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  • engine refuse to REV - intermittent

    I had problem of intermittent rough idle and stall. I suspect its related to the MAF so I got a re manufactured unit recently. First impression it worked, but when I drove her out the engine suddenly refuse to rev... even if its in neutral gear (no load). No matter how low I floor the throttle it just sits still and runs pretty rough (like to stall but remains ok). Its like misfire. I pull my car off the road, wiggle the MAF connector a bit and the engine seems to work again for a while.

    The act of wiggling the MAF connector suggests that it could be due to the poor contact of the MAF connector; however it cant explain why the engine refuse to rev (I would expect the engine would be able to rev even if the MAF is not connected at all)... could this be related to ignition module? or something else?

    I would try to take a closer look at the MAF connector tonight...
    RS2 >> Ferrari: Performance/look ratio

  • #2
    You need to clean or replace the terminals in the MAF connector
    Panthero Coupé quattro 20vt
    Indigo ABY coupé
    Imola B6 S4 Avant

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    • #3
      I checked all the pin on the MAF connector, its very good condition thus dont think it is the issue. I had also borrowed another MAF from a 968CS, it result same problem. The issue now becomes more prominent, I cant even start the engine at all. I check with VCDS and it had virtually no fault codes (the previously shown MAF intermittent code is gone). The only code remain is

      00537 Lambda (Oxygen Sensor) Regulation
      08-10 Control Limit Surpassed - Intermittent

      I dont think it is related to the problem I am experiencing now.. Considering the fact it has no fault codes, I am now thinking of fuel issues (The fuel pump is newly installed recently though). Can anyone suggest me new direction on this?
      RS2 >> Ferrari: Performance/look ratio

      Comment


      • #4
        MAF and Fuel Pump Testing

        1. Test the MAF using the info below

        2. Confirm that the fuel pump is working. Use this AAN fuel pump testing DIY as a guide: http://forums.quattroworld.com/s4s6/msgs/260108.phtml

        ***************************************
        Testing the G70 MAF is found in the C4 Bentley in section J24, Volume One, pgs. J24-77 to J24-85. The following is a short-form summary of this info and is not complete:

        1. Testing for ground: Disconnect the harness connector from the MAF. Set your DMM to 20 ohms and look for continuity between Pin 1 (Pin 6 is the empty position) and ground on the engine or chassis. Not continuity = you have a ground issue involving that Brown/red wire. Start tracing back, looking for a broken wire. Won't be fun.

        2. Testing for connection to the injector circuit: Turn the DMM to 20 VDC. Connect to Pin 5 and ground. Turn on the ignition. You should get some positive DC volts.

        3. Checking MAF function: With harness connector removed, switch DMM to 200 ohms. Connect DMM probes to terminals 1 and 2 on the MAF (1 is on the right, 6 is on the left). Record the resistance. Disconnect leads and "Short" the circuit (press probe ends together). Display value must equal value recorded previously.

        If the difference is greater than 0.1 Ohm, replace MAF.

        Re-connect the MAF sensor harness connector. Peel back the rubber boot on the connector to expose the terminals. Switch the DMM to 20 VDC. Connect the DMM to the back side of Terminals 1 and 3. Turn the ignition switch to "ON" (run) but don't start the engine. Should be 1.2 to 1.5 Volts. Start the engine and let idle. Voltage reading should now be 2.5 volts. Increase the engine speed briefly (manually move the throttle position to more open). Voltage should increase to 3.0 to 5.0 volts (depending on engine speed). All the of the specified voltages must be obtained. If NO = replace MAF.

        MAF Testing worksheet: http://12v.org/urs/G70_MAF_TESTING_WORKSHEET.pdf

        RS2'd 93 UrS4 5 spd sedan
        94 UrS4 V8 6 spd manual avant

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        • #5
          Throttle Position Sensor would be my bet. I've had this when I've forgotten to reconnect it after doing work on the car and had a brief problem with my new build, as I was using a TPS that had sat for a while but that's cure it. It can be replaced with a spare easily enough. HTH
          Cheers'en, AndyC
          1994 ABY Coupe - Projekt Alpinweiss

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          • #6
            G69 / F60 Throttle valve position potentiometer /idle switch information

            Originally posted by Rusty View Post
            Throttle Position Sensor would be my bet. I've had this when I've forgotten to reconnect it after doing work on the car HTH
            BTDT. Scared me.

            Here is some info that might help:

            G69 / F60 Throttle valve position potentiometer /idle switch information:

            http://forums.quattroworld.com/s4s6/msgs/20405.phtml
            Based on this schematic, it makes the test procedure a bit easier to understand:

            Testing the F60 Closed Throttle (Idle) Switch is as follows:

            Across Pins 4 and 6 on the switch:
            Closed = 0 ohms (continuity)
            Open throttle (slightly) = infinite ohms (open)
            If either fails, adjust switch as per procedure above.

            Testing the G69 Throttle Position Potentiometer:

            Across Pins 1 and 2 on the switch:
            Must be 1500 to 2600 ohms

            Across Pins 2 and 3 on the switch:
            Throttle closed = 750 to 1300 ohms
            As throttle is opened from closed to WOT = increase to 3600 ohms
            If NO, replace sensor.

            The above test info is now available as a single sheet that you can print-off and take out to your UrS when the need arises.

            http://12v.org/urs/G69F60ThrottlePos...hTestSheet.pdf

            RS2'd 93 UrS4 5 spd sedan
            94 UrS4 V8 6 spd manual avant

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            • #7
              Originally posted by Rusty View Post
              Throttle Position Sensor would be my bet. I've had this when I've forgotten to reconnect it after doing work on the car and had a brief problem with my new build, as I was using a TPS that had sat for a while but that's cure it. It can be replaced with a spare easily enough. HTH
              This is what I thought too, but the thing is I've got no fault code related to this at all.. I havent checked the electrical value of the pins but I've done a simple test. I did hear the switch kicking when the throttle wire is left from close according to the information below

              http://forums.quattroworld.com/s4s6/msgs/20405.phtml
              RS2 >> Ferrari: Performance/look ratio

              Comment


              • #8
                Originally posted by UrS4boy View Post
                1. Test the MAF using the info below

                2. Confirm that the fuel pump is working. Use this AAN fuel pump testing DIY as a guide: http://forums.quattroworld.com/s4s6/msgs/260108.phtml

                ***************************************
                Testing the G70 MAF is found in the C4 Bentley in section J24, Volume One, pgs. J24-77 to J24-85. The following is a short-form summary of this info and is not complete:

                1. Testing for ground: Disconnect the harness connector from the MAF. Set your DMM to 20 ohms and look for continuity between Pin 1 (Pin 6 is the empty position) and ground on the engine or chassis. Not continuity = you have a ground issue involving that Brown/red wire. Start tracing back, looking for a broken wire. Won't be fun.

                2. Testing for connection to the injector circuit: Turn the DMM to 20 VDC. Connect to Pin 5 and ground. Turn on the ignition. You should get some positive DC volts.

                3. Checking MAF function: With harness connector removed, switch DMM to 200 ohms. Connect DMM probes to terminals 1 and 2 on the MAF (1 is on the right, 6 is on the left). Record the resistance. Disconnect leads and "Short" the circuit (press probe ends together). Display value must equal value recorded previously.

                If the difference is greater than 0.1 Ohm, replace MAF.

                Re-connect the MAF sensor harness connector. Peel back the rubber boot on the connector to expose the terminals. Switch the DMM to 20 VDC. Connect the DMM to the back side of Terminals 1 and 3. Turn the ignition switch to "ON" (run) but don't start the engine. Should be 1.2 to 1.5 Volts. Start the engine and let idle. Voltage reading should now be 2.5 volts. Increase the engine speed briefly (manually move the throttle position to more open). Voltage should increase to 3.0 to 5.0 volts (depending on engine speed). All the of the specified voltages must be obtained. If NO = replace MAF.

                MAF Testing worksheet: http://12v.org/urs/G70_MAF_TESTING_WORKSHEET.pdf

                Yes I've done this test before I rebuild my MAF, I did get some intermittent wrong reading according to the criteria listed, hence I rebuild it. now my MAF fault code is completely gone but just couldnt start the car properly. When I first change the new MAF, everything work perfectly until I drive the car out and suddenly the throttle is not responding to my right leg...then the engine kinda stall... Talked to my mechanic who rebuild the engine he suspected there's something wrong with the fuel supply though he had actually install new fuel pump.
                RS2 >> Ferrari: Performance/look ratio

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                • #9
                  Are you sure that a hose or vacuum pipe hasn't been left off somewhere or there's some other air leak? When the engine's running, can you hear any air 'whistling' noises?

                  Comment


                  • #10
                    Originally posted by pcfnet View Post
                    I checked all the pin on the MAF connector, its very good condition thus dont think it is the issue. I had also borrowed another MAF from a 968CS, it result same problem. The issue now becomes more prominent, I cant even start the engine at all. I check with VCDS and it had virtually no fault codes (the previously shown MAF intermittent code is gone). The only code remain is

                    00537 Lambda (Oxygen Sensor) Regulation
                    08-10 Control Limit Surpassed - Intermittent

                    I don't think it is related to the problem I am experiencing now.. Considering the fact it has no fault codes, I am now thinking of fuel issues (The fuel pump is newly installed recently though). Can anyone suggest me new direction on this?

                    That codes would suggest to me that you have a fuelling issue. Either mechanical problem or the ECU is receiving a bad signal (maybe MAF) causing it to fuel incorrectly causing the AFR to be outside of the lambda control range. I'm sure PRJ would be able to tell you under what conditions the ECU throws that code.

                    I think the non-start is another problem all together.
                    Panthero Coupé quattro 20vt
                    Indigo ABY coupé
                    Imola B6 S4 Avant

                    Comment


                    • #11
                      Originally posted by pcfnet View Post
                      I had problem of intermittent rough idle and stall. I suspect its related to the MAF so I got a re manufactured unit recently.
                      Unless it is OEM bosch unit herein lies your problem.
                      http://tuner.ee - http://www.facebook.com/tuner.ee

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                      • #12
                        I had a similar problem with my s6.
                        Fuel pump was playing up so I changed it for a new one. It still wouldn't start ,
                        So I undone the fuel line to the fuel filter, which is under the bonnet on an s6, to see if there was any fuel. It was full of pressure and lots of air.
                        Tightened it up and its been alright ever since.

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                        • #13
                          ^^^^ Recently been called out to exactly the same issue on a car that had not been run for 2.5yrs after it apparently kept stalling got recovered and then the owner passed away. Took fuel pump out of tank ran it on bench to spin it alive. Put it back in and car started on the button after pump prime with a power probe but completely gutless didn't react to throttle. Then died again. So did the fuel pump relay upgrade direct wiring to the battery using the original feed to trigger the relay and car has been 100% since.
                          UrS6 Stroker + HTA3586 =

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                          • #14
                            Here is an update. My mechanic came and check the fuel line (in the engine bay), attempt to start and there's a lot of fuel coming out from the line. So definitely not any issues with the fuel supply. Then finally start the engine but very unstable, almost stall. Remove the throttle position sensor, no difference the engine remain runnig in a unstable condition; Repeat the process by removing the maf, still the same. Then we go through the resistance check on the throttle position sensor and found the reading does not match with the testing procedure online (when the throttle good to WOT, the resistance didn't go high enough).

                            I didn't check the maf test because I did attempt to run a known good condition 968 maf on my car but remain can't start the engine.

                            Still I can't explain why the engine didn't show a fault code from this sensor but I think I'm going to try a new part with this sensor and hope the problem can go away.
                            RS2 >> Ferrari: Performance/look ratio

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                            • #15
                              078133154 Throttle Potentiometer

                              Originally posted by pcfnet View Post
                              Still I can't explain why the engine didn't show a fault code from this sensor but I think I'm going to try a new part with this sensor and hope the problem can go away.
                              General Info: http://forums.quattroworld.com/s4s6/msgs/20405.phtml

                              The 078133154 throttle potentiometer shows up as NLA on some websites (but not others). It is also a Bosch 0280120431.

                              https://www.ecstuning.com/Search/Sit...3154/ES283732/

                              http://genuineaudiparts.com/parts/in...&siteid=214407

                              However, it was used on B3, B4, C4 and D2 engines from 1991 to about 1999; 5's, V6's and V8's, so finding a good used one should still be possible.

                              RS2'd 93 UrS4 5 spd sedan
                              94 UrS4 V8 6 spd manual avant

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