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Ask Chuck Your Own Question
Chuck, ASE Certified Technician
Category: Mercury
Satisfied Customers: 2100
Experience:  33 Years experience,Ford Senior Master,ASE Master,L1 Advanced Engine Performance
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Hi! I have a 1988 Mercury Grand Marquis 5.0 liter 302 fuel injection.

Customer Question

Hi! I have a 1988 Mercury Grand Marquis 5.0 liter 302 fuel injection. The problem I'm having is with the black smoke from the tailpipe, sputtering and jerking. I installed new valve cover gaskets because I was leaking oil from the valve cover. I'm not a mechanic, by the way. Well after I installed the valve cover gaskets and put every thing back together, I cranked the car up. Immediately I noticed a cloud of black smoke coming from the tailpipe, and it wasn't going away. As a matter of fact, it still hasn't gone away. I also noticed a hissing noise coming from behind the top part of the engine, sounded like air was escaping from somewhere. I couldn't figure it out. The next day, my speedometer stopped working all of a sudden. I've tried throttle body and intake cleaner to see if it would help with the black smoke. It didn't. It'still smokes, sputters and jerks, and my gas mileage is terrible now. What should I do to get my baby back running in tip top shape?
Submitted: 7 years ago.
Category: Mercury
Expert:  Chuck replied 7 years ago.

On the firewall you should see a black sensor(MAP sensor). Make sure you hooked the vacuum line back up to it. Sounds like you may have knocked it off when doing the valve covers. That would explain the black smoke and also the hissing noise you are hearing.


Here is a pic of what it looks like.