XJ40 ( XJ81 ) 1986 - 1994

Transmission exhaust smoke

 
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Old 06-07-2019, 10:41 PM
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Default Transmission exhaust smoke

Hey hey everyone, can you believe it I'm back with a new xj40? Having some exhaust smoke issues, definitely burning trans fluid which is somehow coming out the exhausts

Replacement for my ex-j 👌🏻
and levels are going down- however I cant figure out how its ending up in the engine to come out the exhausts. Happens warm only, at high revs. Help me out, anyone had this issue?
 
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Old 06-08-2019, 03:08 PM
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First off, good to see you back.
I am not sure its possible for that to happen. How did you come to this conclusion? By "levels" do you mean trans and motor oil both? if so, i would suggest looking under to see if the trans fluid might be dripping onto the exhaust with the smoke then being blown to rear by the cooling fan. We definitely need more background. Hope you have better luck with this one.
 
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Old 06-08-2019, 06:36 PM
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Thanks! It's definitely from inside the exhaust, I'm going off the trans fluid burning smell, only trans fluid levels are lowering nothing else. I've been given hints regarding a modulator on the gearbox which if failed, can suck fluid into air intake. So far no luck locating if there is one.
 
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Old 06-08-2019, 08:02 PM
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I believe that U.S. spec cars are "all-electronic"and so wouldnt have a vacuum connection.... If yours does have a vacuum modulator, you should be able to locate a line to it on the intake (or nearby)? Maybe it is shown on the vacuum routing sticker on the fender liner.. I suggest though, that vacuum is low at high rpms, so less fluid would be drawn than , say, at idle. What year is it? Its a very "interesting" problem.....
You could try searching for the part online, that would at least confirm its existence.
In checking XKs unlimited, they show one for the GM 400 trans. hmmmmm curioser and curioser..
 

Last edited by jerry_hoback; 06-08-2019 at 08:11 PM. Reason: more info
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Old 06-08-2019, 11:25 PM
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Hi BeckBeck!

It's great to hear from you again, and that is a beautiful XJ40! What is the year and engine?

I cannot think of any logical means by which transmission fluid could wind up inside your engine or exhaust.

Have you checked underneath for transmission fluid leaks? Leaking transmission fluid could smell hot simply boiling on the outside of the transmission case, or it could work its way back toward the transmission output flange and be slung onto the exhaust pipes.

Common leak points include the oil pan gasket, the dipstick tube nut, and the cooler lines (the fittings at each end at the radiator and transmission, or the joints along their length where rubber hose meets metal pipe). Less common but more serious leaks can occur at the input and output seals. The output seal can be replaced without removing the transmission, but replacing the input seal requires removing the transmission from the car.

Your smoke from the exhaust could indicate that your engine is running rich, perhaps due to a stuck-open coolant thermostat or a failed Coolant Temperature Sensor (CTS). Does the engine run rough when it is generating the smoke?

Have you checked the VCM for any stored Diagnostic Trouble Codes (DTCs)?

Cheers,

Don
 

Last edited by Don B; 06-08-2019 at 11:30 PM.
 
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