15 replies to this topic

[spiguy]

Hi Folks,

Looking for some opinions. Have a '92 SPi cooper. Car is running fine, I suspect a little lean possibly,
but not entirely sure about that. Idles sweet and everything too. I've noticed however that on occasion,
if the car is idling and I give it a sharp blip on the throttle, it can backfire in the inlet. Doesnt
happen every time, and no such issues when driving. It does need to be a sharp blip to cause it.

I've still to service the dizzy cap and rotor arm and leads, although I have renewed the plugs and
also it has a recently cleaned and oiled K&N filter element in the standard air box. Vac pipes seem
to be in good condition too.

I have a theory that it could be due to the fact this car uses the throttle switch system. I had to replace
the throttle switch when I bought it, as it was seized shut, so it is a brand new switch which I have tested
and it is fine,however I wonder if maybe there is a response time associated with the ECU detecting that
the switch has opened. I know that if you rev the car with the switch shorted (as was the case when I viewed
the car) it will backfire.

I will check the throttle pot etc and inspect the condition of the dizzy cap and rotor arm but just wanted
to see if anyone else has encountered this and resolved it?

There is a similar thread on here, but it didn't really provide much insight in my case.

Thanks!

 

[IainStallard]

Mini occasionally does this but only very rarely, I've always thought it was me expecting too much from the engine!

[spiguy]

he he. Yeah maybe. I suppose there could be something in that actually, as when you rapidly open the throttle the ECU will need to respond and adjust fuelling extremely quickly, maybe it just can't respond quickly enough under certain conditions. Doesn't seem to happen when the car is cold - ie mixture is a bit richer anyway. Maybe it's such a lean mixture at idle on the injection car (emissions etc.) that suddenly opening the throttle butterfly just makes it go very lean for an instant resulting in a wee backfire?

 

Maybe I just shouldnt do it!

[mikespicooper]

what is the mileage of the car?

If over 80000 km then check the lambda sensor or renew it is better...

Also check the dizzy shaft for any excess play and the ignition timing...

Backfiring is also caused by engine timing if the timing chain tensioner is badly worn or if the timing chain has stretched...

[brivinci]

Mine does the same thing. From an idle, burry the throttle into the carpets and the motor cant keep up. It stumbles and eventually backfires in the intake. I have other issues to sort out but this is one for sure. What you Mike has me really thinking. I have a duplex chain and I know its totally worn out. It only has 2-3000 miles on it but the last chain I had on there only lasted 1000 miles before totally stretching. I think this one has as well. It is SUPER noisy. Calver says the quality of the chains these days are garabage. He sells one that he specially sourced...and its cheaper then what Swiftune charged me to replace the one that went bad in 1000 miles. Yeasm Swiftune charged me to fix their mistakes. Sad.

 

I am now thinking that maybe the chain having loads of slack ( and no tensioner...which I reinstall this time) might be causing my timing to bounce around.

[firstforward]

I believe MED are selling the best chains.

[brivinci]

I should find the pix of the one I got from Swiftune. The stretch was unreal at any mileage, let alone just under 1000.

[minimat]

Mine does this too.

[Steve220]

Repaired a mini recently having this. The timing was out.

[FlyingScot]

Repaired a mini recently having this. The timing was out.

On a fuel injected one???

FS

[Steve220]

Repaired a mini recently having this. The timing was out.

On a fuel injected one???
FS

Chain had stretched enough to take it out of timing, with the air box off the top of the unit and blipping the throttle whilst warm there was a back fire. I had a similar issue with a friend's k series Spi although it ended up making a mess of the air box.

[FlyingScot]

Interesting thanks. Might be worth checking Craig

FS

[spiguy]

yikes. How do you check the timing chain - without lots of dismantling that is ? Not going to be doing this just now though, my daily driver is off the road (pug 306 td) with its interior in bits as I go through the nightmare of replacing the heater matrix. Shocking job!

 

Thing is, if you take it just off idle, and then blip it, it never does it. It doesn't even do it every time anyway, just once in a while (not that I am in the habit of doing this at all really!)

 

Any other symptoms of chain stretch?

[FlyingScot]

If its not to bad and doesn't do it all the time I would leave it most minis will have worn timing chains and the ECU will adjust the timing within spec anyhow.
Sounds as if apart from this it's running okay.

FS

[spiguy]

Thanks FS. Yeah, I'm not going digging around looking for anything serious yet!