Pinging... Finally Gone !!!

Discussion in '1994 - 1995 Specific Tech' started by MLC Stang, Jul 8, 2003.

  1. All,

    I'm sure this subject title will pull in a lot of viewers! I have been reading every post on pinging and its possible causes/fixes on this board and other Mustang forums for the past several months in an effort to stop my stock '95 GT from pinging.


    SHORT Version of STORY:
    After spending a lot of money on the usual suspects for causing pinging (ignition system and fuel system), a lousy $45.00 sensor was the cause all along! Which one? The ACT (Air Charge Temperature) sensor that screws into the air inlet ducting between the MAF and the throttle body. NO CODES, no nothing from the PCM computer relating to the ACT, but it was definitely the problem. New ACT is installed and my pinging is gone!

    Like I said, I've thrown a lot of money at my ignition and fuel systems to try to solve this problem, but to no avail… the car still pinged at anything over 3/4 throttle runs when it got to about 4,000 RPM and above. My engine is box stock and has just turned over 80K miles. It's always been a strong runner, but its been pinging for about the last several thousand miles of that.

    I did it all: new plugs and wires, new TFI ignition module, new PIP module (Hall effects sensor) in the distributor, new fuel pump, fuel filter, and fuel pressure regulator, ran lots of fuel injector cleaner through it, and ran the top engine carbon deposit cleaner from Run-Rite through it with their drip feeder. Still pinged! Then I started to notice that it pinged a lot worse when it was really hot and humid outside, not when the outside air was cooler. A lot of posts on this forum said the same thing… that their pinging is really bad in hot weather. I could get all over it on the way in to work in the morning when it was cooler, but on the way home in the high 80s to mid 90s it pinged like crazy at anything from 3/4 throttle to full throttle runs. The pinging would come in at around 4 grand and stay unless I backed off, which I always did. No fun at all!

    I'm an experienced carburetor tuner and I know full well the purpose of the choke on a carburetor. I also know that the ACT and ECT (Engine Coolant Temperature) sensors combine to perform the function that the choke used to. Between the two of them, they give the PCM computer enough information about engine temperature and outside air temperature to properly modify the air/fuel ratio for correct combustion under all conditions… IF everything is working right.

    The problem lies in these sensors. They are both thermistors (thermal transistors) whose resistance varies with temperature. They output a voltage signal to the PCM that is inversely proportional to the temperature of the medium that it is immersed in. The ACT for incoming air temp and the ECT for engine coolant temp.

    So why didn't my computer store a trouble code for the ACT if mine was bad??? Good question. Here's my take on that. (I'm an ME so I did some extra checking with an EE at work to get more educated on thermistors.) I know from my EEC-IV reference manual, that the PCM computer only checks to see if the ACT is sending a voltage signal that is within the range of normal values for that sensor, about 0.3 volts to 3.7 volts. If the PCM receives any signal in that range it says "fine" the ACT is "working" and I'll accept its input. But, the PCM has no way of knowing if the ACT is actually sending the CORRECT voltage for the actual temperature of the incoming air. When the ACT is new, it probably is. But, the thermal properties of thermistors can degrade over time with use. That means at some point, it can actually be sending a voltage that is just a little bit off of the correct voltage for the incoming air temp at any given moment. At 86 degrees F, the ACT output voltage should be 2.62 volts. At 104 degrees F the voltage should be 2.16 volts. That's only 0.46 volts difference to represent a temp diff of 18 degrees! The hotter it gets the less difference in voltage exists between respective air temps. The graph is a curve, not a straight line. As such, you can see how close the tolerances are on this device. A little bit off is a lot!

    I have taken several pages out of "Ford Fuel Injection & Electronic Engine Control" by Charles Probst, SAE, combined them into one PDF file, and posted them on my web site for you all to read. BTW this book is a 450 page "Bible" of EEC-IV electronic engine controls. The pages I posted have to do with the ACT and ECT, how they work, and how to test them. I hope they are of some value to you. Here's the link...

    First, disconnect your negative battery terminal before removing/replacing any engine control sensor. This clears any trouble codes that may exist and tells the computer to start using the input from the new sensor(s) once its turned back on. Remember that it will take 5 or 10 minutes of driving for the computer to relearn its inputs after you do this. So do some conservative driving for the first few minutes and allow some time for it to settle out. Removing the original ACT is not easy since it is usually really crusted in place. It is actually threaded and unscrews from the air duct. It is not a push/pull fit. You need a huge open end wrench or crescent wrench to do it. (I think it was a 1-incher.) But, there's a trick. First unscrew and remove the hose clamp that secures the ACT in the rubber sleeve in the air duct. Then get a channel lock or similar adjustable pliers with some teeth on it and hold the rubber sleeve while you start to unscrew the ACT sensor to break it free of the sleeve. If you don't hold the sleeve with something you will never get it out and end up damaging the mounting sleeve on the air duct. You can also take a very small screwdriver and slide it in between the ACT body threads and the rubber sleeve to break the years-old crusty seal a bit, then do the above to unscrew it and remove it.

    You must install the replacement ACT so that the stream of air inside the air inlet ducting is free to pass directly over the thermistor portion of the ACT. The thermistor element is housed in the U-shaped tip of the ACT body. It must be installed so that the stream of air can pass straight through the U-shaped housing tip. If installed sideways (90 degrees out) the air stream will hit the side of the U-shaped housing and not pass directly over the thermistor. That's bad! You will see what I mean when you have one in your hands. Just pay attention to the alignment of that U-shaped housing in relation to the top of the ACT so that you know it is indexed properly by looking only at the top once you start screwing it into the air duct. There are two flat surfaces on the top sides of the ACT connector. The U is parallel to one of them. That's the one to use to know its indexed right. Mark it with something before you install the ACT.

    Just a note to mention that I replaced my ECT several months ago. I noticed that my cold idle was a bit funky compared to my idle once the engine warmed up. Same story… had to be the fuel injection equivalent of a choke, i.e. the ECT, but again NO CODES! I replaced the ECT anyway, and my cold idle problem was gone.

    I can't promise you that running out and replacing your ACT and/or ECT is going to give you the same results that I got. But if you have the exact same symptoms that I do it may be worth a try. Having chased this rabbit for several months and finally finding a fix, I decided I'd better give back some of the experience I received from so many of you by reading this forum. Oh, almost forgot… I'm running regular unleaded now.

    Ford Part Numbers:

    ACT sensor: F32Z-12A697-C (2003 list price $49.27)
    ECT sensor: F2AZ-12A648-A (2002 list price ~ $45.00)

    Good luck, hope this helps somebody out.

    MLC Stang
  2. Nice! One of the mechanics at work who's been working on the cop cars for about 20 years was trying to explain some sensor(s) to me and he wasn't doing the best job, I just nodded as he rambled. Yours was a much better explanation.

    Now it makes way more sense! I'm so trying that! Now I'm all excited. If this doesn't work, new heads it is then and thats 2 more sensors to add to the bunch that I've replaced within the past couple months. . .
  3. Wow that an excellent article. Really great! :nice:
  4. Nice post. Wow only one reply. Thanks for all the info!
  5. Damn...Thats about the only thing i didn't change trying to get mine to stop...i did clean it o few times though, still no luck..

    Super write-up...!!!!with P/Ns to boot...I love it...
  6. damn, how long did that take you write up?
  7. I just replaced mine after reading that. I swapped it with a Niehoff FF134P from Checker for $13.99. I'll know tommorow if it did anything.

    BTW, Whats with that Run-Rite thing? I goto their site and I can't get any info on where to get it done or where to buy any profucts or get any pricing. How did you go about getting yours done?
  8. Great post :spot:
    I will replace mine and see if it works.
  9. RIO5.0,

    Yes, I did try cleaning my old ACT before replacing it.

    I figured if you can clean the MAF element, you can clean the thermistor element on the end of the ACT. It wasn't really all that dirty, but I cleaned it with rubbing alcohol and a Q-tip, and put it back in. It didn't help, the car still pinged. As soon as I put the new ACT in, the pinging was gone.

    I'm convinced that my EE friend at work was right, a thermistor's thermal properties degrade over time.


    It only took me about 15 minutes to write that all up, but its what I do for a living, so I've had lots of practice. I'm an ME, and I work as a technical writer. I spend all day writing installation and operation manuals, maintenance manauls, service and troubleshooting manuals, etc. Used to do it in the microcomputer industry, now I do it in the broadband communications industry.


    I bought the Run-Rite product from Pep Boys. However, they do NOT sell the drip feed vacuum bottle you need to connect to your intake and drip the stuff into your engine.

    I called Run-Rite tech support and told them I needed one and convinced them I was capable of performing the procedure correctly. They sold me one direct. They apparently are concerned that someone who doesn't know what they are doing will screw something up. Doesn't make sense to me to sell the fluid at Pep Boys but not the installation tool. Go figure.

    MLC Stang
  10. Gonna give it a try myself. Thanks for the info! :nice:
  11. Awesome! :nice:

    This "could" be my nitrous pinging woes that "sometimes" occurs when the track warms up. Interesting. Well written too!

    Tad cheaper to try then those O2 sensors as well and easier to GET to. (no garage) :rolleyes:

    Maybe just maybe this will allow me to get back to some good timing settings. Running 6 or 7 degrees of timing SUCKS!
  12. Mine went away after I installed a 255 pump and pro-m MAF, different strokes I suppose.
  13. After driving around today in the 105* + heat today, I was pleased to see that changing the ACT sensor made a pretty big difference!

    However, it still has a slight pinging above 4000rpm where before it was REALLY bad above 3k. I think I'm gonna see what happens when I get the heads cleaned out. In the meantime, I'm happy with my power band being down low with the 5 degree timing and shifting around town at 3500rpm untill I can afford to get that work done.
  14. Zero Signal,

    It semed to take about a day of driving under various conditions (medium acceleration to hard acceleration) for the PCM computer to learn to use my new ACT sensor's input signals.

    PS) Temps have been in the high 80s and low 90s in Atlanta for the past few days, and still no pinging. Hope it stays that way!
  15. :worship: wow thats some good info!

  16. OK, I was playing with my act-iat whatever you want to call it. When my car hot I checked the resistance and it was at 9 ohms for the sensor. Well, I have the old one off of my car sitting around so I check it and it's at 20 ohms. I know that the resistance get lower when it gets hotter. So I start my car with the new one that is installed in the car and it dies when I shift it in to gear. I then unplug the sensor and plug in the old one w/o installing is and start the car and it doesn't die when I shift it into gear. I did this many times and had the same results. Now with the old sensor sitting in the engine compartment and it's 100* out side, I checked the resistance and it was at 13ohms so I tried it and it hesitated when I shifted it into drive. Then I cooled the sensor off and got it up to 18 ohms and it didn't die when I shifted it in to gear.

    Am I crazy or does this look like the problem?

    Tonight I went and bought some 22ohms resistors and wired it into the plug and left the sensor unplugged it drove great tonight and had a lot of power. I wont be able to see how it acts in the heat tomorrow.
  17. sweet - more needed info on electrical sensors ( i hate them )

    thanks man
  18. Any new input from the guys that recently tried this?? Any followups?
  19. Well, it's about F 97 out side right now and I drove the car for about 30 min and stopped for a few min and went to the store. I started it back up and shifted it in to gear and it didn't die. On the way home I drove it really hard and got no pinging and it ran really strong. Once I got home I stopped the engine and started it again and shifted it and it didn't die. It cost me $1.00 for a 5 pack of resistors part # 271-1128. Next I'm going to try to find an adjustable resistor so I can fine tune where I want it.
  20. Changed mine today. It did nothing for me.