Why is the burn weak since the f/a is still normal????????? You may have a proper stoichiometric ratio but once it's mixed with EGR it is NOT STOICHIOMETRIC any more, at least to the motor and the guy who invented physics. You have mixed burned molecules along with unburned, the unburned will not be as close to each other as before and the mix WILL BE TILTED. It will NOT burn as easy as before when pure f/a and nothing else. Dilution affects EFFECTIVE f/a ratio to where it will not act like before. I say EFFECTIVE because textbook f/a does not apply here, the motor is smart enough to know the difference even if people ain't. When the burn is patchy, parts of the mixture don't ignite but pass out the exhaust. The PCM will pick up on that. It will also try to correct based on the patchy mixture which will have varying amounts of oxygen in it. Throw a laptop onto car and you can watch it. What is the definition of "stoichiometric"? 14.7/1 a/f ratio. Of what use is that? It's the amount of air required to burn every last bit of fuel. That's assuming it's WELL MIXED AND PROPERLY SPREAD OUT so ignition source can set it off and so it can stay burning until most of it is gone. When you mixed burned product with that, you CHANGED IT, it will not perform as before. By the way the 10% I picked because the usual "cruise" amount or so. If you think about the extremely small amount of f/a needed for idle, then a stuck EGR could very easily be 30% of idle mixture.
the burn is weak because, as you stated, the A/F is more spread out in the entire mixture. the burnable mixture is still stoich though because the exhaust gas is now inert, just like the nitrogen in the air. it goes in, and comes right back out, unchanged. the amount of burnable air/fuel that is pulled into the engine is still 14.7:1. you will have the right amount of air to burn every last bit of fuel, but because its spread out more due to the exhaust gas taking up room in the combustion chamber, it wont burn effectivily.
after thinking about it, i think we are both trying to say the same thing. while the actual amount of air and fuel would be 14.7:1, the exhaust gases spreads them to far apart to burn effectivly, resulting in a weak burn/incomplete burn/misfire.
Oh this is getting so dangerous....Are we saying here that Ford cannot now make a gauge that can hit the red zone on its' own??? Also, on the post above you clearly stated that the PCM does NOT control the gauge, you really need to make up your mind. Either it does or it doesn't..........if the gauge were anywhere accurate, it would have already been in the red zone. My point also is that once they hooked up the PCM to that gauge please don't tell me that they won't use that ability for other, shadier things, such as the ability to make you think motor is normal temp when it's not. It's just not in the corporate mantra anymore. I have bought car after car from these people and watched a steady stream of things happen that in my view are calculated to do nothing but separate customers from their cash in as large quantities as possible.
I never said the gauge couldnt hit the red zone on its own, just that the sending units were poorly calibrated. i presume ford saw engines from the contour/cougar/ZX2 overheat without the gauge ever hitting the red zone. so as a fail safe, they hooked the PCM up to the gauge and programmed it to pull the needle all the way to the red zone, IF the PCMs sensor saw dangerous temps. im sure that if you were to heat up the gauge sending unit enough it would pull the needle into the red zone, problem is, the temp needed to do that is aparantly higher than what is safe for engines.
i suspect the PCM is only hooked up to one side of the gauge to pull it to the red zone if needed, however i wouldnt be suprised if ford had hooked it up to the gauge fully in order to keep the needle in the middle all the time either.
ps, would you please answer in just one post. double posting is technically against forum rules, and its rather anoying.
