Black smoke, kills spark plugs
#1
07-18-2018, 03:00 AM
Join Date: Jul 2018
Posts: 8
Likes: 0
Received 0 Likes
on
0 Posts
Black smoke, kills spark plugs
Hello!
I have an 1989 B250, 318 TBI with the 727 gearbox (4spd). I just got it, last owner couldn't get it to run good. Here's the problem.
It runs well for about 20-30 minutes on all 8 cylinders. After that time it starts to run rich, with black smoke coming out from the exhaust. Soon it will start to lose power, and lose cylinders, and eventually it won't be able to run anymore due to the spark plugs being drowned by gas. Here's the thing, if you disconnect the battery for a couple of minutes, resetting the ECM, it will run for another 20-30 minutes, not always on all 8 because the plugs are blacked out, but it runs. If you clean the plugs, it runs on all 8 like clockwork.
I've read some error codes, and here it gets even more weird, it will show one error code, for example the temperature sensor to the ecm. I changed it, and the code disappeared. Another test drive and it shows an error code on the air temperature sensor on the throttle body. I changed that one too, and gave it another go. Then it showed an error code to the idle motor?! So I figured that it was the ECM itself, so I've changed it, but I haven't given it a test drive yet, will do this week.
I suspect that it isn't anything mechanical, because you can drive for a certain time after disconnecting the battery.
Have anyone here been having this problem? I've been googling like a madman, but I haven't found anything that drowns the spark plugs so bad that it won't run.
I have an 1989 B250, 318 TBI with the 727 gearbox (4spd). I just got it, last owner couldn't get it to run good. Here's the problem.
It runs well for about 20-30 minutes on all 8 cylinders. After that time it starts to run rich, with black smoke coming out from the exhaust. Soon it will start to lose power, and lose cylinders, and eventually it won't be able to run anymore due to the spark plugs being drowned by gas. Here's the thing, if you disconnect the battery for a couple of minutes, resetting the ECM, it will run for another 20-30 minutes, not always on all 8 because the plugs are blacked out, but it runs. If you clean the plugs, it runs on all 8 like clockwork.
I've read some error codes, and here it gets even more weird, it will show one error code, for example the temperature sensor to the ecm. I changed it, and the code disappeared. Another test drive and it shows an error code on the air temperature sensor on the throttle body. I changed that one too, and gave it another go. Then it showed an error code to the idle motor?! So I figured that it was the ECM itself, so I've changed it, but I haven't given it a test drive yet, will do this week.
I suspect that it isn't anything mechanical, because you can drive for a certain time after disconnecting the battery.
Have anyone here been having this problem? I've been googling like a madman, but I haven't found anything that drowns the spark plugs so bad that it won't run.
#2
07-18-2018, 02:21 PM
Temp sensor would do that. If the PCM thinks it is REALLY cold out, (and it's not.....) it will DUMP gas into the engine. Another option would be the Oxygen Sensor. PCM doesn't start paying attention to it till the motor warms up a bit, or, runs for some indeterminate length of time...... If the sensor is telling the PCM that the engine is running lean, PCM will try to add gas. If the sensor doesn't react, the PCM keeps adding gas.... to the point it will flood out the motor. If you aren't getting codes for the temp sensor any more, try just disconnecting the O2 sensor, and see if the engine runs any better. (that WILL set a code......)
#3
07-18-2018, 06:18 PM
Join Date: Jul 2018
Posts: 8
Likes: 0
Received 0 Likes
on
0 Posts
Temp sensor would do that. If the PCM thinks it is REALLY cold out, (and it's not.....) it will DUMP gas into the engine. Another option would be the Oxygen Sensor. PCM doesn't start paying attention to it till the motor warms up a bit, or, runs for some indeterminate length of time...... If the sensor is telling the PCM that the engine is running lean, PCM will try to add gas. If the sensor doesn't react, the PCM keeps adding gas.... to the point it will flood out the motor. If you aren't getting codes for the temp sensor any more, try just disconnecting the O2 sensor, and see if the engine runs any better. (that WILL set a code......)
Thanks for answering, yes, the next test drive I make I'll disconnect the O2 sensor immediatly if it starts pouring black smoke, and see if it makes a difference. I've suspected the O2 sensor for a while now because almost everything else has been changed! We'll see this weekend I guess!