97 Coupe, dead cylinders on the back half
Thread Starter
8th Gear
Joined: Jan 2015
Posts: 8
Likes: 0
From: MI
97 Coupe, dead cylinders on the back half
Alright guys, I've got a tough one. LS1 corvette, ran out of gas (may be related) one night due to a faulty level sender. Next day it dropped cylinders, I've been able to identify cyls 5, 6, and 8.. possibly 7.
- Pulled the injectors, soaked them, cleaned the rails. Rail pressure is solid, I've got a gauge in the car.
- Verified injector harnesses are sending signal. Fired up, same problem.
- Swapped a known good injector/coil to a known bad cyl, issue didn't move.
- New plugs, new wires, no change. ...
- Spot checked compression, Cyl 2 is ~180psi, Cyl 6 (bad) is ~170psi
I have compression, spark, and fuel... But I can hold my finger on the header primary tube on the dead cylinders while it's running.
LS1 short, LS6 heads, Comp cam, P1SC on 8psi, 60# injectors, TR6 plugs gapped at 35, full non-catted exhaust
I'm lost, any ideas? Would the rear knock sensor failing cause only the back half to malfunction? Would a valvetrain issue have cold compression but not seat the valves while it's running? ECU?
Any help would be greatly appreciated
- Pulled the injectors, soaked them, cleaned the rails. Rail pressure is solid, I've got a gauge in the car.
- Verified injector harnesses are sending signal. Fired up, same problem.
- Swapped a known good injector/coil to a known bad cyl, issue didn't move.
- New plugs, new wires, no change. ...
- Spot checked compression, Cyl 2 is ~180psi, Cyl 6 (bad) is ~170psi
I have compression, spark, and fuel... But I can hold my finger on the header primary tube on the dead cylinders while it's running.
LS1 short, LS6 heads, Comp cam, P1SC on 8psi, 60# injectors, TR6 plugs gapped at 35, full non-catted exhaust
I'm lost, any ideas? Would the rear knock sensor failing cause only the back half to malfunction? Would a valvetrain issue have cold compression but not seat the valves while it's running? ECU?
Any help would be greatly appreciated
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
I AGREE,, or a bad valve. Had a Friend with the EXACT same symptoms. Had a bad #7 valve.Get an Inferred Thermometer and measure the same spot on all eight intake manifold runners right before it attaches to the head while the engine is running. If one or two are a LOT hotter than the rest, look at those valves, springs and or piston lands.
If exhaust gasses enter the intake manifold on one of the rear cylinders, it will MOSTALY effect the REAR cylinders.
Bill
Racer
Joined: Mar 2010
Posts: 330
Likes: 0
From: Houston Tx
So you have 4 dead cylinders? Compression is good on those cylinders looks like from what you posted. Have you checked to see if you have spark on those cylinders? If it was one cylinder I would say a bad coil pack but 4 cylinders all at the same time? even a broken spring like mentioned above would still only be one cylinder. Are you getting any miss fire codes? Or have they tuned out your miss fire
Racer
Joined: Mar 2013
Posts: 372
Likes: 2
From: lancaster pa
So you have 4 dead cylinders? Compression is good on those cylinders looks like from what you posted. Have you checked to see if you have spark on those cylinders? If it was one cylinder I would say a bad coil pack but 4 cylinders all at the same time? even a broken spring like mentioned above would still only be one cylinder. Are you getting any miss fire codes? Or have they tuned out your miss fire
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
So you have 4 dead cylinders? Compression is good on those cylinders looks like from what you posted. Have you checked to see if you have spark on those cylinders? If it was one cylinder I would say a bad coil pack but 4 cylinders all at the same time? even a broken spring like mentioned above would still only be one cylinder. Are you getting any miss fire codes? Or have they tuned out your miss fire
I would not in 100 years thought that a bad valve on ONE cylinder could have made FOUR cylinders loose power but,, it did.
If it would have happened to a cylinder in the front of the intake manifold, it would have had some what less of an effect but, a cylinder at the rear of the intake manifold,, the air flow is different and the exhaust gasses entering through the intake has an effect on more cylinders.
BC
Team Owner
Joined: May 2001
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From: Dear Karma, I have a list of people you missed.
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15-'16
I would not in 100 years thought that a bad valve on ONE cylinder could have made FOUR cylinders loose power but,, it did.
If it would have happened to a cylinder in the front of the intake manifold, it would have had some what less of an effect but, a cylinder at the rear of the intake manifold,, the air flow is different and the exhaust gasses entering through the intake has an effect on more cylinders.
BC
If it would have happened to a cylinder in the front of the intake manifold, it would have had some what less of an effect but, a cylinder at the rear of the intake manifold,, the air flow is different and the exhaust gasses entering through the intake has an effect on more cylinders.
BC
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Thread Starter
8th Gear
Joined: Jan 2015
Posts: 8
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From: MI
Sorry guys, I thought I updated this. Outkast called it... turns out it was a failed spring on cylinder 7, that also bent the pushrod. I'll be swapping in 105 wall Trend rods and double springs... undecided on springs so far. Hoping I didn't damage the valve but I'll get it all back together and check compression before I call this job done.
Since it was an intake spring, air was running back into the manifold and performing witchcraft on a few more cylinders.
Since it was an intake spring, air was running back into the manifold and performing witchcraft on a few more cylinders.
Racer
Joined: Mar 2013
Posts: 372
Likes: 2
From: lancaster pa
When mine broke I used a rubber band around the stem to keep the valve from dropping. I then raised and lowered it in the guide to check for binding and then pulled it up into the seat while spinning it in my fingers to check for a bent head. Good luck with your rebuild, hopefully all is well. What was the brand of spring and mileage?
Thread Starter
8th Gear
Joined: Jan 2015
Posts: 8
Likes: 0
From: MI
When mine broke I used a rubber band around the stem to keep the valve from dropping. I then raised and lowered it in the guide to check for binding and then pulled it up into the seat while spinning it in my fingers to check for a bent head. Good luck with your rebuild, hopefully all is well. What was the brand of spring and mileage?
Tech Contributor
Joined: Dec 1999
Posts: 32,910
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From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
