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MAF sensor troubles.

Discussion in 'Stock 1991 - 1994 Explorers' started by Zinith, October 25, 2017.

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    1. Zinith

      Zinith New Member

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      Okay, so I'm on my 3rd MAF sensor, and the problem still isn't resolved.
      When I'm driving down the road, it seems to run just fine. Getting started from a stop it feels quite hesitant, and it bogs down a little too. But if I give it more gas, it picks up and goes just fine.

      The problem is when its sitting idle, it surges in RPM. And when its in gear, it jerks back and forth due to the surging. It still surges when its in park, but doesn't jerk back and forth.

      Can anyone suggest something for me to do?

      What are ways I can do to troubleshoot this, & or the OBD1 computer.

      Winter is coming in my area and I've noticed it acts much worse the colder it is. And I fear it might cause a wreck at some point. Especially on Ice.
       
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    3. Rhett

      Rhett Let Them Eat Cake Elite Explorer

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      If you're on your 3rd MAF sensor, I'd say the problem is elsewhere.

      Have you checked / cleaned your Idle Air Controller (IAC)? Throttle Position Sensor (TPS)?
      Coolant Temp Sensor?
       
    4. Zinith

      Zinith New Member

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      Ive got a new IAC valve (Is this what your talking about? Or is what your talking about something different?), and a new TPS.

      The last time I checked the codes, it was throwing the code that says "The MAF sensor is or was out of range"(i think its 157, if i remember correctly). And I remember it also throwing the code for the ECT sensor every now and then.


      Also, something to add that I've forgot.
      The only way its able to drive, is with the MAF sensor unconnected.
      All the stuff I described is when its unconnected.
      When it is connected It stalls shortly after its connected.
       
    5. Rhett

      Rhett Let Them Eat Cake Elite Explorer

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      Code 157 is mass air sensor voltage low or grounded...that is a clue that tells me your problem is in the wiring...possibly.

      Since you have hooked up three (3) different MAF sensors, and still the problem -- I'd take a good long look at the wiring TO the MAF. Check for chafing, and other damage. Do you have a voltmeter? I would also search here, for the voltages each wire is supposed to carry. This can get you started:
      http://www.explorerforum.com/forums/index.php?threads/maf-sensor-test-procedure.263750/
       
    6. Rhett

      Rhett Let Them Eat Cake Elite Explorer

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      By the way, I'd change the engine coolant temp sensor (ECT) also. That can do wonders sometimes.
       
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    7. timtimtimajim

      timtimtimajim Elite Explorer

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      x2 on this. I was having a rough idle issue when warm until I changed the ECT sensor
       
    8. Centaurious

      Centaurious Active Member

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      Also check the air tube between the MAF housing and the throttle body for torn seals or holes worn in it causing air leaks.
       
    9. Dragon90815

      Dragon90815 93 XL Restore Elite Explorer

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      code 157 low voltage or grounded on pin C of MAF. test pin C with connector disconnected and key on Engine off it should read about 5 V. (mines is 4.2)(If not then follow wire to ECM. I think it's pin 60.)
       
    10. luvmonterey

      luvmonterey Member

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      I was having all kinds of problems with my MAF and replaced it. Still had problems. Turns out it was the EEC relay, a $10 part that takes 10 seconds to replace. As a test, you can swap in the A/C relay, which has the same specs. I had problems with engine surge and it was caused by the idle air control valve. You can pull it and try to clean it with carb cleaner, but it may need to be replaced. I also had issues with rough idle. It was caused by a combination of things; vacuumed leaks around my air intake tube seals, bad EGR, and ECT sensor. It was a frustrating process, but I was finally able to get the issue resolved.
       
    11. Dragon90815

      Dragon90815 93 XL Restore Elite Explorer

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      traced signal of pin c to ECM no change in voltage. open ECM (ECM-IV) and found capacitor exploded. 10uf 63v (there is only one of them) R/R. runs good no code 157 and 998.
       
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    12. Zinith

      Zinith New Member

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      Alright, so its winter now, and it brings even more confusion. NOW it runs just fine with the MAF sensor connected (my guess is because its so bloody cold outside).
      The last thing I did to my explorer, was take off and completely clean the throttle body. But that day, it was like 40 degrees F and raining outside with the wind chill making it feel like 10.
      Since that day in (I think end of October, beginning of November) I haven't done anything at all to it.
      That same day I tried to unhook the ECT sensor (so i could test it) but it was positioned to where I couldn't even grab it. I even made extension probes for my multimeter with a bent and sanded down paper clip. I don't remember the readings it was giving me, but im certain I remember them being off. And unless by some grace of god, the only way it seems I'm going to be able to get that out is by taking off my entire intake manifold. (Which prob should happen anyways, since it needs cleaned reeeeally bad.)

      Btw, is it normal for the inside of the intake manifold to look like its coated inside with a layer of oil? Cuz it doesn't seem right to me.

      I also tried my best to follow the wires back to the computer (theres like two spots I cant see at all) from the MAF sensor and they all look perfectly fine. I redone all of my grounds in my engine bay and the one right next to the computer. I even brushed the pins on the ECM off with a wire brush.
       
    13. TDG

      TDG Elite Explorer

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      Every one that I have seen the inside of looked like that and they ran without issue - if it's not using any more oil than normal I would not worry about it.

      If you were unable to disconnect the ECT sensor to measure the resistance then yes, the readings will be off when you back probe it because the electronicals of the PCM have some resistance as well. The most ideal location for testing would be at the PCM harness itself under the passenger side footwell kick panel (mine comes off with 2 screws and christmas tree fastener) Pin 7 (LG/R) is the ECT sensor feed and Pin 46 (GY/R) is the signal return for that sensor as well as a number of other sensors (IAT / O2 / TPS / DPFE etc) If you back probe those 2 pins and measure key on voltage it should be in the neighborhood of 3.something depending on outside temperature (mine was 3.17 on a 50ish degree morning) starting the engine and letting it warm up should show the voltage gradually drop to around .61 volts if you have a stock thermostat (190ish) and a little higher for colder thermostats.

      If you absolutely must have resistance readings you could disconnect the PCM harness at the unit and take measurements but that will potentially reset any learned states and it's best not to disconnect things that do not need disconnecting.
       
    14. Roadrunner777

      Roadrunner777 Well-Known Member

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      Oil in the intake is coming from blowback, worn rings and/or seals. It's coming through that little hose that comes off the oil filler. The only problem this could cause would be IAC gumming up, which you have replaced. Just FYI, you are further along the right path, IMHO.
       
    15. Rhett

      Rhett Let Them Eat Cake Elite Explorer

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      The inside of mine is usually that way. I did remove it and clean it last summer, as a part of fixing my clogged up EGR port. It ran fine that way for many years though. I think the EGR trucks (93.5-94) are usually dirtier in the upper intake, more so than the 91-92-93.5's that I've seen. Maybe one of you guys can design a catch can for us. heh.

      You can change your ECT without removing the upper intake manifold -- all you need to remove is the throttle body (as well as the shroud/fan assembly). That should allow you to put a wrench on the ECT. In my case one of the wires to the ECT was damaged. I cut off the offending section, soldered and heat shrinked a new wire. If you do this, be sure your wires do not contact the throttle body mechanism as it moves back and forth.
       

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