Valve float in stock LT4?
Thread Starter
Burning Brakes
Joined: Jun 2022
Posts: 845
Likes: 212
From: Florida
Valve float in stock LT4?
Team,
I'm trying to chase down a high-RPM stumbling/bucking problem. After figuring out the fuel pump was not keeping the pressure up above 5K making the car nosedive, I replaced the old unit with a new one and that issue was resolved. However, a new issue or perhaps an issue that was masked by the fuel pressure situation has come up.
The car pulls strong all the way to 5.5K RPMs...at that point I get a bucking/stumbling/misfire causing a lack of acceleration. I have no codes, and I have replaced quite a few parts as routine maintenance (pretty much ALL sensors and ignition components). The original Opti is still in place and was freshened up a few months back. The car is driving very nice, actually.
Could this engine be experiencing valve float even though is all stock?
I'm trying to chase down a high-RPM stumbling/bucking problem. After figuring out the fuel pump was not keeping the pressure up above 5K making the car nosedive, I replaced the old unit with a new one and that issue was resolved. However, a new issue or perhaps an issue that was masked by the fuel pressure situation has come up.
The car pulls strong all the way to 5.5K RPMs...at that point I get a bucking/stumbling/misfire causing a lack of acceleration. I have no codes, and I have replaced quite a few parts as routine maintenance (pretty much ALL sensors and ignition components). The original Opti is still in place and was freshened up a few months back. The car is driving very nice, actually.
Could this engine be experiencing valve float even though is all stock?
Thread Starter
Burning Brakes
Joined: Jun 2022
Posts: 845
Likes: 212
From: Florida
Thread Starter
Burning Brakes
Joined: Jun 2022
Posts: 845
Likes: 212
From: Florida
I know what you are saying....my questions is: Am I diagnosing a fuel pressure problem as a possible cause of the power loss?
As I stated in my original post, I have ~42psi of fuel pressure under load all the way up the RPM range.
As I stated in my original post, I have ~42psi of fuel pressure under load all the way up the RPM range.
Melting Slicks
Joined: Oct 2003
Posts: 2,189
Likes: 830
From: Chapel Hill NC
2025 c3 ('68-'73) of the Year Finalist - Unmodified
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Are you hitting the rev limiter? Maybe your tach could be inaccurate?
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Pro
Joined: Jul 2007
Posts: 538
Likes: 117
From: New Braunfels Texas
How many miles on the car? If it's more than ~80k, valve spring check would be my next step. Just pull springs on number one. It's not too difficult. Otherwise it still might be the opti even though you have been in there. Also check spark plug wires if you haven't already of course.
Last edited by XLR8-R; Mar 13, 2025 at 03:03 PM.
Drifting
Joined: Jun 2020
Posts: 1,709
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From: Stay dangerous my friends
And you didn't state anything like that in this post... what original post. Good luck buddy.
