Smoking YD25

[johng]

There's some history on the Forum about this, but I'm still searching for answers.
My Pathfinder, 130k, (Sorry, I'm looking wider than the PCoA Forum!) was first noticed smoking a few months ago.

At about 90kmh towing the caravan, just as the engine loaded up for an incline, the whole back corner of the car was a cloud of black smoke. At cruise, no smoke with or without the caravan.

Going up Bells Line of Road recently, where the speed limit is generally 80kmh, I was feeling sorry for the guys behind me, even without the caravan on.

Aside from the smoke, the car performs as well as it ever did. Fuel economy seems unchanged.

I've tried everything I can think of. Air and fuel filters, Boost Control Valve replaced. The EGR was blocked and DPF dealt with years ago. Never had any smoke issues before or after, except the past few months.

My Palmer Performance OBD logger shows turbo boost varies from near zero at idle to 23psi under hard acceleration. The fuel rail pressure ranges from 4000psi at idle to 25000psi under hard acceleration. I believe these are within range. There's no fault codes in the ECU.
Finally, I've just backed the car into the garage, and filled the garage with smoke.

Has anyone experienced anything like this? Any help much appreciated.
John

 

[Old.Tony]

Black smoke is always overfuelling, never anything else. Overfuelling means either too much fuel, or not enough air - but the term specifically means more fuel than can be combusted in the amount of oxygen present.

There are several reasons for this.

1) EGR - you might check your blanking plate to make sure it hasn't developed a hole. It's happened before.

2) Turbocharger - but since you're getting 23psi of boost I'd not worry about that

3) Injector wear. This is a tough one because to actually test it you'd need to replace the injectors. You can examine the fuel flow rates (the ECU does report on fuel flow rate per minute) and this is directly relevant to the amount of fuel being injected into the motor, but it relies on the injectors being in good order in the first place and so won't give you an answer. The only real measure is the amount of smoke and a recorded drop in fuel economy.

4) CAS timing. Unlikely since the car runs so well when not loaded.

5) Injector harness connector debris and/or ECU earth issues. Clean and refit both.

6) Excessive blow-by. Blow-by is combustion gas that passes the piston rings and enters the crankcase. It then leaves the crankcase via the ventilation hose at the top of the rear of the camshaft cover into the hose connected to the air intake in front of the turbocharger. Under high loads, slightly worn piston rings/bores will result in much more blow-by. To test this theory, disconnect the PCV hose from the air intake, block the intake opening so nothing can get sucked into the turbocharger, make sure the hose is directed towards the ground (do NOT do this long term, it's highly illegal and dangerous to motorcycles). If the smoke has gone, you may have worn or sticking piston rings.

What I'd do if mine did this: head to Supercheap and buy some Liqui Moly Fuel System Treatment. Works for petrol and diesel. If you have half a tank of fuel ore more, just empty the bottle into the tank and start driving. Give it about 200-300km before hitching up and trying again.

If the fuel system cleaner doesn't do the trick it's possible that some contaminant (for example, water) has gotten through and scored/damaged the injector nozzles.

 

[johng]

Thanks for your comprehensive reply Old Tony.

I've just taken a look at the EGR blanking plate and it's still OK.

I didn't mention in my original post that I've cleaned the MAF sensor in conjunction with my other checks.

One unknown that is plaguing me is that the new Boost Control solenoid valve appears to fail the bench test as stipulated in the manual, depending on whether voltage is applied or not. I checked it before I installed it. It's testing exactly the same as the original. Not sure how you convince Nissan or return a faulty part to Nissan that hasn't been installed by them. Do you know how this works?

In terms of the other checks as you mentioned, the smoking was a sudden thing on one trip and was so out of character that I assumed there must be some obvious component failure. So I doubt it's blow-by, or even injector issues. I'll let you know how I go with exchanging the Boost Control valve.
Thanks,
John

 

[tweak'e]

reset the fuel learning.

 

[johng]

Thanks for the tip. I'll try anything!
I'll let you know if any change.
John

 

[johng]

An update.
I've reset the Pump learning and ran a can of Liquid Moly Diesel Purge Plus through.
It's supposed to be more direct than the treatment you put in the tank. You insert the fuel supply and return lines directly into the can and run the engine at various speeds until it stops, around 30 mins or so.
So far as I can tell, I haven't filled the garage with smoke, but will have to do a long run and preferably with the van on to really confirm improvement.
I'll report back in due course.
Thanks for the suggestions and input.
John

 

[happy john]

Run that tank down then refill to half next time and add another can. Drive hard too!

 

[camo.b]

Yep...filter change...liquimoly purge and a pump reset cleanes up a lot of issues