vaccum advancement problem on '89 chevy silverado 1500?

ok. i asked my mechanic why my vehicle will run good at some points and bad at others. i also told him that since ive had the truck it has been losing horse power. because whenever i slam the gas the engine will rev up but it wont go till 30 seconds later i have asked him if it was the transmission and he said no because my transmission is fairly new. he said it was a vaccum advancement problem and i was wondering how to fix it?

3 Answers

  • 1 decade ago
    Favorite Answer

    If the engine RPM's are increasing but the car speed is not, that sounds like a transmission issue to me. I would find another mechanic. Seems like he has not had enough experiance with older cars. when you mat the gas peddle do your RPMs rev up and then slowly drop down as the speed of the car slowly increases then progresses normally? Thats the classic sign of a transmission slip. when your vacuum advance stops working or is out of adjustment, you have engine ping and poor fuel economy. The motor would also sound like it's over worked and is struggleing to move the truck. If you can give me a little more information I can help you diagnois the issue more. But I think your mechanic is worng about the vacuum advance.

    Source(s): Your E-mail wasn't very clear. But it still sounds like a transmission issue to me. If you know how to check the transmission fluid, run the truck up to opertaing tempature and while parked on level ground, check the transmission fluid. If it is brown or smells burnt, the transmission is starting to fail. You may be able to get a little bit more mileage out of it by having the transmissions power flushed, but for the most part the transmission is on it's way out. Again take it to another shop and get a 2nd opinion. but I think your current mechanic needs more experiance with older cars.
  • 1 decade ago

    Dear Vacuum-

    I can tell you for a fact that it is not a Vacuum Advance issue.

    It is indeed a transmission issue.

    The transmissions on these trucks are not vacuum controlled like the old GM and Ford transmissions. The truck if equipped with a V-8 is probably equipped with the first generation 4L-80-E transmission which is an electronically controlled and shifted transmission.

    There is a pressure sensor that sends signals to the vehicle's computer to designate shift changes. The other sensor that is in play at this time is the Throttle Position Sensor.

    If the engine revs up then the transmission catches and launches your vehicle, it is a transmission problem.

    Chevrolet 101:

    The Vacuum Advance went away when GM changed to the 350C, (Corporate Engine). It no longer uses the large E-Coil distributor that used to be on the engines. This system is totally electronic and uses several sensors to advance engine timing, fuel needs, retard timing, control RPM, shift transmission, control emissions and many other functions.

    The transmission is shifted using information from throttle position, engine RPM, transmission oil pressure, current gear selection, vehicle speed, engine loading, exhaust gas sensors, manifold pressure, and intake volume, (Vortec Equipped Vehicles).

    This information is sent to the ECM, (Electronic Control Module) and based on the information received by the input controls, (you) the transmission is shifted to the correct gear to provide optimum engine power delivery.

    If one of these sensors is not functioning properly the entire system tries to compensate using the ECM's pre-programmed data to make the decisions as to what needs to happen when. If the data is in error the results will be in error.

    In the transmission several factors come into play. Pressure sensors detect the differing pressures through the valve body which controls the shifting patterns of the transmission. If one of these pressure sensors is faulty, the transmission will not shift properly. If the main oil pump in the transmission is not delivering proper pressure, all of the sensors will be reciving faulty data, the transmission will not shift properly. If the fluid level is low, or the transmission filter clogged due to lack of service, the transmission will not shift properly. If the fluid is burned and has lost is lubricating and pressure properties, this too will effect transmission shift patterns.

    My guess at this point is that you have a problem with the sensors in the valve body of the transmission. GM had several problems whith the pressure sensors and shift solenoids in them.

    I would suggest that you have the vehicle serviced by Chevrolet and let them have a good look at the issue. They will be able to locate and solve the problem with your truck.

    I hope I was able to help you out. Good Luck!

    Source(s): General Motors Service Parts Pro
  • 1 decade ago

    Find another mech, your truck does not use or have vacuum advance, period. The truck will have a detent cable that you can try adjusting at the rear of the throttle body. That can improve or delay the shifting somewhat.

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