Air/fuel mixture March 12, 2005, 02:09:42 AM First, whats the purpose of the hole in front of the upper intake on a 5.0? Its covered with a black plastic piece that has some type of seal under it to make it airtight. Anyways, last December I made a trip up to Seattle and got a decent 28mpg on that drive. A couple days later I drove back and got around 18. Traffic and weather were pretty much the same so everything there was even. Ever since, I'm unable to get above 18mpg on complete freeway tanks of gas. Outside of the ordinary things to look for, would that hole in the upper intake cause a problem like this? Around that time I was messing with it because the seal isn't holding and the piece is starting to hang off. I'm guessing that its sucking in a bit more air than it'd like to through the throttle body because of the obvious hole in the intake which leads me to believe that the sensors will try to make up for the extra oxygen by injecting additional fuel. Am I off base or somewhat close to the potential problem? I'd check for codes but iirc, autozone no longer reads codes for free which is a slight nuisance....and I thought speed density didn't meter the air/fuel content coming out of the exhaust and correct it, but rather drew in enough air/fuel based on fixed numbers based on the rpm's...so wouldn't such a problem run lean if anything? Other than a quick fuel economy drop, the car still runs great, idles fine, etc Quote Selected
Re: Air/fuel mixture Reply #1 – March 12, 2005, 02:32:08 AM If you are talking about the air plenum right behind the a/c compressor. The end of the plenum has a what looks like a big freeze plug in it. The plastic piece is just to make it look better. Quote Selected
Re: Air/fuel mixture Reply #2 – March 12, 2005, 05:24:36 AM Quote from: slamedcatIf you are talking about the air plenum right behind the a/c compressor. The end of the plenum has a what looks like a big freeze plug in it. The plastic piece is just to make it look better.Yep what slamedcat said.....The Cobra intakes don't have anything on them.... Quote Selected
Re: Air/fuel mixture Reply #3 – March 12, 2005, 05:46:16 AM Quote from: Seek...and I thought speed density didn't meter the air/fuel content coming out of the exhaust and correct it, but rather drew in enough air/fuel based on fixed numbers based on the rpm's...so wouldn't such a problem run lean if anything? Other than a quick fuel economy drop, the car still runs great, idles fine, etcYou're a little off on the SD system... It makes assumptions on how much air is entering the engine by RPMs, throttle opening(TPS), and how much vacspooge is on the MAP sensor. It then corrects A/F ratio by reading the o2 sensors and makes adjustments to compensate.Poor fuel milage can be from bad o2, engine temp(ECT), or MAP, sensors. Would also be a good idea to check for vacspooge leaks especially to the MAP. Also occasionaly the F/P regulator sticks and causes too much pressure which can cause a over rich cond the EEC can't correct.You really should get a code reader on it to get a starting point... Quote Selected
Re: Air/fuel mixture Reply #4 – March 12, 2005, 01:11:33 PM Wait, you are right, its just for looks. I've seen other intakes have no piece there but didn't know if there was anything behind the SO intake. I know I need a code reader...was that thread on places to buy them/recommended readers here or on the old board? Quote Selected
Re: Air/fuel mixture Reply #5 – March 12, 2005, 03:35:05 PM picked up an Equus digital code reader and for some reason on the first run with the engine on, it said the car was a 6 cylinder and on the second, it didn't check the cylinder number at all - just gave me the go ahead to push the accelerator to the floorAnyways, got codes 33 (EGR valve not opening properly), 44 (Thermactor air system fault), and 94 (Air diverter solenoid circuit fault) both times. Quote Selected
Re: Air/fuel mixture Reply #6 – March 12, 2005, 04:25:42 PM speed speed density also uses a bap sensor. its the same as the map sensor but is used to measure air density outside of the engine instead of in the manifold like the map sensor does. the computer compares the 2 signals. the maf meter replaces the need for a bap. anyway. not that any of that helps you. if the intakes freezer plug is letting air by thats definetly not a good thing. Quote Selected
Re: Air/fuel mixture Reply #7 – March 12, 2005, 05:12:45 PM Quote from: shame302speed speed density also uses a bap sensor. its the same as the map sensor but is used to measure air density outside of the engine instead of in the manifold like the map sensor does. the computer compares the 2 signals. the maf meter replaces the need for a bap. anyway. not that any of that helps you. if the intakes freezer plug is letting air by thats definetly not a good thing.actually, you got the map and bap backwardsmap is used on speed density, it measures the vaspoogee in the manifoldbap measures something with the air, so the computer can fully determine the amount of air its getting, in addition to the MAF Quote Selected
Re: Air/fuel mixture Reply #8 – March 12, 2005, 06:43:27 PM cleaned the egr system and throttle body, vacuum's fine, cleared codes and re-read...still getting code 33 :disappoinat least it read it as an 8 cylinder Quote Selected
Re: Air/fuel mixture Reply #10 – March 13, 2005, 10:16:31 AM Its barametric pressure (BAP). I would check the 12v ref to those sensors that the codes indicated. I believe all of them share the same scource for that 12v and also check all youre ground wires. If they are green where the connector is crimped on cut it off and crimp and solder on a new connector. There is an orange one on the engine(injector) harness grounds to the back of the head. Each o2 sensor has a ground to the head. drivers side of block to fire wall and neg batt term to block and neg batt term to inner fender and one sticking out of a harness by passenger headlight to the radiator support or header panel whatever you call it. Quote Selected
Re: Air/fuel mixture Reply #11 – March 13, 2005, 11:26:45 AM Quote from: Seekcleaned the egr system and throttle body, vacuum's fine, cleared codes and re-read...still getting code 33 :disappoinat least it read it as an 8 cylinderFor code 33 the Ford Emissions Diagonstics Manual, says to apply vacspooge to the egr valve while monitoring resistance of the sensor. Should gradually decrease from no more than 5500 ohms to no less than 100 ohms. If thats OK, check the vac lines and EVR(regulator) solenoid.At any rate I can't see a minor EGR problem causing a big drop in milage.... Quote Selected
1988 Thunderbird Sport, Former 4.6 DOHC T56 conversion project. 
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