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Old 12-21-2015, 06:47 AM   #1
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Default Rough idle, Backfire throug intake and black smoke

Hello everyone

My names Joel Reisinger and I am the owner of a 1987 Buick Electra Park Ave with a 3.8l V6. It has about 86000 miles on it.

When I got the car it didn't really run at all because the pre owner messed everything up. He began tinkering with the car because of black exhaust gasses. All sensors were disconnected, a lot of vacuum hoses were unplugged and there were six different spark plugs in the engine.
I connected all the sensors and vacuum lines back up and replaced the spark plugs, the spark plug wires and the oil (the old oil had a strong petrol smell).
Now the car runs but only very bad and smokey (still a lot better than when i got it). When i press the accelerator pedal sometimes it revs right up and sometimes it just doesn't want to rev and backfires into the intake. The pre owner mentioned that the car runs worse when it gets warmer which would indicate a problem with maybe a water temp sensor. But measuring them with my multimeter it looks as if they are ok (I replaced one that gave a bit of a suspicious reading). Disconnecting the MAF doesn't change how the car runs.
Actually it seems to run far too rich. Disconnecting the injectors, one at a time, didn't change the black smoke. So i don't think its a stuck injector.
Unfortunately I don't have an OBD1 tester so i can't check for any codes.


Does anyone have an idea what to check next? I am really clueless right now...

Thank you very much!
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Old 12-22-2015, 09:08 AM   #2
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Just from the uneven idle I would start with spraying carb cleaner around the intake to check for vacuum leaks.
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Old 12-23-2015, 10:29 PM   #3
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You can check for flash codes, by jumpering A to B in the ALDL connector, then turn key to on(don't start), and right down the flash codes......initially it will flash "12"(one flash, pause two flashes), three times.....then it will flash any codes in the vehicle....when it flashes 12 again, you have all the codes.....

A vac leak, as suggested could cause the vehicle to run rich......so could an exhaust leak at the ex manifold to exhaust pipe connection(those exhaust donuts are known to leak).....

Since the car has been running so bad for a long time, I would also suspect that the O2 sensor must be carboned up, and is giving false readings....another indicator would be if it flashes a code 44.....
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Old 12-25-2015, 12:11 AM   #4
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I would also check fuel pressure, and the fuel pressure regulator to make sure it is not leaking. You simply unplug the vacuum hose from it while the engine is running to see if fuel is coming out of the vacuum connector. If there is fuel, replace it.
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Old 12-28-2015, 01:09 AM   #5
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Default rough idle, backfire through intake and black smoke

Not that this is the issue, but I had an 87 Electra many years ago. The timing gear is nylon/plastic nonsense and is easy to fail. The ignition coils/module is prone to leaking the green stuff and misfiring. That rich condition will bugger up your converters.
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Old 03-22-2016, 01:08 PM   #6
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Thank all of you for your replies. The car is now running! The preowner messed with the rockerarms and they all were completely loose which caused all the backfiring. Also one of the ignition coils was bad. But now the engine is running nicely, but the catalytic converter did fail, so i replaced that.
Only problem thats left is that the car begins to shake when accelerating slowly in third gear. When i press more on the gas pedal the shaking gets worse until the transmission decides to downshift. Sometimes the car stalls when coming to a stop... I will try flushing the transmission but is this a common problem with these? I have read somewhere it might be an electrical problem?
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Old 03-27-2016, 07:05 PM   #7
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Bad Spark plug wires can cause that under a load like going up a incline.
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Old 04-11-2016, 12:39 PM   #8
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The problem is solved! The spark plug wires were good but one of the (brand new) injectors was dead. I installed one of the old injectors and the car finally ran on all cylinders (did not realise it didn't before) and didn't shake anymore when accelerating.
I also solved the stalling, the throttle adjustment screw and the tps were not adjustet correctly. Oops!
Only thing thats left now is replace the engine mounts which got shot during all that shaking :-/
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