Help! LT1 Bucking Under Load
Thread Starter
Safety Car
Joined: Oct 2000
Posts: 4,234
Likes: 355
From: Albuquerque, NM
Help! LT1 Bucking Under Load
I'm posting this for a fellow forum member who is out of state buying a 1994 LT1 six speed. He does not have internet access so he'll be calling me Saturday morning to see what the consensus is. We'd really appreciate any help.
During the test drive, he reported that the car would "buck" (loose all power) while accelerating in 4th, 5th, and 6th gears. When not accelerating the car would run fine. He said it was definitely related to the load on the engine. 1st and 2nd seemed to be a lot better.
To me it sounded like a fuel problem - pump, filter, injectors (?) except that it was related to load on the engine more than RPMs. I would not rule out a spark problem. To me it does not sound like the opti, but I can't be sure. The check engine light does NOT come on.
Any help I can give this guy would be appreciated.
During the test drive, he reported that the car would "buck" (loose all power) while accelerating in 4th, 5th, and 6th gears. When not accelerating the car would run fine. He said it was definitely related to the load on the engine. 1st and 2nd seemed to be a lot better.
To me it sounded like a fuel problem - pump, filter, injectors (?) except that it was related to load on the engine more than RPMs. I would not rule out a spark problem. To me it does not sound like the opti, but I can't be sure. The check engine light does NOT come on.
Any help I can give this guy would be appreciated.
Team Owner
Joined: Aug 2000
Posts: 40,156
Likes: 45
From: San Pedro CA
I would start with the coil and coil wires.
Also, check the plugs and plug wires.
In my experience, when a car is bucking under load like that, it's LIKELY to be spark related.
Also, confirm fuel pressure. If the pump is failing, then it will fight you big time. I would love to know what the history is, e.g., when was the last fuel filter replaced?
Also, check the plugs and plug wires.
In my experience, when a car is bucking under load like that, it's LIKELY to be spark related.
Also, confirm fuel pressure. If the pump is failing, then it will fight you big time. I would love to know what the history is, e.g., when was the last fuel filter replaced?
Thread Starter
Safety Car
Joined: Oct 2000
Posts: 4,234
Likes: 355
From: Albuquerque, NM
Thanks Bogus. I just spoke with a mechanic at a Corvette specialty shop, and that's pretty much exactly what he told me. He said to check the fuel pressure, but he figures it's probably a bad spark plug wire or bad spark plug (cracked porcelain insulator), especially if the plugs and wires are original.
It would be worth replacing the fuel filter unless it has been done recently. In any event, I'll tell the guy that the problem is likely something fairly minor.
It would be worth replacing the fuel filter unless it has been done recently. In any event, I'll tell the guy that the problem is likely something fairly minor.
Advanced
Joined: Apr 2004
Posts: 75
Likes: 0
From: Worcester MA
My 94 is in the shop for this EXACT problem right now. The mechanic will be working on it tomorrow morning. I had one blue puff of smoke when the car sat overnight upon startup. I am having the valve seals replaced and plugs/wires. I hope the bucking was a slightly fouled plug from the leaky valve seal, but it only puffed smoke once, so i'm not sure. Hopefully it's not the opti!!!
Melting Slicks
Joined: Apr 2003
Posts: 2,150
Likes: 6
From: NS
Originally Posted by bogus
I would start with the coil and coil wires.
Also, check the plugs and plug wires.
In my experience, when a car is bucking under load like that, it's LIKELY to be spark related.
Also, confirm fuel pressure. If the pump is failing, then it will fight you big time. I would love to know what the history is, e.g., when was the last fuel filter replaced?
Also, check the plugs and plug wires.
In my experience, when a car is bucking under load like that, it's LIKELY to be spark related.
Also, confirm fuel pressure. If the pump is failing, then it will fight you big time. I would love to know what the history is, e.g., when was the last fuel filter replaced?
Totally agree. I have first hand experience with this. Check your plugs, wires, and coil. Get yourself a ST-45 spark tester and follow the procedure in the Service Manual. In my case the little platinum puck on the ground electrode was lost from most of the factory AC plugs and my gap opened up to 0.065" to 0.070". I have since switched to NGK TR-55 plugs.
Some people may not understand why spark does this. It's due to cylinder pressure. The higher the cylinder pressure the more voltage you need to jump the gap on the spark plug and ignite the fuel mixture. The highest cylinder pressures occur when the engine is under load at lower RPMs. You'll get misfires in higher gears when going up hills or just trying to accelerate allowing the engine to "lug". You'll also have misfires at high RPM at WOT which you'll most likely sense as a big loss of power, almost like a rev limiter.
Advanced
Joined: Apr 2004
Posts: 75
Likes: 0
From: Worcester MA
I was with the mechanic today and we took out the original spark plugs and wires getting ready to pressurize the cylinders in order to do the valve seals. I was inspecting the wires and found that one had been cut open against a piece of metal near the engine (#8 cylinder). Problem found. Just need to finish the seals on Monday, replace the plugs and wires and vroom.......
Thank God it wan't the opti
Thank God it wan't the opti
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