Mechanics

FIFTH AVENUE,RUNNING ROUGH AND BLACK SMOKE FROM TAILPIPE

1986 Chrysler 5th Avenue • V8 2WD Automatic • 94,000 miles

I have just bought a 1986 Chrysler Fifth Avenue, car has 94000 miles, for the first couple or days it ran great, then it started running rough, and got worse with black smoke coming from the tailpipe and staining the driveway, I have replaced the fuel pump and filter, checked all vacuum lines, removed carb and checked gasket that goes between manifold and intake, drained gas and put fresh gas in, new knock sensor as it was broken, air filter is good, not sure if it might be the lean burn, blocked exhaust, carb just needs rebuilding, car had sat for along time before I got it, but as I said before it ran great for a couple of days, any help would be much appreciated, I have spent alot of time so far and some money, not to bad yet, thanks


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Florida44
April 26, 2011.



I think you should just sell this car. Oh, and I'd be willing to take it off your hands although I really always wanted a dark red one!

Based on age and mileage, I'd start with the basics, spark plugs, wires, distributor cap and rotor. Next, check for an EGR valve stuck open, often due to a chip of carbon stuck in the valve. You can unbolt it and slide a thin sheet metal shim under it to block the ports as a test.


Caradiodoc
Apr 26, 2011.
Thanks for the response, plugs, wires cap and rotor were all installed by previous owner they all have very few miles on them, I did remove cap and checked it for cracks or burns, looked good so did rotor, EGR seems to be ok, swapped a lean burn cmputer today right from a good running car and it made no difference, then I took the exhaust off so it was just running with the manifolds, still was running the same, haven t put exhasut back yet as it is to hot, so still looking for the problem


Tiny
Florida44
Apr 27, 2011.
The instant you stop the engine, look down the inside of the carburetor to see if fuel is still dribbling in. If it is, there is dirt in the needle and seat preventing it from closing. Unlike fuel injected cars, there isn't much that can cause a carbureted one to get too much fuel.

You can also try pinching the rubber hose feeding the fuel pump. If the engine clears up, suspect the needle and seat again. It will run on the remaining fuel in the float bowl for about a minute. Incorrect float height will cause that too but that isn't going to change on its own. Since it ran fine a few days ago, you know the float height is okay.


Caradiodoc
Apr 27, 2011.
Again thank you for your response, I will look at the carburetor tomorrow after I bolt the exhaust back up, it was run with old fuel and the old fuel filter at first before it started running bad, here is a pic of the stained driveway, as you said its not a complicated car compared to what is around today, I m sure once it is figured out it will be a nice driving car, thanks


Tiny
Florida44
Apr 27, 2011.
That looks more like carbon being washed out of the exhaust system by water. Black smoke from running too rich will leave the tail pipe too but that will float away. Too much fuel won't leave anything on the ground.

I have a '93 Dynasty with only 4,100 miles and it has always done the same thing. One of the byproducts of a properly working catalytic converter is water vapor. That's why there is usually a small drain hole at the back of the muffler, on the bottom. Since yours is higher mileage, what you might try is to get the engine up to normal temperature, then spray some water into the carb while the engine is idling. Don't get carried away with pouring it in. A mist from a spray bottle works well. The cool liquid will shock the carbon in the cylinder heads and valves and will help it break off. That water will also slow down the combustion and make it more even vs. A rapid "bang-and-it's-over-with". That is why engines seem to run so smoothly when you're driving in the rain.


Caradiodoc
Apr 27, 2011.
I put back the exhaust system, I did try your tip spraying the water in the carb, there doesn t seem to be the black smoke any more at this time and maybe running a little better but not much, seems a little smoother at higher speeds haven t driven it far though, it is still making that put put put put sound out of the tailpipe, could it be the carbon build up sticking a valve, as I said before the car had sat for about two years and before that very local driving, older person owned it and never went very far, so not much chance to burn anything off, any other tips for trying to get rid of the carbon, thank you


Tiny
Florida44
Apr 28, 2011.
Carbon buildup seems to be much less of a problem than many years ago, but who knows what happened with the previous owner. I CAN share that a former instructor had a regular customer who had a running problem about twice per year. He had it figured out that each time that car showed up, he took it out on the highway and started out at around 30 mph and stomped it to the floor for about five seconds. The engine ran fine after blowing out the rust and spider webs. Now, that was back in the mid '70s but still worth considering.

Another thing you might think about, since you mentioned the "putt-putt", is a burned valve. This too goes back to the '70s and affected a '78 LeBaron I still have sitting in my yard. The problem was mostly a problem of leaded gas going away. That lead acted as a lubricant and softened the valves landing on the seats. Some people said it was due to lower quality metals being used for the valve seats but it wasn't the seats that burned away; it was the valves.

The offending valve was one of the two middle ones on the passenger side. When cold, the heat-riser valve in the right exhaust manifold closes and the blocked exhaust from all four cylinders has to go through that one port, through a passage in the intake manifold to warm the base of the carburetor and choke thermostatic spring, then out the left side. That increased flow through that one sad passage might be a contributing factor to the burned valve but that only occurs for about five minutes when the engine is first started and is still cold. I can't say for sure if that's the causes of the burned valve but it does always seem to be the same one that is affected.

I am fairly certain the problem was addressed by 1986. Still, since you're hearing that sound at the tail pipe, you might want to consider performing a cylinder leakage test. Check the auto parts stores that rent or borrow tools to see if they have a tester. It involves pumping regulated compressed air into each cylinder, one at a time, when the piston is at top dead center on the compression stroke. To make it easy, there is a whistle you can hook to the tester's hose to tell you when the piston is coming up on the compression stroke. When it stops whistling, you're there. The gauge on the tester shows the percent of leakage, and you can listen in four places for the results of that leakage. If the exhaust valve is leaking you will hear hissing at the tail pipe.


Caradiodoc
Apr 29, 2011.
Hi, again thanks for the info, took out the spark plugs and checked and cleaned them today, looked almost new and gap was right on, then did a compression test all cylinders were right around 150, put everything back started it up and it was running smooth as can be, let it idle for a while then drove it a few miles, then I was making a turn and had to brake kinda hard as a truck cam flying around the corner, then the roughness started again, it isn t as bad as a few days ago, no more black smoke so far or carbon on the driveway, so I am thinking it has to be fuel maybe fuel pickup in the tank or aomething in the carb as the quick sudden braking moved some junk around in the tank or carb, it was a treat to drive it nice and smooth, thanks


Tiny
Florida44
Apr 29, 2011.