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.
IT'S FIXED! THE PING IS GONE!!!
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!
LONG Version of STORY with TECH DISCUSSION:
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!
RERERENCE PAGES:
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...
http://www.usnaaaa.com/pingisgone.pdf
NOTES ON REMOVING & REPLACING THE ACT:
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.
THE ACT MUST BE INDEXED!!!:
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.
NEW ECT FIXED MY COLD IDLE:
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.
SUMMARY:
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
what a difference that makes eh?
