Please Help With Low Rpm Warm Hesitation/sputter

Discussion in 'Fox 5.0 Mustang Tech' started by flashback87, Jul 29, 2014.

  1. My car has started to hesitate/stumble at low rpm's. it happens most when i am in a higher gear (3 or 4) and give it about half throttle below 2,000 rpm's. it happens more when it is warm too. I have pulled the codes and they are all smog/egr related (koeo 31, 95 ... koer 31, 44, 94) which i have removed. i did not wire in the fuel pump realy when i did the maf conversion. Here are the thing i have done.

    1. check plugs and made sure gap was .054. plugs looked good but cylinder 3 was pretty white
    2. cleaned iac, tb , maf and electrical connectors.
    3. set base idle multiple times
    4. replaced fuel filter
    5. replaced o rings on fuel injectors
    6. replaced cap, rotor, and tfi
    7. advanced timing to 16 degrees. car seemed to do a little better when timing was more advanced. i made sure the balancer was at "0" when tdc.

    Last year the car ran great, idled right at 700-750 rmps with now surge or stumble. this year it all started with a surging idle i could not figure out and now it is missing/hesitating at low rpsm.

    What do you guys think.

  2. 95 is fuel pump circuit. Check pump and fuel pressure.
  3. i thought that code was only showing up because i did not wire in the fuel pump relay into the cpu when i converted the car to maf. Is that right or is it a bigger issue?

  4. Ah, gotcha. I would still check fuel pressure, just because you have replaced most of the electrical stuff. If you have a buddy with a good distributor, I would try that too. The pip can cause some goofy timing issues.
  5. sorry, forgot to add my fuel pressure was at 35 psi with vacuum line hooked up.
  6. Out of all the codes you got the code 31 would cause the hesitation/stumble on a cold engine or warm engine. You may need to clean your egr valve or replace the egr valve position sensor..that should fix the code 31. Also if you are not running cats don't worry about the code 44 and 94 and for the code 95 check for loose wires/grounds and the fuel pump relay.
  7. I have no egr because i have gt40p heads and intake.

    Could this still be the fuel pump relay even though my code 95 is probably due to the fact i did not wire it into the cpu during the maf conversion? i have 35 psi of fuel pressure with vac lines hooked up.

  8. Okay now i know why code 95 ..the ecu checks the fuel pump circuit it's because of the maf conversion/not wiring to the it's not seeing that during the koeo test causing the code 95. How did you bypass the egr/egr valve position sensor ?and did you plug anything into the harness for the egr position sensor? Because that code 31 would cause the problems your are having. Also how long have you had this code since bypassing the egr?
  9. You guys with idle/stall problems could save a lot of time chasing your tails if you would go through the Surging Idle Checklist. Over 50 different people contributed information to it. The first two posts have all the fixes, and steps through the how to find and fix your idle problems without spending a lot of time and money. I continue to update it as more people post fixes or ask questions. You can post questions to that sticky and have your name and idle problem recognized. The guys with original problems and fixes get their posts added to the main fix. :D

    It's free, I don't get anything for the use of it except knowing I helped a fellow Mustang enthusiast with his car. At last check, it had more than 134,000 hits, which indicates it does help fix idle problems quickly and inexpensively.
  10. I just confirmed gaps on all my plugs, .054, and ran some seafoam through the intake. It did not help.

    I did realize that the miss is only at low rpms. Like when i am in first and letting out the clutch and starting off it will miss a little. but when i am in higher rpm's it drives fine and pulls hard. it seems to only happen below 2,000 rpms.

    I checked the power going to the coil with koeo and it was at 11.6 volts. Also, The primary resistance on the coil checked out but the secondary was off just by a little ( I think it was 7.6 instead of the minimum of 8.o) It seems pretty close but would it have an effect on this low rpm miss?

    Anything else i should check? All the codes i have are smog and egr related which has all been removed from the vehicle because i have gt40p heads and intake.

    #10 flashback87, Aug 2, 2014
    Last edited: Aug 2, 2014
  11. just wanted to give an update that my miss is gone.

    I think what cured it was the plugs. I have gt40p heads and when i put in the explorer motor i used the plugs that were recommended for a 2000 explorer, autolite ap104 platinum. After doing some research it seemed autolite's 764 were a better choice. So i put these in gapped at .054. Now it does not miss at low rpm's.