Help, strange engine behaviour even for a R25
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  1. #1
    Fellow Frogger!
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    Default Help, strange engine behaviour even for a R25

    I'm still trying to get the 88 R25 converted from auto to manual into reasonable going order. Had problems with cold starts, but when warm was OK. I thought the coolant temp sensor might be dodgy, and measured the resistance and found it about a factor of 10 too low when cold (230 ohms instead of about 2800). Replaced it with a spare sensor that measured up to spec at low temp and that cured cold start problem.

    Went for a quick test drive and noticed the engine was idling very fast an roughly when I returned. Turned the engine off and removed the coolant temp sensor connecter as I thought that it might be stuck on the cold setting, but the resistance was OK (240 ohms). I left the connecter off and tried starting the engine - went fine. Put the connecter back on and the engine died. Took it off again and the engine started OK after a bit of cranking, put it back on and the engine revs started fluctuating rhythmically and eventually started to increase steadily to about 2500 before I turned it off. This pattern occurred randomly each time I replaced the temp connecter after removing it to be able to start the engine.

    Next, I decided to check what would happen when I removed the air regulator valve connecter. When I did this with the temp sensor connected, the erratic behaviour disappeared.

    So either disconnecting the coolant temp sensor with the air regulator valve connected or disconnecting the air regulator valve with the temp sensor connected seems to cure the hot idle problem . But I need both the temp sensor and air regulator for cold starts, and to maintain idle speed when the engine is under load e.g. a/c on.

    I'd be very grateful for some advice on this one as I am completely baffled by the problem. The replacement temp sensor was probably from a 85 leaded engine - is it different from the ULP one, and could this be the cause of the problem? There's no doubt that this 25 is going to put up the sort of fight our cricketers could learn from.

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    Renpete

  2. #2
    1000+ Posts Europa's Avatar
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    The IAC (Idle Air Control) valves can get gummed up and refuse to actuate. You might want to check that it is clear of oil and debris and that the valve opens and closes with voltage applied appropriately.
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  3. #3
    1000+ Posts Haakon's Avatar
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    Try disconnecting the battery to clear fault codes. When the ECU gets a dud reading from a sensor, it reverts to a preset setting. Might be stuck on that, even though it should be getting valid data from the replaced sensor. Reset it to get it to get its act together and aknowledge the good sensor.
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  4. #4
    farmerdave
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    Quote Originally Posted by Europa
    The IAC (Idle Air Control) valves can get gummed up and refuse to actuate. You might want to check that it is clear of oil and debris and that the valve opens and closes with voltage applied appropriately.
    The other thing to check in relation to this valve is the connections in the plug and the first few cm of wire leading away from it.
    The valve itself should snap open or shut in a positive way when power is applied to it, not just slowly open or shut.

    Farrmerdave

  5. #5
    Fellow Frogger! MARK BIRD's Avatar
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    Quote Originally Posted by Renpete
    I'm still trying to get the 88 R25 converted from auto to manual into reasonable going order. Had problems with cold starts, but when warm was OK. I thought the coolant temp sensor might be dodgy, and measured the resistance and found it about a factor of 10 too low when cold (230 ohms instead of about 2800). Replaced it with a spare sensor that measured up to spec at low temp and that cured cold start problem.

    Went for a quick test drive and noticed the engine was idling very fast an roughly when I returned. Turned the engine off and removed the coolant temp sensor connecter as I thought that it might be stuck on the cold setting, but the resistance was OK (240 ohms). I left the connecter off and tried starting the engine - went fine. Put the connecter back on and the engine died. Took it off again and the engine started OK after a bit of cranking, put it back on and the engine revs started fluctuating rhythmically and eventually started to increase steadily to about 2500 before I turned it off. This pattern occurred randomly each time I replaced the temp connecter after removing it to be able to start the engine.

    Next, I decided to check what would happen when I removed the air regulator valve connecter. When I did this with the temp sensor connected, the erratic behaviour disappeared.

    So either disconnecting the coolant temp sensor with the air regulator valve connected or disconnecting the air regulator valve with the temp sensor connected seems to cure the hot idle problem . But I need both the temp sensor and air regulator for cold starts, and to maintain idle speed when the engine is under load e.g. a/c on.

    I'd be very grateful for some advice on this one as I am completely baffled by the problem. The replacement temp sensor was probably from a 85 leaded engine - is it different from the ULP one, and could this be the cause of the problem? There's no doubt that this 25 is going to put up the sort of fight our cricketers could learn from.

    Renpete
    As a matter of intrest the temp sensor from a TR 4cyl Magna is the same and easily available new

  6. #6
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    Quote Originally Posted by MARK BIRD
    As a matter of intrest the temp sensor from a TR 4cyl Magna is the same and easily available new
    Thanks guys for the tips.

    I haven't tested the air regulating valve yet - I'll do it when the weather clears up as the car is outside. I've disconnected the battery, but it didn't stop the problem. Does it reset the computer to preset values for all engine management parameters?

    To confuse me further, I've been told that there are 2 types of coolant temp sensors.
    PTC 022 part no 7700730022 fitted to phase 1 engines (leaded), and
    NTC 571 " " 7700737571 fitted to phase 2 engines (ULP)
    I think the PTC is positive and the NTC is negative.

    The sensor I fitted was from a 85 leaded engine so presumable its the PTC, whereas the engine in the car is a ULP one that presumably uses the NTC sensor. I guess the wrong sensor would confuse the computer.

    Mark, does the Magna sensor fit the leaded or the ULP R25, or both?

    Probably need to get the car to Alpine Motors here for testing on their XR25?

    Renpete

  7. #7
    Fellow Frogger! MARK BIRD's Avatar
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    Quote Originally Posted by Renpete
    Thanks guys for the tips.

    I haven't tested the air regulating valve yet - I'll do it when the weather clears up as the car is outside. I've disconnected the battery, but it didn't stop the problem. Does it reset the computer to preset values for all engine management parameters?

    To confuse me further, I've been told that there are 2 types of coolant temp sensors.
    PTC 022 part no 7700730022 fitted to phase 1 engines (leaded), and
    NTC 571 " " 7700737571 fitted to phase 2 engines (ULP)
    I think the PTC is positive and the NTC is negative.

    The sensor I fitted was from a 85 leaded engine so presumable its the PTC, whereas the engine in the car is a ULP one that presumably uses the NTC sensor. I guess the wrong sensor would confuse the computer.

    Mark, does the Magna sensor fit the leaded or the ULP R25, or both?

    Probably need to get the car to Alpine Motors here for testing on their XR25?

    Renpete
    I have used it on both Also suits the R19 I think.

  8. #8
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    Quote Originally Posted by MARK BIRD
    I have used it on both Also suits the R19 I think.
    Thanks Mark for the info.

    I ended up putting the old temp sensor back to see what would happen, and to my surprise it has decided to behave itself. So far cold starts OK even on a frosty CBR morning, and hot starts fine. I had given the sender some sharp taps on the bench to see if doing that made any difference to the resistance reading on my multimeter, and it seemed to increase the resistance when cold. Don't know why - if it gives trouble again, I'll replace it with a Magna one.

    Renpete

  9. #9
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    Quote Originally Posted by Renpete
    Thanks Mark for the info.

    I ended up putting the old temp sensor back to see what would happen, and to my surprise it has decided to behave itself. So far cold starts OK even on a frosty CBR morning, and hot starts fine. I had given the sender some sharp taps on the bench to see if doing that made any difference to the resistance reading on my multimeter, and it seemed to increase the resistance when cold. Don't know why - if it gives trouble again, I'll replace it with a Magna one.

    Renpete
    Well, what a surprise. The coolant sensor for the TR 4 cyl Magna that fits the R25 is $71 (and in stock locally) and genuine one from the Renault agent here is $52.15 (but 4 weeks ex France). Thought the Magna one would be a lot cheaper. Hopefully, I won't need to make a choice.

    Renpete

  10. #10
    farmerdave
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    Quote Originally Posted by Renpete
    Well, what a surprise. The coolant sensor for the TR 4 cyl Magna that fits the R25 is $71 (and in stock locally) and genuine one from the Renault agent here is $52.15 (but 4 weeks ex France). Thought the Magna one would be a lot cheaper. Hopefully, I won't need to make a choice.

    Renpete
    Renpete,
    Is the Magna price through a Mitsu dealer? Tridon lists the sensor as a TCS040 if that helps any.
    4 weeks ex France seems a long time, Renault agent in Auckland can usually get stuff in 10 days at the most.

    Farmerdave

  11. #11
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    Quote Originally Posted by farmerdave
    Renpete,
    Is the Magna price through a Mitsu dealer? Tridon lists the sensor as a TCS040 if that helps any.
    4 weeks ex France seems a long time, Renault agent in Auckland can usually get stuff in 10 days at the most.

    Farmerdave
    Farmerdave,
    Yes the Magna price is through the Mitsubishi agent in CBR. The funny thing is that the same firm is also the Renault agent in CBR, but Mitsu & Renault spares are dealt with by different sections.

    Don't really know why the long delay. Maybe its caused in part because the agent in CBR has to place the order with Renault Aust in Melbourne and they may have to wait until there are sufficient orders to warrant placing an order in France.

    Where can the listing for Tridon be found? Was there a price for the sensor as I have a feeling that the problems with the old sensor I put back after bashing it on the bench will return with a vengence.

    Hope to spend about 3 weeks on holiday in the South Island after Xmas, starting out from ChCh. Might be an opportunity to visit wreckers there for small hard to get bits for my R25s - if the family lets me

    Renpete

  12. #12
    Demannu-facturing! Demannu's Avatar
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    Quote Originally Posted by Renpete
    To confuse me further, I've been told that there are 2 types of coolant temp sensors.
    PTC 022 part no 7700730022 fitted to phase 1 engines (leaded), and
    NTC 571 " " 7700737571 fitted to phase 2 engines (ULP)
    I think the PTC is positive and the NTC is negative.
    Positive Temperature Coefficient (PTC) and Negative Temperature Coefficient (NTC).

    PTC resistance increases with an increase in temperature, NTC the resistance decreases with an increase in temperature.

    If you get the wrong one, your car will run like a sick dog.
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  13. #13
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    Quote Originally Posted by Demannu
    Positive Temperature Coefficient (PTC) and Negative Temperature Coefficient (NTC).

    PTC resistance increases with an increase in temperature, NTC the resistance decreases with an increase in temperature.

    If you get the wrong one, your car will run like a sick dog.
    Scott,

    Yeah, I thought so. Is the colour of the sensor for a R25 any guide as to whether it is NTC or PTC? The one from the ULP engine is black (seemed to works OK again but there is now a little hesitancy when driving off from a cold start so may be on the way out again.....?) and the one from the leaded engine which is definitely a NTC from the resistance readings I got, is grey. However, colour may not mean a thing. But although the car starts well with the grey one, it runs like a dying dog if restarted when hot.

    Does anyone have a good coolant temp sensor from a ULP R25 or eqivalent for sale?

    Renpete

  14. #14
    farmerdave
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    Renpete,
    Tridon stuff is available through Repco and other parts shops- they have a book full of thermostats and fan switches etc. It's a useful thing to have when you start mucking about trying to make old cars go better.

    Farmerdave

  15. #15
    1000+ Posts Europa's Avatar
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    If it's just $50 for a new one, wouldn't it be easier just to purchase it rather than stuff around? - or do you mean just a short term fix whilst the part arrives in Australia..

    Get your oval plate details ready and ring Marchants, they can certainly have the part delivered quicker (and quite possibly cheaper)
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