I have a 1997 F150 4.6L and have been experiencing pinging for quite some time. It is very similar to the other descriptions that I have read on this site. I have tried a number of remedies from injector/intake cleaning, the intake gasket was recently replaced due to a coolant leak. The plugs and wires were also replaced at the same time. I have not noticed much difference since doing the gasket etc. However, I did read some time ago that cleaning the air flow sensor wires was a possible fix. Well today I cleaned the wires and in doing so I removed the small aluminum plate that is held on with 2 screws to help get to the backside of the wires also. After cleaning everything I put it back together and took it for a test drive. I was quite amazed that there was absolutely no pinging whatsoever. Upon returning I remembered that I did not put the plate back in place so I took things apart and put it back on. Out of curiosity I took it for another test drive and found that the pinging is back. Does anyone know what purpose the plate serves and if it is possible to just run without it. No doubt it is there for a purpose but why would it make such a significant difference to the pinging problem. I am guessing that the only way to get a full expanation would be to speak directly with Ford but I would be grateful if anyone could shed some light on this.

Thanks

 

clean the EGR ports.. if that doesnt fix it do an injector flush and then clean the MAF with some electronics cleaner or non residue parts cleaner

 

Did you even read his post ??

 

Good (old) F150!
.
The mass air tranfer function seems to be running on the lean side for air signal.
I would guess that letting air in thru another entrance has cooled the element enough to fool the PCM into metering a richer fuel signal to the injectors.
Air / fuel ratio changes the fuel's combustion speed in the cylinder.
When leaner than it is supposed to be, the flame speed gets faster for the same ignition advance so becomes too fast and ping is the result. This is the same thing that would happen if you could advance the ignition timing just a little to far.
As to gas octane, the flame speed is variable with air/fuel ratio over a short range in any engine so you can see these type results, at times.
This is also the same reason why there is a need to go to 93 octane with a blower because the extra cylinder pressures cause the flame speed to increase so it has to be slowed by using higher octane fuels.
As to how to handle this issue it may be as simple as replacing the air meter unless you have an aftermarket intake that is causing the lean air meter transfer function to take place.
The other way is to have a chip with the program adjusted to change the tranfer function back into the range it is supposed to work for 87 octane gas.
You may not understand all this but here is the case for it explained as simple as I can make it..

 

I dont know what the plate is for but when was the last time your fuel filter was changed?

 

yeh im curious what this "plate" really is... i have no clue... but i gave em the common ping solution.. since its a 97 im sure the EGR is gunked

 

The only stuff I have seen about it calls it a "mounting plate".

It looks like its removal could let the MAF see more air flow perhaps.
Its removal also might have let air flow through where the mounting plate was and up past the sensors in the MAF.



Possible vacuum leak fooling the MAF into thinking there is more air flow?

 

yeh but any leak after or around the MAF will cause it to almost die on idle

 

So, I take it you talked with the vacuum leak personally to provide this statement.



Don't mess with my theory. I think Im in line for a Nobel Peace prize for this.

 

With all the info you have been giving lately you have my vote!!!

great work bro.

 

lol yes i did in my dream last night... damn MAF's talk to much

 

As yet I have not cleaned the EGR ports and the fuel filter is probably a lot older than it should be. Having looked at the air flow meter picture that you posted mine is different and I am not referring to the mounting plate. The plate is actually beyond the wires at the outlet end of the venturi. An earlier reply suggested that there is possibly more air getting in with the plate removed than the meter is actually seeing but I would suspect that this would cause a more lean mixture which should be picked up by the O2 sensors. I will try cleaning the EGR ports and replacing the filter, it makes sense that restricted fuel would cause a leaner burn thus resulting in higher cylinder temperatures and ultimately the pre-ignition that I am getting. If anyone else has any ideas I would be glad to hear them.

Thanks

 

Im talking about a tiny amount of air flow across the heating element and the thermistor that would make quite a diffence to the thermistor that would not amount to a hill of beans to the air/gas ratio that the engine receives. It could also be as simple as redirecting the airflow from the heating element in a different flow pattern around the thermistor.

http://www.autoshop101.com/forms/h34.pdf

 

It is a calibrated design.
Even change the direction of air across the heated element changes the tranfer function. That's why it is calibrated.
If you think is dosn't- so be it.
Lot of people on this board have put aftermarket air intakes on and had the same effect, a CE lamp from it.

 

I agree, its calibrated to work in the environment it was engineered for. Change the air intake and you have changed the environment. Get oil or dirt on the elements and again the environment is changed. He changed the engineered environment (this plate thing) and I can only guess what exactly happened.

See sensor contamination.

http://autorepair.about.com/library/faqs/bl827d.htm

If he is referring to a backplate like the one at this link and it is removed it will make a difference.

Quote:

"Note that air passes through the tube containing the wires, and then up the shaft to the opposite side of the housing before continuing to enter the intake. This reduces airflow through the tube. If there is soot or some sort of blockage in this tube, airflow through the MAF sensor will be even lower. Since the device works by measuring a part of the net flow, restricting the part still further will reduce the readings for a given airflow. Conversely, removing the back plate will permit more air to pass over the wires for a given airflow and will result in a higher than correct reading."

http://www.fordscorpio.co.uk/maffunction.htm