86 MC LS with 4.3l Transmission shift too soon

[shanestan]

Hi new to the sight. My wife bought this car while I was on deployment and now I get to fix all the problems going on with it. The car seems to shift too early from first to second causing the engine to bog down (low rpms). I am thinking it is one of the shifters. I am not familiar with this model but have worked on GM cars in the past. Not sure if it is electronic shift but i am sure it is. Want to do some troubleshooting on it and I am prepared to remove the shift body for inspection. I am sure the filter needs to be replaced when I do this.
Any suggestions on what to start with?

[maxwedge]

Welcome to AF and welcome home! The trans could be a 200c or a 350 , there could be a tv cable that is bad or out of adjustment or a bad vacuum modulator, don't fool with the valve body that is almost never the issue. See if there are 2 cables attached to the carb linkage. Do you have cruise control then there could be 2 or 3.

[shanestan]

Thank you for your reply! The engine is the 4.3L (in the subject)TPI with cruise control. The 350 sounds too large for 6 cyclinder so i think it is the 200c you mention. What is the tv cable? I definetly understand the modulator but I think it is electronic and will replace it. This thing is loaded. Will take some pictures and post in the "Show off Your Ride" section soon.

[shanestan]

SO i have done alot of work! So far I have replaced:
Plug wires(one plug wire did not match and looked very old)
Plugs (old plugs indicated running rich)
Rotor
Distributor cap
Distributor Coil
Transmission filter and CORRECT amount of new fluid
U joints
Replaced AC/Fan blower
Car runs much much better and shifts like it is supposed too.
Next up is:
new shocks
flush brake lines
clean the interior
Promise to get puctures up when I can.

[shanestan]

Well I spoke too soon. The car continues to not shift properly (intermittently). Shifts too early and will not down shift properly when coming to a stop. I have replaced the MAP sensor, and doublechecked spark plug wires, one was not all the way on. It seemed to help at first but it started back to sputtering. I bought the car from a one time owner (retired Army) and the car is completly stock. Engine is a 4.3l TBI with a 2004R transmission. Ujoints have been replaced. Most of the vacuum lines have been replaced. Sometimes when the car is idling (idle is smooth) the check engine lite comes on but goes off after driving away. The code points to the MAP sensor but even after being replaced, it will still come on which points to a vacuum problem. This happens with the A/C on and off. Either the engine is not producing enough power at idle to keep fluid pressure in tranmission at proper level or the tranmission is pump is dying. Any other suggestions?

[Blue Bowtie]

Shane,

Read Maxwedge's reply again. Your transmission is not electronically controlled unless someone swapped in a transmission and ECM from a 1993 or later. The shift points are controlled by the governor, and either a vacuum modulator at the rear of the transmission or a Throttle Valve (TV) cable attached to the throttle linkage. Misadjustment of the TV cable and/or problems with the governor will affect the shift points. A misadjusted or damaged vacuum modulator can have a similar effect, but it usually causes a late or higher RPM shift.

[Blt2Lst]

Do a search on TV cable adjustment for the 200R4. It is easy to do and will probably solve your shifting problems. I had the same problem with my car, I had to replace my TV cable to get it right but now it shifts smooth.
Start with trying to adjust yours first..

[clark40]

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