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SMT8 | Frequently Asked Questions


Frequently Asked Questions.


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

The SMT8 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 of your piggy-backs will work on a 2005 ST Fiesta, and have you got records of it being done successfully? I have branches and free flow exhaust fitted with an induction kit.

We have fitted a SMT8 to a supercharged 2012 Fiesta 1600. The SMT8 will be able to do the job here.

For a E36 M3 S50B30, which piggy-back would you recommend? It's a E21 323i swap, original ECU, original loom, MAF, OEM coils, only K&N Filters, want to get the most out of the NA engine first, then if everything works fine a supercharger.

The SMT8 will work here.

If I want to advance my timing on the SMT8, do I need to adjust the ign parameters of the ignition map?

In the Ignition Map, the parameters have the max advance and retard limits.

Is the SMT8 unit compatible with my v35 350gt 2003? I have a HKS turbo kit to install and I want to know if this unit works as a piggy-back.

The SMT8 is compatible with the 350Z. We recommend that a Perfect Power Dealer do this installation.

Which model would go with a 206rc, 180hp?

Go for the SMT8 on the 206, but we recommend a dealer do the installation.

Which wire should I start the installation of the SMT8 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 to 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 much easier as you know which connection to concentrate on.

My teeth per turn and edges per turn are correct but my RPM is "bouncing"?

If your RPM is "bouncing", it is a good idea to turn the negative crank edge ON/OFF in the system definition feature on the software.

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

Yes, the SMT8 can use a lambda probe, but one probe at a time or one per SMT8 unit.

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

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

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

The SMT8 can modify 2 x 0-5 volt channels

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

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

Can I use the SMT8 piggy-back to remove my air flow 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 to fine tune it.

Can SMT8 piggy-back work with bipolar signal, instead of balanced signal?

The unit is primarily designed to work on a balanced signal but it can work on a bipolar signal. Refer to diagram.

Does the SMT8 have two tuning maps?

Yes, the unit has two tuning maps.

Can I use the SMT8 in conjunction with my race prepped Eprom?

Yes, the SMT8 will work and can be tuned in real time.

How many outputs are there for injectors or other devices on the SMT8?

The SMT8 has 3 outputs for injectors or relays.

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

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

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

The SMT8 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 will cover all your needs.

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

If you are 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 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.

Assign wire 7/10 injector 1 in the setpoint map.

I have assigned the right wire to injection 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.

There is a m/s time but still no injection?

Ground pin 1 of 10 to the chassis of the car

The m/s time shows 0 m/s.

Change the injection no.1 AMP side table to 1.00.

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 n a 4 cylinder engine with a 60-2 rpm wheel is : 30 teeth per inject.

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 tuning software when the engine is idling?

Use the system definition feature in the LetRipp tuning software 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 in the LetRipp tuning software.

My crank signal 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 wires) then the signal is magnetic. If there are three insulated wires and one wire will be 5 volts, one will be ground; the remaining wire is the digital signal.

I have heard of the term balanced 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 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


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?

First 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, and all fields should be zero.

When I use the SMT8 to control the boost on my turbo car the engine light keeps coming on and the error code is about the N75 value. 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 can control it directly. What you need to do is wire a 1 kilo ohm quarter watt resistor onto the ecu wire and onto switched 12 volts.

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.

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 wires. Tee onto the 2.9 volt wire with the AFR IN and WB out wires of the SMT8.

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 wires, use pin 5 of 12 from the sensor and pin 10 of 10 to the ECU.

I have an ECU scanner and I am watching the slow and fast fuel trim, what should these values be?

Both trims must be positive and negative, then everything is good and the ECU won't modify your tuning. If the values are always negative then the ECU is trying to make the fuel mixture leaner. If the values are always positive then the ECU is trying to make the fuel mixture richer.

If I tune the load sensor to make the fuel richer the lambda closed loop makes it leaner before I get a chance to start tuning the lambda map. What should I do?

You will have to project what values should be in the lambda map before you start tuning the load sensor.

Why do negative numbers in the lambda map make the fueling richer?

The voltage of the lambda reading is reduced with negative entries and the ECU determines this as a lean condition and makes the fueling richer.

Why is there no continuity through the PWM circuit on the SMT8 V3?

A "pull-up" is needed on the input. You can use pin 6 of 12 with pin 2 of 16.