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    Thread: Car skips and loses power in upper RPM range

    1. 01-04-2009 10:25 AM #1
      1989 jetta GLI, CIS-E, 2.0 block. Car seems to run well up through 4k RPMs. I hit 4K and have power loss and sort of bucking/skipping. Issue is present 90% of the time. Car starts and runs well other than that.


      Modified by eurocarsareTrouble at 5:44 AM 1-6-2009


      Modified by eurocarsareTrouble at 5:45 AM 1-6-2009


    2. 01-04-2009 01:58 PM #2
      has the car had any maintenance done to it?

    3. 01-04-2009 03:12 PM #3
      Plugs, cap rotor, grounds cleaned, fuel filter, air filter. Coolant temp sensor tested. Unplugged O2 sensor, did not change anything... Could that mean it's bad?? Fuel injectors changed w/ new seals. Car sat for 2 years before I got ahold of it. Going to change fuel filter again tomorrow. Exhaust tone changes when problem occurs. Like it is breathing too much air maybe?

    4. Member ps2375's Avatar
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      01-04-2009 03:38 PM #4
      Quote, originally posted by eurocarsareTrouble »
      Also, car has CA emissions. Is that why I feel underpowered? How do I bypass that crap?
      It feels that way cause it's obviously not running correctly. How long have you been driving it since it was sitting?
      Tradition is the art of making the same mistake repeatedly, on purpose.

    5. 01-04-2009 03:40 PM #5
      I've been driving it about 6 months now. This issue sort of always took a back seat because of all the other stuff that needed attention.

    6. Member ps2375's Avatar
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      01-04-2009 04:00 PM #6
      Do you know what the AFR is? Have you checked the fuel system out?(other than changing fuel filter)
      Tradition is the art of making the same mistake repeatedly, on purpose.

    7. 01-04-2009 04:02 PM #7
      I am not familiar with the AFR. The fuel system got new lines, accumulator, injectors and seals. I have not checked pressures or CO% or really anything.

    8. Member ps2375's Avatar
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      01-04-2009 04:07 PM #8
      That would seem to be the next step. (AFR= Air Fuel Ratio)
      Tradition is the art of making the same mistake repeatedly, on purpose.

    9. 01-04-2009 04:19 PM #9
      I have a new fuel filter to install tomorrow, I think while in the garage I will test the idle mixture on the DPR. Is that what you mean by checking the AFR? If not, how do I go about checking it?

    10. Member ps2375's Avatar
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      01-04-2009 05:03 PM #10
      that will give an indication, but an exhaust analyzer or a wide band sensor will be more definitive.
      Tradition is the art of making the same mistake repeatedly, on purpose.

    11. 01-04-2009 05:47 PM #11
      It feels more like a mechanical problem to me. I will have steady power up to a certain RPM and suddenly it feels like somebody cut my n*ts off. Almost like the air plate in the fuel distributor has a "hitch" in it's movement. I guess I will pull the boot off and clean that all up too.
      What do you think about the O2 sensor? It was suggested I disconnect it and see if it came out of it. I did that and nothing changed. Like I said before it runs fine, the problem only occurs at high RPMs, much worse under load. (uphill)

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      01-04-2009 06:20 PM #12
      It could be a fueling problem, but to tell, you need a way to check the AFR,, hence a wide-band sensor to check the mixture.
      Tradition is the art of making the same mistake repeatedly, on purpose.

    13. Member nick526's Avatar
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      01-05-2009 02:01 PM #13
      do you have a cat on there? sounds to me like you have a restricted exhaust.
      RIP: Mk2 jetta (stolen ), Mk4 jetta (side-swiped, totaled ), Mk4 GTI (totaled by teenage girl )

    14. 01-05-2009 05:00 PM #14
      Yes, I have a Brospeed header, 2.25 cat and full 2.25 exhaust. Cat is not plugged.

    15. 01-05-2009 05:45 PM #15
      Changed the fuel filter today and it was full of crap. Did not help, though. Checked DPR with ammeter and it was steady at 19.7 Running the throttle up to 3K rpm made it fluctuate a little. I cranked the mixture screw in a little to see if I could richen it up, no help. Same symptoms.


      Modified by eurocarsareTrouble at 6:30 PM 1-5-2009

    16. 01-05-2009 09:32 PM #16
      I miss my Sentra

    17. 01-06-2009 07:06 AM #17
      19.7MA????????????? holy crap thats high.....

    18. 01-06-2009 08:29 PM #18
      That value is what I would expect if the O2 sensor input to the ECU were grounded.

    19. 01-06-2009 10:19 PM #19
      All right, I will look into that. So after a bit of driving it seems that the problem is brought on during WOT. If I accelerate gently through the power band it goes strong and steady. If I mash the gas pedal or if the car is under load (again, more pedal) I get my power loss. Does this shed any light?

    20. 01-06-2009 10:23 PM #20
      My index finger is beginning to extend towards my ECU. The finger next to it is extended towards the POS aftermarket headlights I just got.

    21. 01-07-2009 08:42 AM #21
      Quote, originally posted by eurocarsareTrouble »
      All right, I will look into that. So after a bit of driving it seems that the problem is brought on during WOT. If I accelerate gently through the power band it goes strong and steady. If I mash the gas pedal or if the car is under load (again, more pedal) I get my power loss. Does this shed any light?

      Maybe, maybe not. If the O2 sensor is not working or the ECU is not seeing it, nothing is working right and we cant even verify the idle CO current is right and everything "fuel" depends on that to be right.

      Since the 19.7ma you see when the engine is warmed up doesnt appear to fluxuate and that is the normal behavior if the O2 sensor is shorted, I would address that first and see what other symptoms remain or change.

      My approach would be to monitor the O2 sensor output with its sensor lead disconnected from the cars harness usinf a DVM while running the engine and see how it behaves.

      I would watch it at idle with everything warmed up and adjust the CO screw a little to see that it indicates rich (above .5V) and lean (below .5V). (If that works, leave the CO adjustment where the O2 sensor says .5-.6V.) Then open the throttle some and see that the voltage changes. From there I would proceed depending on the results.


    22. 01-08-2009 08:41 AM #22
      Ok, sounds easy enough. In case you have not figured it out, I am pretty inexperienced There are 3 connections to the O2 sensor, 2 in one connector and the third separate connected by a blade connector. What do I disconnect and where do I monitor the voltage? Do I leave the single connector hooked up and monitor across the two in the small harness connector? Sorry to be so retarded.

    23. 01-08-2009 02:52 PM #23
      No problem.

      The single connector is the sensor output and the 2-pin connector is the sensor heater. Leave the heater hooked up. Unplug the single connector and monitor the DC voltage from this connector coming from the sensor with the multimeter + and connect the multimeter - to a ground. TheO2 sensor generates a small voltage on its own so it doesnt need to be wired up to a power source to read it, but the heater wires are needed or the sensor may take forever to warm up.

      I almost forgot. You need to use a high impedance meter. All the digital multimeters out are high impedance but many of the older analog meter - pointer types were not.


      Modified by wclark at 2:54 PM 1-8-2009


    24. 01-08-2009 08:56 PM #24
      Simple. I will check tomorrow after my drive to the office and let you know what I discover. It would be nice if is as simple as a bad o2 sensor. Thank you very much.

      I need a garage.


    25. 01-09-2009 05:46 PM #25
      Ok, o2 sensor reads 0.86 when engine is fully warmed up. Revving the throttle causes the measurment to drop to 0.0 and into the negative.

    26. 01-09-2009 06:54 PM #26
      Quote, originally posted by eurocarsareTrouble »
      Ok, o2 sensor reads 0.86 when engine is fully warmed up. Revving the throttle causes the measurment to drop to 0.0 and into the negative.

      I wonder if the ground path between the O2 sensor body and the engine is any good...

      With a good sensor and good grounds I would expect .1-.9V and nothing outside of that. The sensor should be grounded to the exhaust downpipe by virtue of being bolted into it, and the downpipe to the head, through the cast manifold if a stock setup.

      I would try something like putting a battery jumper cable between the O2 sensor body and a bolt on the head and measure again.


    27. 01-09-2009 07:49 PM #27
      After the battery jumper cable test, see if you can adjust the CO screw so you have .5V from the O2 sensor. Keep track of how much you have to turn it in case it needs to go back later. .5V should set it in the vicinity of where the DPR current should be at idle when operating normally. The .85 probably represents the highest output of the sensor and the actual AFR may be richer than it can indicate.

      On a properly working setup with the O2 sensor unplugged from the ECU you can expect to see the reading go low (lean) as an engine is throttled up with no load but when held steady it should come back at least into the O2 sensors range.

      By the way an O2 sensor is very nonlinear with a steep rate of voltage change around 14.7 AFR or Lambda = 1 (about .45V). Here is an example of how most look:





      Modified by wclark at 7:53 PM 1-9-2009


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