I recently bought a 93 blazer from a friend with less then 100k miles but it had a slight fluid leak from the front seal. It runs great and drives fine but back around christmas time I got stuck in a nice plow drift on my way home and with digging and rocking got it out but while doing so I heard something like a loud snap/crack. Now I am feeding the transmission about a gallon of fluid a week to keep it on the road with the snow on the ground since my other car just can't do it (plus flats). A friend of mine says that it smells like it is burning transmission fluid and that most likely it is the vacuum/transmission modulator sucking fluid into the engine. When the transmission fluid is low/gone the engine runs great but when I dump fluid in the engine runs rough and hesitates. I suspect he is right knowing his background but thought I would get a second opinion.

 

wait a minute, are you dumping tranny fluid in the engine oil or in the transmission

"When the transmission fluid is low/gone the engine runs great but when I dump fluid in the engine runs rough "

 

Err sorry that was worded badly. No I am dumping it in the tranny. I wasn't fully awake when I typed that up apparently.

 

i would bet a leak somewhere external , should be noticable since you're losing alot of fluid.

 

See that's the thing. There is a small leak. Doesn't account for that amount of tranny fluid at all though. It also doesn't explain that engine running like crap when there is fluid in the tranny. I'm talking at idle with the s10 in park. It can be running great but about 10-15 minutes after I add fluid to the tranny it starts running like crap and almost dying.

 

does it do it when its sitting still or when its moving

 

what trans do you have 700R4? The 700R4 doesn't have any vaccum lines on it. Or all of them i have seen didn't. That is weird...

 

It does it when it is sitting still and when I hit stop lights/signs. I'm not sure if there is a modulator on this one or not, it has been too wet and sloppy to get underneath and check it properly.

 

The 700R4 does not use a vacuum modulator like the older TH350 did. It has a TV (throttle valve) cable which connects to the throttle and modifies the line pressure and shift timing.

With that said, the 4wd system does have vacuum lines running to the vacuum switch for the engagement of the front axle. If the input seal on the front of the transfer case were to fail, it could overfill the transfer case and push past the vacuum switch contaminating the entire vacuum system on the truck if left be. You could diagnose this issue very easily by removing the fill plug on the back of the transfer case.

 

Ok tranny is a 4L60E ie 700r4 with electronic control. So no vacuum modulator on the tranny but there is teh posiblility that it is being contaminated from the transfer case. Ok I'll try to find a dry spot and check that out.