Scan tools are a good aid in swapping engines.
It would give you a good insight into a problem, or indicate that you need a wiring expert before it’s too late. Below I will try to cover some of the most important factors to keep in mind when using them, specifically for most popular engine conversions.
1 Find wiring diagrams
This is where to start – find a reliable official diagram. Don’t rely on internet sourced colour charts, don’t rely on hand drawn charts. Remember, once you let the smoke out, you can’t put it back in. It makes more sense to spend 20 usd for 2-day subscription and download all you need officially.
For US market engine donors
Factory repair manuals for Lexus LS400 of all model years:
Some rare JDM ones:
I would also don’t trust “educational” youtube videos, or at least be reasonably skeptical about them. Good exception is this channel though.
2 Engine types covered
I will talk about OBDII or JOBD compliant engines – all VVTI UZ (1997+), most VVTI JZ’s , and newer ones like 2GR, 1UR etc. I omit non-vvti engines for a few reasons:
Significantly less live data available
Aging problems (loom , seals, leaky capacitors in ECU )
Less power and torque compared to VVTI counterparts
Few “projects” end up as roadworthy cars. All those turbos and thick rods are usually wet dreams rather than real life. The more stock your engine is, the better are chances that the project will run at all some day. And stock vs stock, vvti is better.
3 Wiring of DLC3 socket
If a car (engine donor) is OBDII or JOBD compliant, it has trapezoid shaped socket under steering column, like this one
Typical wiring of the socket (1997 Toyota Land Cruiser 100 as example):
Note that on the picture, all wires run through connector named IJ1. That’s fairly common for Toyotas: diagnostic port is part of body loom, not engine loom. So it’s normal that your engine does not have it. Note that engine loom has fewer connectors than ECU has. This is normal too. This is partly why wiring experts are get paid.
So we’re about to wire the diagnostic socket. As can be seen from the example diagram, it uses very few wires: two earths (pin 4,5) , one constant power supply (fused, at pin16) and digital signal line (ecu pin SIL to pin 7 of the socket – international standard for data transmission protocol called K-Line). This is typical for 1997-2003 Toyota / Lexus cars, while 2004+ cars would mostly use CAN bus instead of K-line.
Standard pinout of diagnostic port of every OBDII compliant car (not just Toyota) is given above.
Short note on ecus with CAN bus
Facelift 3UZ ecus (those for 6-speed auto transmission), as well as 2GR, 1UR, etc use CAN bus for both chassis communication and diagnostics. That’s nothing fancy if we remain within this article’s topic and don’t go into further details. Use unshielded twisted pair of wires to connect pins CANH of ECU to CANH of the socket (see pinout above), and CANL of the socket to CANL of the ECU. Make sure the line is terminated
For more details, read this.
For less details, make sure that each end of the twisted pair is terminated i.e. it has resistor of 120 Ohm connected between CANH and CANL pins. At least one such resistor has to be placed near the socket.
The other one may be soldered inside ECU (2GR for example), or you should place it near ECU (3UZ). Use DMM to find out if you should wire the other resistor, or ECU already has it.
4 When your scan tool works
Always. Even if ECU is immobilized. Even if there’s no engine. So you may start practicing on table without going to garage. You will need 12V power supply capable of delivering 1A of current, with current limiting. 12V car battery and 1A fuses as an option.
I assume you have your wiring diagram by now, so I will refer to it from now on. Your minimal amount of wires connected to ECU goes below
Earth, Power and Diagnostic line to OBD socket as outlined above
Earth to ECU – pin E1
Constant power supply to ECU – pin BATT, FUSED!!!
Switched power supply to ECU – pins IGSW, +B – FUSED!!!
Remember it’s not enough to start your engine. It’s not the purpose of the article. We’re only covering diagnostics to prevent text bloating.
Note: JDM ECUs have convenient self-diagnosis feature. When ignition is on, connect pin TC (or TE1, depending on model year) to earth. Warning light will start blinking out 2-digit trouble codes.
So if your ECU is a JDM one and you want to try it out, wire the warning light:
pin W of ECU goes to one end of small (1Wt or less) bulb or a LED
The other terminal of the bulb is connected to +12V switched
locate pins W and TC using your wiring diagram, engine control system section.
5 Scan tools
You should use particular software + hardware combo. I will give some useful examples
You can do the most having a Windows laptop with Toyota TechStream software and Tactrix OpenPort 2 dongle. This setup is costly and is probably an overkill for you at the moment. You may do some search to find out if cheaper alternatives exist.
If you’re plan to work with more than one engine conversion, get a standalone scan tool from their lineup here.
Finally, the cheapest solution is this: ELM327 dongle. There are lots of them available. I only recommend those with Wi-Fi connection (Bluetooth modules are also available), and only version 1.5 (version 2.1 is also available).
To communicate with it, use Android phone (for example get a used one for cheap, you don’t need to put a SIM card in). Software: ELMSCan Toyota (free demo available in Google Play)
Only install apps from Google Play, don’t trust unofficial stores.
You may also like Torque Pro app, but I find it too hard to be set up, and having too few features.
6 What to look for
When you completed the above steps and successfully connected to your ECU, you should see something like this
Now that you made sure the setup is functional, you may wire the scan port in your engine swap project and start using it
The bare minimum that you can do now is read 4-digit OBDII codes and post them on the forums hoping that someone can help you out. Chances are few, but it’s way better than description like (it’s hunting, hesitates under 2000 rpm and has strange noise if I depress accelerator pedal)
Most brilliant part of a scan tool, however, is the ability of reading live data.
7 Most important live data
In this final chapter, I will only cover the data you should look for, without in-depth explanation. So you have a good starting point knowing what to search for, or find an expert that will do that for you
Mass airflow . Must be 4.0 – 5.5 g/sec for 1UZ and 3UZ, warmed up, idling . Wrong reading may indicate a few failures, like wrong design of aftermarket MAF housing.
Engine temperature. ECU is considering engine to be warmed up when the temperature reaches 80 C
Ignition advance . 10 deg. BTDC in check mode (TC is connected to E1) . 13-16 deg when warmed up, idling. 16-20 deg WOT, over 4000 RPM. Values below 10 deg BTDT (or even negative values) usually indicate problems such as faulty knock sensors, faulty ECU, etc. The only exception is a/t operation: ignition is set to full retard on upshifts and downshifts.
Engine speed (RPM) . Must be a steady reading. Random reading would indicate crank angle sensor problem, or faulty ECU, or faulty wiring.
Long term fuel trims (LTFT) on banks 1 and 2. Bank 1 corresponds to LH head as seen from cabin. Must be as close to 0% as possible in all RPM and load ranges (idle, cruising, WOT). Values between -10% and +10% are acceptable, while positive values are generally sign of something wrong).
Values out of this range will clearly indicate some kind of fault (MAF sensor, MAF housing or piping, engine temperature sensor, primary O2 sensors)
O2 sensor signal. Look for upstream sensors (ones installed in manifolds). Signal of each sensor should oscillate between 0V and 0.9V a few times per second when warmed up, idling. Reduced range may indicate sensor or engine problem. Lean condition (air leak, deceleration, or active test run from scan tool) should force both sensors to 0. Rich condition (WOT, spraying “engine start” liquid , or running active test from scan tool) should force both sensors to 0.9V
Remember the above data is bare minimum, but these tests are a good starting point.