84 Shuddering Under Acceleration
Thread Starter
2nd Gear
Joined: Apr 2026
Posts: 2
Likes: 1
84 Shuddering Under Acceleration
Hi, just got an 84 Crossfire I'm working on restoring a few months ago. Just got it on the road a few times these past couple weeks, up to about 45mph on back roads. When driving over 30mph and accelerating more than just a slight bit to maintain speed, but not enough to downshift, the car shudders in a way that almost feels like going over a rumble strip, but less intense. If I let off slightly, or accelerate harder so that it downshifts, it smoothes out. How should I go about diagnosing/fixing this?
Melting Slicks
Joined: Dec 2009
Posts: 2,226
Likes: 284
Does it do it before it hits 150*? I'm thinking torque converter clutch. The early cars had weird programing to lock it up as soon as possible for fuel economy reasons. You can try unplugging it and driving it for a day. The connector is on the driver's side of the trans.
Thread Starter
2nd Gear
Joined: Apr 2026
Posts: 2
Likes: 1
To be honest it normally only does it on uphills, and I let it warm up to about 170 in the driveway before going anywhere. Out of town right now but will try unplugging it and driving on Weds. If that is the case, what parts should I try checking/replacing? I've read that it might be the solenoid.
1st Gear
Joined: May 2024
Posts: 1
Likes: 0
Shudder under acceleration
Hi, just got an 84 Crossfire I'm working on restoring a few months ago. Just got it on the road a few times these past couple weeks, up to about 45mph on back roads. When driving over 30mph and accelerating more than just a slight bit to maintain speed, but not enough to downshift, the car shudders in a way that almost feels like going over a rumble strip, but less intense. If I let off slightly, or accelerate harder so that it downshifts, it smoothes out. How should I go about diagnosing/fixing this?
I had a very similar issue with my 1987 Corvette. I believe it’s the fuel pump. there may be a port on a fuel rail for you to check fuel pressure while driving.
Melting Slicks
Joined: May 2002
Posts: 2,254
Likes: 411
From: Muskogee OK
Cruise-In VI Veteran
On a stock 84 pump you'll probably see 9 to 11 psi without modifying the regulator , even then we "upgrade" to an 85 pump to get higher pressure. The xfire likes 13psi, but with the stock set-up 11 is about all that's even possible
Racer
Joined: Oct 2013
Posts: 287
Likes: 90
had something similar, but the same, on our Buick. had shuddering/slight hesitation on long uphills, especially at part throttle that I diagnosed as a fuel issue. put in a few cans of fuel injector cleaner, cleaned the MAF sensor and throttle body, replaced the MAP, checked the plugs (were ok). no codes. brought it to a dealer who had his tech plug a PC into the ECM and was quoted $1700 for a new torque converter due to a lockup prob.
based on the advice of my mechanic, I added a vial of Lube guard "Shudder Fixx" and the problem disappeared never to come back. this was in 2019.
another case of labatt's blue to my mechanic.
based on the advice of my mechanic, I added a vial of Lube guard "Shudder Fixx" and the problem disappeared never to come back. this was in 2019.
another case of labatt's blue to my mechanic.
