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Thread: Hesitation\hard idle (sometimes)

  1. #1
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    Hesitation\hard idle (sometimes)

    Solved the problem, sold the car.
    Last edited by 90coug; 06-27-2017 at 08:56 PM.

  2. #2
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    Good evening

    Fuel pressure test would the next troubleshooting step. Next would be inspecting/troubleshooting the MAF sensor.


    Good Luck.

  3. #3
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    Quote Originally Posted by sam jones View Post
    Good evening

    Fuel pressure test would the next troubleshooting step. Next would be inspecting/troubleshooting the MAF sensor.


    Good Luck.


    Quarterhorse shows the maf voltage moving as it always has so I don't think that's an issue. Have a fuel gauge on the test port, reads 30-40 at idle. Problem is car only has issues when driving around and occasionally at idle.

  4. #4
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    Good morning

    How is fuel pressure after shut down? Do pressures pass the leak down test?

  5. #5
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    Quote Originally Posted by sam jones View Post
    Good morning

    How is fuel pressure after shut down? Do pressures pass the leak down test?


    Good morning,

    Yea, the pressure stays after engine is cut off. Might be worth checking again but the few times I did it was okay. Seems as though the Regulator and Injectors are holding pressure as they should. No odor of gasoline ever. Still leaning towards an intermittent pump or clogged filter. I'll see about changing filter today, no high hopes on that. My gut tells me I'm dropping the tank...

  6. #6
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    Look at 34 seconds in....the computer starts dumping fuel for some reason....
    Matt Haub
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  7. #7
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    Quote Originally Posted by DrFishbone View Post
    Look at 34 seconds in....the computer starts dumping fuel for some reason....
    Yea, I think that's because I'm playing with the pedal. That log was me pulling out of the driveway in reverse. Placing it in drive and then flooring it going nowhere. I then went back into the garage.

    I take it you're looking at the STFT 1&2 being high 29's?

    Not sure what to make of that. I'm wondering if that's what the computer is commanding but it's not actually happening? As you can see RPM is staying low. The IMAF and TP are in sync, but yea, STFT is high...
    Last edited by 90coug; 06-01-2017 at 12:38 PM.

  8. #8
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    You're either losing spark or fuel on that one side....the other bank looks to be running okay, but rich (looking at HEGO's....or IEGO's here) ....I think that rules out fuel pressure and fuel pump issues. Both STFT's are high in an attempt to fix the lean condition one of the O2 sensors is seeing (passenger side)....but in doing so, gets the driver side reading too rich and throws the code 173. I would have expected that you'd get a passenger side lean condition code, judging by the datalog.

    I'd check your O2 sensor wiring real close...it looks like it almost completely loses signal intermittently and starts adding fuel to fix its perceived lean condition, but instead is just bogging you down until the engine is running fast enough to use the extra fuel.

    It would be interesting to see what a WBO2 was reading too.
    Matt Haub
    Shootouts: '09 SS 1st | '10 Mod1 2nd | '11 Bracket 3rd | '12 Bracket 1st | 2013 | '14 Bracket 3rd | 2015 | '16 Bracket 1st & Mod2 2nd | 2017 |
    Black '89 5spd - 281K miles, MPx, E85, Alky-Inj RWHP: ? RWTQ: ? Best 1/4mi:12.521, MPH:107.23mph
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  9. #9
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    Quote Originally Posted by 90coug View Post
    Yea, I think that's because I'm playing with the pedal. That log was me pulling out of the driveway in reverse. Placing it in drive and then flooring it going nowhere. I then went back into the garage.
    Your STFT's go bonkers before you played with the throttle (seee TP volts)
    Matt Haub
    Shootouts: '09 SS 1st | '10 Mod1 2nd | '11 Bracket 3rd | '12 Bracket 1st | 2013 | '14 Bracket 3rd | 2015 | '16 Bracket 1st & Mod2 2nd | 2017 |
    Black '89 5spd - 281K miles, MPx, E85, Alky-Inj RWHP: ? RWTQ: ? Best 1/4mi:12.521, MPH:107.23mph
    35th Anniversary Auto 46k miles | Red '93 Auto 186k miles
    My Garage

  10. #10
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    Duplicate post....
    Matt Haub
    Shootouts: '09 SS 1st | '10 Mod1 2nd | '11 Bracket 3rd | '12 Bracket 1st | 2013 | '14 Bracket 3rd | 2015 | '16 Bracket 1st & Mod2 2nd | 2017 |
    Black '89 5spd - 281K miles, MPx, E85, Alky-Inj RWHP: ? RWTQ: ? Best 1/4mi:12.521, MPH:107.23mph
    35th Anniversary Auto 46k miles | Red '93 Auto 186k miles
    My Garage

  11. #11
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    Quote Originally Posted by DrFishbone View Post
    You're either losing spark or fuel on that one side....the other bank looks to be running okay, but rich (looking at HEGO's....or IEGO's here) ....I think that rules out fuel pressure and fuel pump issues. Both STFT's are high in an attempt to fix the lean condition one of the O2 sensors is seeing (passenger side)....but in doing so, gets the driver side reading too rich and throws the code 173. I would have expected that you'd get a passenger side lean condition code, judging by the datalog.

    I'd check your O2 sensor wiring real close...it looks like it almost completely loses signal intermittently and starts adding fuel to fix its perceived lean condition, but instead is just bogging you down until the engine is running fast enough to use the extra fuel.

    It would be interesting to see what a WBO2 was reading too.

    Thanks, Matt. I think you might be on to something. I'll inspect the wires on the O2's and see what I can find. When referencing banks 1&2. Which side is 1 and which side is 2 ? I think I've always been confused by that. I've always assumed bank 1 was passenger side of the block.

    Also, code 173 is telling me right side is rich. Wouldn't that be passenger?
    Last edited by 90coug; 06-01-2017 at 05:00 PM.

  12. #12
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    Quote Originally Posted by 90coug View Post
    Thanks, Matt. I think you might be on to something. I'll inspect the wires on the O2's and see what I can find. When referencing banks 1&2. Which side is 1 and which side is 2 ? I think I've always been confused by that. I've always assumed bank 1 was passenger side of the block.

    Also, code 173 is telling me right side is rich. Wouldn't that be passenger?
    I think whichever side has the #1 cylinder is bank 1. In our case, the passenger side.

    Have you reset the codes and gotten the 173 again? I'd rely on your datalogs more than your codes either way
    Matt Haub
    Shootouts: '09 SS 1st | '10 Mod1 2nd | '11 Bracket 3rd | '12 Bracket 1st | 2013 | '14 Bracket 3rd | 2015 | '16 Bracket 1st & Mod2 2nd | 2017 |
    Black '89 5spd - 281K miles, MPx, E85, Alky-Inj RWHP: ? RWTQ: ? Best 1/4mi:12.521, MPH:107.23mph
    35th Anniversary Auto 46k miles | Red '93 Auto 186k miles
    My Garage

  13. #13
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    Quote Originally Posted by DrFishbone View Post
    I think whichever side has the #1 cylinder is bank 1. In our case, the passenger side.

    Have you reset the codes and gotten the 173 again? I'd rely on your datalogs more than your codes either way
    Right, thanks for the clarification. So, I didn't find any issues with the wiring for the O2's. I then went back to the logs. There are times where bank #1 is adding fuel and bank #2 is removing fuel and the engine is doing nothing more than idling. So my inclination at this point is a massive air leak. All I can think of is the intake manifold gasket.

    I have reset the codes, yea. It keeps coming back and I'm not surprised by what I'm seeing on the ST and LT FT's. I mean, I see one bank high in the positives while the other is deep in the negatives. Adding fuel, removing fuel and that must be because it's drawing air on one side. I'm thinking the side where it's always adding fuel is probably the side the manifold has worked itself loose.

    The fuel filter isn't clogged and the engine is surely getting fuel so I don't think there is a fuel delivery problem at this point. Not ruling it out but it seems unlikely.

  14. #14
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    Quote Originally Posted by 90coug View Post
    There are times where bank #1 is adding fuel and bank #2 is removing fuel and the engine is doing nothing more than idling. So my inclination at this point is a massive air leak. All I can think of is the intake manifold gasket.

    I have reset the codes, yea. It keeps coming back and I'm not surprised by what I'm seeing on the ST and LT FT's. I mean, I see one bank high in the positives while the other is deep in the negatives. Adding fuel, removing fuel and that must be because it's drawing air on one side. I'm thinking the side where it's always adding fuel is probably the side the manifold has worked itself loose.
    Reading fuel trims can be a good debug method... Quoting off the 'net:


    Use Fuel Trim to Diagnose Vacuum and Fuel Delivery Leaks.

    With the engine idling, look at the Short Term Fuel Trim (STFT) and Long Term Fuel Trim (LTFT) values. Normal range may be high as plus or minus 8, but closer to zero is best. If the numbers are +10 or higher for STFT and LTFT, your engine is running LEAN. Rev the engine to 1500 to 2000 RPM and hold it steady for half a minute or so. If the fuel trim numbers drops back down to a more normal reading, it confirms the engine has a vacuum leak at idle. This is because vacuum leaks have less of a leaning effect on the fuel mixture as engine speed and load increase.

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