Black Somke On Start And Disappear

[LancerL]

One of my friends has a brand new 1500CC petrol car with EFI engine which just completed 40k on mileage. One day I observed that there is a little black smoke coming from the exhaust and in the same second with starts of the engine it disappear immediately. I asked him to do the same for couple of times and each time it comes for a bout 1-2 seconds and disappear with the engine start (Engine also starts in like half turn without any issue)

I worried is there anything gone wrong with the EFI system or this is the usual way of EFI systems.

Please advice.

Thanks.

Edited June 3, 2014 by LancerL

[Rumesh88]

A bit unlikely for a EFI engine to give out black smoke even at the start although a rich mixture is injected for a cold start. Does the same happen when the engine is warm (after driving for 10 mins)?. According to you observation what can happen is that the engine starts with an over-rich mixture for some reason and then corrects it all by itself. What about the results of a recent ECO test or any abnormality in consumption? Better if you can confirm the proper working of the intake air temp (IAT) sensor and the engine coolant temp (ECT) sensor by scanning. If it happens only in cold start the scanning should be done under the same condition.

[Davy]

Black smoke is mostly due to partial fuel combustion. So we're looking at a problem in the air/fuel/ignition systems. When was the last time a proper EFI tuneup was done on this car?

If at all a tuneup was done:

- Was the air filter cleaned/replaced? (air)

- Were the injectors cleaned? (fuel)

- Were the spark plugs cleaned/replaced? (ignition)

If a tuneup was never done, I'd suggest getting a complete EFI tuneup done.

[LancerL]

Filter and plugs were replaced about 5,000Km back. but injectors have never cleaned since this is done only 40,000Km.

I heard from someone today that this EFI cars comes with an automatic choke where it gets turned on at each startup to make the start easy and gets off once the engine stable. I'm not really sure about his statement, please correct me if I'm wrong.

[LancerL]

A bit unlikely for a EFI engine to give out black smoke even at the start although a rich mixture is injected for a cold start. Does the same happen when the engine is warm (after driving for 10 mins)?. According to you observation what can happen is that the engine starts with an over-rich mixture for some reason and then corrects it all by itself. What about the results of a recent ECO test or any abnormality in consumption? Better if you can confirm the proper working of the intake air temp (IAT) sensor and the engine coolant temp (ECT) sensor by scanning. If it happens only in cold start the scanning should be done under the same condition.

You mean rich mixture is possible at cold start? (Is this called automatic choke?)

I could not check when engine is hot will update soon on it.

But i observed a engine RPM goes nearly 1,300 at startup and comes down and get stady to about 800 with this.

[Crosswind]

Is there a heavy smell of petrol when you get black smoke?

[Sampath Gunasekera]

By the way, what is car make and model?

[Davy]

Filter and plugs were replaced about 5,000Km back. but injectors have never cleaned since this is done only 40,000Km.

I heard from someone today that this EFI cars comes with an automatic choke where it gets turned on at each startup to make the start easy and gets off once the engine stable. I'm not really sure about his statement, please correct me if I'm wrong.

The Idle Air Control Valve (IACV or ICV) is what is referred to as the "Automatic Choke" by many. This is mounted onto the throttle body and is usually cleaned during an EFI tuneup. And yes, this can be a direct culprit. The ICV might be stuck, closing the air passage in the throttle body resulting in a puff of smoke when the engine is started.

Since you've already replaced the air filter and plugs, I can again suggest that you get an EFI tuneup done which includes cleaning the throttle body (and ICV) and the injectors (preferably ultrasonic).

[Rumesh88]

You mean rich mixture is possible at cold start? (Is this called automatic choke?)

I could not check when engine is hot will update soon on it.

But i observed a engine RPM goes nearly 1,300 at startup and comes down and get stady to about 800 with this.

Yes. It is in fact the "automatic choke function" implemented in ECU software as opposed to the actual "choking" of the air intake that you find in a carb type engine. At the cold start the IACV together with IAT and ECT decides the idle speed (RPM going to 1300 in this case) and the mixture at the cold start which is a bit rich compared to the warm engine idle mixture. However, it should not be rich enough to give out black smoke. Your cold start RPM seems to be normal.