Bucking/Missing at low RPMs
Thread Starter
Le Mans Master
Joined: Mar 2006
Posts: 5,262
Likes: 0
From: E. Amherst NY
Bucking/Missing at low RPMs
OK -- Here's the deal. '86L/700R4/D36
Between Sunday morning and Monday evening, I put 400 miles on the car. Both before and after that, its been doing this, but it now seems worse.
When we're at like 1100-1200 rpms in gear, the car seems to buck -- like there's drivetrain slop. At highway speeds, I'm getting some vibration, enough to notice and make the ride uncomfortable. It almost kinda feels like the rear end is skipping or bouncing. The bucking has been there for some time now, and until now my solution has been to drop it down a gear to bring the revs up. At last check, the feeling is still there at speed in neutral. I'm getting sick of masking the problem and am now out to fix it.
My first thought is u-joints. I'm quite certain the vibration is coming from the rear end.
Within the last 5,000 miles or so, I have replaced the following:
Transmission, converter, injectors, IAC, ECM, mufflers, rear y-pipe, changed the rear gear oil (added the GM additive
), cap, rotor, wires, and a few other things I'm forgetting. Driveshaft u-joints have been replaced -- at least I paid to have them replaced.
The car did this before the new transmission and converter.
Thoughts?
Between Sunday morning and Monday evening, I put 400 miles on the car. Both before and after that, its been doing this, but it now seems worse.
When we're at like 1100-1200 rpms in gear, the car seems to buck -- like there's drivetrain slop. At highway speeds, I'm getting some vibration, enough to notice and make the ride uncomfortable. It almost kinda feels like the rear end is skipping or bouncing. The bucking has been there for some time now, and until now my solution has been to drop it down a gear to bring the revs up. At last check, the feeling is still there at speed in neutral. I'm getting sick of masking the problem and am now out to fix it.
My first thought is u-joints. I'm quite certain the vibration is coming from the rear end.
Within the last 5,000 miles or so, I have replaced the following:
Transmission, converter, injectors, IAC, ECM, mufflers, rear y-pipe, changed the rear gear oil (added the GM additive
), cap, rotor, wires, and a few other things I'm forgetting. Driveshaft u-joints have been replaced -- at least I paid to have them replaced. The car did this before the new transmission and converter.
Thoughts?
Thread Starter
Le Mans Master
Joined: Mar 2006
Posts: 5,262
Likes: 0
From: E. Amherst NY
Footbraking it at the dragstrip, it will occasionally stumble. I haven't had it at the track in nearly a month, so I haven't really tested it lately.
As for noises, for 2-3 seconds every once in a while it will make a low pitched whine -- like you're making a hard turn at low speeds. Only in neutral or park. Did it in drive once, maybe twice. Thats it.
Again, it did this both before and after the tranny rebuild.
As for noises, for 2-3 seconds every once in a while it will make a low pitched whine -- like you're making a hard turn at low speeds. Only in neutral or park. Did it in drive once, maybe twice. Thats it.
Again, it did this both before and after the tranny rebuild.
Last edited by Corvette Chris; May 27, 2009 at 06:10 PM.
Thread Starter
Le Mans Master
Joined: Mar 2006
Posts: 5,262
Likes: 0
From: E. Amherst NY
OK...
Just drove it with the computer datalogging, and then without the computer and ALDL hooked up. Car ran phenomenal with the datalog going. As soon as I disconnected it and restarted, same thing -- bucking at the low RPMs, rougher idle...
Found a few issues while datalogging.
1. Getting on the highway, I got on the throttle. Knock count went from like 10 to 98 very quickly.
2. While cruising on the highway -- at 71 mph, the datalog went to 35mph for 3 segments. O2, BLM, EGR duty and Knock count dropped. After the 3, it went back to 71.
3. BLM and base pulse jump around a fair amount. I already knew it was doing that though -- stock tune. No cam, heads, headers, yada yada.
Just drove it with the computer datalogging, and then without the computer and ALDL hooked up. Car ran phenomenal with the datalog going. As soon as I disconnected it and restarted, same thing -- bucking at the low RPMs, rougher idle...
Found a few issues while datalogging.
1. Getting on the highway, I got on the throttle. Knock count went from like 10 to 98 very quickly.
2. While cruising on the highway -- at 71 mph, the datalog went to 35mph for 3 segments. O2, BLM, EGR duty and Knock count dropped. After the 3, it went back to 71.
3. BLM and base pulse jump around a fair amount. I already knew it was doing that though -- stock tune. No cam, heads, headers, yada yada.
Thread Starter
Le Mans Master
Joined: Mar 2006
Posts: 5,262
Likes: 0
From: E. Amherst NY
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
Pro
Joined: Jun 2008
Posts: 531
Likes: 0
From: Calgary Alberta
Try a bottle of fuel injector cleaner and a full tank of a different brand of premium gas.
I experience very similar issues, thought it was MAF and various other things - when it started, I filled up with Chevron 94 and it continued - wasn't until I filled with Shell 91 V-Power. I still feel cheated - I always trusted Chevron 94
I experience very similar issues, thought it was MAF and various other things - when it started, I filled up with Chevron 94 and it continued - wasn't until I filled with Shell 91 V-Power. I still feel cheated - I always trusted Chevron 94
Thread Starter
Le Mans Master
Joined: Mar 2006
Posts: 5,262
Likes: 0
From: E. Amherst NY
Try a bottle of fuel injector cleaner and a full tank of a different brand of premium gas.
I experience very similar issues, thought it was MAF and various other things - when it started, I filled up with Chevron 94 and it continued - wasn't until I filled with Shell 91 V-Power. I still feel cheated - I always trusted Chevron 94
I experience very similar issues, thought it was MAF and various other things - when it started, I filled up with Chevron 94 and it continued - wasn't until I filled with Shell 91 V-Power. I still feel cheated - I always trusted Chevron 94
Thread Starter
Le Mans Master
Joined: Mar 2006
Posts: 5,262
Likes: 0
From: E. Amherst NY
Haven't checked for codes in a while. Will be sure to check laster today. As for the K&N -- last time I had the filter out was probably a year or two ago -- possible. Will grab some MAF cleaner too. 