surging idle with an erratic miss between 1500 - 2500 RPM

Discussion in 'Fox 5.0 Mustang Tech' started by 90stang5speed, Jan 27, 2013.

  1. 90stang5speed

    90stang5speed Member

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    so far, these are the mechanical things I have tried to fix the drivability issue. I have changed plugs, wires, cap & rotor, and fuel filter. Made sure base timing is set at 10 BTDC with spout out. I have done a compression test. 165 psi at all cyl. I have done a cyl leakage test and didnt hear or feel any air coming out of the intake or exhaust. I pressurized the intake plumbing to 20 psi and sprayed eng with soapy water to check for vacuum leaks. I checked the coil with a spark tester. with the tester set for 40,000 volts it would have good spark for a couple seconds then start to break up. set at 30,000 it would spark continusly while the eng cranked. Im not sure if this means my coil is on its way out as ive only see a coil work well or just not at all. I installed the ignition box out of my old car to see if this will help but havent driven the car to know.

    this is my resently built old motor in a new car so I might have some electrical gremlins that I havent found yet or an issue with my tune. the eng was running good in my old car but I have since added an Edelbrock super victor EFI intake and 1.72 roller rockers and a 05+ slot style MAF in a 4" pipe.

    any tips or sugestion would be great. how do i attach my curent tune so, if anyone has time, they can check it out to see what Im doing wrong and let me know so I can adjust. thanks.
     
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  2. liljoe07

    liljoe07 Active Member

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    Whats the wideband read at idle?
     
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  3. 90stang5speed

    90stang5speed Member

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    I need a new sensor for my wide band so I havent installed it yet. Im just using the factory HEGO's and trying to adjust based on what i see from long term fuel trims (KAMRF) and comanded LAMSE. to try to answer the question though. once the car is warm the comanded AFR is usually around 13.x -14.x but if i sit at idle for a long time the comanded AFR starts climing until it hits the limit and trips OL. I adjusted my injector offset vs bat voltage to lower numbers and that seemed to help. it will idle much longer now before leaning and, so far, hasnt hit lean max to trip OL. The idle RMP can go from 600+ to 900. spark fluctuates between mid teens to uper 20's. I just down loaded a template to "lock" idle spark at 30deg. I havent ran the car yet with that setting. I probably wont until monday. when I had the plugs out they looked like it has been running lean. my long term trims are only adding about 5% at most during cruise though. i also just set high and low slope to the same value but, again, I havent ran the car yet.
     
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  4. liljoe07

    liljoe07 Active Member

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    lambse climbs because you are going rich. which inturn will cause surging. is the fuel psi still at 60?
     
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  5. 90stang5speed

    90stang5speed Member

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    Yes. fuel pressure is at 60 but i scaled the injectors up to match. either way, the same issue is there at 40 psi and injectors set at 42. I will set it back to 40 psi and take that part of the problem away. any other tips would be great
     
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  6. liljoe07

    liljoe07 Active Member

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    what are the narrowband voltages doing?
     
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  7. 90stang5speed

    90stang5speed Member

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    theyswitch back and forth from full rich to full lean. Im not sure if im understanding what you are asking for other that that. I would post one of my data logs but I havent figured out how to do that yet
     
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  8. 90stang5speed

    90stang5speed Member

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    Well, I did some double checking this morning and I think I finally found the problem. I have a pretty bad vacuum leak at the intake manifold were it meets the head on the passenger side. My engine make the most vaccum around 1800 rpm. 19 inhg. at idle its only around 11 - 12 inhg. my assumtion is that Im to lean at cruise and Ive been trying to compensate by tuning around the leak. Then when Im back at idle with less vacuum. my MAF settings are to rich and the HEGO's see it and do their best to lean it out. I will fix the intake gasket on friday and adjust from there.
     
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  9. liljoe07

    liljoe07 Active Member

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    Correct, thats how Closed Loop works. If Lambse is rasing, the 02's are seeing a rich condition. So it raises Lambse trying to lean it out. Once it reaches its Adaptive limit, it should throw a rich code if the computer can not compensate enough.
     
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