so iv got an 89 bronco 302 aod i bought the truck a few years ago and have just started working on it recently the problem i have is that after driving an hour my check engine light comes on . i get codes 41 hego switching not detected or alwalys lean. 52 power steering press im not worried bout that one its the 41 and . ive replaced my oxygen sensor and checked the wiring going to it iv got 12v going down on one which is connected to the heater wire for the hego sensor the other wire goes to the pcm and then to ground the last one is my signal wire . if i have the ignition on engine off a have 4 volts at that wire coming from the pcm . when its running and hot i have about 1 volt but dosent change unless i rev up the engine then itl bounce from 1 to .50 volts . so basically the hego isnt switching when the truck is idling is this normal? but anyways i cant get rid of this code 41 when i do the koer test evn after resetting the computer . ive done a full tune up the truck plugs wires cap rotor pcv valve set the timing . the truck also barley passed the e test it was high on the hc hydrocarbons and it seems to have a bit of a high idle around 850 900 but i cant find a vacume leak. ive been on this problem over a week now so im stumped i duno what to do now . so any help would be greatly appreciated thnxs

 

Use a handheld vacuum pump/gauge to test each vacuum line/component. Suspect each one is bad, test to disprove that theory. ANY leak in the exhaust system can throw a code 41. Fix those items first, the code 41 will probably disappear.

 

i went out and rechecked my vacume lines took them all right off the engine and checked each one with the vac guage i previously ckecked them with the smoker and found nothing ive also checked my egr valve to see if it was open at all it wasent and ive swaped in another map sensor from my daily driver but its still idling around 800 to 900 rpm that seems way to hight compaered to my other trucks but there both stick i canty see that making a difference though ive also cleaned my throttle body and iac.

 

Fuel pressure may be a bit low. Might be worth checking. If not already done I would be inclined to change the fuel filter.

 

Thanks for the details of what you have done so far. I had a devil of a time tracking down various vacuum leaks on my '92 F350 w/5.8L engine when I acquired it last fall. After replacing various reservoirs and vacuum lines I still had an idle higher than I wanted I eventually tracked it down to a bad gasket between the upper and lower intake. It passed the "spray carb cleaner" test with flying color, but after replacing it when I was rerouting the PCV vacuum line the idle RPM is now normal.

DTC 41 is also quite common if you have any leaks in the exhaust that is upstream or very near the O2 sensor when downstream.

 

ya im gona bring home my fule pressure guage and check it at idle and at driving conditions tomorow night . i took my torch and sprayed oxygen around the uper plenum gasket but didnt knotice any changes but as u said that dosent mean that its fine . its wierd sometimes it will idle 750 the next time will be 900 even up too a thousand so im really starting to lean towards sometype of a leak somewhere. and i just resealed my exhaust system at work. but i can sometimes hear the smalest of a leak on the rightside bank where the manifold ataches to the y pipe its super small but i guess that could cause it. thnxs for the help by the way.

 

You are welcome. I hope our input helps you fix your problem.

 

so i checked my fuel press its between 35 and 40 so that seems okay what i did do is put on another iac which caused my idle to drop to 750 ish and idle more where it should be which then droped my voltage from the o2 sensor while idling hot from, the 1 volt are to the below .5 v area so from my constant lean reading to a rich reading but it still seems to get stuck on the lean though . i manually gave the engine egr while idling and nothing happend whatsoever i know the valve did open i watched it. so maybe someone has welded the egr tube shut? i also stuck my vac guage on the vac line going to the egr valve and goosed the engine no vacuum . if my egr valve isnt working would this give me lean problem?

 

No it would not. The EGR is only active during part throttle cruise conditions. The PCM sends a signal to the EVR which modulates vacuum to the EGR valve.

 

but obviously i do have a problem though it should have bogged when i gave it egr on idle right?

 

The engine should have done something, usually an increase in RPM because of the vacuum leak you induced by opening the EGR valve.

 

well i dont know what else to check i was monitering mo o2 voltage and it seems to be staying up around the 1 volt area and dosent wana move much . thats with the truck idling hot. i poped the tube off the bottom of the egr valve and there is exhaust gas coming through while its running so obviously that isnt pluged. im totally lost on this now and i dont know what to do.

 

wait i almost failed my e test on hc which is unburnt fuel right ? and when i monitor my o2 sensor its around 1 v area most of the time. that also reads rich right? then why am i getting a code for lean conditions ?? 41

 

Someone could have put a pop can or something between the egr and the plenium to disable the egr system or the holes plugged. I fought the whole code 41 deal until i bought a non bosch sensor. Bought a ngk brand and all has been well for a few years now

 

The O2 sensor switches between approximately 0 and 1 volt. If you are using a DVM the meter will not capture a true reading on a standard factory style O2 sensor. It will require an oscilloscope. A leak in the exhaust system near the O2 sensor can "trick" the O2 sensor into thinking there is a lean condition, the PCM will start dumping in more fuel to compensate. Here is a link for an overview of how the O2 sensor is supposed to work: Ford Fuel Injection Oxygen Sensor (HEGO)