94 Gt 5.0 Running Horrible Plz Help

Discussion in '1994 - 1995 Specific Tech' started by Captain1997, May 30, 2014.


  1. Captain1997

    Captain1997 Member

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    Need some help!
    Got a 94 stang I just did a 5.0 swap. I'm running a complete 88 gt 5.0
    Running a 94 5.0 wire harness. And also running the 88 ECM
    I have deleted the egr and all smog items.
    Had to change distributor due to location of the module
    Used a distributor out of a 94 f150
    It starts but runs horrible. I believe it's a timing issue spent all day messing with timing and can't get it right.
    Do I need a 94 ECM?
    Do I need a mustang distributor?
    I'm totally lost help!
     
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  2. toyman

    SN Certified Technician

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    The pin outs on the ECM are different even though the connectors are the same. The site I was going to refer you to is down but you could try a google search for both ECMs.
     
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  3. Captain1997

    Captain1997 Member

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    94 running horrible update
    Purchased a new not used ECM for it it definitely runs better mid to top range but idles terrible up and down,and also when getting on it around 2500 rpm it just cuts out like you turn the key off.
    I found when it does cut out I can stab the clutch in and hit the gas it seems to pick back up and go again.
    I took the idle air control apart and cleaned it.
    The only thing i do not have hooked up is the oxygen sensors due to the fact the 88 sensors are 3 wire and the 94 is 4 wire and cannot seem to find where the knock sensor plugs in. And also running a R fan/fuel pump control box which is from the v-6.
    The oxygen sensors being unhooked shouldnt make it cut out and not idle. At least my 96 f150 still ran great when i unhooked the oxygen sensors.
    Do I really need the S Fan/fuel control box?
    Im really puzzled.
    Im going back out to look it over again see if Imissed anything.
    Im sure its something stupid.
    Any advise would be really appreciated
    Thank You
     
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  4. toyman

    SN Certified Technician

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    O2 sensors are critical for the ECU. Without that feedback the engine will run rich to be on the safe side to avoid a lean condition which could destroy the engine. It's important because at any given moment the O2 feedback lets the ECU recalculate the fuel load by adjusting the injector pulse rate which is in part being calculated based on the MAF signal for the air mass flowing into the engine. Without the O2 feedback the ECU has no way to evaluate the effective fuel requirement.

    There are no knock sensors on these models.
     
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  5. Captain1997

    Captain1997 Member

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    Ok Im lost and getting frustrated Installed a brand new ECM New Bosch O2 sensors pulled the throttle body apart Installed new gaskets cleaned the IAC installed new gasket.
    Played with the timing ended up leaving it at 12 degrees.
    Still have horrible idle Up and down all over the place.
    drive it down the road and it has plenty of power matter of fact it will break the rear tires loose in 3 gears without problem but the idle issue makes the car undriveable.
    what am I missing? Seems like a timing issue because when its idling it seems to be running very rich.
    again im running a complete 88 gt 5.0 motor in a 94 v6 car
    bought all wiring from a 94 gt 5.0 and installed it
    new 02 sensors (changed from the 88 3 wire sensors to the 94 4 wire sensors)
    swapped distributor from a f150 (because the module on the 88 gt is on the distributor and the f150 is on the fender as the 94 mustang should be)
    cleaned and installed new gaskets in the upper intake IAC and throttle body
    new plugs
    new wires
    new battery
    running just a cold air intake with out a MAF (tried plugging the MAF in and car will idle so bad it will quit)
    This was a great running motor when it was pulled out of the 88 donor
    I have checked and triple checked vacuum leaks sprayed carb cleaner on everything on the intake while it running to see if i have and vacum leaks and none found so I dont know
    I do know Im getting really frustrated with this thing!
     
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  6. toyman

    SN Certified Technician

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    Let's start with some basic understanding of the ECU and sensor input. Without the MAF the ECU has no clue as to the air mass entering the engine. Since it doesn't know this it has no way of effectively determining the fuel needs other than by feedback from the O2 sensors. This would result in erratic fuel adjustments. The point is these sensors need to be operational and within spec. What's common to these sensors is the ground return path. So make absolutely the battery to engine and engine to chassis grounds are solid. These should be at least 2 gauge cables. Next pull the codes to see what the ECU is logging. You do not need to see a CEL. Just pull the codes and report them. The TPS I'm assuming is from the 88. They were adjustable. Confirm the KOEO TPS signal is about 1v and moves smoothly to WOT at 4.7+v.
     
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  7. Captain1997

    Captain1997 Member

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    Ok haven't had a chance to pull codes check engine light is not on.
    I did install 2 very heavy ground wires from the engine to the frame and it made a world of difference!
    Now the only problem I have is it idles great without the air cleaner plugged in. MAF sensor and I'm assuming air temp sensor.
    When I plug the air cleaner in it idles real crappy


    Is the MAF sensor bad?
    Note....I'm using the v6 air cleaner so the sensors are for the v6.
    I was told the air cleaners and sensors in them are identical to the v8.
     
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  8. madspeed

    madspeed Colonel Mustard
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    88 ecu is non maf, was a mass air conversion done, if so, how?
     
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  9. Captain1997

    Captain1997 Member

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    As deceive earlier I put the 88 motor and Trans in a 94 v6 car.
    Using all 94 5.0 wiring and ECM 94 o2 sensors pin out and changed plug on TPS deleted EGR.
     
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  10. toyman

    SN Certified Technician

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    Your first post says you are using an '88 ECM. Which is it, '88 or '94, and if it's a '94 which one is it?
     
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  11. Captain1997

    Captain1997 Member

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    Decided to go with A 94 ECM and wire harness
     
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  12. toyman

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    Okay, but which one? There are 4 different ones IIRC. 2 for autos , 1 for manual and 1 for the cobra.
     
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  13. Captain1997

    Captain1997 Member

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    ECM is 94 5.0 t5 manual Trans
    Non cobra.
     
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  14. toyman

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    The ECU is new and you are sure it's a T4M0? Codes pulled yet? MAF for the '94 installed and known to be good? TPS signal voltage verified KOEO in idle position is about 1v and reference voltage is 5v back probing TPS sensor ground? Is the only issue is an idle surge and then dying?
     
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