On or around Mon, 17 Apr 2006 18:52:28 +0100, "Richard Wilkinson"
<
[email protected]> enlightened us thusly:
>Ill try changing the air filter, it looks a bit grubby and clogged.
>
>Is there anything else i can do to "tune" the engine? (without going over
>the top and modding the engine)
Apart from the air filter...
hmmm. I saved this lot somewhere... aha:
==================================================================
disclaimer: If anything you do following reading this breaks your engine,
don't come crying to me. You do this type of stuff at your own risk.
First service the engine, including air filter, diesel filter and valve
clearances.
Then check that when you put the pedal to the floor it does actually open
the pump to the stop - the cable can be slack, if so, take up the slack in
the cable, till there's just a little bit of free play with the throttle
pedal released, to make sure it goes back to idle properly.
Next check the free-revving speed: make sure the engine's thoroughly warm
and has plenty of oil; as per the MOT smoke test, which is basically what
you're doing. Floor the throttle, wait for the engine speed to stabilise
(takes about 2-3 seconds), note the RPM and release the throttle. You need
a rev counter for this, which is no problem on the disco. It should do
about 4500 rpm. You can set it to just under 5000 without apparently
harming things; though of course you don't rev it that hard in normal use.
Do this by moving the maximum speed stop on the pump, which is the stop
which the pump lever hits when it's "open". Move it a little at a time and
check the revs you're getting. Note that it has a seal on it, you'll have
to remove that. If that bothers you, leave it alone.
Having done that, instruct an assistant in the technique of doing the revs
thing, and watch the exhaust (or put a mirror up so you can see the exhaust,
I guess - if the exhaust comes out sideways you can see the exhaust in the
driving mirror. Rev the engine as before, let it idle for a few seconds,
then repeat, and look for smoke. If there's a lot of black smoke, it's
running too much fuel; if there's no obvious smoke it can be turned up. The
fuelling adjuster is on the "back" end of the pump, i.e. the opposite end to
the pulley. The adjuster comes out parallel with the fuel outlet pipes,
above them and towards the off side of the vehicle. It has a 13mm locknut,
and a threaded rod which protrudes, the end of the rod has a 6mm hex on it.
There will be some kind of seal on the adjuster, which may hide the locknut.
slacken the locknut and then turn the adjuster in by no more than 1/4 turn,
re-tighten the locknut and look for smoke as before. You're aiming for a
situation where there's a slight amount of black smoke as the engine is
accelerating, but no obvious smoke once it's up to revs. If you get a lot
of smoke, you've gone too far, so back it off a bit. The adjustment is
quite sensitive, a quarter turn is usually enough.
If you have a friendly MOT garage, you can do the last phase with the aid of
the smoke checker for MOTs, and make sure you've got it nicely below the MOT
threshold; otherwise, you may fail the test. In the event of it being
slightly too smoky on test, the best bet is to back the maximum speed off to
the book value of 4500, which will probably solve it - if it doesn't, then
you've over-done it on the fuelling adjustment anyway.
The point about adjusting the maximum speed is not to allow it to rev very
fast on the road - it improves the mid-range performance at full throttle,
by allowing the pump to "open" slightly more. Some people will tell you
this doesn't happen, but I go with what I've experienced.
Having done these things, It should be going OK. If it still lacks power,
then you need to consider whether there's anything else wrong with it. One
thing that can affect power is a dirty intercooler. The intercooler can get
partly blocked inside with nasty oily stuff. If you don't seem to get much
power when it should be "on boost" (i.e. over about 2000 rpm) then this is
worth checking. The same symptoms can be had from low boost pressure, but
this is one thing you do need the right gear, i.e. a pressure gauge and
adaptor, to check.
On some TDis, there is an EGR valve. This can stick open, causing exhaust
gas to enter the inlet manifold when it shouldn't be. Personally, I blocked
it off on the one we run.
A final point is pump timing. On the one we have, I recently replaced the
timing belt and took good care to get the timing aligned as per the book.
This engine has always felt rather "flat" in initial acceleration.
Experience on petrol engines led me to wonder if it was a bit retarded, so I
tried advancing the pump timing a bit. You'll want the various kinds of
timing pins to do this. If you're not happy messing with the pump timing,
then get someone who knows what they're about to do it for you. I advanced
ours by something around 6 degrees (didn't measure it, natch) and it now
seems to pick up more briskly. Don't overdo it.
--
Austin Shackles.
www.ddol-las.net my opinions are just that
"Festina Lente" (Hasten slowly) Suetonius (c.70-c.140) Augustus, 25
)