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351 cleveland misfire problems...


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#1 yehbaby351

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Posted 10 June 2012 - 05:21 PM

hi guys,

currently im trying to license a v8 xf however emmission test has to be done and im having trouble with misfire in 8 th cylinder..

i know its the 8th cylinder because if i take off spark plug lead from each cylinder, the motor sounds different when at idle. if i take 8th cylinder lead off, engine sounds exactly the same......

this is what i have

351 cleveland d block, mild cam ( nothing toooo fancy)
brand new holley 600
egr plate from thermaquad and adapter plate to suit holley
new leads, plugs, dizzycap and rotor
electronic dizzy and crane fireball amplifier thingy (old one) however it sparks great
standard intake cast manifold and standard cast exhaust manifolds
original factory xd xe air cleaner


TESTS I HAVE DONE

timing is at 10 degrees
compression test all cylinders 148- 150
cylinder leakage test all in the green (perfect)
blocked off the egr valve
tested pcv valve on rocker cover all is fine
sprayed carby cleaner around for vacume leaks

dizzy has not been replaced so im thinking it could be that.........

but then again carby could be very lean as the plugs are very white at the ends

when the car is driven at 60 - 70 km , it is stuttering and not smooth but is drivable, when you floor it, its got power and goes good

what can it be ... hope i have explained enough

#2 666frd

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Posted 10 June 2012 - 05:24 PM

have you tried lead and plug ?
Ipswich City Auto Electrical
Cnr Cemetery & Whitehill Roads
Raceview QLD 4305
P: 07) 3496 1912
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#3 yehbaby351

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Posted 10 June 2012 - 05:29 PM

lead and plug as in spark plug and leads....

i have replaced all of them

#4 666frd

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Posted 10 June 2012 - 05:33 PM

ok what about spark plug gap you should have no less the 0.8 m but 1.1 is ideal
Ipswich City Auto Electrical
Cnr Cemetery & Whitehill Roads
Raceview QLD 4305
P: 07) 3496 1912
F: 07) 3496 1616
E: icae@live.com.au

#5 yehbaby351

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Posted 10 June 2012 - 05:42 PM

Spark plug gaps were not touched from new. They were sparking when tested with lead so don't think it will be that

#6 yehbaby351

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Posted 10 June 2012 - 05:45 PM

At the moment the only thing I haven't replaced new is the dizzy...

Carby is new but was mucked around with by Carby guy so I'm leaning towards these two things

#7 666frd

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Posted 10 June 2012 - 05:53 PM

new plugs are .75 and you can have spark with the plug out but under compression and fuel it may not spark with that small of a gap
Ipswich City Auto Electrical
Cnr Cemetery & Whitehill Roads
Raceview QLD 4305
P: 07) 3496 1912
F: 07) 3496 1616
E: icae@live.com.au

#8 yehbaby351

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Posted 10 June 2012 - 05:59 PM

Will try changing it tomorrow.. Should I change just that 8 cylinder only to see if that makes a difference

#9 666frd

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Posted 10 June 2012 - 06:16 PM

i'd do them all it only takes 10 mins to do and if that doesn't work the only other thing i can think of is a air leak between the manifold and head
Ipswich City Auto Electrical
Cnr Cemetery & Whitehill Roads
Raceview QLD 4305
P: 07) 3496 1912
F: 07) 3496 1616
E: icae@live.com.au

#10 yehbaby351

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Posted 10 June 2012 - 06:21 PM

I did spray Carby cleaner around intake and head but nothing changed. I would have thought revs should have picked up

#11 666frd

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Posted 10 June 2012 - 06:24 PM

ok and i don't think rev would pick up much if at all if the leak is small and around just the one port
Ipswich City Auto Electrical
Cnr Cemetery & Whitehill Roads
Raceview QLD 4305
P: 07) 3496 1912
F: 07) 3496 1616
E: icae@live.com.au

#12 adamant3513

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Posted 10 June 2012 - 07:03 PM

I would swap no 8 plug/lead with no 4.If miss moves to no 4 cyl youve found your problem. If miss is still in no 8 cyl it could be worn dizzy shaft.If not it still could be vac leak(air being pulled into port from INSIDE the manifold) or some thing mechanical, such as burnt valve etc...but you seem to have covered that area.
Where you said it goes away under load i would be thinking more vac leak or maybe yes, carb being lean at idle and cruise.

#13 yehbaby351

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Posted 10 June 2012 - 07:48 PM

Do u think it might be leaking between intake and exhaust ports

#14 adamant3513

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Posted 10 June 2012 - 08:25 PM

No.I dont. Im not sure what you mean by that either.
Maybe i should have said 'under' the manifold where you cant see.And cant spray carb cleaner.

#15 yehbaby351

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Posted 10 June 2012 - 08:44 PM

Maybe I should try changing intake manifold gasket. Will try changing spark gap first, then I will change leads from 8 to 4 and if that's doesn't fix it,, will do gaskets for intake manifold..

If it still does it then it's gonna have to be Carby or dizzy . That's all that's left

Thanx guys for the help.. Hopefully it will be an easy fix

#16 XF 372

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Posted 10 June 2012 - 09:10 PM

mine had a misfire a few years back pain on light throttle etc but was fine under big load, turned out to be worn dizzy shaft, new dizzy and was fine

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#17 grabber

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Posted 10 June 2012 - 09:49 PM

Yeah, I know that feeling, I went to hell with one Clevo.

As advised, It does not matter if the leads are new, swap that spark plug (there has been many new faulty plugs), and change the leads over.

The last new holley I bought had bits of metal thread inside it 3 times, that caused it to run like a dog. Once I cleared this problem my car was fit for Allan Moffat to race in this years Bathurst. May be worthwhile removing the bowls to have a looksee...

Curious to know the colour of No. 8 plug.

Perhaps recheck all of the outlets on the carby so every thing is connected. Be sure that the carby joints, linkages and hoses are not sucking air. This sucks when this happens!

Did you use the right gasket for your manifold?

Is the any cracks in your new dizzy cap?

Try without the air filter.

Check the choke is fully disengaged.

Also, driving really fast all the time on open roads helps your soul and that is also good for your car. Cars have feelings too you know.

If this fails change your dizzy and the coil.

I reckon it's the lead. If you reckon it works stick your best mates finger in there to check it for real...lol...:hihi:

I hope this helps!

Edited by grabber, 10 June 2012 - 09:56 PM.


#18 jeffb5.8

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Posted 24 June 2012 - 10:20 PM

How do you go yehbaby351, problem solved?




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