steelerguy

My 89 chevy pickup has a 305 engine and a 3 speed transmission with about 180,000 miles. I have been experiencing severely delayed shifting after 30 minutes or so, particularly on very hot days. We get a lot triple digit days here in Phoenix, AZ. Have changed the throttle position sensor, fuel filter, fuel pump that crapped out, PCV Valve & have had the vehicle speed sensor removed cleaned up & reinstalled. The reason for this was the replacement one from autozone was not the correct one ($26.99 was worth a shot). The part # on the sensor was 8655291 which NAPA could get for $105 plus $10 S&H). Found it on www.rockauto.com for $76 plus S&H if I do decide to change it. After the truck sitting for most of the weekend and reinstalling the VSS (plus reinsulating the 2 wires at its plug that may have been intermitently shorting) it has not hard shifted yet on my 2nd day of driving. However, it has worked well before after a driving break & we are experiencing a cold front of only 96 degrees, overcast with monsoon storms. I'm not even sure the hot weather is a contributing factor as it gets & stays hot here.

I just passed emmissions testing today with flying colors, not even halfway to a failure in any catagory. However, after driving for a bit and shutting down to run an errand, I notice white smoke coming from the exhaust for just a bit. Noticed it yesterday evening on another stop. From what a mechanic told me, white is transmission fluid & blue is oil. White can also be coolant but you should be able to smell that coolant smell. I believe that he said the vacuum problem causes transmission fluid to be drawn into the combustion chamber instead of being held in place by system pressure.

(3 days later) the smoke began intermittently emitting on the highway and particularly during a hard shift.

I have heard that vacuum problems at the transmission can cause this as well as the intermittent hard shifting. What do I test & are the parts replacement/repairs a major deal?

Thanks for any help you can offer.

Steelerguy

Kevcules

The only thing that can cause white smoke out your pipe is coolant whether you can smell it or not as far as I know. I've never heard of tranny fluid getting to your combustion chamber unless you POUR it in.

Snowgoer05

The only way you would be taking tranny fluid into you motor is though the vacume line ont he back of the throttle body you will see a bunch vacume lines there should be one that follows its way back down the motor and it should be on the left side of the intake not ont he throttle boddy but possibilty should follow its way down to the tranny to a vaccum chamber on the tranny thats the only way you could suck tranny fluid into the motor after time this unit is the unit that tells the tranny when to shift when you hit the gas you open the air to the motor thus causing the motor less resistance the vacume chamer catches the change and tells the tranny to shift Shis is a possibility but very rare to check the vacume chamber without removal find a tube the same size remove the line from the intake and put your tube on it extending it so you can reach it with your mouth and suck on it if you are able to suck air then its bad and if not it hold the pressure then it another problem i will check back to see hew it went

steelerguy

Thanks for your help Snowgoer05. There was tranny fluid in the vacuum tube as soon as I took it off so no need to check it out. Replaced the vacuum modulator with a new one from Carquest for $20. One bolt with a mounting bracket that you want to be sure goes on the way it was took about 10 minutes. Shifting better than ever with no smoke. Topped off the fluid lost from burning and what leaked out of the modulator receptacle. Wasn't very much.

jveik

yeah that vaccuum modulator line is always a beotch to me

Kevcules

Cool
I knew about the modulator valve being vacuum charged by the intake manifold but never heard that it could fail, and draw fluid into, and through the engine. Thanks for the info! These forums are a great place to learn.