cylinders 1 and 4 running rich but 2 and 3 are runing lean???????????????????

snowman51789

snowman51789

Petty Officer 2nd Class
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Sep 8, 2010
Messages
131
today i was testing the compression on my 92 3.0lx merc and i noticed that the spark plugs on cylinders 1 and 4 (assuming cylinder 1 is the front cylinder) were very dark/black (rich) colored while the plugs in cylinders 2 and 3 looked to be light colored (lean). i put new plugs in and ran it for about an hour and the new plugs showed the same thing. any thoughts as to what could cause that???

compression was #1 155 #2 145 #3 140 #4 135

resently replaced parts
plugs (begining of year and today)
wires
cap and rotor
rebuilt carb
replace all fuel filter's
checked fuel pump pressure
 
Bondo

Bondo

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Re: cylinders 1 and 4 running rich but 2 and 3 are runing lean???????????????????

Ayuh,.... I'd guess, 1/2 of yer Carb is boogered up....
 
snowman51789

snowman51789

Petty Officer 2nd Class
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Sep 8, 2010
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Re: cylinders 1 and 4 running rich but 2 and 3 are runing lean???????????????????

Thats what I was originaly thinking but if I remember right, isn't the area under the carb and open area before the intake ports?? In other word, its not like one barrel gose to 2 specific cylinders and the other barrel goas to the other 2. And have you ever herd of this problem?
 
snowman51789

snowman51789

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Re: cylinders 1 and 4 running rich but 2 and 3 are runing lean???????????????????

Bump
 
D

Doernuth

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Re: cylinders 1 and 4 running rich but 2 and 3 are runing lean???????????????????

Could be a breach in the intake portion of the manifold gasket on the 2 and 3 cylinders. If it is sucking extra air through the gasket it will burn lean.
 
snowman51789

snowman51789

Petty Officer 2nd Class
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Re: cylinders 1 and 4 running rich but 2 and 3 are runing lean???????????????????

Hmmm that would make sence. Is there any way I could test that theory?
 
L

littlebookworm

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Re: cylinders 1 and 4 running rich but 2 and 3 are runing lean???????????????????

Spray some WD-40 around the intake manifold with the engine running. If ther's a leak, the engine will speed up slightly when the oil hits the leak area. Hy
 
snowman51789

snowman51789

Petty Officer 2nd Class
Joined
Sep 8, 2010
Messages
131
Re: cylinders 1 and 4 running rich but 2 and 3 are runing lean???????????????????

Oh I alread did that but I used starting fluid. N there was no change
 
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