Steve Lovelock
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| posted on 27/5/08 at 02:50 PM |
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back firing on slow down / gear changes etc.
Hello,
Had my first run in the car to the SVA test (passed!!!) and DVLA so did some data loging and tuning on route. Ran very well, really pleased with the
engine. However, I am getting a lot of back firing on over run & slow down and not sure what to look at. Any ideas? (MSnSE, GSXR TBs and
Redtop).
Cheers
Steve
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Mr Whippy
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| posted on 27/5/08 at 02:53 PM |
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great isn't it, pop pop bang!!
oh the joys 
I use to pump the gas pedal several times at gas stations so the Falcon went bang when I started it up
Fame is when your old car is plastered all over the internet
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BenB
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| posted on 27/5/08 at 03:05 PM |
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It might just be a mixture problem.
Otherwise a leaking exhaust gasket (or leaking connection on the exhaust system) can cause the same symptoms...
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matt_claydon
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| posted on 27/5/08 at 03:05 PM |
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quote:
Originally posted by Steve Lovelock
Hello,
Had my first run in the car to the SVA test (passed!!!) and DVLA so did some data loging and tuning on route. Ran very well, really pleased with the
engine. However, I am getting a lot of back firing on over run & slow down and not sure what to look at. Any ideas? (MSnSE, GSXR TBs and
Redtop).
Cheers
Steve
You need to tune the area of the map which is in play during overrun (ie low MAP, rpm above idle). I found I needed higher values than I expected.
Once you've got it tuned you can turn on 'overrun fuel cut' which will completely remove the banging and save you fuel, but
it's good practice to get the VE values correct first.
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Mr Whippy
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| posted on 27/5/08 at 03:09 PM |
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Mind though with such a short exhaust you are bound to hear things not normal on a production car. If your gunning it up to a corner running rich and
the old exhaust is like red hot don't be too surprised if all that fuel doesn't light up. I get foot long flames out the buggy’s exhaust
on overrun.
Fame is when your old car is plastered all over the internet
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Paul TigerB6
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| posted on 27/5/08 at 03:21 PM |
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I would start with the possible leaking exhaust gasket as a first stop seeing as you have just built the car and given it a good run to SVA - probably
just needs the manifold nuts / bolts tightening up now its all settling.
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mookaloid
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| posted on 27/5/08 at 03:27 PM |
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Backfiring is unburnt fuel exploding in the exhaust ports this can mean 2 things:
1. unburnt fuel is getting through the system - which suggests incomplete combustion - I would suggest a bit more ignition advance to ensure complete
combustion.
2. the unburnt fuel is being ignited in the exhaust ports because they are running too hot. this could be because the ignition is running too late in
the cycle - i.e fuel is still being burnt as the exhaust valves open - this is a bad thing as it the exhaust valves run too hot and can cause
premature wear in the valves and seats!
Try advancing the ignition timing a little. As long as it doesn't pink you should be ok.
Cheers
mark
"That thing you're thinking - it wont be that."
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Steve Lovelock
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| posted on 27/5/08 at 03:40 PM |
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Thanks for the responses. I will check the exhaust gasket as it didn't do it at first which may indicate that its a leak and getting worse. I
will also continue to work on the VE map and then look at the over run fuel cut out. I have not touched the timing settings on the MSnSE so they are
all as downloaded in the original set up, unless MLV does this too?
Any ideas where in the manual it addresses this timing issue?
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madteg
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| posted on 27/5/08 at 06:24 PM |
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overun
Have just sorted the same problem, played with overun settings still had problem. I advanced ignition timing from 34 on overun to 60 and it has cured
it, it seems that the fuel was filling exhaust up on overun and exploding when conditions was wright also as soon as i came back on throtle it banged
aswell. What ecu are you using.
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Steve Lovelock
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| posted on 27/5/08 at 09:37 PM |
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That sounds like it, it's a Megasquirt and spark extra.
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martyn_16v
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| posted on 28/5/08 at 08:34 AM |
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Aye, you can use masses of advance on overrun. I don't think i've ever been as high as 60 but around the 50 mark. You'd have a hard
time doing anything to damage the engine in this load area (within reason, don't go trying a 100degree advance for the fun of it) so feel free
to have a play to see what happens.
Overrun fuel cut is a fantastic feature, it'll make the car a lot more civilised. Make sure you set the rpm cut off point and the MAP limit
sufficiently far from idle though, otherwise you'll be kangarooing down the road. About 1800rpm and 10kPa below my idle value suits my driving
style.
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