Riddle Me This !
Thread Starter
Burning Brakes
Joined: Jan 2004
Posts: 1,158
Likes: 6
From: Winter Springs Fla
Riddle Me This !
06 Z06 , built 441ci LS7 nitrous car .
I went out saturday night and won 5 races with several pulls in most races , then on my way home a good 30-40 minutes after racing , it drops cylinder #4 at a stop light and start running rough .
No valve train noise , no motor noise or anything , but #4 is running colder than the rest .
After testing the next day , i have strong spark , good injector flow and perfect compression across that bank .
#4 is burning at 250 degrees at 1 minutes after cold start and the other cylinders on that bank are at 700ish .
Noid testing the injectors on that bank showed no variance .
Spark testing on that bank showed no variance .
Ive rebooted the computer several times.
Ive swapped plugs , wires , injectors , coils and coil harness .
Pulled the valve cover , inspected the valve train and rotated the assembly , valves are opening and closing normally .
The cylinder is firing but not all the time and you can hear that cylinder missing at idle and off idle .
Im at a loss here and looking for anything to help !
Ive been building and racing cars for 40 years and this has got me stumped .
I went out saturday night and won 5 races with several pulls in most races , then on my way home a good 30-40 minutes after racing , it drops cylinder #4 at a stop light and start running rough .
No valve train noise , no motor noise or anything , but #4 is running colder than the rest .
After testing the next day , i have strong spark , good injector flow and perfect compression across that bank .
#4 is burning at 250 degrees at 1 minutes after cold start and the other cylinders on that bank are at 700ish .
Noid testing the injectors on that bank showed no variance .
Spark testing on that bank showed no variance .
Ive rebooted the computer several times.
Ive swapped plugs , wires , injectors , coils and coil harness .
Pulled the valve cover , inspected the valve train and rotated the assembly , valves are opening and closing normally .
The cylinder is firing but not all the time and you can hear that cylinder missing at idle and off idle .
Im at a loss here and looking for anything to help !
Ive been building and racing cars for 40 years and this has got me stumped .
Thread Starter
Burning Brakes
Joined: Jan 2004
Posts: 1,158
Likes: 6
From: Winter Springs Fla
Checked valve stem length , pushrod length and straightness , rocker arm bearings , bodies and shafts are perfect .
Also flashed the tune with a known good copy .
Also flashed the tune with a known good copy .
Last edited by zoomz; Jul 3, 2016 at 12:04 PM.
Le Mans Master
Joined: Dec 2003
Posts: 5,561
Likes: 448
From: Atlanta metro Ga.
I was going to vote for broken ring land or cracked cylinder liner - but you said you checked compression and all was well.
Maybe put one of those USB bore scopes down there, see what you can see.
What about mech stethoscope on that injector, make sure it is firing consistently - you could also start swapping parts (coil and injector) to see if the problem follows.
Maybe put one of those USB bore scopes down there, see what you can see.
What about mech stethoscope on that injector, make sure it is firing consistently - you could also start swapping parts (coil and injector) to see if the problem follows.
Last edited by Dan_the_C5_Man; Jul 3, 2016 at 01:59 PM.
Thread Starter
Burning Brakes
Joined: Jan 2004
Posts: 1,158
Likes: 6
From: Winter Springs Fla
I was going to vote for broken ring land or cracked cylinder liner - but you said you checked compression and all was well.Checked , compression and leak down , all normal
Maybe put one of those USB bore scopes down there, see what you can see.Checked while the motor was being turned over .
Everything moving correctly
What about mech stethoscope on that injector, make sure it is firing consistently - you could also start swapping parts (coil and injector) to see if the problem follows.Checked voltage and pulse and compaired it to other cylinders . Ive swapped everything , some things twice .
Maybe put one of those USB bore scopes down there, see what you can see.Checked while the motor was being turned over .
Everything moving correctly
What about mech stethoscope on that injector, make sure it is firing consistently - you could also start swapping parts (coil and injector) to see if the problem follows.
Checked voltage and pulse and compaired it to other cylinders . Ive swapped everything , some things twice .That's the only thing I havnt done yet but it gets a great spark :/
Last edited by zoomz; Jul 3, 2016 at 04:58 PM.
Thread Starter
Burning Brakes
Joined: Jan 2004
Posts: 1,158
Likes: 6
From: Winter Springs Fla
The problem was a lifter .
There were 2 roller bearings missing from the main roller assembly .
If the rollers bearings rotated just right it would fire the cylinder .
Thank god there was no damage done to the billet cam or the roller surface on the bad lifter .
The motor started to finally tick a little which led me to tear the head off , but prior to that , it never made a noise while testing .
There were 2 roller bearings missing from the main roller assembly .
If the rollers bearings rotated just right it would fire the cylinder .
Thank god there was no damage done to the billet cam or the roller surface on the bad lifter .
The motor started to finally tick a little which led me to tear the head off , but prior to that , it never made a noise while testing .
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