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Thread: Stalling when in drive auto? Any ideas

  1. #41

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    If it turns out to be the MAF, cleaning won't do anything. Please read this post I made on the OZ VR4 forum from when I traced and repaired the fault on one of mine, it's really a quite simple repair so here's a copy and paste:

    The hardest part of the repair is getting the top lid off without breaking any of the four little plastic tabs which hold it on. In my case it seemed that there could have been a bit of silicone sealant also keeping the lid on which made it harder so I ended up breaking two of the tabs and having to improvise some clips to take their place. So, remove the MAF from the car and if you like, dismantle it from the plastic airway parts to make it easier to handle. Then remove the lid. Under the lid you'll see a metal shield which is held in place by springy tabs. Just ease the shield out, try not to bend it so it will fit back nicely later.

    NOTE: the purpose of the shield is to prevent any radio frequency signals nearby from affecting the operation of the MAF. Test at idle with it removed but DO NOT take the car onto the road without it in place: I do not accept responsibility for any crashes caused by sudden changes to the car's operation while driving due to some nearby radio emission e.g. your cellphone!!!!!

    Our MAF works by the incoming air, which has had turbulence caused by the special inlet and shaping, passing over two heated wires causing their temperature to vary. As with most metals the electrical resistance of these wires is temperature dependent so we have a variation of resistance in response to the airflow. To allow this resistance change to be measured accurately the current which flows through the wires to heat them must be carefully regulated. This is accomplished by having a precision resistor in series with each wire, the voltage which appears across this resistor is compared with a reference voltage in some simple electronics and the resulting error signal is used as feedback to the current control transistors. This means that when the car is switched on these resistors also heat slightly due to the current flowing through them, and when the car is switched off again they cool. As with most things they expand and contract slightly with this heating and cooling. They are soldered to copper tracks on a fibreglass based circuit board which has a different amount of thermal variation and this causes stress to be applied to the solder joints at each end of these resistors, eventually causing the solder to crystallize and become an intermittent connection which is very susceptible to vibration. In my case the car would often idle but when any throttle was applied the vibration caused the contact to make and break rapidly giving extra pulses from the MAF to the ECU. The ECU saw this as heaps more airflow and ramped up the fuel to the point where the mixture would not ignite stopping the engine and producing rather a lot of black smoke occasionally.

    The repair:

    I'm assuming you or someone you'll get to do this for you is confident with soldering of electronic components:

    Locate the two larger resistors which are flat rectangular items on the circuit board towards the top right of the board if the socket which connects to the car loom is on your left. Mine had the value 6R2 written on them, I expect all MAF's will have the same value resistors, it could be written 6E2 by some manufacturers. Using a small soldering iron somewhere around 30 to 50 watts power and preferably temperature controlled carefully melt the solder on both ends of one of these resistors and lift it away from the PC board. A pair of fine tweezers may be helpful but don't damage the resistor. You may have to keep heating the ends alternately a few times to get it off (don't force it) unless you have one of the special soldering tools which heats both ends at once.

    Don't do both resistors at once as all resistors have some production spread of actual resistance and this has been accurately compensated for at the factory (you'll see some tubular resistors on stand-off legs which have been chosen for exact calibration) so you don't want to mix them up.

    Once it is removed, use the iron and some fresh electronics grade resin cored solder (preferably 60/40 leaded not lead-free as it cracks too easily) to reflow and clean the lands on the PCB where the resistor attaches. Then do likewise with the terminations on the actual resistor. When fully satisfied that all is clean and good to go, solder one end of the resistor back onto the PCB, leaving the resistor sticking up at a small angle so the other end is clear of its land on the board (if you're not too familiar with these things, they're not directional so can face either way). Now take a piece of scrap automotive electrical wire and strip it down to get some fairly thin single strands of copper and cut a strand about 5 or 6 mm long. Solder one end of this flat to the free land on the PCB and then curve the other end around to meet the resistor end flat-on. Now solder it. This provides a bit of 'give' by movement of the wire for the expansion and contraction so should help to prevent the problem from happening again. (I didn't do this when I fixed mine, I just soldered them back as they had been on the board and thought of this idea later so I will do it sometime).

    Repeat for the second resistor.

    Don't be tempted to just reflow the solder on the resistors in place: you won't get to the solder under them and it will be a very short term fix if it fixes it at all.

    When you're happy that everything is connected correctly (it's possibly worth gently pulling on the curved wires to be sure they're really soldered properly) then refit the MAF to the car and test with the car stationary and tapping on the circuit board (not too hard that you break something though) with something insulating like a plastic pen to see that there's no change in engine operation at higher revs due to some other problem. All going well, fit the shield in place and go for a test drive (it won't pop out if you got it out without bending the metal fingers). If it passes the drive test then refit the plastic cover, putting some silicone sealant on if you wish (that may also hold it OK if you broke some tabs!) but use neutral cure silicone not RTV as RTV has an acid solvent which will corrode electronics.

    Hope this helps you or someone else sometime. Several of the Aussies have done this and reported it fixed their fault successfully.

  2. #42

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    Quote Originally Posted by Davezj View Post
    garry isn't it the other way round the single pin sensor drives the dash and the 2 pin sensor drives the ecu input.

    it doesn't really matter about the the dash sensor, you could disconnect that one and it would only effect the the gauge on the dash, but the ecu temp sensor failing can mess up the fueling, depending on if it fails short or open.
    i can remember off hand which way round it will be but one method of fail will signal the ecu that coolant temp is permanently hot or it will signal the ecu that the coolant is permanently cold.

    fail showing hot will cause issues as the car warns up as it will cause lean fueling i think.
    fail showing cold will cause issue once the actual coolant temp is hot as it will continually over fuel the car as the ecu thinks the engine is not warm and need the extra fuel that is initially fed to the engine to make cold starts smoother.

    but as you have an intermitant failt it is probably the wiring going to temp sensor rather than the sensor itself.
    Many thanks for the input Dave.
    As I have already ordered both sensors as they were so cheap from Viamoto I will probably go ahead and fit them to at least cancel out yet another possible cause. I will definitely give the wires a good check while changing them.
    Not sure if this makes sense but am hoping that the sensor is maybe reading hot or just giving a mixed message to the ECU from a cold start causing an incorrect fuel mix.

  3. #43

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    Hi Tony, I had a potential MAF fault recently and came across this thread I've had a a look at the circuit board as you suggested. I'm not really sure what to look for when you say crystalised solder. I've taken some pictures there does seem to be some brown stuff as you can see. Notably a couple of the tabs on the cover were broken so it looks as if someone may have been in before. I've taken some pictures maybe you can suggest if these solders need redoing. Thanks Steve.

    IMG_20211228_175458_227.jpgIMG_20211228_175544_526.jpgIMG_20211228_175446_485.jpgIMG_20211228_175530_990.jpgIMG_20211228_175501_729.jpg

  4. #44

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    Please read my description fully.
    It's ONLY the two resistors with 6R2 written on them which can be seen clearly in your pictures. They're the only ones which get hot and thus thermally stress the joints. The solder may not look bad but once they are removed it will be seen. Please follow the instructions carefully and exactly or have someone with soldering skills do it for you. I can see that yours have not yet been resoldered even if someone has been in there before for some reason.

  5. #45

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    Hi Tony, Thanks for adding the post for repairing the MAF and mentioning that cleaning the sensor wont fix the problem. The simple repair looks a bit scary to me as I have no confidence in my soldering or electrical skills. Wish you lived a bit closer to fix mine!
    Definitely worth fixing as a new one costs around£750. I just worry about making mine worse than it is, not being 100% its at fault anyway.
    Hope Steve manages his fix , would be good to hear how it went.

  6. #46

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    LOL yes if you were here I'd surely do it for you. It really isn't as scary as you think, don't you know anyone near you who dabbles in electronics and would do it for you for the price of some of their favourite beverage?

  7. #47
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    @Braddy40 if you're willing to post your MAF to me, and cover the cost of returning it to you, I'm happy to do the soldering aspect of it for you, as per the instructions posted above.

    Will mean your car is off the road for a few days whilst it's in transit to and from me.

    Garry

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    Quote Originally Posted by Confused View Post
    @Braddy40 if you're willing to post your MAF to me, and cover the cost of returning it to you, I'm happy to do the soldering aspect of it for you, as per the instructions posted above.

    Will mean your car is off the road for a few days whilst it's in transit to and from me.

    Garry
    That would be amazing Garry! Many many thanks. Might use the time its off the road to sort out a couple more jobs, weather permitting.
    I will PM details etc. And of course also include costs for your time as well as postage costs. Thanks again!

  9. #49

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    @Confused that's a great offer you've made to @Braddy40 and a good solution for him, thank you. Once confirmed the fault is fixed, would you consider offering the same service to other members who are sufficiently close to you to make it practical? Perhaps for @CHESHIRECAT as he was the one who asked first and doesn't seem confident either?
    I'd have done the same but it would seem a bit ridiculous to post something all the way from UK to NZ just to resolder four joints. Freight internationally is horrendous both in price and in time delay now due to COVID-19 having stopped almost all flights.

  10. #50
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    I definitely would be willing to - it looks like @CHESHIRECAT has done half the hard work already by removing the cover!

    Feel free to PM me if you'd like me to attempt the fix as described.

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    Quote Originally Posted by Confused View Post
    I definitely would be willing to - it looks like @CHESHIRECAT has done half the hard work already by removing the cover!

    Feel free to PM me if you'd like me to attempt the fix as described.
    Thanks for the offer Garry much appreciated. I spoke to Mike at viamoto recently and he mentioned the diode was faulty on his brothers legnum. I've done a diode test with a multimeter and I think the diode itself maybe faulty. The test guide instructed to remove one side of the diode for the circuit before performing the test which I was unable to do however, so I am not 100% sure if that is the issue. There are some PCB repair shops near me so I will try and get it looked at once they open again.

    Thanks also to Tony for your help.

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    Quote Originally Posted by CHESHIRECAT View Post
    Thanks for the offer Garry much appreciated. I spoke to Mike at viamoto recently and he mentioned the diode was faulty on his brothers legnum. I've done a diode test with a multimeter and I think the diode itself maybe faulty. The test guide instructed to remove one side of the diode for the circuit before performing the test which I was unable to do however, so I am not 100% sure if that is the issue. There are some PCB repair shops near me so I will try and get it looked at once they open again.

    Thanks also to Tony for your help.
    Hi Steve, I also heard that the diode can be at fault and replaced. Was hoping that the soldering fix might be linked to the diode . Found this test in a manual that I haven't managed myself but hopefully will be of some use to you.IMG_20211230_125233_291[14452].jpg

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    Ah thats awesome, the manual i have i think only had a test requiring a test loom.

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    Well I've run the test as instructed. The resistance value at 20c was good and it changed as i heated it, although i'm not to confident on how accurate my probe thermometer is measuring air temp. It seemed slow to react. So the upper reading wasn't bang on. So maybe my diode is ok. Bit strange, i might take it to be looked at anyway.

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    Quote Originally Posted by CHESHIRECAT View Post
    Well I've run the test as instructed. The resistance value at 20c was good and it changed as i heated it, although i'm not to confident on how accurate my probe thermometer is measuring air temp. It seemed slow to react. So the upper reading wasn't bang on. So maybe my diode is ok. Bit strange, i might take it to be looked at anyway.
    Well done for running test. Maybe the diode is on its way out if that is possible . Not sure if your cars issues are intermittent as whatever we are testing could be working ok at the time of the test. Getting the suggested soldering sorted is a good move as we are at least canceling out another possible cause.
    Would be interested in finding out what the results are if you get it looked at. Cheers.

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    Quote Originally Posted by Braddy40 View Post
    Well done for running test. Maybe the diode is on its way out if that is possible . Not sure if your cars issues are intermittent as whatever we are testing could be working ok at the time of the test. Getting the suggested soldering sorted is a good move as we are at least canceling out another possible cause.
    Would be interested in finding out what the results are if you get it looked at. Cheers.
    yes its possible. I had an issue the same as OP that that happened once, but the car has been off the road for the last month. I also seem to have an issue where the revs are not raising as I would expect on cold mornings, which made think it was a MAF issue. I also had a strange experience when changing the idle speed stepper motor, the instructions said to turn the speed adjuster screw all the way in and hold the rpms at 2000 until the engine was warm. then back it out the 650rpm. However when in screwed it in the revs dropped instead of rose, so i backed it out instead but the revs only rose to a max of 1000rpm. I did replace the oring on the screw has its was square and hard but I have not run the car since. So, there is something odd going on I'm just not sure what. I may try measuring and adjusting the stepper motor position manually. I have also checked the ecu temp sensor and that passed ok. I did a flashy dash when the car had the stalling issue and got error codes for MAF and ECU.

    If anyone has any insight or ideas I am open to them. Thanks Steve

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    Hi Steve, Focusing on the MAF is probably the way to go for now as we may have similar symptoms with our cars. You may have read further back on the thread that I have replaced most possibilities .
    Sounds like you bought the stepper motor from Mike/ Viamoto as he also included a similar guide with mine. I was lucky with fitting mine, keeping the battery disconnected doing the job and when reconnected didn't need to make idle screw adjustment.
    BUT I have carefully turned my idle screw half a turn to the left rather to the right to slightly increase my idle as it was quite low also making an accurate start point marker.
    Not 100% if this is correct and someone please correct me if I am wrong but It does sound like the FTO, GTO and Evos react better to idle screw adjustments where as our cars don't like it as much.

  18. #58
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    If you've mucked about with the idle screw, without correctly locking the idle valve using a MUT or EvoScan, then you'll really struggle to get it to idle properly, as you would have always been fighting the ECU adjusting the stepper.

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    do you have a link to the thread you did about full idle setup using evoscan to lock the stepper motor and set the idle with the BIST (Base Idle Set ???) screw.

    https://www.clubvr4.com/forum/showth...ght=BIST+screw

    post 10 gives a good description of what to do to set the idle correctly if you have adjusted the BIST screw randomly.
    Last edited by Davezj; 05-01-2022 at 11:52 PM.

    Bye for Now!

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    Quote Originally Posted by Davezj View Post
    do you have a link to the thread you did about full idle setup using evoscan to lock the stepper motor and set the idle with the BIST (Base Idle Set ???) screw.

    https://www.clubvr4.com/forum/showth...ght=BIST+screw

    post 10 gives a good description of what to do to set the idle correctly if you have adjusted the BIST screw randomly.

    Thanks guys, thats bad news. I followed the instructions that were included with the stepper motor. I will look into getting a cable and evoscan. It never ends...

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