Puffs of black smoke

[devinchi]

Vehicle info: '95 D90 w/ 3.9l

I have searched, but didn't find an answer to this, but if I missed it, please point me to it.

When I acellerate hard, or if I happen to be in a gear that is too high and have the pedal to the floor, I have black smoke coming out of the exhaust. It is accompanied with a rattling knocking sound similar to a diesel engine. Is this at all normal?? I have heard a similar noiose to a lesser extent in other vehicles when I over-gear, but this is a bit worrysome.

[Doug]

I have that problem too -- but intermittently. Seems like some sensor might be sending a bad signal to the ECU. Anyone else have this issue?

How could pre-ignition cause, or go together with, black smoke (rich mixture)?

Doug W.

[Hans]

generally, when you really stomp the gas, EFI computers ignore all the sensors and just dive straight into "extra-rich" mode.

But, the knocking makes me think you have something going on, maybe some detonation in the engine or it could also be from something rattling in the exhaust. The stock catalytic convertors are known to rattle at times. (either that, or you're using too low octane fuel. These things are supposed to take 91)

How many miles on it? Has it always done this, or is it a new thing?

-Hans

[Mike Hippert]

I have/had the same thing, I had to fill the tank with 87 once and it ran even worse and knocked bad when going up hill. I have a feeling that mine has something to do with timming as I don't have a good way to check my timming and I have kind of guestamated it. I was going to play with some things to try and figure it out but without a T-case I am stuck for now.

[Doug]

It's odd. Sometimes I never have ping (most of the time), then other times it's terrible. I add octane booster and that fixes it 80%, but then it'll go away and i can run on premium (no booster) without issues for a while. So bizarre. Anyone else have this issue?

I've never seen the black smoke myself -- only had it reported once during a convoy....

Doug W.

[evilfij]

I am fighting that issue now as well. Mine is just a bit off in the way it runs WOT. I am going with a bad vacuum advance or even a bad mechanical advance, but I have not looked into it yet.

[devinchi]

generally, when you really stomp the gas, EFI computers ignore all the sensors and just dive straight into "extra-rich" mode.

But, the knocking makes me think you have something going on, maybe some detonation in the engine or it could also be from something rattling in the exhaust. The stock catalytic convertors are known to rattle at times. (either that, or you're using too low octane fuel. These things are supposed to take 91)

Makes sense, I have run a few tanks of 87 in it not knowing any better.



How many miles on it? Has it always done this, or is it a new thing?


It just turned 60K yesterday, and I dunno if this has happened before, only owned the truck for about 700 miles (last 3 weeks).



I've never seen the black smoke myself -- only had it reported once during a convoy....

I had a co-worker tell me about it, and was watching in the mirror on the ride for the rest of the day.

[devinchi]

Well....... new plugs and wires, and some octane boost (to fix the 87 that is in there) and it seems to be better, but I believe it is still running rich...... so maybe I have a bad O2 sensor.

[stevewhitaker]

Mine was running rich (94 ST) and getting lousy gas mileage until I replaced the O2 sensors. Now I can get as high as 18 MPG, but average about 16.5 on the highway and am not fouling the plugs.

[Doug]

Timing checked out fine on mine. Still pinging. Guess it's time to replace the O2s.

Doug W.

[rover4x4]

If I stand in it Ill get some black smoke also. Otherwise truck runs fine. Is it overfueling or just stuff in the top end getting "blown out"