Niva komp service.pdf

GadgetBoy’s Niva 1.7TBi 101

This document is intended to explain the voodoo magic that is the

GM/Lada Throttle Body Injection system as fitted to the Niva. It

does not cover the Bosch Sequential system however the theory is

the same. This article is not a repair manual nor is it intended to be

however it may assist you in diagnosis of a fault and enable you to

understand what the system does and how it does it. Remember, if

you fiddle with anything it’s your responsibility .

TBI Throttle Body Injection is a very versatile, highly adaptable form of

electronic controlled mechanical fuel injection. TBI provides the optimum

mixture ratio of air and fuel at all stages of combustion. TBI has immediate

response characteristics to constantly changing conditions and ensures the

engine runs as close as possible to a stochiometric air / fuel mixture ratio,

greatly reducing exhaust gas emissions. Because its air / fuel mixture is so

precise, based upon much more than simple engine vacuum and other

mechanical metering means, TBI naturally enjoys an increase in fuel economy

over a simple mechanical form of fuel introduction such as an outdated

carburetor.

The TBI form of EFI is controlled by the ECU (Electronic Control Unit) which

controls the TBI based EFI system through all stages of operation according

to data received regarding the current state of engine performance, speed,

and load. The main component of this system is the TBI throttle body injector,

which is mounted on top of the intake manifold, much like a carburetor. The

throttle body injector is composed of two different parts; the throttle body itself,

and the injector assembly. Hard to understand, isn't it? The throttle body is a

large throttle valve which is controlled by a simple mechanical linkage to the

accelerator pedal. Depressing the accelerator pedal will force the throttle

valve open further and further, increasing the flow of air through the throttle

valve and instructing the ECU to add more fuel, thus producing more power,

faster speed, and acceleration.

Attached to the body of the TBI unit are two sensors; the TPS throttle position

sensor, and the IAC idle air control assembly. The ECU uses the TPS to

determine the accurate position of the throttle body valve, it's degree of

cycling, and how open it is (0% to 100%). The ECU takes readings from the

IAC in order to maintain a constant idle speed during normal engine operation,

during all stages of power, load, and combustion.

The fuel metering assembly contains a fuel pressure regulator (FPR) which

dampens the pulsations and turbulence generated from the very high

pressure fuel pump. Think of the FPR as a conditioner that smoothes out the

flow of fuel from the outside to the inside of the fuel metering assembly. The

FPR also maintains a constant, steady pressure at the injector assembly. A

single fuel injector is mounted over the throttle valve, synchronized, and

raised slightly over a venturi (narrowing radius) throat. The injector is

controlled by the ECU through an electrically initiated solenoid (switch). The

precise amount of fuel delivered by each injector is varied by the amount of

time that the solenoid holds the injector plunger open for operation.

A high pressure, high volume electric fuel pump is used with the TBI system.

This pump is located within the fuel tank itself (which can be a bugger if you

have to replace it). Once the ignition key is inserted into the ignition, and the

ignition moved to the I position, the fuel pump relay instantly initiates the

pump, beginning the transfer of fuel (via the pump) from the tank to the

injector. A safety relay in the system shuts the pump off after two seconds, to

keep the fuel from flooding. Failure of the fuel pump relay will allow the fuel

pump to operate only after four pounds of oil pressure have built up. A high

capacity fuel filter, similar to an in-line variety, is located on the left side of the

vehicle, at the rear of the engine.

Two common mistakes when working with the EFI system. The fuel system is

pressurized. If you remove a fuel line, you could/will get a face full of fuel! The

fuel pump used on the EFI system is much more powerful than that found on

a carburetor installation. For this very reason, the second problem is that you

cannot use a EFI fuel pump to feed a carburetor, and you cannot use a

normal carburetor mechanical style fuel pump (low pressure) to feed an EFI

system. In order to work on any part of the EFI system, you must first

depressurize your fuel system!!!!!

The ECU found in the Niva has the capability to 'learn' or modify it's

programming with regard to differing fuel requirements over time. Don't get

excited. This is not HAL from 2001: A Space Odyssey, and it's certainly not

some super advanced neural net processor like the T800 Endoskeleton had in

Terminator and T2. It's quite a bit simpler, but it’s a complex computer

nonetheless, and it can adjust to different conditions easily. It learns, just like

a human child, and that's the best way to put it. It doesn't forget when you turn

your car off either. But, if you ever change your battery, or your battery goes

dead for any reason, your computer will lose it's stored 'memory' and will have

to relearn everything. It's a quick learner, but it's something you don't really

want to go through all the time.

The computer's instructions are contained on a PROM (Programmable Read

Only Memory), which means that the computer can change it's operation

according to pending needs. It then stores this new information, and how it

should act, on the PROM chip. Since the PROM isn't volatile, it doesn't lose

it's information when the battery power is cut off or the keys are taken out of

the ignition.

But the computer takes a little while to adapt. So if you add a snorkel and the

car doesn't feel right, don't get depressed. The computer has just been

handed a new parameter, it's working under new data and conditions, and it

could take it a little while to figure out that the changed air flow isn't just a

fluke, and that it should adjust to the new 'constant', but adjust it will. Be

patient. The computer can make up for quite a bit of ham fistedness, but only

to a limit.

And after that limit is exceeded? Well, you could always learn to program your

own chips... But I don't think it will come down to getting that serious.

The system is very adaptable. The more you get away from the original

operational parameters of the stock motor, the more the computer has to

adapt. The more it has to adapt, the closer it gets to the point where it simply

cannot adapt. If this limit is reached, and the computer cannot adapt any

more, the ECU does the equivalent of a confused child in school. It raises it's

hand and says "I don't understand what to do!" by turning on that annoying

little "CHECK ENGINE" light.

Most people think that the CE light is a bad thing. This isn't true. While it can

indicate a possible malfunction (repair or replacement) of a component within

the system, it can also be a way to talk to your computer. A primitive way, but

a good way nonetheless. We'll get to that later.

Think of your CHECK ENGINE light not as an indicator of failure, no, instead

think of it as a text message from your ECU. When someone wants to talk to

you, they text you, don't they? Your mobile on your belt vibrates or beeps or (if

you are a total poser), plays some musical tune (like Crazy Frog...) that totally

annoys everyone within listening distance. Well, think of the CE light as the

same thing as a text from the ECU, only no vibration (you hope no vibration!)

and no music. The CE is simply the ECUs way of saying "Hey, got a second?

I need to talk to you!" It can't play a musical tune, so it does the only thing it

can to get your attention; it flashes the CE light and keeps it lit until you

answer its text.

It could be important, it could be minor. But the important thing to understand

and to remember is that your ECU is asking you for a few minutes of your time

in order to talk over some really important stuff. If you ever see your CE light

come on, I think you need to stop what you're doing and have a chat with your

computer. You do this with a paper clip! In the left hand footwell on the A-

Panel there is a chunky plastic cover attached with Velcro or screws. Behind

this you’ll find a fuse box and a weird connector. This connector is your door

to a beautiful relationship with your ECU. Make sure the ignition is off and get

your paper clip and unfold it and re-bend it into a “U”. Now insert the ends into

the two left most contacts on the bottom row of the weird connector. This

simple action translates the computer's language into something you can

understand. The computer will talk to you in very short codes, called either

error codes or trouble codes. There is no speech involved, but the computer

will 'flash', blink on and off, your CE light. A long flash is read as the 'tens'

place, and a short flash is the 'ones' place. So, if you are talking to your

computer and the computer flashes the CE light two long times followed by

three short blinks, then that is Code 23. Understand? It's not that hard. The

codes are listed at the end of this document.

So, the next time that your computer wants to talk to you, listen! The computer

is your friend and you don't ignore friends when they need to talk. And make

sure that your CE light is working properly. Remember, if the bulb is out, your

ECU could be trying to talk to you, but you'll never know it!

Think of the ECU as a spider, in a web. At each end point of the web is a

sensor or other control device. When something causes a disturbance in the

web, the 'vibration' or sensor reading is sent down the 'web' to the 'spider'

(ECU) which reads the information and reacts accordingly. Now, how TBI gets

its input, well, that is supplied by various sensors located around the engine,

in the engine bay, and around the vehicle itself. Let's talk about some of those

now...

Sensors, Inputs and Outputs Used

TPS - Throttle Position Sensor, the TPS measures the position of the throttle.

Really complicated stuff there. The position reading indication sent by the TPS

to the ECU determines the amount of fuel to order the injector to inject, and

modifies the duty cycle of the injector as needed. The degree of cycling of the

throttle body valve is used to compute the duty cycle of the injector during

high pressure fuel firing.

CTS - Coolant Temperature Sensor, the CTS measures engine coolant

temperature.

MAP - Manifold Absolute Pressure, the MAP sensor measures the amount of

load that is on the engine by sensing the difference between the pressure in

the intake manifold and atmospheric pressure. It compares what's going on

inside (kinetic) with what is going on outside (ambient). The MAP controls fuel

mixture and timing. The MAP measures vacuum in the manifold.

O2 - Oxygen Sensor, the O2 sensor is mounted in your exhaust manifold or

exhaust pipe. The O2 sensor measures the amount of oxygen in the exhaust

stream. Too much oxygen indicates not enough fuel or a lean condition. Too

little oxygen indicates too much fuel or a rich condition. The ECU then takes

steps to correct this problem by adjusting the air / fuel (mixture) ratio.

The ECU also makes use of other inputs to determine proper fuel

requirements. They are as follows:

• Absolute Engine RPM is obtained from data received from the ignition

module.

• Battery Voltage is supplied to the ECU.

• The ECU knows when the engine is trying to start and adjusts fuel

accordingly thanks to communication with the crank sensor.

The ECU controls the following items to maintain good power, mileage, idle

and favourable emissions.

Fuel Injector - The ECU controls the amount of time that the injector is

spraying fuel. This amount of time is called the 'duty cycle' of the injector.

Within some parameters, it can be overdriven to increase performance, but

too much is not a good thing. The faster an injector is forced to fire, the less

efficient it becomes.

IACS - Idle Air Control Sensor, the IACS is an adjustable air leak into the

engine. It is a power valve which moves back and forth, constricting and

enlarging, in order to adjust the air mixture. The ECU controls the leak to get a

good idle. The readings from the IAC allow the ECU to adjust the motor's

operations and idle accordingly.

MATS - Manifold Air Temp Sensor- Also the Manifold Absolute Temperature

Sensor, provides input on manifold temperature and allows the ECU to adjust

mixture accordingly.

Ignition Timing - the ECU controls the amount of timing advance or retard

needed depending on engine RPM, power load and detonation detected.

Timing will be advanced as needed to meet performance load parameters. It

will be retarded, again as needed, to minimize or eliminate detonation.

Idle - The ECU also has control over the idle RPM, for example when the

engine is cold it idles a little higher. Temperature readings to determine if an

engine is cold or not are taken from the coolant temp sensor, and from the

oxygen sensor. Once temperature reaches operating ranges, the ECU idles

the engine back down.

Fuel Pump - The ECU also controls the fuel pump, turning it on before start,

and keeping it on during cranking and run. Fuel pump pressure is also

controlled by commands sent to the pump by the ECU. More load equals

greater fuel pressure.

VSS - The Vehicle Speed Sensor, which tells the ECU whether the engine is

under load or on the over run.

OA -Octane adjuster. DO NOT TOUCH THIS!

Emissions Canister purge

The ECU has the following outputs to help us. This is data that the ECU sends

to the driver / operator as part of it's operation:

CE - Check Engine light. It warns you of malfunctions with the system. When

you see this light come on, get your paper clip.

ALDL - Assembly Line Diagnostic Link. This is the proper name for the weird

connector. As well as using the paper clip to get codes from the CE light this

is a data interface you can connect a scanner to or a computer with a suitable

software package. This will give you considerably more information than the

CE light. It can even be used to drive “Fast and Furious” style digital

dashboards.

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