Flat engine under acceleration/too rich/ECU?
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  1. #1
    Tadpole
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    Default Flat engine under acceleration/too rich/ECU?

    Hi Folks,

    first time poster so I hope this is in the right place.

    I have 2 questions regarding a pug 205 1.6 Litre auto injection. Car has done a total of 33,000 miles and is 9 years old.

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    1. Seem to having a problem when the car is under load/accelerating. It feels a little sluggish, engine has a 'flatness' to it, and although it isnt 'missing' it feels as though it is struggling a little.Problem seemed to appear over 300 miles of driving.

    Changed leads and checked the brand new plugs, and they are sooty but NOT oily. This tells me that it is too rich, but the car management system is controlled by an ECU so mixture/timing is predetermined (not adjustable) and ignition is electronic/breakerless. I have also checked the air filter and this is fine, and changed the fuel filter in the last 8,000 miles so I would be surprised if it was an injector problem.

    I can only assume that its either a duff ECU or tappets need adjusting (a basta*d of a job on this xu engine, as the camshaft has to come out!), any other ideas?

    2. I have a secondhand ECU from a 205 1.6 gti (I think its Bosch). On my car its a Magnetti. Is there any reason why I couldnt swap them over to test the ECU? i.e. are they wired up differently? Would I do any damage?

    Thanks for any help.

  2. #2
    Moderator Alan S's Avatar
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    When was the last time you had the injector nozzles cleaned?

    Judging on the age verus the mileage, my guess would be that this car would have done it's fair share of short runs, so I'd be inclined to start off by replacing the fuel filter then look at getting the injectors ultra sonically cleaned.
    Sounds to me like the poor little bugger's got the automotive equivalent of asthma.

    Alan S
    If it ain't broke, use a 12" shifter.....that usually does the trick!!

  3. #3
    Tadpole
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    Hi Alan,

    thanks for such a quick response!

    I have had the car 2 years and never cleaned the injectors (is this a job I could do myself or is it better left to a pro?). I have replaced the fuel filter (a sealed canister type) in the last 8,000 miles.
    I have been using a well known injector cleaner that you add to the petrol tank when you fill up over the period that I have owned the car, should this not have helped?

    Also if the injectors were clogged would I still be running too rich on all cylinders, surely I would be getting fuel starvation?

    As for the previous owner he was an old boy who use it to collect his newspaper from the local shop, so yes it did little runs.

    Cheers mate

  4. #4
    1000+ Posts alan moore's Avatar
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    Possibly the engine temp sensor for the ECU is faulty, telling the ECU the engine is always cold, and so pumps in more fuel. You would usually see black smoke at the exhaust at idle when the engine is warm, if this were the case.

    Usually the range of resistance Vs Temp is quite large, say 2500 ohms at 20C and 200 ohms at 80C, although I do not know what readings your Pug should have. Perhaps the workshop manual?
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  5. #5
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    Hi,

    where would I find the engine temp sensor (inlet manifold?). Also what other sensors might affect the ECU (i.e. resulting in a rich mix) indirectly and where would I find them? so that i can visually check them.

    I know where the Lambda o2 is.

    Cheers

  6. #6
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    Ecoman my car had the same problems as yours and after doing all the standard things - plugs , leads, injector clean etc arrived at the engine temp sensor , replaced it and the car was transformed . Seem to age over time and loose sensitivity or calibration and even with the diagnostic computers must have to look for that specific fault to find if it is within spec. I found economy, power and free reving returned, good luck with yours.
    Cheers- GavinS 25 GTX 1987 build 2165cc auto - TBR. Renault is properly pronounced "Rhen-oh."
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  7. #7
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    Hi,

    anybody tell me where I might find this sensor, what it looks like, and how much it would cost for a replacement (if not too expensive I might just get one and put it in)...and if it turns out to be the problem I will be a 'happy bear'!

  8. #8
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    Hi Everyone,

    I think i've found the air temp sensor (bolted into the inlet manifold).

    What I am looking at is a threaded fixing with a grey 2 pronged connector at one end, a black cage (4 legs) at the other end. Within this is a thermistor (red blob of plastic), thats quite dirty!

    I assume that once the engine gets up to temp the thermistors resistance decreased so allowing current to flow, and thus giving an 'electronic' switch to the ECU. This then adjusts the mixture to be a bit leaner.
    Is this so?

    Following on this logic, if the thermistor is knackered the ECU doesnt get the signal, and so keeps the mixture rich all of the time?

    So in the plug is 2 sockets (marked 1 and 2) with a grren wire on one and a blue on the other. I dont have a multi-tester to hand (although I may be able to borrow one) but does anybody have the ohm values for hot/cold of this sensor? (no they are not in the Haynes manual I have).

    As an alternative once the engine is warmed up could i bridge these two terminals with a bit of wire to simulated the lowered resistance?

    Thanks for any help.

  9. #9
    1000+ Posts alan moore's Avatar
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    I was talking about the engine temp sensor. This has a far greater cotrol over the injection than the air temp sensor. The water temp sensor will be near the thermostat housing. I expect there will be two there, one for the ECU and the other for the guage on the dash. I expect a manual would point out which is which.

    Ten pounds should buy one.
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    I've got a similar problem with the AX.

    Does it happen straight away (as soon as you start the car), or 5 to 10 minutes after?

    My car is fine for the first 5 to 10 minutes, and then suddenly starts missing at low RPM, and the fuel economy is worse than usual.

    Would i be right in thinking that this is more likely to be the Oxygen Sensor, than an engine temp sensor?

    Cheers
    Ken

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    Quote Originally Posted by ecoman
    Hi Everyone,

    I think i've found the air temp sensor (bolted into the inlet manifold).

    What I am looking at is a threaded fixing with a grey 2 pronged connector at one end, a black cage (4 legs) at the other end. Within this is a thermistor (red blob of plastic), thats quite dirty!

    I assume that once the engine gets up to temp the thermistors resistance decreased so allowing current to flow, and thus giving an 'electronic' switch to the ECU. This then adjusts the mixture to be a bit leaner.
    Is this so?

    Following on this logic, if the thermistor is knackered the ECU doesnt get the signal, and so keeps the mixture rich all of the time?

    So in the plug is 2 sockets (marked 1 and 2) with a grren wire on one and a blue on the other. I dont have a multi-tester to hand (although I may be able to borrow one) but does anybody have the ohm values for hot/cold of this sensor? (no they are not in the Haynes manual I have).

    As an alternative once the engine is warmed up could i bridge these two terminals with a bit of wire to simulated the lowered resistance?

    Thanks for any help.

    You're thinking digitally!
    A thermistor doesn't switch, it will change its resistance as the heat changes and thus provide a range of resistance values depending on the temperature.
    An air temperature sensor is usually used to compensate for differing air density caused by varying temperature. For example it can be used ijn conjunction with a MAP sensor to calculate the amount of fuel required.
    Cars with Air Flow Meters don't need a temp sensor as this is already taken into account, thinner air won't open the AFM as much.
    Graham

  12. #12
    Tadpole
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    Hi Guys,

    Ok so lets reply to all 3 posts:

    Hi Alan (Moore), I have found 2 sensors by the thermostat housing, I assume that one of these is for the temp light (no gauge in mine) in the dash, I dont know what the other one is for, one has a red spade connector if that helps?. BUT I have also found the sensor in the inlet manifold (described in a previous post) that I am pretty sure is the engine temp sensor, any care to confirm this from my description OR is this the air temperature sensor?

    Hi AxGT (Ken), mine seems to be hardly noticeable when cold but as the engine warms up it becomes more noticeable. At low revs it doesnt really appear to be a problem, only when I put the engine under load.

    Hi Graham (Wallis), you are so right...BUT a thermistor can be use to give a potential difference trigger and so be used to control an OP AMP in the ECU...dont know whats inside the ECU though, never had a look inside one, any ideas?

    Thanks everyone for your contributions.

  13. #13
    1000+ Posts alan moore's Avatar
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    The water temp sensor with two pins will be the one for the ECU, the other I expect only has a single pin if it is for a light.

    AXGT The temp sensor is still the most likely option and a whole lot cheaper than a Lambda (oxygen) sensor.

    It sounds like you all should invest in a digital multimeter. Even a cheap one would be accurate enough in your cases. The oxy sensor should show about 0.5volt on its' output when hot and everything is happy.

    Your engine temp sensor should be approx 2500 ohms at 20 degrees C and approx 250 at 80 degrees.
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  14. #14
    Fellow Frogger! AxGT's Avatar
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    alan, you aren't kidding with the price difference

    Time for some diagnostics later this week

    Cheers
    Ken

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    Hi Alan and anybody else,

    borrowed a multitester, found two sensors (both single pin/spade), one red, one green. In my Haynes workshop manual they are referred to as coolant temperature sensors, and it says that one is for the dash light/panel (I do not have a gauge) and the other is for the ECU BUT it doesnt tell you which is which!

    So

    At cold the ohms values are as follows:-

    green 1 (max resistance)

    Red 0.9

    After letting her run for about 10 mins so she is warm:-

    Green 1 (max)

    Red 0.35

    This is with one lead on the pin and the other on an earthing point.

    Thoughts?...Is the green one duff? and is for the ECU? or is it for the temp light and only switches (lowers resistance) when it get bloody hot?

    Sorry this is taking me a little while but you 'Aussies' have had a few more generations to evolve than us 'Poms'!

  16. #16
    1000+ Posts Rod Hagen's Avatar
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    Don't know if this helps you make up your mind, ecoman, but the ECU coolant temperature sensors on both the 306 and 406 are the ones with a green wire (in both of these cars, though, the temp gauge sensor has a blue wire unless air con is fittted , in which case a "Bitron" sensor with a brown wire is used) .

    I should note that Haynes (for both 306 and 406) warns against attempting to actually test the ECU coolant temp sender circuit yourself because of the potential for damage to the ecu.

    Another possible area where the problem could lie might be the MAP sensor on the inlet manifold, especially if the problem occurs primarily under load.

    Cheers

    Rod
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  17. #17
    1000+ Posts alan moore's Avatar
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    I expect your green one is for the overtemp light, and would only work as a switch. Your red one should then be your ECU sender. I would think that you may be reading the scale on your multimeter wrong. .9 being .9 x 1000 ohms, being 900 ohms and .35 being .35 X 1000 ohms, 350 ohms, in which case it would seem to be partially working.

    Look back at the figures given at the website that you mentioned, and I think your lower figure (higher temp)should be closer to 200 Ohms.

    I can't find the site I looked at that gave all the figures. Was a 205 site in England.
    Last edited by alan moore; 7th December 2004 at 12:28 PM.
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  18. #18
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    Thanks Guys,

    Rod is the MAP sensor the one that I have described lower in my post? Its screwed into the inlet manifold and appears to have a thermistor in it.

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    Quote Originally Posted by ecoman
    Thanks Guys,

    Rod is the MAP sensor the one that I have described lower in my post? Its screwed into the inlet manifold and appears to have a thermistor in it.
    The MAP sensor is usually in the ECU and it reacts to pressure, so no thermistor.
    It will be connected to the inlet manifold via a piece of small diameter hose.
    Graham

  20. #20
    1000+ Posts Rod Hagen's Avatar
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    Quote Originally Posted by ecoman
    Thanks Guys,

    Rod is the MAP sensor the one that I have described lower in my post? Its screwed into the inlet manifold and appears to have a thermistor in it.
    Not sure where it is on the 205 ecoman. With Bosch systems on 306's it is located on the inlet manifold. With Marelli systems it is at the front of ECU on the right hand front wheel arch. Look for the vacuum connection to distinguish it from other types of sensors.

    The one you are describing sounds more like an inlet air temperature sender.

    Cheers

    Rod
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  21. #21
    Fellow Frogger! AxGT's Avatar
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    Well, my issue isnt the temp sensor- just tested it then, and it was pretty close to what alan moore specified. Looks like the o2 sensor is the next thing to check out.

    Cheers for the help so far guys.

    Ken

  22. #22
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    Ok Guys,

    had another look at the beast this weekend and there seems to be bloody sensors everywhere! so I have draw a picture of my findings (see attachment).

    HISTORY
    Mine was one of the last 205's to be made (1995) so does not appear to be 'just as in the Haynes manual'...it seems to be an assembly of all the parts that they had left! but

    ECU is Magnetti Marelli, pretty sure injector is a MMFD mono-point G6, engine is a 1.6 auto (XU5M3/L)

    so looking at first picture (engine bay from above) I have a airhose coming from the radiator to the air filter box. Midway along this is a circular junction with a rubber hose (1) going to x, and below this circular junction a metallised intake pipe taking hot air from exaust manifold.
    After air filter box I have a 'special' rubber hose going to fuel injector unit (FI), half way along this at x is two 6mm rubber hoses (1 and 2), with 2 going to front of injector body.
    Bolted to the fron of the car is a sensor (S4) that is detailed in second picture (is this the MAP sensor?), with a third 6mm rubber hose going to the inlet manifold. These sensors are in addition to those described in previous postings above!

    TESTS
    After initially running for 1 minute I pulled hose 1 away from x, result= nothing but at x a slight sucking could be felt.
    I then pulled hose 2 from x, results=revs increased and and a sucking could be felt at HOSE (not x). If I then blocked rubber hose with finger revs dropped. In both tests, when tube reconnected I think I could hear a diaphragnm being operated.
    I then pulled rubber hose off S4, result= revs drop slightly, I then blocked HOSE with finger and revs dropped ver, very badly.

    FINAL PICTURE
    Below previously described temp sensors that were screwed into block by terrmostat (see postings above), I found a lime green square block sensor (the two described befor were cylindrical. It has two pins with a green wire on one and a white on the other, where it goes god knows (it disappears into a loom like most on this car) but the plug could only be fixed one way around. I tried to measure it with a multitester but it is so hidden its impossible to do!
    Any idea what this one is?

    Sorry for such a long posting but I wanted to be as descriptive as possible. Also sorry for such an ongoing posting, but going to a main dealer with a test rig seems almost like admitting defeat (I have always done all of my own mechanics)...I think I will soon have to admit defeat though!

    Thanks for any help you can offer.
    Attached Files Attached Files

  23. #23
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    Quote Originally Posted by ecoman
    Ok Guys,

    had another look at the beast this weekend and there seems to be bloody sensors everywhere! so I have draw a picture of my findings (see attachment).

    HISTORY
    Mine was one of the last 205's to be made (1995) so does not appear to be 'just as in the Haynes manual'...it seems to be an assembly of all the parts that they had left! but

    ECU is Magnetti Marelli, pretty sure injector is a MMFD mono-point G6, engine is a 1.6 auto (XU5M3/L)

    so looking at first picture (engine bay from above) I have a airhose coming from the radiator to the air filter box. Midway along this is a circular junction with a rubber hose (1) going to x, and below this circular junction a metallised intake pipe taking hot air from exaust manifold.
    After air filter box I have a 'special' rubber hose going to fuel injector unit (FI), half way along this at x is two 6mm rubber hoses (1 and 2), with 2 going to front of injector body.
    Bolted to the fron of the car is a sensor (S4) that is detailed in second picture (is this the MAP sensor?), with a third 6mm rubber hose going to the inlet manifold. These sensors are in addition to those described in previous postings above!

    TESTS
    After initially running for 1 minute I pulled hose 1 away from x, result= nothing but at x a slight sucking could be felt.
    I then pulled hose 2 from x, results=revs increased and and a sucking could be felt at HOSE (not x). If I then blocked rubber hose with finger revs dropped. In both tests, when tube reconnected I think I could hear a diaphragnm being operated.
    I then pulled rubber hose off S4, result= revs drop slightly, I then blocked HOSE with finger and revs dropped ver, very badly.

    FINAL PICTURE
    Below previously described temp sensors that were screwed into block by terrmostat (see postings above), I found a lime green square block sensor (the two described befor were cylindrical. It has two pins with a green wire on one and a white on the other, where it goes god knows (it disappears into a loom like most on this car) but the plug could only be fixed one way around. I tried to measure it with a multitester but it is so hidden its impossible to do!
    Any idea what this one is?

    Sorry for such a long posting but I wanted to be as descriptive as possible. Also sorry for such an ongoing posting, but going to a main dealer with a test rig seems almost like admitting defeat (I have always done all of my own mechanics)...I think I will soon have to admit defeat though!

    Thanks for any help you can offer.

    This engine seems to be closely related to the XU5M3/Z used in Australian delivered autos and the 1.6 SI model.
    This has a catalytic converter and uses an oxygen sensor, I had an issue with the heater wires to the oxy sensor a year or so back and similar symptons are starting to occur (flat spot etc.). At 220000km I think it is time for a replacement!
    Does your car have an oxygen sensor? This is screwed into the exhaust pipe.
    Graham
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  24. #24
    Tadpole
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    Hi Graham,

    yep mine is a model with a cat and yes it does have a O2/Lambda sensor.

    The car although a 95 model has only done 33000 miles (46000km) though, would the sensor have gone in this time. Also I thought the O2 sensor only accounted for a very slight alteration in the mix?

  25. #25
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    Quote Originally Posted by ecoman
    Hi Graham,

    yep mine is a model with a cat and yes it does have a O2/Lambda sensor.

    The car although a 95 model has only done 33000 miles (46000km) though, would the sensor have gone in this time. Also I thought the O2 sensor only accounted for a very slight alteration in the mix?

    When the heater connection to the oxy sensor went open circuit the car would run very badly until the sensor was heated enough by exhaust gas to begin working properly. After stopping at traffic lights the problem would return.
    By this you can see that the sensor has a big effect on the operation of the engine.
    60000km is one of the stated figures for sensor life that I have seen and given the car is 10 years old it is possible that it might be at fault.
    Graham

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