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

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

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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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

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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.

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.

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

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?

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.

That sounds like it, it's a Megasquirt and spark extra.

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.