Backfire/misfire
Turbo Mini Forums

Morning guys, im quite new to this turbo stuff so bear with me!

My car has a gt17 turbo and a metro turbo carb, 1310 A series.

I did a trackday in it yesterday and it was running great for the first part of the morning. But after about the 5th run out when it was getting quite hot, as soon as boost kicked in around 4k rpm it would lose all power and misfire/backfire like crazy! Up until 4k rpm it was ok, but its not at full boost until 4k rpm.

Its got stage 7 spark plugs which i think are suitable after doing some research?

Thanks in advance for any advice :)

Edited by Moggyton on 17th Jun, 2016.

Ive just checked the carb oil... And theres hardly anything in there. Could this be the problem?

What ignition system you using

Electronic ignition

Edited by Moggyton on 17th Jun, 2016.

Ive put some 80w90 in the carb but its still backfiring when boost comes in...

What coil are you running?
It is possible that the spark energy cannot cope with the cylinder pressure at high boost. Also how are the plug gaps?

Coil was changed when it was mapped by aldons so its one of theres.
Spark plugs are gapped to 0.032"
Like i say, it ran faultlessly all morning which is what confuses me.

Do you have an AFR gauge ?

Sounds to me like it is running lean on boost so start looking for air leaks.

I do have an afr gauge. I thought abouta boost leak but i cant find anything :(

What does the AFR gauge show once the misfire starts ?
It should jump either right up or right down depending on what the underlying problem is (I'm assuming it's a wideband, if it's just a narrowband it will tell you nothing worthwhile).

Schrödinger's cat - so which one am I ???

Yes wideband, ill have to go for a drive and have a look, im sure it was going lean!

Fuel pressure/supply would be an obvious thing to check.

And no such thing as "stage 7" spark plugs, so presumably you mean plugs with an NGK heat range of 7 ?

Assuming you havent bust something, it could be as simple as the pipe off the FPR.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

Fuel pressure doesnt drop when boost comes on.
By stage 7 im referring to the heat rating.
I have checked all fueling pipes but ill have another look.
Cheers

And for clarity...is this problem there all the time now ?

In your first post you stated it only happened when things were very hot ?

And you say fuel pressure does not drop.....but you also do not say fuel pressure rises as it should when boost comes in ?

Details are important.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

Schrödinger's cat - so which one am I ???

Problem is still there yes. Even when the car is just starting to get warm.
Fuel pressure still rises when boost comes on as far as i know and this is when it backfires/misfires. Sounds like more of a backfire as you can hear it popping in the exhaust
Cheers

Ill take it for a drive shortly and report back about the AFR readings.
Cheers!

Have you done a compression test and/or checked valve (tappet) clearances ?

If it is a "backfire" (fuel burning in the exhaust) you may have killed one or more of the exhaust valves during the trackday especially if valve clearances were tight before it got hot.
A burnt exhaust valve could allow a lot of fuel/air to be pushed into the exhaust under boost.

Un-leaded head ?

Schrödinger's cat - so which one am I ???

Un leaded yes