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. You're trying to make a tired, 30-year old engine do more work than it's ever done before- something might break. 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. Oh, and you need to weld an O2 sensor boss to your exhaust pipe).
*edit* It turns out that many AFR gauges don't go above 20:1. That's not particularly useful for tuning a diesel, where it'll almost always be above 25:1. Check the specs of the AFR before buying, and consider the Innovate Motorsports gauge.
For reference: below 18:1AFR you're just making smoke and heat. Light cruise should be 25:1 or higher. Take care when choosing your air/fuel gauge, some gauges will go no higher than 22:1. They're still useful for tuning, since your goal is "no lower than 18:1", but not as informative as a gauge that goes all the way to 99:1.
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. Each engine is different, so measurements taken on one engine might not work on your engine (we tried applying the measurements from my engine to another engine and it was not pretty).
Easy power gains that don't impact engine reliability:
-Larger, less restrictive exhaust. Even on a stock engine, this will give you faster turbo spool and lower EGTs as the engine breathes better.
-Fit a new air filter. The stock paper filter is more than adequate for any amount of power you'll make. (K&N filters are terrible at filtering, and diesels do *not* like dirt in their air. Actual science here and Less convincingly-formatted but still good science here)
Tuning: 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.
Step 4:Set the idle adjustment quite short, to about 1/3 of its length. On mine it was about 10mm from the bracket.
Step 5: Re-orient the linkage on your AC idle-up vacuum solenoid so it won't interfere with the accelerator lever. 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. (The accelerator pedal is probably bent down after 25 years of being stomped on).
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 3 full turns. On mine this ended up about 12mm from the top of the tube. This makes the spring softer, which will allow more fuel earlier on the boost curve, making the turbo spool up much faster.
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).
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: it may be covered by an anti-tamper cover, which comes off fairly easily. Measure the screw's length. Figure out what arrangement of spanners/sockets/screwdrivers you're going to use to adjust it. Crack the locknut loose.
But first, Disclaimers: This sounds easier than it is. You probably know less than you think. Attempt at your own risk. You're trying to make a tired, 30-year old engine do more work than it's ever done before- something might break. 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. Oh, and you need to weld an O2 sensor boss to your exhaust pipe).
*edit* It turns out that many AFR gauges don't go above 20:1. That's not particularly useful for tuning a diesel, where it'll almost always be above 25:1. Check the specs of the AFR before buying, and consider the Innovate Motorsports gauge.
For reference: below 18:1AFR you're just making smoke and heat. Light cruise should be 25:1 or higher. Take care when choosing your air/fuel gauge, some gauges will go no higher than 22:1. They're still useful for tuning, since your goal is "no lower than 18:1", but not as informative as a gauge that goes all the way to 99:1.
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. Each engine is different, so measurements taken on one engine might not work on your engine (we tried applying the measurements from my engine to another engine and it was not pretty).
Easy power gains that don't impact engine reliability:
-Larger, less restrictive exhaust. Even on a stock engine, this will give you faster turbo spool and lower EGTs as the engine breathes better.
-Fit a new air filter. The stock paper filter is more than adequate for any amount of power you'll make. (K&N filters are terrible at filtering, and diesels do *not* like dirt in their air. Actual science here and Less convincingly-formatted but still good science here)
Tuning: 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.
Step 4:Set the idle adjustment quite short, to about 1/3 of its length. On mine it was about 10mm from the bracket.
Step 5: Re-orient the linkage on your AC idle-up vacuum solenoid so it won't interfere with the accelerator lever. 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. (The accelerator pedal is probably bent down after 25 years of being stomped on).
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 3 full turns. On mine this ended up about 12mm from the top of the tube. This makes the spring softer, which will allow more fuel earlier on the boost curve, making the turbo spool up much faster.
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).
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: it may be covered by an anti-tamper cover, which comes off fairly easily. Measure the screw's length. Figure out what arrangement of spanners/sockets/screwdrivers you're going to use to adjust it. Crack the locknut loose.
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