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'Tuning' a 2.5NAD


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I believe there is an external adjustment for the DPS that wasnt available on the earlier DPC. I've read somewhere about reducing the fuel 3% for every 1000ft elevation so you dont end up over fuelling in the rareified air and melting pistons/heads.

I've asked the question today to my diesel engineering guy-I'll let you know the answer.

Im tinkering/tuning my 2.5NA as well but its in a 110.

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How strange, I was going to ask something similar.

I have a 2.25 diesel, but with a later style fuel distributor (with an electrical shut off valve).

I don't seem to be getting full revs, the engine pulls well but then just stops at 48mph in top gear, this despite 7.50x16 tyres. As far as I know this means I'm only getting about 2,700rpm. Does this sound reasonable or can the maximum speed be adjusted, like it can on the older style distribution pumps? The haynes manual suggests it should rev to 4200rpm.

As for tuning, you can adjust the timing. This has a big impact on engine performance. This is done by rotating the distribution pump on it's mount. There is a way to do it 'properly' but it requires a special tool. You are better off just moving it a bit at a time and seeing what the idle is like, if it makes the idle better it's probably closer to correct. If on a test run you get smoke on overrun you need to turn it clockwise, if you get knocking you need to turn it anticlockwise (at least that's my experience).

The fuel injectors are easy to check. The haynes manual claims that, with the engine on idle, if you loosen the fuel rail to an injector and the idle doesn't change that injector is probably faulty.

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Certainly for the 2.25 you don't need the special tool - and can follow the instructions for the early version of the pump without the mark on the base - ie line up the 'A' mark with the flat end of the circlip inside the pump and the appropriate mark on the flywheel.. When you've done it you'll understand why Rover discontinued this method - as the marks are very difficult to see and the pump drains when the cover is removed.

If your pump is properly timed and the thing isn't smoking I'd start by making sure the throttle really is opening fully then the maximum fuel screw (throttle stop). Rover's instructions were to see if blacksmoked at 48 in 3rd - and if it did - shut the screw down till it didn't quite.

May be worth checking your electric fuel stop is opening properly.

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Cheers, I spoke to a few people (including a local specialist) and they said they just do it by ear. I figured doing that was better then setting it 'properly' without the tool. My understanding was that without the tool (I haven't found anyone with one yet), you line it up but you haven't accounted for wear/backlash in the pump and it'll still be out.

I'm pretty sure the throttle is opening fully, at least with your foot on the floor you can't move the mechanism any more. Where is the maximum fuel screw on these fuel pump/distributors? I really need to learn a bit more about how they work (this is my first diesel), any decent books or manuals around?

p.s. sorry for the slight thread hijack!

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just come back from my diesel engineer's. Increasing the fuelling on a 2.5NAD is dead easy. On the inside vertical side of the pump body next to the engine-and about an inch or so back from where the pump bolts to the timing case is a lock wired cap, snip this off, underneath is a 10mm headed drilled/lockwireable headed bolt with a 13mm locknut. Undo the locknut, screw in the 10mm headed bolt, tighten the locknut again. I've wound in about two turns and its made a small difference, torque has increased-holds longer in gear on hills and black smoke has increased slightly. If you turn it too far-you get too much smoke apparently, so a turn at a time and try it.

Only N/A-dont try it on your TD you'll kill it-the pump has more adjusters than the N/A

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