1990 Caprice 307 Stock - Surge at highway speed

Discussion in 'General Automotive Tech' started by Danjdurand, Jan 17, 2023.

  1. Danjdurand

    Danjdurand New Member

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    I've done a quick search and haven't seen this posted in the Forums. I have a completely stock unaltered 1990 Caprice Wagon with the 307. There are no codes on the car and honestly runs great except what I can best describe as a surge at highway speed. It doesn't matter if it's in drive or over drive it almost feels like the torque lockup is engaging and disengaging. Any thoughts at all from the amazing wagon gurus on how to Troubleshoot?

    Thanks very much in advance...
     
  2. Silvertwinkiehobo

    Silvertwinkiehobo "Everything that breaks starts with 'F.'"

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    When it 'surges,' does the engine speed up but the car slows down? That would be the indication of a torque converter clutch problem. But, if the engine slows down, and the car commensurately slows, I would say it has a fuel problem, either the pump/filter, or the carb itself. The Dualjet and Quadrajet carbs use the same style of throttle position sensor, which is installed under the air horn and actuated by the accelerator pump arm. They typically get a wear spot over the years, and can cause a drop to zero volts if the rheostat winding is fully worn off. That could cause a type of surging.
     
  3. Danjdurand

    Danjdurand New Member

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    That's awesome advice! Thanks so much...it's definitely the latter which is why I was certain it wasn't transmission. That would explain the random stalling too I bet.

    I'll report back in the spring when she comes out of hiding and I can have a boo....
     
  4. Silvertwinkiehobo

    Silvertwinkiehobo "Everything that breaks starts with 'F.'"

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    Now would be the best time to address the diagnosis and possible repair. Do you have a DMM? You use that to "sweep" test the TPS. Yo hook the positive lead to the signal return, and negative to the engine ground, and very gently and slowly push the TPS plunger down. Googling your car's info and engine/carb hopefully will give you the min/max voltage spec.
    When you do the test, you want to see the voltage slowly and consistently rise as you press down. Any drop as you push down makes the TPS bad.
     
  5. elB

    elB Well-Known Member

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    Unplug the TCC lockup solenoid connector from the side of the transmission as a test. They are known for going bad - sticking or failing to stay engaged and it causes the same problem. I had a 1989 Caddy with the same problem and had *planned* to change the solenoid out but never got around to it, just drove it for 2 years without it plugged in. It doesn't really impact running except for sacrificing 1-2MPG above 55MPH and you won't get the car randomly stalling after coming to idle when it fails to disengage.
     

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