i have a 98 f-150 with the 5.4...it had a rough idle to it so i ran a code scanner and it said bad o2 sensors...so i changed the front 2 sensors but it still idles rough and has the cel on...so i took it uptown and the o2 sensors are reading 0 volts and the guy said that my pcm might be messed up or some wires might be bad....what i was wondering was if i put an edge evo on it would it adjust the fuel mixture so it would run normal at idle???

 

If you have a PCM or wiring harness issue, no programmer in the world is going to fix that.

The first thing I would check is the harness coming from the O2 sensors to make sure that they are (1) plugged in and (2) not burnt or damaged. I know you just changed them, but never hurts to be sure. Check as much of the harness as possible for signs of abrasion or melting, especially around exhaust components and machined edges like the back of the head.

If a sensor is reading 0 Volts, it is an indication of a grossly lean condition. Since this is also associated with a rough idle, I'd be looking for a vacuum leak somewhere around the intake manifold or throttle body. Also check the vacuum hoses and PCV valve for leaks.

If you have a small propane torch, you can use it to help find the source of a leak. Turn it on LOW without lighting it and pass the tip around any mating surfaces and around vacuum hoses. Any change in idle speed will indicate a leak. Do this in short bursts so as not to build up a large amount of unburned propane under the hood and DEFINITELY do this OUTSIDE!

I used to also use a garden hose to help find small vacuum leaks, but if the leak is large enough you could actually ingest enough water to hydro-lock the engine. Not good.

Hope this helps.

Bill

 

so if it is vacuum leak it would only run rough at idle?? cuz mine drops to like 700 rpm and vibrates the truck but then when your on the gas or driving it runs and sounds fine...i'll check to see if i can find a leak and thanks for your help

 

BTW - no during that propane diagnostic procedure. Beer would be ok, though.

 

Yes, a vacuum leak will be most noticable at idle. While it could cause some issue during cruise, the amount of vacuum in the manifold combined with increased volume of fuel and airflow will drasticly minimize the effects of a vacuum leak. Where there would be cause for concern is if the leak is isolated to a particular cylinder (ie. manifold gasket or vacuum port situated over a single intake port) it can cause a lean condition that could damage that cylinder.

Again, this is going entirely on the assumption you have a vacuum leak. Could be a zillion other things.

Good luck.

Bill

 

ok gotcha...one more quick question...ik the programmer won't fix the pcm or wateva is wrong with the truck...but will it make it idle smooth even with wateva is wrong still being wrong??

 

weshova,

That's like asking a doctor if an enema is going to fix a tingling sensation in the leg. I don't know. It could, although I doubt it.

I'd be more comfortable knowing what exactly was wrong first. As a mechanic for 15 years, I never believed in throwing parts a problem to solve it. I did everything I could to understand the problem and isolate the cause. I know it's not much help, but it's all I can offer.

Bill

 

thanx for all your help...ik that my thinking wasn't the best solution but i was thinkin about getting a programmer anywayz and didn't want to spend a lot of fix my truck if the programmer would clear up the idle...but i think my truck is goin to the shop 2day or 2marra to see exactly wat is wrong with it...thanx again...wes

 

Best of luck, bro. I hope it is some thing simple and CHEAP!

Bill

 

Any word yet on what happened to the truck? Got that curiosity thing going!

 

Sorry truck hasn't moved yet i guess...lol me being in college i don't have much say of what goes on at home...but they have been busy with harvest and other breakdowns...after discussing it though i think im going to hook it back up to a buddies code reader and pry change the other 2 02 sensors and see what happens

 

the other 2 just read that the cats are working-phil

 

thats what i thought....but i read on the internet that some vehicles use all 4 o2 sensors and all three repair shops told me that all 4 must be working for the computer and truck to operate correctly...but then again they pry just want my money

 

Well - this is the internet too! Who ya gonna believe, them or us?

simple:

front two = PCM A/F ratio control

rear two = cat health monitoring only

 

alright i was at home and ran the code scanner on my truck...i got the error code P1000...i guess it means something with the OBD II failing to do a drive cycle...any clarification to this?? cause i have no idea what that means...also im pre sure the back 2 o2 sensors are junk cause they are reading 0 mV while the front two are around 779...i was also looking for the map range but i couldn't fine it on the scanner...do you think the MAP sensor could be a possible problem?? i have no idea but i was talkin to a guy in the bar and he said his truck did the same thing as mine and it was that