Running Well But Misfire For First 20 Second Or So On Idle?

[ATK 142 1 Cars]

Car has a slight misfire for the first 20 seconds or so on a cold start. Bit of throttle and the misfire clears and it then runs fine.

 

Plugs, leads, ignition amp, tachy relay, fuel pump are all new.

 

Any ideas what could be causing this niggling misfire?

[welshpug 1,662]

too much fuel possibly.

[ATK 142 1 Cars]

CTS is new as well by the way.

 

How to test or adjust fuelling?

[dcc 855]

what colour are the plugs

[ATK 142 1 Cars]

Light grey ish powder

[wicked 103 3 Cars]

A leakage in the charcoal canister circuit; rusted canister (hole) or in hoses.

There is a valve that opens the first x seconds after start to burn the vapor from your fuel tank.

[ATK 142 1 Cars]

Do UK cars have a charcoal cannister?!

[Anthony 1,003]

Only CAT models, so yours won't.

[ATK 142 1 Cars]

1.9 non cat so thought it wouldnt have one.

[ATK 142 1 Cars]

Oh forgot to say, dizzy cap and rotor arm are both new as well

[dcc 855]

fuel pressure regulator, fuel pump, bad earth/voltage drop to fuel pump...

 

is the coolant pressuring?

[ATK 142 1 Cars]

Fuel pump is brand new Dan.

 

FPR is old, how do you test this?

 

No idea on the coolant pressure either? But it's not overheating, I'm not losing any coolant and the rad, rad fans etc are all working properly.

[dcc 855]

I think meirion has written an article on testing it with a foot pump. I have yet to see one fail though.

 

I would be checking fuel pump voltage - low voltage = longer to get up to pressure. can you isolate the cylinder with the issue? or does it vary from 1 pot to another?

 

does it feel down on power? I remember reading you had your car set up following a hg change, could be an issue there, or even a collapsed downpipe?

 

This happened on a friends car I am currently changing the engine on.

 

​

[ATK 142 1 Cars]

Just seen the testing article that Meirion wrote. If the FPR was at fault, are they straightforward to change?

 

My mate checked the voltage to the fuel pump after I changed it and it is getting the correct voltage.

 

Pressure test etc all ok on engine.

 

Thing is the misfire clears after 20 seconds or less, and after that it is fine and the power is fine. So I'm thinking (with my very limited mechanical knowledge!) it must be fuel or ignition related rather than anything else.

[scbond 15 1 Cars]

When you set it up in the last few days did you check the AFM or SAD? Would be worth doing a full set up after checking the size of the valve bypass in the SAD and then include tweaking the AFM while setting up.

[ATK 142 1 Cars]

SAD is working correctly (was brand new about three months ago) and wouldnt think this would affect a misfire. AFM is brand new as well, have played with AFM mixture but no luck so set it back to how it was.

[scbond 15 1 Cars]

Without the additional air while cold coming through the SAD it can cause a slight miss that requires a touch of throttle to clear. I had this very problem and once I adjusted the valve it was fine.

 

SAD might work properly, intact they rarely stop working, but it might be badly adjusted. It's unlikely with a new one but it is worth checking as I doubt they have one setting for all.

[ATK 142 1 Cars]

Hmm, original SAD before new one was fully open adjustment wise and still did it so dont think its that in my case, see what your saying though.

How easy is it to replace the fuel pressure regulator?

[scbond 15 1 Cars]

If your old one was fully open and the car still struggled when cold then, you're right, it won't be the SAD.

 

Pretty sure the FPR is just held to the fuel rail by one or two bolts. I'd try testing it first though...which Mei has done and can be found by a quick search (sorry, on phone at the moment).

Edited December 2, 2014 by scbond

[luggy 13]

 

Thing is the misfire clears after 20 seconds or less, and after that it is fine and the power is fine. So I'm thinking (with my very limited mechanical knowledge!) it must be fuel or ignition related rather than anything else.

 

Quite interested to see how you resolve this.

 

Had a similar quirk on my old 8v, didn't really think it was an issue as performance wasn't affected.

 

Could be a leaky fuel injector as it would take that bit longer to clear the excess fuel from the cylinder?

[ATK 142 1 Cars]

thought that might be a possibilty but injectors were refurbed two yrs ago. Still might cause a problem though. changing FPR shortly so will update soon!

[oldkiteman 6]

had a similar problem on my gentry,only it lasted for about 60 secs.It turned out to be temp sensor over richening mixture when cold causing engine to hunt.a new sensor cured it.rob

[ATK 142 1 Cars]

CTS already replaced

[Ramigojag 19 1 Cars]

Short misfire on startup can point to head gasket failing

[Alan77 78 1 Cars]

Possible head gasket, as moisture in the cylinders gets initially burnt off on start up.

I had this happen on mine.