Black smoke - fiddling with air to fuel ratio

[Gripped]

Our Bongo has always been a bit smokey, and puts out black soot when you boot it.

My mechanic says it's running rich "on boost" i.e. the turbo is putting in air but the fuel pump is putting in too much fuel - hence black smoke.

So today (after some instruction), I took the fuel pump diaphragm control out, and turned the toothed wheel anticlockwise by 90 degrees to tighten up the spring, and reduce the amount of movement in the diaphragm - thereby reducing fuel output under load.

So far, it seems to have helped a bit. The other option was to increase boost on the turbo. So my questions are:

1) has anyone tinkered with the fuel pump diaphragm thing?
2) was it successful?
3) has anyone increased boost, and if so what difference did it make?

Cheers !

(PS, I seem to becoming an amateur mechanic this year - what with doing the valve timing and the cam belt myself.)

Thanks to this forum that is !

[hijimhere]

what engine/year?

[The Great Pretender]

Another option is adjusting the maximum fuel delivery screw. Is the anti tamper cover still fitted over it? I would return your adjustments to standard and back off maximum fuelling until you get rid of smoke then fine tune if needed.

[Gripped]

Sorry it is a 2.5 td, year 1996.

Thanks for the advice . Where is the fuel delivery screw?

[skater]

I've been experimenting with turning the diaphragm.

When I removed the metal cover I noticed the diaphragm had a 0 stamped on it which was at the 1 o'clock position.
( 12 being the engine, 3 being the front of the Bongo )

I tried small adjustments clockwise and by 6 o'clock position I had a good improvement in pulling oomph but have now gone back to 5 because there seemed to be a bit too much smoke for my liking.

Don't know if you know but there is an off-boost adjustment too.

The hex screw on top of the domed cover has a lock nut. Screwing in the hex bolt increases fuel when the turbo is not spinning.

Maybe that is too far in and causing smoke before the turbo winds up properly.

I looked at adjusting the wastegate on the turbo to give more boost but it's not a threaded rod so you can't just turn some bolts to shorten it so I left it.

On these older mechanical pumps there are a few different things you can screw in and out to change slightly different aspects of fuel delivery but the problem is they all interact to varying degrees so we could really screw things up ( pun intended ) if we're not careful.


http://www.patrol4x4.com/forum/nissan-p ... ips-76576/
Don't know if this link will work but it's one of the ones I looked at.

Good luck, James.

[Gripped]

Thanks for all the input.

Will continue tinkering....

[The Great Pretender]

Did you find the fuel screw? It is close to the stop solenoid at the rear of the pump. If the anti tamper cover is missing your overall fuelling may have been altered. If it has been turned up it will alter fuelling from tickover to full boost. I would make that my starting point.
Good link skater.

[Gripped]

Will have a look later.

On another note, does anyone know the standard diaphragm setting for the Bongo ? I took mine out before I checked what position it was in. OOOPs