Frequently Asked Questions.


What do the values of the SMT8-L's ignition map actually mean on the engine's timing?

The SMT8-L doesn't know what the engine's timing is but it can advance or retard it. Positive values in the ignition map will advance the timing and negative values will retard the timing. Any value used will be added or subtracted from the base ignition timing. Zero entry will be the stock or base timing.

Which wire should I start the installation of the SMT8-L piggy-back with and which wires should follow thereafter?

+12 volts switched power. Earth/Ground. Throttle Position. Airflow meter or manifold pressure sensor. Lambda Sensor. Crank Sensor. This is the recommended order in which t install. Install each connection and then verify that the engine operates normally. If at any step the engine does not operate normally then the troubleshooting on the installation is much easier as you know which connection to concentrate on.

The RPM in the SMT8-L LetRipp tuning software and Rev counter do not match?

Check your teeth per turn and edges per turn. Refer to the SMT8-L manual.

What does "teeth per inject" mean?

The number of teeth on the rpm input that the unit will count before it will fire the extra injector. An example of this on a 4 cylinder engine with a 60-2 rpm wheel is : 30 teeth per inject.

Can the SMT8-L piggy-back work with wide band lambda and narrow band lambda probes?

Yes, the SMT8-L can use a lambda probe, but one probe at a time or one per SMT8-L unit. The SMT8-L can work with two narrow band probes.

Can the SMT8-L piggy-back alter a road speed governor?

Yes, the SMT8-L can alter a road speed governor as it has a frequency channel for this purpose.

How many analog channels can the SMT8-L piggy-back modify?

The SMT8-L can modify 3 x 0-5 volt channels.

Can the SMT8-L piggy-back compensate for engine and air temperature changes?

Yes, the SMT8-L can compensate for air and engine temp change as it has inputs for both of these sensors.

Can I use the SMT8-L piggy-back to remove my airflow meter and use a MAP sensor instead?

This can be done but requires extensive tuning. We rather recommend using a less restrictive air flow meter and a SMT8-L to fine tune it.

My engine has two additional MAP sensors as well as a MAF sensor. Can the SMT8-L work on my car?

Yes, the SMT8-L piggy-back has 3 analog channels, which can be used on your car.

Does the SMT8-L piggy-back have two tuning maps?

Yes, the unit has two tuning maps. One can be setup for performance and the seconds map can be set for economy.

How much power can I expect to gain from fitting the SMT8-L piggy-back to my car?

Power figures vary from car to car but if the SMT8-L is installed and tuned properly you can expect the maximum performance from your engine.

Is the SMT8-L piggy-back the right choice for my car?

The SMT8-L is an advanced piggy-back unit with many features. You need to decide what you need out of the piggy-back and see if the SMT8-L will cover all your needs.

If I am not using the air and engine temperature inputs, what should I do in the maps of the SMT8-L piggy-back?

If you are not going to use all the inputs then it is best to make the air and engine temp side maps zero in the tuning software.

Why does my throttle position start at 14% and end at 85% on the SMT8-L piggy-back?

This is because the voltage of your throttle position starts at 0.7 volts and ends on 4.25 volts. If your TPS voltage starts at 0 volts and ends at 5.0 volts then the range would be 0% to 100%.

My extra injector is not working. I have used wire 7 of 10 on the SMT8-L.

Assign wire 7/10 to injector 1 in the setpoint map. I have done this but still nothing is happening? Open the injector number 1 m/s time in the data display. The m/s display must show a number when the extra injector is working. It shows a m/s time but still nothing? Ground pin 1 of 10 to the chassis of the car. The m/s time still shows 0 m/s? Change the injection no.1 AMP side table to 1.00.

What does analog mean?

A circuit or sensor that ranges from 0-5 Volts.

I have wired my airflow meter into the analog 1 circuit, but now my engine will not start.

Firstly, check the wiring. The wire from the meter must go to pin 7/12 and the return wire to the ecu must be pin 5/10. Secondly, check the parameters for analog 1, the upper limit should be 5.00, the lower limit should be 0.00 and the ±% should be 0.00. Thirdly, check the analog 1 map and side tables; the main map and the engine and air temperature maps should be zero. The AMP side map should be one. Lastly, check the protection map. All fields should be zero.

The RPM in the SMT8-L LetRipp software and Rev Counter do not match?

Check your teeth per turn and edges per turn. Refer to the manual.

The engine does not start after cutting the crank signal?

Do not cut the crank signal just yet; leave the crank signal wire uncut. Tee the SMT8-L crank input pin 8/10 onto the crank signal.

I have teed onto the crank sensor with pin 2 of 14, the +crank input, but I don't see any RPM in the LetRipp software when the engine is idling?

Use the system definition and turn the high crank level on or off.

My RPM is double that of the rev counter. How do I get the correct RPM?

Double the edges per turn in the system setup screen.

My crank signal is on one wire. How do I know if it is a magnetic or digital signal?

Easiest way is to check the signal with an oscilloscope, but not many people or workshops have this tool. Check the actual sensor, if there are two insulated wires and one screen wire (exposed wire) then the signal is magnetic. If there are three insulated wires, one wire will be 5 volts, one will be ground and the remaining wire is the digital signal.

I have heard of the term balance crank signals. What does this mean?

This term means that there are two magnetic signals which are exactly opposite each other at all times.

I keep getting an ignition error and the SMT8-L will only retard the timing. Why?

The teeth per turn setting is wrong. Below are some examples for common crank/cam signals :
Signal Teeth per turn Edges per turn
60-2 60 58
36-1 36 35
36-2 36 34
24+1 12 12
24+2 12 12
1 pulse per fire 4 cylinder 2 2
1 pulse per fire 6 cylinder 3 3
1 pulse per fire 8 cylinder 4 4


When I use the SMT8-L to control the boost on my turbo car, the engine light keeps coming on and the error code is about the N75 valve. How do I fix this?

The ECU was controlling the N75 valve, but now you have cut the wire to the N75 valve so the SMT8-L can control it directly. What you need to do is wire a 1 KOhm quarter watt resistor on the ECU wire and onto switched 12 volts. The reason that this needs to be done is because the ECU is monitoring the return 12 volts from the N75 when it is not in use.

I have used wire 8 of 10, but I cannot get the boost solenoid to pulse no matter what values I use in the boost map?

Assign wire 8 of 10 in the set-point map to boost control.

I am trying to pulse the boost solenoid at 50% but the actual boost PWM is 63% in the data display?

Either you have a boost gain higher than 0.0 in the parameters map or you have values in the boost air temperature map.

Am I able to modify the ETC signal with a SMT8-L piggy-back?

Yes, you are able to modify the ETC signal. There are a few types of signals that the SMT8-L can modify. Refer to the manual on how to set it up for your type of ETC.

What is ETC?

ETC means "Electronic Throttle Control" otherwise known as drive by wire. The throttle doesn't have a cable attached to the pedal. When you push the pedal the computer opens the throttle.

The engine has two narrow band lambda sensors before the catalytic converter. Can I modify both using the SMT8-L piggy-back?

Yes, the SMT8-L has two narrow band circuits. Both lambdas are tuned with one map.

If I want to tune the wide band sensor must I cut the 2.9 Volt wire on the wide band harness?

No, do not cut the wire on the wide band harness. Tee onto the 2.9 volt wire with the AFR IN and WB out wires of the SMT8-L.

If I want to tune the narrow band sensor must I cut the 0-1 volt wire on the narrow band harness?

Yes, you will need to cut the wire on the narrow band harness. Use pin 5 of 12 from the sensor and pin 10 of 10 to the ecu.