Car bucking untill push in clutch !!

Discussion in 'Fox 5.0 Mustang Tech' started by lx2c6, Oct 13, 2006.


  1. lx2c6

    lx2c6 New Member

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    hey fellas , i have a annoying problem thats driving me crazy , heres the skinny on my woes , quickly heres what i got ,
    brand new 302
    forged bottom end
    forged pistons
    pro comp heads 2.05/1.60
    24lbs inj
    accufab tb 70mm+egr
    ford motorsport maf conversion kit
    73mm C&L
    gt-40intake
    smog delete
    a/c delete
    190lph Fp
    FP set @ 40
    timing @13
    erson cam 544/544''
    new plugs , wires , distributor
    new flywheel , clutch 2 yrs old , 70% life ( motorsport king cobra)
    stock t-5
    Heres the problem as im driving at lets say anywhere under 1500 rpm's the car will buck violently ( like it does when when a newbie driver first starts out driving stick and they let the clutch out with out enough gas and it bucks back and forth untill the clutch is put back in ) thats the same characteristic that my ride is having under 1500 rpm no matter what gear i could be driving in 5th and as soon as it goes around or under 1500 and i let off the gas it will buck. as soon as i hit the gas again it goes away and if i push in the clutch it goes away , same with parking lot driving i push in the clutch and the bucking goes away . I checked codes and i do have a speed sensor code along with some emissions codes ( prolly due to no smog) , i checked the speedo gear on the cable side and it looked fine , my car is a 87 w/o cruise control im not sure what else to check PLEASE HELP . sorry for the long novel , any help will be greatly appreciated thanks !!:hail2:
  2. stangjunkie

    stangjunkie New Member

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    my car does same thingi just shift early or late but im curious as to the solution


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  3. vristang

    vristang Advanced Member

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    Can you verify that the C&L is correctly cal'd for your 24's?
    I have some C&L info on my site, if you need to check the actual diameter of the sample tube.


    Really though, this is not too unexpected.
    By using an aftermarket MAF and larger injectors, you are introducing a certain amount of error in the airflow and fuel flow calculations.
    Yes the MAF is supposed to be 'calibrated' for the injectors, but there is always some % error.

    Also with a larger MAF on the stock computer, the Load calculations performed by the EEC will be incorrect.
    The Load Calculation is used by the EEC to adjust / fine tune the fuel injector puslewidths and ignition timing.

    If the Load numbers are off, so will the injector PW's and ignition timing.
    This is what usually causes the low load/rpm bucking.


    A custom tune will correct the issue.
    You can take the car to a dyno shop, and have a chip burned.
    OR
    You can invest the time and money needed to purchase your own tuner/chip system.
    the tweecer seems to be the most common, but the PMS is pretty common in the Mustang world as well.

    Both will take time to learn.

    In the mean time (before a tune), you may be able to play with the base timing to minimize the bucking, but you will sacrifice performance in other areas.

    Hope that helps,
    jason
  4. stangjunkie

    stangjunkie New Member

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    i have stock maf and stock injectors and i have same problem exactly
  5. ch47600

    ch47600 Founding Member

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    I think that many of us suffer from this. Both of my mustangs have done this. In asking around the consensus that I got is that the engine is running too rich. Do you have a fuel pressure regulator hooked up? If this is the case maybe it's an easy adjustement.

    Good luck...
  6. bigblock52

    bigblock52 New Member

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    hey lx2c6 its off topic but I see that you run pro comp heads and was wondering how you liked them. the flow numbers look great but I have heard some complaints on quality. what do you think?
  7. lx2c6

    lx2c6 New Member

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    they are actually a really good head so far ( only got about 1200 miles on them ) but so far so good i really wish i had them ported though before i put them on because they flow exceptionally well stock , but when they are ported its a whole other world with them , quality wise i have no complaints :lol:
  8. lx2c6

    lx2c6 New Member

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    i appreciate your reply , to tell you the truth it is running rich and i have tried to turn down the regulator down to around 35 ( just to see ) if i could lean it out a little bit to see if it corrected the problem , that brings me to another question , why am i running so rich ? u stand behind the car and its an overwhelming smell , everything that i listed on my first post is new , block , maf , intake etc, my o2's are brand new as well , i have no cats , before i replaced the motor and all that i listed , the car ( stock inj , maf etc) was running super rich , this was before i converted to maf , so the computer in the maf conversion kit is new , the maf , i went through all my wires ( literally ) in the main engine harness and replacing wires and pins that looked worn or partially damaged , so im kinda at a stand still with these problems , i kinda figure im in need of a tune and the two problems are related , but i know of people who do combinations like mine and they never need a tune ? my combo isnt wild its pretty simple so i dont see why the computer cant make the adj when alot of other people have crazy combos and dont have these problems . again sorry for the long post and thanks for the reply's and help and please kep them coming i can use any bit of info thanks again :hail2:
  9. vristang

    vristang Advanced Member

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    When using an aftermarket MAF, which is calibrated to an injector size, you are 'tricking' the ecu about how much air is being consumed.

    This will correct for the computer thinking that the stock MAF and injectors are still there, which should provide the correct AFR.

    The problem is that the mass of air being consumed is also used to calculate the Load.
    Load is then used to fine tune the ignition timing and injector pulsewidths.

    There is always a certain percentage of error when you try to use what is essentially the wrong part. Aftermarket MAF's are the wron part, until the computer knows exactly what part has been installed.

    This percentage of error can vary from engine to engine, even if the same parts are used.

    Sometimes things work out well, and the eec is able to adjust.

    If the error is outside the range of the eec's abilty to fine tune, then problems will occur.
    The eec can adjust up to ~12-15%.

    This is my theory anyway.

    jason
  10. 95Vert

    95Vert New Member

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    yet another good read.
  11. vristang

    vristang Advanced Member

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    Wait a minute....
    It only bucks under 1,500 rpm?????

    I am not sure that my bone stock 302 could run under 1500 without bucking? :shrug:

    Maybe you just need a set of gears to bump your cruising rpms up a little? :nice:


    Now that I actually paid attention to all of the original question, I'm not sure there is anything wrong.

    With the tweecer I have been able to get my 408w to run smoothly down to ~1200. But that took some effort.

    If you want to run that low of an rpm, you may need to tune for that rpm.


    jason
  12. lx2c6

    lx2c6 New Member

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    I forgot to post i am running 3:73's in the rear , again thank you everyone who replies with an opinion or thought -Lx :hail2:
  13. dragnazz5.0

    dragnazz5.0 My "0" key d0esn't w0rk, s0 I have t0 use the zer0

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    its just because of the cam. my car did it with the efi setup and it still does it with the carb swap. ive never been in a mustang that didnt do it.
  14. 90cobra

    90cobra New Member

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    i have a comp cams 544/544 and my car does it under 1500 too
  15. 95Vert

    95Vert New Member

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    My car is doing the same thing. Good to know that it's normal.
  16. MyLittlePony90

    MyLittlePony90 New Member

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    It is because you have a manual, if you want to bucking to stop while under 1500 then you need to switch over to a C4 or AOD. Nothing is wrong with your car. As far as the gas smell it is because you need to get a tune done by a shop.
    Good luck
  17. 95Vert

    95Vert New Member

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    Hey guys, FYI, I cleaned my MAF and readjusted my TPS and it doing a lot better now. I can be in 5th gear ar 40mph in 1400rpm range and it won't buck. It seemed to smooth everything out.

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