Troubleshooting LG4 down on power
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Car: 1982 Trans-Am
Engine: 355 w/ ported 416s
Transmission: T10, hurst shifter
Axle/Gears: 10 bolt, true-trac, 3.73
Troubleshooting LG4 down on power
Hey guys;
I'm helping a buddy, he's got an LG4, with an auto. Non-cc Q-jet. Rebuilt tag on the q-jet.
He just bought the car, history is unknown. No modifications, bone stock- covered in dust/crud and untouched.
Car was stalling at first. Found a vacuum leak between intake manifold nipple and trans modulator.
Put new plugs in it, installed an MSD spring/weight kit, and drove it around the block a few times. Pulled the plugs, rest of the 7 look great, and #3 is carboned. I pulled the valve cover and watched the rocker arms move - no problems there. I disconnected the plug wire, and put in a spare plug, and held it against the exh manifold - good spark.
When driving the car, it's down on power, and idle vacuum is ~15". That seems low for a stock 305 to me?
Checked compression, 180 across the board. Beautiful.
Checked timing. Seems to enjoy using ~40* timing to idle?? I verified the timing with a piston stop.
Driving it around it seems to be pinging under load - to me it seems like it's missing on one hole.
My first thought is an intake manifold gasket leak between valley and #3 cylinder.
Any alternative thoughts i'm missing that might explain either;
- low vacuum
- carboned #3 cylinder
- loss of power
- massive timing to keep it running
??
Thanks
I'm helping a buddy, he's got an LG4, with an auto. Non-cc Q-jet. Rebuilt tag on the q-jet.
He just bought the car, history is unknown. No modifications, bone stock- covered in dust/crud and untouched.
Car was stalling at first. Found a vacuum leak between intake manifold nipple and trans modulator.
Put new plugs in it, installed an MSD spring/weight kit, and drove it around the block a few times. Pulled the plugs, rest of the 7 look great, and #3 is carboned. I pulled the valve cover and watched the rocker arms move - no problems there. I disconnected the plug wire, and put in a spare plug, and held it against the exh manifold - good spark.
When driving the car, it's down on power, and idle vacuum is ~15". That seems low for a stock 305 to me?
Checked compression, 180 across the board. Beautiful.
Checked timing. Seems to enjoy using ~40* timing to idle?? I verified the timing with a piston stop.
Driving it around it seems to be pinging under load - to me it seems like it's missing on one hole.
My first thought is an intake manifold gasket leak between valley and #3 cylinder.
Any alternative thoughts i'm missing that might explain either;
- low vacuum
- carboned #3 cylinder
- loss of power
- massive timing to keep it running
??
Thanks
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