Just the other day I was leaving the woods with a load of firewood in my 94 F-150 4X4 300-6, took off down the highway, everything was going fine until I let off the gas going down a hill and all of a sudden the check engine light popped on. I was only a couple of miles from home so I kept going, got to the bottom of the hill, got back on the gas and then the light went out. So I started thinking, ok the truck is just having a little fit. I started to down shift for my driveway, and the light came on again. I checked all the normal stuff, oil, anitfreeze, and everything was good, so I figure it has to be a sensor. Over driving it the last couple of days I have noticed that when the engine is cold the light won't come on, only when everything is warmed up, and then only when I let off the gas or it is at idle it will pop on, step on the gas and the light goes out after a couple of seconds. I am thinking O2 sensor, but don't know, and can't get the truck into the shop unitl late next week. Any ideas??? HELP PLEASE!!!! P.S. the motor has 150,000 miles on it and I replaced the O2 sensor about 50,000 miles ago. Thanks Paul

 

Get a paperclip & pull the codes:
http://www.broncodata.com/tech/codes.htm

 

Here are the codes that I got.
113-Intake Air Tempuerature (IAT) circuit open/below -40 deg. F
173- Right HEGO indicates rich
179-Adaptive Fuel lean limit reached at part throttle, right side rich.
Now what does this mean???? O2 sensor?? What else??? Thanks Paul

 

[updated:LAST EDITED ON 04-Jan-03 AT 04:25 PM (EST)]Usually these codes are sent as something upstream in the system is the cause. I would get similar codes on an EEC-IV Escort and it turned out the MAF (Mass Air Flow) Sensor was bad. So the system was compensating for the eroneous signal the MAF was sending to the computer by enriching the fuel/air mixture and thus giving the indicated codes (mine was a pulse injector width code and the O2 sensor indicating a rich mix). I "easter egged" it and replaced the O2 sensor and cleaned out the injectors figuring the codes were telling me these were bad. That wasn't the case. It was only after I accidently left the MAF unplugged that the symptoms went away. My point is the actual problem may not show up in the codes.

From your codes it sounds like you're intake temp sensor may be at least partly at fault, as it is telling the computer it's open(usually a fail safe condition), and the computer is adjusting the fuel mix to compensate. From the codes it appears the condition is only affecting the "right hand side" (I think this is the #1-3 cyl on the 6... correct me if I'm wrong). Why it would only do it to the right side is odd, since the temp should be from a single source. Then again you may have a faulty O2 sensor on the #4-6 exhaust manifoldt and both the 4-6 and 1-3 sides are running rich but not showing it in the codes.

Don't you just love these computers and sensors? Try seeing if you can keep them cleared or read them as soon as you can when the check engine light comes back on. You may not get all of the same codes and could help you pin-point the source.
Hope that didn't confuse you too much. I tend to ramble.

-Kerry

 

>Why it would only do it to the right side is
>odd, since the temp should be from a single source. Then
>again you may have a faulty O2 sensor on the #4-6 exhaust
>manifoldt and both the 4-6 and 1-3 sides are running rich
>but not showing it in the codes.

On my 94 there is only one O2 sensor. It is located on the passager side, at the Y pipe that connects cylinders 1-3 and 4-6.

 

Until MAF, there was only 1 HEGO, so all the codes that were used referred to the R side, even though trucks don't have 2 HEGOs. Just ignore that - it doesn't refer to the engine banks or even the injector banks. It refers to the ONE oxygen sensor, but the code numbers are the same as used for the R HEGO on vehicles with 2.

 

So it is the O2 sensor?

 

I guess it helps to own an FI 300, then I'd know about the one O2 sensor. I do stand by my assessment that it's not the O2 sensor as you had a failure code in the air inlet temp sensor. Before doing anything, I'd take a good look at the temp sensor and make sure it's clean around it and the connector is doing fine. Then I'd check the actual sensor out before replacing it. If it's fine, check the O2. Check the inlet hose for obstructions.

I can't think of anything upstream of the temp sensor that would cause it to give a failure code.

Hope that points you in the right direction.

-Kerry

 

I've had to run codes down several times and I agree with Pilkington. One bad condition can send a bunch of erroneous secondary codes. I think of all of the sensors, if its an O2 sensor, the computer will tell you that one. The manuals tell you how to test the sensors with an ohmeter to determine if they are faulty. MAF is an easy one to start with, use pins to probe the wires.

 

Stephens
His engine is speed-density (MAP). 4.9Ls didn't go MAF until '96; their last year. :-X23

I agree with kspilkington - just because you see a code referencing a specific sensor, it doesn't necessarily mean there's anything wrong with that sensor. It just means something is causing that sensor to give an unexpected reading, but not necessarily a fault WITHIN that sensor. HEGOs don't often go bad.

 

Ok, Ok... I understand about the difference in air flow sensing... he's got a temp sensing flaw. Is there a sensor in his intake that senses this or is this part of HEGO? Just trying to boost my knowledge level, for the most part.

-Kerry

 

The ACT (air charge temp aka IAT) sensor, ECT (engine coolant temp) sensor, & temp gauge sensor are the only OE temperature sensors on that truck (unless it has the E4OD). The ACT has a delicate thermocouple that CAN be damaged or coated with oil residue, but they're fairly reliable. I'd check the ACT wiring first, and only pull the ACT if the wiring tests good. Haynes tells how to test all the sensors.

 

I would just replace the ACT. This really isn't just throwing parts at the problem, as I have seen these fail before. I just did one on my girlfriend's Escort yesterday, and that really woke the car up. Besides, they are cheap, like $12-14. And they do get coated with crap, mostly from the PCV valve.

Jared

 

>I would just replace the ACT. This really isn't just
>throwing parts at the problem, as I have seen these fail
>before. I just did one on my girlfriend's Escort yesterday,
>and that really woke the car up. Besides, they are cheap,
>like $12-14. And they do get coated with crap, mostly from
>the PCV valve.
>
>Jared

Heck of alot cheaper than a MAP sensor for an Escort... that one cost me around $200 rebuilt! Then I traded it off the same day I fixed it for the Exploder....

Thanks for the infor Steve/Jared... oh yeah, I'm the one who's not having the problem. Well now I know

-Kerry

 

Next question, where is the ACT(IAT) sensor?? I found a sensor that is in the intake tube going to the #1 cylinder. Could this be what I am looking for?? Thanks for all your help guys!!!!