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Tech Experts: 2 of 8 cylinders running rich??

JuicedH22

By JuicedH22
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JuicedH22 Newbie

JuicedH22

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Are you coming off a fresh rebuild? I had a Honda motor do this on cylinder 4 and it turned out to be a soft sleeve/ unseated rings not allowing a full burn and running rich.

 

fresh rebuild, but no sleeving done, stock bore. If it were unseated rings, I would expect the leakdown to be low, which it was not...

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schmuckingham Veteran

schmuckingham

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fresh rebuild, but no sleeving done, stock bore. If it were unseated rings, I would expect the leakdown to be low, which it was not...

 

 

I know it is weird but I had the exact same issue, stock sleeve was soft and 4 passed a leakdown but not compression.

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JuicedH22 Newbie

JuicedH22

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not sure what the intake manifold has to do with it? but sure...

 

FAST102

NW102 TB

 

TR6 plugs

TFS 235 heads, 12:1 CR

flat-top wiseco pistons, rings gapped to 022/024

comp cams custom grind cam... 247/255 113+3 lsa, 25 degrees overlap...

ls7 lifters, stock rockers...

Siemens DEKA 60lb injectors, FAST rails

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Mensan Newbie

Mensan

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not sure what the intake manifold has to do with it? but sure...

 

http://www.flowbenchoz.com/Smokey.htm

 

The intake manifold determines how air enters the intake port and significantly effects atomization and flow, which has direct effect on combustion. If there is turbulence or a restriction caused by the manifold it will not allow as much air in, and fuel will still be added as expected for combustion at full expected CFM, which results in a rich mixture and incomplete burn.

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Cordell Rookie

Cordell

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Do a running compression test on those cylinders and at least 2 others for comparison. It would show better if it has airflow problems to them, usually used to help diagnos valvetrain problems but in the case of a fresh rebuild it could be other things. It sure sounds like it would be poor airflow to those cylinders after you've moved other parts around and such. Short of setting up a dial indicator to check valve lift at those cylinders I'm not sure what else it could be that hasen't already been discussed.
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accel_is_my_drug Collaborator

accel_is_my_drug

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not sure what the intake manifold has to do with it? but sure...

 

FAST102

NW102 TB

 

TR6 plugs

TFS 235 heads, 12:1 CR

flat-top wiseco pistons, rings gapped to 022/024

comp cams custom grind cam... 247/255 113+3 lsa, 25 degrees overlap...

ls7 lifters, stock rockers...

Siemens DEKA 60lb injectors, FAST rails

 

Crappily design intake manifolds can easily starve a few cylinders and let others get way too much air.. Usually half-assed aftermarket ones have never had a proper transient CFD done to see the airflow distribution along a bank while each cylinder is sucking in air.

 

I would guess FAST would be OK, but I wonder how sort of taper that rolled runner design has between the front runners and rear runners,

 

I suppose just because something is expensive, doesn't necessarily mean it is designed well...

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ImUrOBGYN Newbie

ImUrOBGYN

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Hasn't been mentioned and since I'm not familiar with your particular branded modifications the the LS motor... How bout any of the coils not firing properly? I know you said no detected misfires, but that doesn't mean there isnt an issue of sorts.
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JuicedH22 Newbie

JuicedH22

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Intake isnt new, I had this intake on for 3 years.... and it never had a miss. The 102TB is new to the equation however, and I suppose could be part of hte equation... Though many many many people run a FAST102/102 set up, not sure how mine would be different.. Only way I can see it being the intake is if I had a severly ripped/torn gasket or it fell out and i didnt notice it... which is not the case...
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JuicedH22 Newbie

JuicedH22

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Is it a 'mirrored' set of cylinders i.e. the 2 back cylinders? Or two random cylinders?

 

Its cylinders 2 and 6, which are on the same bank/side of the engine (passenger) but not next to each other... ALTHOUGH they are next to each other in firing order, which may or may not be a coincidence...

 

 

I will say, my prime suspect at this point is hte harness, which I fucked with while hte engine was out to relocate the coil harness connection. While I did not cut any wires ore splice anything... the wires were all reaaaalllly hard and 'stuck' to each other from years of heat... I do wonder if I somehow cracked a wire or something.... unfortunately a harness swap is a complete PITA for just 'testing'..... I want to see if there is some kind of scope I can put on the connections to measure what is happening electronically at the connections to the injectors and coils....

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JuicedH22 Newbie

JuicedH22

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coil and injector wires go from plug all the way to ecu, would need to repin there, which is doable, but a complete PITA....

 

 

Did more 'stuff' tonight, but no progress...

pulled intake manifold off to make sure there was no leak at gasket/seals...

replaced the valve seals on those cylinders just to be 'sure' it wasn't valve seal leak

had my pals at Cincy Speed do a leak down to confirm my numbers... they did, leakdown was normal

before that I also put a borescope in the spark plug hole to see if oil had built up and was puddling on the piston (i.e. bad rings leaving oil in cylinder and puddling in chamber)

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