// discovery 2 td5 · pre-remap_

Before remapping your TD5: the health checks that actually matter

A map makes a healthy Discovery 2 TD5 pull harder. It will not fix a boost leak, a tired fuel pump, or a dirty sensor — and tuning on top of one of those problems usually just makes the fault harder to diagnose and more expensive to fix.

symptoms that mean "check first, tune later"

Some signs are obvious: hesitation under load, black smoke, a flat spot that wasn't there before, or a stored fault code. Others are easy to miss because they feel like "just how a TD5 is" — a boost gauge that never quite gets there, a motorway cruise that feels gutless compared to what owners describe online, or fuel economy that has quietly worsened over months. Any of these is worth 20 minutes of checking before you spend money on a tune.

most likely causes

Three systems account for most "it's just not right" TD5s:

Boost control — a leaking or split wastegate modulator hose (there are three small ones), a sticking modulator, or a seized wastegate actuator arm will stop the ECU holding correct boost.
Fuel supply — a weak lift pump, a clogged filter, or (as one owner found the hard way) high- and low-pressure fuel lines swapped during earlier work, will starve the engine under load exactly the way a "needs a tune" TD5 does.
Sensors — an oil-fouled MAP sensor or a weak MAF will feed the ECU bad information, so even a perfect map is working from wrong numbers.

quick checks, in order

Do these from cheapest/safest to most involved. Stop and fix as soon as something comes back wrong — there's no value in checking everything if step one already explains the symptom.

Scan for fault codes and clear-and-retest. A Nanocom or equivalent. A repeat overboost or sensor fault after clearing is a strong lead on its own.
Watch live MAP (manifold absolute pressure) data on a safe, steady drive. Typical figures on a healthy stock TD5: key-on/engine-off, roughly 100 kPa absolute (that's just atmospheric pressure at sea level), 100–125 kPa absolute at idle, rising toward 210–230 kPa absolute under full-load boost. Owners and the ECU's own overboost trip agree the ceiling sits around 230 kPa absolute — above that, the ECU pulls fuel to protect the engine and turbo. Caveat that matters: some tools and forum posts quote boost as gauge pressure (pressure above atmospheric) rather than absolute pressure — that's why you'll see the same trip point described elsewhere as "about 130 kPa boost". Know which one your tool is showing before you compare it to any number, including these.
Check the wastegate modulator's three small hoses, its electrical plug, and the wastegate actuator arm for splits, chafing, or seizure. This is the single most common cause of boost-control complaints and costs nothing to inspect.
Check fuel pressure at idle and again under load if you can measure it. A healthy TD5 lift pump feed sits around 4 bar (400 kPa). One documented case dropped from 1.5 bar to about 1 bar under acceleration — enough to cause the exact "loses power under load" complaint owners often blame on the map, before turning out to be swapped fuel lines from earlier work.
Inspect the MAP sensor and MAF/air intake path. Oily or sooted deposits on the MAP sensor are a common, cheap-to-fix cause of bad readings.
Advanced, not a default owner step: adjusting the wastegate pushrod to change boost is something experienced tuners do with a gauge connected and a clear target in mind. It is not a general "try this" fix, and it is not something to do before you know boost control is otherwise healthy.

what to fix before buying a map

If you've found a fault code, a boost-control fault, or a fuel pressure that drops under load, fix that first — a map on top of it will not solve the underlying problem and can make it harder to tell what's actually wrong. If everything above comes back clean — no repeat faults, MAP tracking the ranges above, stable fuel pressure, clean sensors — the vehicle is a good, low-risk candidate for a map.