'90 205 GTi ECU whats the deal with injection?
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  1. #1
    Fellow Frogger! two-oh-philic's Avatar
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    '90 205 GTi ECU whats the deal with injection?

    I always that the point of injection was that at any given amount of revs/min the computer would be programmed so that max torque at those revs/min would always be attained when the foot was to the floor. I'm pretty sure my car doesn't go its best at full throttle at about 2500 revs/min. Am I wrong? Is my car out of tune? Or is there something very different about the 205 ECU? What does Fuel only mean exactly and how is that different to other cars?

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  2. #2
    Fellow Frogger! two-oh-philic's Avatar
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    ne1?
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  3. #3
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    Originally posted by two-oh-philic:
    </strong>
    <strong>I always that the point of injection was that at any given amount of revs/min the computer would be programmed so that max torque at those revs/min would always be attained when the foot was to the floor.</strong>

    No - the reason fuel injection is used in preference to carburettor systems is that it can give precise metering of fuel (to suit the engine revs). Engine torque varies with speed as designed... here you seem to be talking about the accelerating torque that is available at a given speed. If so, available accelerating torque is a function of the position on the speed/torque curve where the engine is operating + the load imposed by the driving conditions, e.g. if you try to accelerate from a very low speed in say 4th or 5th gear, the engine will not pick up very well if at all because it's operating way down on the speed torque curve.

    <strong> I'm pretty sure my car doesn't go its best at full throttle at about 2500 revs/min. Am I wrong? Is my car out of tune? Or is there something very different about the 205 ECU? What does Fuel only mean exactly and how is that different to other cars?</strong>[/QUOTE]

    Having made the comments above, the 205 GTi is a very powerful and responsive vehicle. At about 2500 rpm you should have an excellent response and very fast pick up in just about any gear.

    If your vehicle does not pick up in this way, the reasons could be many... and not necessarily ECU related. E.g., what is the condition of the motor, valve seats, rings etc., or even something simple like spark plugs? Or it could be a leaking component of the air intake system and so on.

    As for your last question about Fuel only - perhaps you could elaborate a further. Are you asking about the minimum octane rating of fuel for the GTi?

    Denis

  4. #4
    Fellow Frogger! two-oh-philic's Avatar
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    Wow denis thanks for the response. I'll clarify myself a bit better:

    I thought fuel injection was preffered to carby because lets say u take a carby to get a dyno tune you can't tune the carby to not put too much fuel at low revs but put a lot at high revs because the carby doesn't sense the motor speed. In an EFI car as i understand u can tune the car so that putting your foot down in 3rd at say 2000rpm doesn't just make the engine run rich and get all truck sounding like if you do to a carb car. EFI can detect what the engine speed is. So they are ideally tuned to have greates amount of torque when the foot is to the floor regardless of the revs. That is to say that if max torque achievable at 4800rpm occurs when there some arbitrary fuel level of 10, a fuel level of 10 at 2000rpm will not achieve the max possible torque at 2000rpm because it will be too rich (sort of) and the car will not accelarate well. Rather at 2000rpm lets say max torque is at a fuel level of 3(arbitrary).

    So my question is sort of more like why is it that at 2500rpm my car accelarates better with my foot say 3/4 to the floor than when my foot is flat to the floor. Does this mean my car is out of tune?

    My fuel only question relates to me hearing that the 205 gti S1 ecu is a fuel-only ECU. I'm just wondering what that means and if it is fuel only then what are other ECU's that aren't fuel only.
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  5. #5
    1000+ Posts alan moore's Avatar
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    When your foot is pushed to the floor a switch is operated at the throttle butterfly that allows the fuel mixture to go rich, the lambda sensor is ignored, so at full throttle a less than ideal fuel mixture is produced.
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  6. #6
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    two-oh-philic:
    Wow denis thanks for the response. I'll clarify myself a bit better:

    I thought fuel injection was preferred to carby because lets say u take a carby to get a dyno tune you can't tune the carby to not put too much fuel at low revs but put a lot at high revs because the carby doesn't sense the motor speed. In an EFI car as I understand u can tune the car so that putting your foot down in 3rd at say 2000rpm doesn't just make the engine run rich and get all truck sounding like if you do to a carb car. EFI can detect what the engine speed is. So they are ideally tuned to have greater amount of torque when the foot is to the floor regardless of the revs. That is to say that if max torque achievable at 4800rpm occurs when there some arbitrary fuel level of 10, a fuel level of 10 at 2000rpm will not achieve the max possible torque at 2000rpm because it will be too rich (sort of) and the car will not accelerate well. Rather at 2000rpm lets say max torque is at a fuel level of 3(arbitrary).

    My fuel only question relates to me hearing that the 205 gti S1 ecu is a fuel-only ECU. I'm just wondering what that means and if it is fuel only then what are other ECU's that aren't fuel only.
    Ok... well firstly there are different types of fuel injection systems. The earlier types are mechanical fuel injection systems often called CIS - continuous injection system (see Bosch K Jetronic types fitted to 505 Peugeots). In this type of system, the fuel is supplied at a constant pressure to the injectors. Fuel is drawn into or sprayed into each cylinder at a constant rate when the pressure difference across the injector opens the injector (through the action of the piston drawing in air on the intake stroke). The greater the differential pressure, the wider the injector opens releasing more fuel. So the main variable in this type of system is the air supply to the engine which is controlled by the throttle opening and an overall mixture control plate. There are many sites on the web that explain this type of system more fully.. Example see here <a href="http://ncr-pca.org/tech/tech-cis.htm" target="_blank">http://ncr-pca.org/tech/tech-cis.htm</a>

    Motronic ECU electronic fuel injection system: also under this system fuel is supplied at constant pressure behind each injector. However, the ECU controls the amount of fuel injected to each cylinder by electrically switching the injector in response to a number of variables: engine speed, crankshaft/piston position, throttle opening (the throttle is fitted with a potentiometer that in turn provides a voltage signal proportional to position, and a switch which indicates throttle in the closed position - for engine idling / emission control mostly), an O2 or lambda sensor (oxygen percentage in exhaust - mostly for emission control at lower revs), an idler ‘stepper motor’ for controlling air volumes for correct idle speed/emission control, and various temperatures / manifold pressure (mainly to allow mixture compensation). There are many sites on the Internet that explain the operation more completely, and grabbing part of a description from one site

    “The ECU controls the amount of fuel injected and the ignition timing by monitoring the primary sensor signals for engine temperature, speed (RPM), and throttle position (load). These primary signals are compared to preprogrammed “maps” in the ECU computer chip, and the ECU adjusts the fuel delivery to match the mapped values. An oxygen sensor provides continual feedback to the ECU based upon the amount of unused oxygen in the exhaust, indicating whether the fuel mixture being delivered is rich or lean.”

    Complete details are at: <a href="http://www.enginessw.com/BULLETIN/KServiceManual.pdf" target="_blank">http://www.enginessw.com/BULLETIN/KServiceManual.pdf</a> .. I suggest you have a look.

    Turning to your first question: So my question is sort of more like why is it that at 2500rpm my car accelerates better with my foot say 3/4 to the floor than when my foot is flat to the floor. Does this mean my car is out of tune?

    My answer would be: Not necessarily - as the engine characteristics are mapped. Your action on the throttle at those revs will produce a pre-programmed response from the ECU - varying the amount of fuel that is released. The vehicle response also depends on where on the speed torque curve the engine happens to be and the load on the car at that time.

    My understanding about your second question about ‘fuel only’ is that it refers to the way in which the Motronic ECU operates. As distinct from mechanical fuel injection systems, the Motronic ECU controls the fuel quantity as the variable in the engine.

    One final comment about engine torque and power. I suggest you have a look here:
    <a href="http://www.off-road.com/hummer/tech/power.html" target="_blank">http://www.off-road.com/hummer/tech/power.html</a> This site explains the basics (and differences between torque and power). There are some typical speed/power and speed /torque curves where you can get an idea of the sort of performance that you should get from an internal combustion engine. Note maximum torque does not occur at maximum engine revs.

    One thing that would be quite interesting would be actual performance curves for any of the range of Peugeot engines. I haven’t seen any, but if anyone has and can post, that would be worthwhile.

    Denis

  7. #7
    1000+ Posts alan moore's Avatar
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    Only the Series 3 has motronic, with the earlier cars having the ordinary LE2. The motronic has the coil mounted on the intake manifold, but both go rich with the foot on the floor.
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  8. #8
    1000+ Posts PeterT's Avatar
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    The throttle position sensor on all 205's, has two positions, idle and the rest. If you listen carefully, you can here it switch just as you crack the throttle.

    '92 205 Mi16
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  9. #9
    Fellow Frogger! two-oh-philic's Avatar
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    can anyone tell me exactly what it means to call a car fuel only. especially if mine is the S1 type
    205 GTi (S2 ) rolled

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  10. #10
    Fellow Frogger! two-oh-philic's Avatar
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    sorry i've had the impression that fuel only is sort of a bad thing, is that wrong? if not wrong what is better, if wrong what is worse
    205 GTi (S2 ) rolled

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  11. #11
    1000+ Posts PeterT's Avatar
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    The ECU in your S1 205 only controls the fuel mapping. Ignition advance is done via conventional weights and springs in the distributor.

    In the later 90kW 205's, the ECU controls both the fuel and the ignition. The distributor on one of these engines is empty. It only distributes the high tension side of the coil, to the spark plugs.

    There's advanatages and disadvantages for each. If you're into reliablity, the later is better. If you're a tinkerer, the former is better.

    '92 205 Mi16
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  12. #12
    Fellow Frogger!
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    Denis:

    My answer would be: Not necessarily - as the engine characteristics are mapped. Your action on the throttle at those revs will produce a pre-programmed response from the ECU - varying the amount of fuel that is released. The vehicle response also depends on where on the speed torque curve the engine happens to be and the load on the car at that time.
    Wouldn't you assume that at 100% throttle the mapped response would be better than at 75%, assuming injectors could flow enough fuel and other conditions were fine? It doesn't sound like a flat spot that anyone's noticed before... from the sounds of it.

  13. #13
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    alan moore:
    Only the Series 3 has motronic, with the earlier cars having the ordinary LE2. The motronic has the coil mounted on the intake manifold, but both go rich with the foot on the floor.
    "Go rich" as in what? Wouldn't they want to keep the optimum fuel injection even up to 100% throttle? What's this about?

  14. #14
    Fellow Frogger! two-oh-philic's Avatar
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    Wouldn't you assume that at 100% throttle the mapped response would be better than at 75%, assuming injectors could flow enough fuel and other conditions were fine? It doesn't sound like a flat spot that anyone's noticed before... from the sounds of it.
    That's what i was trying to say!!! I thought the entire point of injection was that full throttle would be mapped to give the best possible torque at any given rpm? If it is, and my car doesn't give best at full, why?
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