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Gtir Motorsport club » General Discusion » Gtir related Discussion » Missfire !

Missfire !

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1 Missfire ! on 22nd July 2017, 12:07 pm

pulsarmad20

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Hello fellas

Car is upto tricks again ! Missfire I can go up the road on boost but not full throttle fine soon as full throttle it miss fires badly like a machine gun going off. If I put the car on grass and floor it it will go with no missfire on the road different story .

What can it be ? I have cheacked leads cap and arm re gapped plugs cheacked for boost leak there was one and sorted it but didn't change anything . Wat else can it be ?

2 Re: Missfire ! on 22nd July 2017, 1:44 pm

shroom

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Have you checked the fault code? Could be on 34 and in limp mode you would need to clear it before it would sort it (could have been the boost leak)

3 Re: Missfire ! on 22nd July 2017, 5:37 pm

pulsarmad20

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Yea I've got no fault codes

4 Re: Missfire ! on 22nd July 2017, 6:54 pm

mike74

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Plugs would be my first guess...closely followed by fuelling problem

5 Re: Missfire ! on 22nd July 2017, 8:32 pm

markface


I agree with the above.
I had the same issue long ago when using bkr7eix and pfr7b plugs. They seemed OK but changed to bcr8es which solved my misfire on-full boost. Correct me if im wrong but heat range on 1.3bar may have been my prob? That as well as a leaking weld on tmic core which I only noticed when I pressure tested the system to my set boost pressure.

Hope you get it sorted

6 Re: Missfire ! on 22nd July 2017, 9:00 pm

Mr B

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gtir technician
gtir technician
Yeh it most likely lean issue and/or weak spark .
R is fussy on plugs, if can't inspect/test leads/ignition well would be worth getting cheap new set to try if no other issues can be found.
Would check/clean maf and double check boost leaks again as well .

7 Re: Missfire ! on 23rd July 2017, 9:07 am

shroom

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Also do you have a dump valve fitted? May be worth taking it off and blocking temporarily to see if that helps they can cause issues sometimes if opening incorrectly or duff

8 Re: Missfire ! on 24th July 2017, 10:39 am

pulsarmad20

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Cleaned maf still no difference , yes I have a dump valve will make sure it's clean and shutting properly . How do I check if it's running lean ? It's pretty much standard at the minute forged engine with everything else standard apart from air filter exhaust and dump valve ..

9 Re: Missfire ! on 24th July 2017, 11:07 am

mike74

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you could pull a plug out and check the colour, that would give you an idea if its lean or not...just pull the plug after a decent run to make sure the plugs aren't fouled up after cold start/running

10 Re: Missfire ! on 24th July 2017, 7:57 pm

Daveymeladdy

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As some Be mentioned already... check for boost leak, it's the source of all evil

11 Re: Missfire ! on 24th July 2017, 8:53 pm

nomad

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Admin
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What about fuel pump ... i would presume it's a aftermarket one... has it come loose in the cage just trying to think of other possibilities like it would be ok when stationary but not when moving ...


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12 Re: Missfire ! on 25th July 2017, 5:39 pm

pulsarmad20

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You are right there nomad it's a walbro 255 been in there 4 years maybe 5 I'll have a look at it

13 Re: Missfire ! on 25th July 2017, 7:35 pm

johnny gtir

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moderator
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Still say plugs me. What plugs you running? When you say boost if you accelerate slow and come on boost it builds up and fine but if you floor it misses or is it full throttle ?

14 Re: Missfire ! on 27th July 2017, 1:05 am

pulsarmad20

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Yes johnny it comes on boost no miss nothing but if I put my foot down it misses instantly . I've got bcr8es in there

15 Re: Missfire ! on 27th July 2017, 8:11 am

mike74

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Could be a weak fuel pump that isn't able to cope with the demand of stamping on the throttle quickly...or maybe even a dodgy fuel pressure regulator giving the same symptoms.
Have you got a fuel gauge installed?
If not I would recommend buying a tee and a gauge. Just install it into the fuel pipe that comes from the fuel filter and goes to the rail.
They're pretty cheap in the grand scheme of things and are actually very handy things to have Smile

16 Re: Missfire ! on 27th July 2017, 10:07 am

Stu

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Admin
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@mike74 wrote:Could be a weak fuel pump that isn't able to cope with the demand of stamping on the throttle quickly...or maybe even a dodgy fuel pressure regulator giving the same symptoms.
Have you got a fuel gauge installed?
If not I would recommend buying a tee and a gauge. Just install it into the fuel pipe that comes from the fuel filter and goes to the rail.
They're pretty cheap in the grand scheme of things and are actually very handy things to have  Smile
You put the fuel pressure gauge on the return pipe off the fuel rail don't you? That will give the reading of the fuel pressure in the rail where you need to read it?


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17 Re: Missfire ! on 27th July 2017, 10:32 am

mike74

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You need to tee it in before the regulator regardless if its OEM or aftermarket. Between the fuel filter and the rail is nice and easy to get to and easy to see the gauge. From the regulator all the way back through the fuel rail and back to the pump will be the same pressure so the gauge can go anywhere really, as long as its on the pump side of the regulator.

Theoretically if you put the gauge after the regulator it should read zero (or at least very low) as this line is just returning fuel to the tank Very Happy

18 Re: Missfire ! on 27th July 2017, 1:55 pm

Stu

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Admin
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Yeah but the presure is on the rail that you need.
Not before it in the feed line..
Thats why you get an adjustable one and adjust it after the fuel feed?


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19 Re: Missfire ! on 27th July 2017, 2:11 pm

mike74

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before and inside the rail should be the same pressure

20 Re: Missfire ! on 27th July 2017, 3:57 pm

Stu

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Admin
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@mike74 wrote:before and inside the rail should be the same pressure
Okay.
Thanks for clearing that up for me Mike.
I have never done one before but couldn't see how the fuel pressure could be read on the rail if the gauge was put in before the fpr lol


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21 Re: Missfire ! on 27th July 2017, 7:48 pm

mike74

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Lol, nae worries. That's how mine is plumbed in anyway...you had me wondering too for a bit

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