heavy black smoke from exhaust pipe

I just got this 1993 Metro with 1.0L motor. it idles rough and black smoke coming out from tail pipe, i checked spark plugs and they look pretty decent except coated with black carbon. There is no check engine light whatsoever. Looks to me the problem is the injector, but i'm not certain, i don't want just go buy a $300 dollar inject and put it on then find out that's not the problem. Is there any way to check the function of injector? I know there is a equipment for testing injector flow, but...hey! i'm just a normal guy who is driving a Metro! don't have that kinda money to get that equipment. Is there anyone had the same problem?
Could it be the map sensor? or even a faulty ECM? Some help plz!:rolleyes:

Beg, borrow or buy yourself a compression tester. I'd put my money on a burnt valve in one of the cylinders. Check compression on all three cylinders and see what you've got. Burnt/broken valves are a common problem on this engine when the EGR system has gotten gunked up from lack of maintenance. Quick and dirty you could pull plug wires one at a time while the engine is running; if you pull a wire and there is no change in the way the engine runs then you have found the affected cylinder.

yeah, i forgot to mention that I already checked the compression and the figures are 195psi through out all cylinders while the engine is hot with throtle fully opened. but somehow i pulled the spark plug while engine is running, #1 cylinder didn't effect the idle....kinda weird...:banghead:

Your compression numbers are great news. Sounds like #1 cylinder is where you should focus. Have you checked plug wires? distributor cap? rotor? perhaps the plug itself is bad, you could trade it with one from another cylinder to check. Might also check the return line from the fuel rail back to the gas tank. I've read several posts where the line was obstructed causing pressure to build and forcing excess fuel through the injector resulting in low mileage. Possibly this could be the cause of your black smoke...How does the car run above idle?

ok, sorry for taking so long to reply, being busy lately. Well, i checked the return line and blow it with compressed air, and i can hear air sound at the fuel filler hole, so I assume the return line is not clogged. when it's above idle, around 2000rpm , the engine runs fine. only at idle engine runs rouge and black smoke coming out from the back. last week I remove the cat. convertor and found out it's damaged and pieces blocking the pipe, so replaced it with a stright pipe and put on a new muffler(also clean out the pipe for remaining pieces from cat), after doing that, the engine seems run a little better, but still, rough on idle. and spark plugs are coverd with heavy black carbon. I already order a reman. fuel injector online and will get it probably by next week. I will wait to see after i replace the fuel injector. hope that will cure the problem.:rolleyes:

tech++ I am sure 80% that the problem you are having is caused by bad MAP sensor it happened to me a while ago , MAP sensor still was reading good but was tricking the ECU to think that car is going ,,faster" than idle thats why the problem is not so bad when you are going over 25-45mph, change it and you will be ok, is not an injector problem.
You can find a used MAP sensor for around 20- 25$ used on Ebay, if you don t find let me know.

Ps- Sorry I already replyed to you to another thread to , leat us know if and when you solve the problem.

ok, i just got the injector yesturday and i put it on today... and the result is... STILL NOT WORKING!!!! Can it really be the MAP sensor?? I really don't want to spend any more unnecessary money... well, it runs much better when the engine is cold, and when the temperture raise up, then it idles really rough and shut down eventually....it has to be getting too much gas....but.. how?? without any codes??.... i'm coming to a dead end now....

Tech if you read my above post you have your answers, MAP sensor is out of range, gives a false reading to the ECM and it will not trigger any codes because it gives a ,,correct" value to the ECM telling him that you are going faster than you are, this is also the reason that it runs well when engine is cold because at start up a cold engine runs rich till it warms up.
Don t waste your time get a new or used MAP and be on your way.

You may also wanna check your O2 sensor...when they fail, your mixture will go full rich, & you'll see a ton of black smoke.

Tech if you read my above post you have your answers, MAP sensor is out of range, gives a false reading to the ECM and it will not trigger any codes because it gives a ,,correct" value to the ECM telling him that you are going faster than you are, this is also the reason that it runs well when engine is cold because at start up a cold engine runs rich till it warms up.
Don t waste your time get a new or used MAP and be on your way.


spy, I understand where you are coming, but what I'm saying is, if the MAP sensor fails, and if I unplug the map sensor, computer should run the engine by a fixed value. by doing so, shouldn't the engine run better? Cuz niether i plug or unplug the map, the engine runs the same. no difference.:frown:

So that should tell you something that the engine runs in a loop, for proper mix the ECM reads MAP,O2,coolant tenperature and air temperature now I don t know what is the rule for CEL trigger is, for ex not all the disconection of sensors triggers CEL light, some do, some force the ECM to run in loop mode meaning that it will run after some value tables from its memory rather than from actual sensor reading.
Mine wouldn t trigger CEL light even if I disconect O2 sensor, but it will trigger it if I disconect the MAP sensor.
Anyways it worth to try a different MAP sensor.

:screwy: ha... i found out something today... I recheck the compression again, and found out #1 cylinder is way out of range, with a 80 psi... one thing i don't understand, last i checked the compression all three cylinder are 180, but that's when the engine is cold, today i checked with engine hot,...and give me a 80 on #1... no wonder it runs good when engine is cold.... what's up with this?? could it be sticky rings? or burned valves??

hey i have had the same problem with my car it ran great and then sputtered, and has ran poor and weak ever since... cly psi is good....
milage is 33mpg... i am going to try the new map sensor,,, but let me know how yours works out... thanks much , and good luck.