Tuning the 4D56 turbo for more powaaaah.

Does your Mitsubishi L300 make a strange noise? Need wheel alignment specs?
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Tuning the 4D56 turbo for more powaaaah.

Post by Growlerbearnz »

Tuning the 4D56 isn't difficult: turn up the fuel, turn up the boost, profit. If you don't go about it methodically though, you can waste a lot of time chasing your tail. This is my method, which hones in on the correct tune quite quickly, with the minimum of re-adjustment. This presupposes that you have a standard engine running normally.

But first, Disclaimers: This sounds easier than it is. You probably know less than you think. Attempt at your own risk. This advice is worth as much as you paid for it. Don't panic. Wear sunscreen.

Don't attempt this the day before going on your world-spanning road trip- it's going to take at least a week of careful observation and tiny adjustments until you're happy with it. At some stage you'll go too far and think "Oh shit, I've broken my engine". You can't break your injection pump, but it can be time consuming to return it to standard, especially if you didn't measure things before adjusting them.

An Exhaust Gas Temperature (EGT) gauge and boost gauge are mandatory before tuning a diesel. You *can* crack a head or melt your turbo if you make the mixture too rich and then drive like a loon.

A wideband O2/Lambda/Air Fuel Ratio/AFR gauge makes tuning trivially easy and accurate. Seriously consider fitting one. (I have the Innovate Motorsports MTX-L and it's brilliant, the only hassle being that it needs to be configured for diesel fuel using their software and a Windows PC with a *serial port* like it's 1989). For reference: below 18:1AFR you're just making smoke and heat. Light cruise should be 25:1 or higher.

Before you change any setting or move anything, measure it and write down those measurements so you can return the pump to stock settings. Take photos. Index things with a centre punch or indelible marker. Being able to undo might be a lifesaver.

You should be measuring at least: idle adjustment, full speed screw length, full load screw length, diaphragm orientation, spring seat height.

Down the rabbit hole we go:

Step1: First up, set your turbo to make a consistent 12psi under full boost. Shortening the wastegate linkage or adding washers under the actuator bracket are the traditional ways to increase boost, but a boost controller is easier to adjust from inside the cab. Getting it settled in may take a few test drives. You may need to blank off or disable the overboost relief valve on the back of the intake manifold. Take note of what your EGTs are during a steady cruise, at full power, and during a long uphill climb. (The stock turbo will do 14psi all day long, but it's easier to get the baseline tuning sorted at 12psi. Run through this guide, get the hang of it, and then try turning the boost up further).

Step 2: Take the van for a drive to thoroughly warm up the engine to normal temperature. It makes it a bit of a hassle to work on, but there's no point tuning on a cold engine, you'll just have to do it all again when it's warm.

Step 3: Adjust the full speed screw (AKA "throttle stop") to about 6mm long. Warning: this effectively disables the injection pump's built in rev limiter. It gives you more power above 3500rpm, and the engine will not "run out of puff" as much as it gets closer to the 4500rpm redline. DANGER! It's now your responsibility to not rev the engine over the redline. Not an issue if you have an automatic as it will upshift before the redline, unless you're in 2nd or Low.
FullSpeedScrew.jpg (90.7 KiB) Viewed 7375 times

Step 4:Set the idle adjustment quite short, to about 1/3 of its length. On mine it was about 10mm from the bracket.
IdleScrew.jpg (86.07 KiB) Viewed 7375 times
Step 5: Re-orient the linkage on your AC idle-up vacuum solenoid so it won't interfere with the accelerator linkage. Adjust accelerator cable if needed so there's still some free play at idle. On an automatic, adjust the kickdown cable so the metal stopper on the cable (under the orange boot) is just touching the threaded tube at idle. Make sure that the IP linkage hits the full speed screw ("throttle stop") before the accelerator pedal hits the carpet. If not, bend the accelerator pedal up a little.
Accel.Cable.jpg (140.58 KiB) Viewed 7375 times
Step 6: Remove the boost compensator cover, mark the diaphragm's orientation so you can return it to stock if needed (on mine there was a small dimple on the diaphragm disc, I took note of where it was pointing). Remove the diaphragm and plunger (rotate it while lifting, eventually it'll come out). If there's a white nylon spacer on the plunger, remove it. (The spacer is the fun police and prevents too much fuel being added while under boost).

Step 7: Measure the depth of the star wheel (so you can return it to stock), then wind the star wheel/spring seat down to 12mm from the top of the threaded tube. This makes the spring softer, which will allow more fuel earlier on the boost curve, making the turbo spool up much faster.
StarWheelMeasure.jpg (98.75 KiB) Viewed 7375 times
StarWheelDepth.jpg (92.24 KiB) Viewed 7375 times
Step 8: Take the diaphragm/plunger and notice how the tapered cone is offset. Reinstall the diaphragm it so the deepest, most offset part of the cone is facing forwards (front of engine).
TaperedPinCU.jpg (55.83 KiB) Viewed 7375 times
TaperedPin.jpg (107.83 KiB) Viewed 7375 times

Step 9: Reassemble the boost compensator. You might want to leave the throttle position sensor off while tuning- you're probably going to be removing the compensator cover a couple more times.

Step 10: Find the full load/mixture screw on the back of the Injection Pump. Measure it. Figure out what arrangement of spanners/sockets/screwdrivers you're going to use to adjust it. Crack the locknut loose.
FuelScrew.jpg (108.04 KiB) Viewed 7375 times
FuelScrewMeasure.jpg (80.41 KiB) Viewed 7375 times
Step 11: Start the engine, and wind the full load screw in until idle is around 750rpm. Tighten the locknut with the engine running. (Winding the screw in increases the baseline fuelling). You'll be using the idle screw to fine-tune the idle speed at the end, but this gets the overall adjustment into the ballpark.

Take it for a test drive, and now the actual tuning begins. There are really only two situations you need to tune for, the rest will take care of itself: full load (think climbing a hill), and accelerating from light load/idle to full speed.

The engine must be thoroughly warmed up before making any adjustments.

First set up for full load, full boost: if you have black smoke and high EGTs (more than 1200F or 650C) at full power, rotate the boost compensator diaphragm (S8) a little to turn the offset cone further away from the front of the engine. Repeat until full power EGTs are acceptable. If you increase your boost later, this is the adjustment you want to fiddle with.

This reduces fuelling when there's boost (duh). Doing this may also lower your idle speed, in which case turn the full load screw to restore idle speed (S11). If you've turned the diaphragm a full 180 degrees (maximum adjustment) and it's still too hot/smoky, there are 2 possible solutions:
1)wind the diaphragm spring seat back up 2 turns (S7) and see if that makes a difference. If it does, great! Your spring was too loose (see the next section).
2)If that doesn't help, your idle screw is too short. Wind it in so it's about 5mm longer (S4), and start from step 5 again.

Next pay attention to light load and accelerating.

Accelerating: if you stomp on the accelerator, especially from idle, you want a brief belch of smoke until the boost hits 8psi or so (engine around 2000rpm). This is good for power because the extra fuel helps the turbo spool up faster. If there's too much smoke (it's your call here), wind the star wheel/spring seat up (S7). This increases the spring pressure on the diaphragm, preventing extra fuel injection until there's enough boost to support it.
NOTE: a compensator spring that's *way* too loose can lead to a smoky idle. The smoke will come out irregularly, in stuttery puffs. This is from the diaphragm bouncing around because the spring isn't holding it still. Same solution as above- wind the spring seat up until the smoky idle stops. That said, if it's that loose you'll also have massive amounts of black smoke while accelerating.
Winding the spring seat up may decrease your power at the top end- watch your EGTs and compare them to those in the previous step.
A spring that's too loose may also cause high EGTs when just puttering around town, or cruising gently on the motorway. Tuning shouldn't have increased your EGTs in these situations.

Once you're happy with how it drives, go to Step 5 and adjust all the cables, linkages, and AC idle-up until they're back in spec. Re-fit the throttle position sensor (if you left it off).

From now on use the idle speed adjuster to fine-tune the idle speed.

Bonus tuning:
If you find you've got everything just as you like it, but the EGTs are still a bit high at full power, try turning the turbo up to about 14psi (The stock TD04-09B turbo will happily make 14psi all day long). That'll add more air at full boost and bring the EGTs down without reducing your power output, but it'll add a lot more heat to the intake air. You'll have to watch out for over-advanced timing- see the next part. Or add an intercooler. If you have an upgraded turbo *and* an intercooler you can go up to 17psi. Above 17psi the benefits drop off, and the risks of increase.

For extra risky points, mark your IP then advance your timing slightly (loosen the 2 nuts at the front, the two short bolts on the adjustment bracket below, crack open the injection pipe nuts on the back, rotate the injection pump towards the engine/counter-clockwise as seen from the pulley end, and re-tighten everything). Advancing the timing will make the idle more "clattery" and give you more power. On my engine the IP is turned 2mm, measured at the slotted bolt holes at the front of the IP. Too much advance can result in engine damage on a hot day- if you're hauling at full power up a steep hill on a hot day and you notice power *decreasing* when you push the accelerator, *back off*. Your fuel is igniting too early, while the piston is still coming up the cylinder.

That said, I've had my IP advanced as far as it will go and nothing *immediately* exploded, but the idle clatter was awful.
Nothing says "poor workmanship" more than wrinkles in the duct tape.
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Tuning the 4D56 turbo for more powaaaah.

Post by sk66 »

Nice write up.

I've thought about messing with mine but it seems to already be adjusted well overall. The only issue I have is when going up long hills in 4th (OD)... the throttle pedal is more of an EGT control rather than power/acceleration. But I get plenty enough fuel to burn it up even at 14-16 psi boost (1400f + if I'm not careful).
1991 L300
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Tuning the 4D56 turbo for more powaaaah.

Post by Growlerbearnz »

sk66 wrote:the throttle pedal is more of an EGT control rather than power/acceleration.
Yup, having to watch the temperature when using full power is one of the tradeoffs. Mitsubishi tuned the engine so it couldn't cook itself when climbing a long hill, which made it a bit weak on the flat.
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Tuning the 4D56 turbo for more powaaaah.

Post by bigsleep55 »

Amazing write up! I need to do a lot of things before tackling something like this.
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Tuning the 4D56 turbo for more powaaaah.

Post by Killbert »

You are literally the man. Thank you so much for sharing such a fantastic and detailed article! I know how much time you put into this!

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