1991 1.9L MAF Sensor | Ford Escort Owners Association (FEOA)

1991 1.9L MAF Sensor

Discussion in '2nd Gen 1991-1996 1.9L SOHC' started by Magzbro92, Nov 7, 2018.

  1. Magzbro92

    Magzbro92 FEOA Member

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    So after months of tinkering and playing with things, I finally solved some of my 91 LX's issues, slapped a new HEGO sensor on, and got a new MAF sensor with the housing, as the CEL codes were indicating those were the issues, and unplugging the MAF sensor made it idle out rather smooth compared to what it was.

    Im not 100% if these videos will link properly but...

    With the new MAF sensor installed and plugged in it has an awful surging to it, and the engine stalls:
    https://cdn.discordapp.com/attachments/344350441552871425/509709877568864257/video.mov

    With the MAF sensor unplugged it runs lean/rich but has a fairly stable idle:
    https://cdn.discordapp.com/attachments/344350441552871425/509709934040973312/video.mov


    I'm kind of at wit's end here and am not sure if this sensor is faulty, or if I need to reset something with the EDIS module, or if there's even a wiring issue. The KOEO test code it gave e was for MAF sensor voltage below minimum.
  2. Joey_Twowagons

    Joey_Twowagons FEOA Member

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    For starters, it looks like you have a first generation IAC on that engine, which might be incompatible.
    When the MAF is unplugged, the car is probably going into "limp home" mode, and just holding the IAC open to a certain idle point.

    By the way, that is a very clean engine bay.
    denisond3 likes this.
  3. Magzbro92

    Magzbro92 FEOA Member

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    I’m not sure what you mean by 1st gen exactly, most of the 91~93 model 1.9s I’ve seen have a similar looking IAC, but mine is a September 90 built model and it would t surprise me to see Ford putting older parts on from the factory. My issue is I’m hesitant to drive it without the MAF sensor using the preset air rate setting, but I’m completely at a loss about what needs adjusting or replacing.
  4. Joey_Twowagons

    Joey_Twowagons FEOA Member

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    The first generation Escort 1.9 FI engines have a screw together IAC like what yours appears to be, while my 1992 Escort has the non-screw type with the connector pointing in a different direction.

    But according to the Rockauto site, the 1991 uses the earlier type of IAC. Seems strange, since the first generation ended in 1990, and second started in 1991.
  5. denisond3

    denisond3 Moderator Staff Member

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    I havent gotten into any 1st gen Escorts, but on my 91LXs (both made in the calendar/production year of 1990)have seen the type with screws holding it together, which seems the same as the later first gen Escorts. I have replaced both of them, due to the problem of the car wanting me to put my foot slightly down on the gas for them to fire up quickly. I put on an IAC from a 92 or 93 that I had lying around, but it didnt make any difference. (The fix for both cars was to glue a slice of shim stock (razor blade) between the casting on the throttle body and the arm of the throttle rod). I figured the early 2nd gens maybe used an earlier rev of the 'tuning tabl' in the computer.
    Later I resused the two IAC's from the 91s when one of my newer Escorts showed symptoms of a sticky IACV. I didnt notice any change in operation, except the stickiness was gone; so they are still in place on those Escorts, both mid 2nd gen ones.
    zzyzzx and Pizzaman5000 like this.
  6. LariRudi

    LariRudi FEOA Donator

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    I think you've prob got this resolved by now, thanks to previous posters, but for the record, check your VIN; if the 10th digit is an "L", then it's a 1990, but if it's an "M", then it's a 1991. Having a build date of Sep 90 makes we REALLY believe that it's a 1991, as the new models most always come out in the Fall of the previous year, making me believe it's a 1991 that was built in Sep '90?????

    Good luck,

    LarryR
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  7. denisond3

    denisond3 Moderator Staff Member

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    Glad to hear from you again LariRudi!
  8. Benlightnd

    Benlightnd FEOA Donator

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    I expect you've figured this out by now but just in case. When you unplugged the MAF,
    the PCM went into open loop which means it's running on preset parameters in the PCM
    rather than considering signals from the sensors. That's why it smoothed out.
    Question becomes which sensor is causing the problem. The IAT is know for this kind
    of issue. Inside them is a small round metal plate that is connected to the shaft and either blocks the air flow or allows more air flow to increase the idle speed. The PCM controls this based on the engines temperature.
    When the IAT is the cause of idle surge, it's normally caused by the metal plate breaking loose from the shaft inside the IAT. When that happens, the PCM can not control the idle
    air flow. The metal plate floats back and forth causing erratic air flow at idle and causing
    idle surge similar to what your seeing.
    This is a mechanical failure and not controlled by the PCM. SO, unplugging the MAF
    would not correct the idle surge.
    IF the IAT is now responsible, then what is ?
    You have to consider what might be affected by unplugging the MAF and sending the
    engine into open loop. On an OBD1 engine, there are only a couple of other sensors to
    think about. O2 and coolant temp.
    IF it were an O2 sensor, you would likely be seeing fault codes to indicate and issue
    with that sensor. You didn't mention seeing those codes so we can discount that
    possibility. That leaves the coolant temp sensor.
    I've replace the coolant temp sensor in my 93 a couple of time for doing something very
    similar to what your seeing. You can check your to see if it's bad before you replace it.
    Simply use an ohm meter and check the resistance across the sensor and see if it's in
    specs. It's a tight fit to get in there but it can be done. Mine have been way out of spec
    each time and replacing them will fix the problem. Unfortunately, the one's I'm buying
    don't last very long. I'm going to have to change brands.
    Anyway, I hope you've already fixed this and all is good. IF not, hear is some food for
    thought.
    Have a great day and good luck with your project
    Magzbro92, zzyzzx and denisond3 like this.
  9. marclar

    marclar Moderator Staff Member

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    you can get a 93+ maf too. the only difference is the 93+ has a larger higher flow housing.
  10. Joey_Twowagons

    Joey_Twowagons FEOA Member

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    If one installed the bigger '93 up MAF on a '91 or '92 with no other changes, would the car run properly?

    What advantages would be gained? I assume the increased size would only be of benefit at high rpm full throttle conditions, when the FI system is in open loop.

    I'm asking because I want to know if it is worthwhile to get one of the '93+ MAFs next time I see one at the junkyard.
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  11. denisond3

    denisond3 Moderator Staff Member

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    I didnt know they were different sizes. I have not taken a close look at any of the MAF's I have had off. Usually I just leave them in the air filter assembly.
  12. Joey_Twowagons

    Joey_Twowagons FEOA Member

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    I just checked Rockauto. They say 1991-93 are the same, 1994-5 are a different part. Interestingly they also list the latter part for a Mazda B3000, which is a heck of a lot bigger engine.
  13. Benlightnd

    Benlightnd FEOA Donator

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    I'm asking because I want to know if it is worthwhile to get one of the '93+ MAFs next time I see one at the junkyard

    There are other posts on here about this subject and other folks who have tried this. Do
    a search and see what results they realized.
    My thoughts are simple. The 1.9's intake design is not conducive to increased air flow.
    The porting in the head is restrictive. The intake valves are too small. The pistons crown
    is not designed to created improved air / fuel mix like higher horsepower engines are.
    I doubt a larger throttle body would hurt anything but I equally doubt it would improve
    anything. Too many other factors come into play.
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  14. Intuit

    Intuit FEOA Member

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    Seems like a large vacuum leak. It would be pulling in air from a source that bypasses the sensor.

    The other thing to check is the Idle Air Control solenoid.

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