QuestionQUESTION: Hi,
I bought a a 96 Cadilaac Deville northstar 4.6L with 157K on it. When it warms up it over heats. I though maybe a head gasket but there's no steam coming from the tail pipe, there's no water mix in the oil and visa vera. The thermostat looks to have been change already. Also, Where is the turbine transmission speed sensor locate? Why does it idle high when the emission control plug in unplugged? Thank you in advance.
ANSWER: My experience with these engines is that you probably DO have a headgasket leak. The architecture of the engine is such that it lets water into the combustion chamber, and combustion gases into the water jacket, but there is no contamination of the oil. If it is using coolant, then that's where it is going. The weird thing is, sometimes they'll overheat, and sometimes they won't, it's kind of weird. Oh, and you usually can only see steam out the tailpipe when it's cold out.
The speed sensor is screwed into the side of the transmission, I believe on the backside. It has to be close to the final drive, 'cause that's the speed it is reading. The high idle with the green plug unhooked is caused by the vacuum leak it creates, leaning the mixture always raises the idle. GM regulates idle with a stepping motor operating a controlled vacuum leak at the throttle body; uncapping the emissions hose creates such a large leak that, even with the idle control totally closed, it still idles high.
---------- FOLLOW-UP ----------
QUESTION: Hi,
Thank you for your input. I was wondering if you've ever heard that the turbine speed sensor on these cars is located between the engine and trans, therefore I would need to split the two inorder to replace the sensor? I just got another opinion and I hope it isn't true.
Answer Frankly, I assumed in your first post that you were referring to the vehicle speed sensor, which plugs into the side of the trans from the outside. I have to admit that I have never had to change the turbine speed sensor. But, I checked into it and, although you do not have to split the engine/trans assembly, you do need to lower it far enough out of the car to get to the cover plate through which the sensor is accessed. In short, it is a code no one wants to see when they scan the computer. I don't know how much you have invested int his car, but it sounds like a good candidate for a quick cash sale or a trip to the local auction.
