Technical misfire/flatspot

[Maninacan]

I've had a read up on other misfire threads and my problem seems a bit different so forgive me....

My 96 sporting cinq has always run like the proverbial sewing machine for about 5 years until a few weeks back when i nearly stalled it in 3rd, then it started to misfire a bit. Few weeks on and it was misfiring badly, almost undriveable.

So i checked around the plugs and leads and found a very nasty no.4 plug. Put a new set of plugs in, cleaned things up and its fixed....almost....

When accelerating there is a prolonged flatspot just after changing up and at around 4000RPM, then the power delivery comes back normally after a short delay of about a second ot two.

It's got a McKritch chip and a GSR induction kit, other than that the motors standard.

any thoughts? cheers, Dan

 

[Pep0]

Hi

Is the missfire the same with the coolant hot or cold?

Noel

 

[Maninacan]

good question - let me try it cold and report back, haven't run it cold since doing plugs (did oil at same time so engine was warm)

 

[Maninacan]

one thing i did notice which i didn't think was relevant but may be, is that the thick breather pipe that goes from the head to the throttle bob bit was loose - seemed that the brass threaded part had just stripped its threads at the bob end and it was just sat in place, but not secured and certainly not airtight. Didn't think it would matter but could that be involved somehow?

 

[Pep0]

It could - any abnormality in the induction system will cause either a hole or fill a hole in the power curve. The induction pipe is like an organ pipe... tuned to a given note...

Try degrease both surfaces and using instant gasket for seal and soft iron wire it in place until you can salve the threads. Note The instant gasket will take a while to set in cold tempertures.

Noel

 

[fingers99]

If that doesn't do it, check out the MAP sensor, pipe and all.