Car lost power, knocking after dyno
Car lost power, knocking after dyno I have a 98 ss with 76k miles on it.
4xx miles ago, I put in a 233/239 cam, with all upgraded valvetrain, ls7 lifters, ls6 oil pump, ls2 timing chain, and the car was running great, at cruising speeds.
Yesterday I drove it 180 miles up to SpeedInc for a dyno tune. The first pull, the car was doing good up until 5,800rpms, it made 370 HP, and then fell straight on its face.
-The second pull, the car LOST 30 HP all across the board, once again totally falling on its face after 5,800rpms, only making 340 HP.
The car made no noises on the dyno, but until I could figure out what was going on, tuning was stopped. I drove the car back home, 20 miles out from my house I got on it in first, into second and now the car knocks/squeals.
The knock is not very consistent, its like it knocks, stops, knocks louder, stops, knocks, ECT.
oil pressure dropped some, but still above 40 PSI warm idle.
Car was driven for roughly 5-7 miles like this to get me off the interstate.
I assume what ever is knocking, STARTED to break on the dyno, possibly being the cause of the car not making power past 5,800, and LOOSING power on the second pull??
I'm just a little confused as to why no sounds were made on the dyno, or on my drive home when something was clearly wrong with the car...
Any way I may have had a problem causing the power loss, and this is a whole new problem? Or would they more than likely be related..
Any ideas would be great!
http://tinypic.com/r/280v0r4/5 Video of knocking
4xx miles ago, I put in a 233/239 cam, with all upgraded valvetrain, ls7 lifters, ls6 oil pump, ls2 timing chain, and the car was running great, at cruising speeds.
Yesterday I drove it 180 miles up to SpeedInc for a dyno tune. The first pull, the car was doing good up until 5,800rpms, it made 370 HP, and then fell straight on its face.
-The second pull, the car LOST 30 HP all across the board, once again totally falling on its face after 5,800rpms, only making 340 HP.
The car made no noises on the dyno, but until I could figure out what was going on, tuning was stopped. I drove the car back home, 20 miles out from my house I got on it in first, into second and now the car knocks/squeals.
The knock is not very consistent, its like it knocks, stops, knocks louder, stops, knocks, ECT.
oil pressure dropped some, but still above 40 PSI warm idle.
Car was driven for roughly 5-7 miles like this to get me off the interstate.
I assume what ever is knocking, STARTED to break on the dyno, possibly being the cause of the car not making power past 5,800, and LOOSING power on the second pull??
I'm just a little confused as to why no sounds were made on the dyno, or on my drive home when something was clearly wrong with the car...
Any way I may have had a problem causing the power loss, and this is a whole new problem? Or would they more than likely be related..
Any ideas would be great!
http://tinypic.com/r/280v0r4/5 Video of knocking
what ended up being wrong with yours?
ah man..that stinks!
I'm headed up there this next week to re-dyno mine.
The first time I was there it threw the driveshaft and I didn't have a loop in it.
Needless to say - I'm not a fan of the dyno process, but a necessary evil to make sure the motor is well tuned.
Let us know what you find. A compression test would be a good start.
I'm headed up there this next week to re-dyno mine.
The first time I was there it threw the driveshaft and I didn't have a loop in it.
Needless to say - I'm not a fan of the dyno process, but a necessary evil to make sure the motor is well tuned.
Let us know what you find. A compression test would be a good start.
ah man..that stinks!
I'm headed up there this next week to re-dyno mine.
The first time I was there it threw the driveshaft and I didn't have a loop in it.
Needless to say - I'm not a fan of the dyno process, but a necessary evil to make sure the motor is well tuned.
Let us know what you find. A compression test would be a good start.
I'm headed up there this next week to re-dyno mine.
The first time I was there it threw the driveshaft and I didn't have a loop in it.
Needless to say - I'm not a fan of the dyno process, but a necessary evil to make sure the motor is well tuned.
Let us know what you find. A compression test would be a good start.
Launching!
Joined: Jun 2005
Posts: 277
Likes: 0
From: SC
What spring pressures are you running and what oil are you running?
Pull the valve covers and check lash on all the valves. Sure sounds like a lost lobe or two but maybe it just floated the valves on the dyno leading to some bent pushrods that showed their asses once you got on it going home. Could be a few things, hard to tell.
Pull the valve covers and check lash on all the valves. Sure sounds like a lost lobe or two but maybe it just floated the valves on the dyno leading to some bent pushrods that showed their asses once you got on it going home. Could be a few things, hard to tell.
Last edited by SSellers; Jul 26, 2013 at 01:15 PM.
That sounds nasty. Start from the top and work your way down. Your cam is probably trashed if you have bad lifters. That squealing though, might be metal on metal contact...... don't start it again.
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Verdad Gallardo What spring pressures are you running and what oil are you running?
Pull the valve covers and check lash on all the valves. Sure sounds like a lost lobe or two but maybe it just floated the valves on the dyno leading to some bent pushrods that showed their asses once you got on it going home. Could be a few things, hard to tell.
Pull the valve covers and check lash on all the valves. Sure sounds like a lost lobe or two but maybe it just floated the valves on the dyno leading to some bent pushrods that showed their asses once you got on it going home. Could be a few things, hard to tell.
Its got tsp 650" lift springs. Mobile 1 full syn.
It don't have a misfire, or at least didn't sound like it, and a snapped pushrod would send a misfire, as ive done it before. I'll be pulling the valve cover and checking it out when I get the car home today.
Has brand new ls7 lifters in it, couldn't imagine them going junk on me. I'm leaning toward a rod bearing, but would that cause power to slowly decrease, then take a final sh*t on me before I could hear and knocking?
Launching!
Joined: Jun 2005
Posts: 277
Likes: 0
From: SC
We're just postulating but once you get the top off you can start ruling stuff out. Just you mentioning it falling flat at 5800 RPM brings in valve float as a possibility which is a nasty thing....basically imagine everything separating apart....lifter coming off cam lobe then slamming back into it. It can take some stuff out for sure. Also running high spring pressures without a good oil at high RPM can lead to pivot or lobe failure (yes, even on a roller) so lash opens up and then bad things happen. Just hard to say and everyone is guessing while the big metal box is still closed up.
We're just postulating but once you get the top off you can start ruling stuff out. Just you mentioning it falling flat at 5800 RPM brings in valve float as a possibility which is a nasty thing....basically imagine everything separating apart....lifter coming off cam lobe then slamming back into it. It can take some stuff out for sure. Also running high spring pressures without a good oil at high RPM can lead to pivot or lobe failure (yes, even on a roller) so lash opens up and then bad things happen. Just hard to say and everyone is guessing while the big metal box is still closed up.
Here is what comes to mind when I hear the symptons.
Oil pressure drop and knock sounds like a rod and main bearing spun. I am guessing #7 piston broke a ring land causing #7 rod bearing to fail then taking out main bearing #4.
Detonation on the dyno run is what broke the piston.
Pm me if my guess was correct.
Oil pressure drop and knock sounds like a rod and main bearing spun. I am guessing #7 piston broke a ring land causing #7 rod bearing to fail then taking out main bearing #4.
Detonation on the dyno run is what broke the piston.
Pm me if my guess was correct.
Oh my. Why oh why did you drive it 180 miles untuned? After a cam install you have to trailer it to your tuners unless you have the means to load a tune or send the computer out. We just did a cam upgrade on my sons 98 and didn't even like running it to load it on the trailer.
Time to tear down top end and remove oil pan. Keep us posted.
Time to tear down top end and remove oil pan. Keep us posted.
Teching In
Joined: May 2013
Posts: 9
Likes: 0
I am experiencing something similar in my 2000 z28. I had the cam replaced recently along with one lifter and rod because one lobe was trashed. After 1k I cut my filter open and it is loaded with metal debris. The magnetic plug looked like it had hair on it. After revving engine I am hearing a valve train rattling noise until it settles down to idle. GM did the work, maybe they messed up in the install Not sure if I should tear down again or look a new engine replacement.
Oh my. Why oh why did you drive it 180 miles untuned? After a cam install you have to trailer it to your tuners unless you have the means to load a tune or send the computer out. We just did a cam upgrade on my sons 98 and didn't even like running it to load it on the trailer.
Time to tear down top end and remove oil pan. Keep us posted.
Time to tear down top end and remove oil pan. Keep us posted.
I had no easy access to a trailer, but was going to rent one until I called texas-speed and they told me it would not hurt to drive it.. bad decision I guess?