Miss at Part Throttle ... Need Help

Discussion in '94-95 5.0 - Specific' started by domhoff13, Dec 30, 2014.

  1. domhoff13

    domhoff13 New Member

    Messages:
    24
    Likes Received:
    0
    Joined:
    Nov 23, 2014
    Location:
    Pittsburgh, PA
    Hi,

    I am currently lost and I do not want to be throwing money at this thing left and right and have it being something simple. I am having an issue with a part throttle miss under any load however at or full throttle (WOT) or sitting in the drive way I am not experiencing it. Car ran fine until one day after some rain would not start and when it did this issue started after it fired up. Also if I disconnect the MAF the car runs fine full power no issues. I have been trying to diagnose this issue for a while but what I thought was going to fix it did not work.

    As far as modifications done to the car I know for a fact that it is at least a 351W that is 0.030 (saw from a bore scope) over it could be a stroker but I am not sure as the previous owner did not know. TrickFlow Twisted Wedge heads, Crane 1.7rr's, unknown cam, SVO lower intake, Comp Polymers Upper Intake, SVO elbow, 30 lb inj., MSD 6AL, Accel TFI coil / MSD Street Fire coil

    1. New Parts - Plugs, Ford Racing wires, Accel Coil, cap, rotor, fuel filter, multiple ICM's, PIP or stator, IAC.

    2. I have checked the continuity and voltage on the MAF it was reading low at .7v at idle and it had a steady increase as throttle was increased no issues that I could visually see Pro-Flow 70mm calibrated for 30lb inj.

    3. The Air Charge Temp sensor had low voltage to it maybe 3.5v not 5v which the book calls for???

    4. Check timing and set at 10* and bumped up to 14* no change (was initially set at well over 20 for initial from P.O.) checked with Spout out

    5. Fuel Pressure 35psi at idle as the throttle is cracked it drops to roughly 30psi then spikes to 39psi.


    Thanks,

    Jared
     
  2. toyman

    toyman Active Member

    Messages:
    874
    Likes Received:
    9
    Joined:
    Aug 25, 2008
    Check the TPS. KOEO voltage should increase smoothly as the throttle is opened. Pay attention to the throttle voltage at about where you would feel the miss.
     
  3. domhoff13

    domhoff13 New Member

    Messages:
    24
    Likes Received:
    0
    Joined:
    Nov 23, 2014
    Location:
    Pittsburgh, PA
    Ok I will take a look at that.
     
  4. domhoff13

    domhoff13 New Member

    Messages:
    24
    Likes Received:
    0
    Joined:
    Nov 23, 2014
    Location:
    Pittsburgh, PA
    Voltage is at .97v then climbs steadily, there are no spikes or erratic readings. Goes up to 4.8v with no issues.
     
  5. CC'S95GT

    CC'S95GT Legend

    Messages:
    10,738
    Likes Received:
    172
    Joined:
    Apr 19, 2008
    Location:
    Hampton ,Ga.
    Has the car been tuned?
    Have you pulled codes? It's possible to have one wothout the CEL being on.
    What plugs did you use?
    While ther car is running, disconnect the MAF sensor. Was there a change in the cars idle?
     
  6. domhoff13

    domhoff13 New Member

    Messages:
    24
    Likes Received:
    0
    Joined:
    Nov 23, 2014
    Location:
    Pittsburgh, PA
    Stock tune. It needs tuned I know that. I want to get back to where I was before I buy the QH and data log. It has the AutoLite 3924's, i was going to put the NGK's it in but it was all that we had on the shelf. The idle does drop to 850. The last time i pulled the codes it was saying giving me one for the Stator failure.
     
  7. toyman

    toyman Active Member

    Messages:
    874
    Likes Received:
    9
    Joined:
    Aug 25, 2008
    When checking sensor voltages ALWAYS use the sensor ground. Also, the battery to engine and engine to chassis grounds are critical for all sensor functions. Physically remove the terminal connections to ensure they are solid.
     
  8. NXcoupe

    NXcoupe Well-Known Member

    Messages:
    1,301
    Likes Received:
    12
    Joined:
    Aug 16, 2009
    why would this be necessary on a three wire sensor?

    If the computer is telling you the stator is bad, then replace the distributor or the pick up coil if you feel frisky enough to press it all apart and replace it yourself. I'd stick a reman in it and give it a try first, make that code go away. Could also be the TFI module failing. It could be something changed in the maf circuit and caused it to go lean now? Just tossing out a guess there. Is the battery in the trunk perhaps?
     
  9. toyman

    toyman Active Member

    Messages:
    874
    Likes Received:
    9
    Joined:
    Aug 25, 2008
    Because that is the ground the sensor uses. If this ground is faulty and you are using a different ground point you have no way of knowing whether this part of the circuit is solid. For example, The sensor reference voltage measured using the block as a ground may be quite different when using the sensor ground.
     
  10. NXcoupe

    NXcoupe Well-Known Member

    Messages:
    1,301
    Likes Received:
    12
    Joined:
    Aug 16, 2009
    On a two wire sensor you are correct. On a three wire sensor, if the signal ground is open, the sensor will read reference voltage because the load is not there because of no ground. In other words, if you have a TPS and the signal return, or sensor ground as you called it, is open, then the green wire on a fox TPS will read 4.8V or higher. So instantly you know the signal ground is open or bad, and needs to be investigated. Going to an engine ground will only tell you the voltage the computer is seeing, as it uses the battery ground for it's ground. Hope this helps out.
     
  11. NXcoupe

    NXcoupe Well-Known Member

    Messages:
    1,301
    Likes Received:
    12
    Joined:
    Aug 16, 2009
    On another note, I thought about this issue on my way home last night from the shop... I'm changing my opinion to a vacuum leak. I'm thinking that when you unplug the maf it may be going richer as the computer thinks there are 24lb injectors in its failed maf tables and injects more fuel, thus your lean miss goes away. Check with a can of brake clean spraying around vacuum lines and intake gaskets, etc. Hope you figure it out.
     
  12. toyman

    toyman Active Member

    Messages:
    874
    Likes Received:
    9
    Joined:
    Aug 25, 2008
    I'm missing something here. Three wires, reference voltage, signal voltage and sensor ground. I'm away from home so I can't check the Service manual to see if there was an explanation as to why one should measure the signal and reference voltage using the sensor ground. However, I'm certain the manual was clear as to the ground source.
     
  13. NXcoupe

    NXcoupe Well-Known Member

    Messages:
    1,301
    Likes Received:
    12
    Joined:
    Aug 16, 2009
    I find that practical application is better. If you take the time to pierce the ground and pierce the signal wire, you will not get a reading of the ground is open. So it's silly to do it that way when you can pierce the signal wire and go to chassis ground and if you get expected voltage, you are good, if it is reference voltage, then you have an open ground. Two ways to arrive at the same conclusion. Running a resistance check on the signal ground is possible, but usually tells you nothing, as the resistance maybe only noticeable when reference is put through it, so doing a voltage drop test is better. Maybe that's what you are referring to here?
     
  14. domhoff13

    domhoff13 New Member

    Messages:
    24
    Likes Received:
    0
    Joined:
    Nov 23, 2014
    Location:
    Pittsburgh, PA
    I took the time to go through everything. There are a ton a spliced parts of the harness and the inj. are too small based on my calcs. I put the bore scope down the the dist. hole and was able to read the markings on the on the crank it is the eagle crank and and rods that are part of the stroker kit. I have decided to end the problems and put a carb on it.

    I will be switching to a Super Victor on it and a carb. I just picked up the new fuel pump for it ... Aeromotive A1000 and the carb bypass that is also boost sensitive for later on down the road.
     
  15. NXcoupe

    NXcoupe Well-Known Member

    Messages:
    1,301
    Likes Received:
    12
    Joined:
    Aug 16, 2009
    Ok, but I thought you didn't want to spend money on a tune? Yet big bucks on a fuel system?
     
  16. domhoff13

    domhoff13 New Member

    Messages:
    24
    Likes Received:
    0
    Joined:
    Nov 23, 2014
    Location:
    Pittsburgh, PA
    Thanks for the help.

    I did not want to spend money on the QH to and then try to tune it why hunting for the gremlins and then possibly find out that I had a bad maf, too small of injectors I wanted to find the issues and I did, it was going to cost more to run the injection than carb. I already have a 750 Holley on the shelf that I had on my Camaro.
     
  17. NXcoupe

    NXcoupe Well-Known Member

    Messages:
    1,301
    Likes Received:
    12
    Joined:
    Aug 16, 2009
    In my experience, you will run into just as many issues when switching over to a carb as you would if you fixed what you have. but if you have the carb mindset then do what's comfortable for you, it's your car.
     
  18. NXcoupe

    NXcoupe Well-Known Member

    Messages:
    1,301
    Likes Received:
    12
    Joined:
    Aug 16, 2009
    I personally hate carbs. I have gone to school for holley carbs, used to tune them and carters, worked for years on them knowing nothing else, but when I got my first efi engine, I never have looked back. Most issues I run into with efi are easily fixed with a little patience, research and knowledge. Carbs are good one day and suck the next. And neither can reach it's full potential without a wideband and knowledge that a dyno gives you or a drag strip. Dyno is faster and simpler imho. That's why I bought one. You are about 4.5 hours away from me and gas is cheap. just sayin.

    Edit: and you have plenty of injector for what you have. Should support upwards of 400 rwhp and a little more with the crank of the fuel pressure regulator.
     
  19. domhoff13

    domhoff13 New Member

    Messages:
    24
    Likes Received:
    0
    Joined:
    Nov 23, 2014
    Location:
    Pittsburgh, PA
    As an ME that has also has a lot of background in the racing community, I am looking to just try to go through everything logically and the injection system is hacked on this car. Oh the inj. are good for 408 bhp at 85% duty. Assuming 39 fuel psi and a bfsc of .5. So if you could explain how that translates to "upwards of 400rwhp" considering a 15% loss I am willing to listen and if you could show your work that would be great. Then factoring in if you have a load or an inertia dyno then yet again you are getting different numbers. I have an engine dyno at my disposal and I believe there are atleast 3-4 chassis dynos in about a 20 mile radius. A dyno is only good for comparing your own results to past ones. Many can go in and change calibration with the touch of a few buttons as you may know.

    As I mentioned before thank you for your help.