allow adaptive mapping, how much fueling can be changed by in one go, that sort of thing.)

You then need to set up a table relating to the voltage that the ecu translates to the actual Lambda value

You then need to set up the target map. Typically, you would put a figure of Lambda 1 in the low rpm/low tps load sites and a value between 0.85 - 0.9 or so in the higher rpm/higher tps sites. (The theory is that you're running at Lambda 1 on low throttle openings, and richer when you give it some beans).

My brain melted at this point and I just marvelled at how good my present map is

Regarding the 2 degrees thing, I am very concious of the heat build up at tickover so I basically don't allow it to idle for very long and switch off when waiting in traffic to keep the heat down to a minimum - its fine on a run though.

im just going off my own experience, don't claim to be an expert, far from it. i have done a fair bit of reading on the subject and put it in to practice on my own car, mostly it has worked out ok for me.

sounds like your getting on well with it. im sure colin will be able to get a bit more out of it on the rollers as he can keep a constant load unlike road conditions it also makes it more repeatable which helps. I would think there is a good bit of play to be found in your ignition map as i would expect it to be reasonably conservative at the moment. you will have to post up the before and after results along with screen shots of the map tables. he managed to find 18hp and a bit more torque on my old engine without too much bother. the good thing is that you have a working map so hopefully the boys can just hone it in. the only thing that worries me is your itb issue on tick over as they will have to map around it, in an ideal world it would be better to get that sorted and redo your map before going down to them and parting with money, but if you cant find a way round it then that's how it will have to be.