I have an 02 f350 7.3 power stroke...Yesterday I noticed the outside temp was reading wrong,it was jumping from 67 to 86 to 92 back to 67..Temp was prob around 90 with high humidity and my a/c was on..So I got to where I was going and when I restarted my truck to go home the fuel guage dropped to empty(I just fueled the day before) and fuel light came on and outside temp still wrong on the overhead digital display...Are these two things related???Stopped the truck restarted it and fuel reads correctly again....Went out today and fuel light back on and on empty...Outside temp wrong again,a/c is on .....I disconnected the batteries when I got home to "reset the system"if there is such thing,fuel guage working but ouside temp wrong..Ideas???Where is the outside temp sensor ?could condensation be running onto the sensor and throwing off my temp guage?Just strange that both these things happened at the same time......I dont think its a fuse or they wouldnt work at all...Help....I should mention all the other guages work correctly...

 

Ok, so the fuel guage now appears to be working, I replaced fuel cap and d/c batteries and reconnected and has been working since.Dont really know if its fixed for good but whatever... Now onto the outside ambient temp guage reading wrong. Im going to guess that these are just two problems that happened on the same day and are unrelated.I found the ambient air sensor in front of the tranny cooler hanging from its wire not in its bracket. I took it off the connector and blew warm air intoit and reconnected it, it read 110 degrees which seemed about right.. Took it for a ride and within 2 minutes it read 67 degrees. Its 88 out. So im gonna assume the sensor is bad and replace ot unless someone else here has another idea or something else to check first.I think ill just try a junk yard to find one cause Im sure ford charges 100 bucks or so for it ..

 

Sounds like a ground is loose. My aftermarket temp gauges read inaccurately if the ground wire is not connecting well. The fact that the fuel gauge was off also leads me to think this.

 

If it is a ground where should i start to look? In the cab? Engine compartment?Its a possibility for sure. I hate throwing money at things to eliminate possibilities...I did find a aftemarket sensor for 30 bucks on the web.. So maybe ill order it to rule it out after i look for a loose ground...

 

Do you have the Haynes Repair Manual? It is in Chapter 12. If you can wait until tomorrow I will look it up for you.

 

Ive got one

 

so Im at work and the only thing I was able to check is the battery terminals for corrosion..The drivers side positive had a ton of corrosion on it under the red plastic cover..I cleaned it up and started it up and fuel is reading correctly..Was this a fluke or could this be the problem??Also the ambient air temp was reading correctly but I wont believe that until I drive some...But could corrosion on the positive terminal cause strange guage or electrical behaviors???

 

I have a Haynes manual but I can't find the reference to the overhead outside temp guage. My outside temp always reads about 20 degrees less than actual. I replaced the sensor and the results stayed the same. A bad ground sounds like it may be the answer.

Is there a ground wire specific to this sensor? Where is it located? Or, do I just check both battery grounds?

 

rtazz, I'm having the same issues. Did disconnecting and reconnecting the battery terminals solve your issue? I'd really rather not drop the tank again to check my fuel sending unit.

 

no it did not. I no longer have that truck but I just gave up on it. Wasnt going to drop the tank. Just lived with it.

 

MattM, I’m having the same issue on my 2002. Rtazz sold his rig before solving the problem. I’m curious if you solved it?

 

Good question. I don't think I dropped my tank again, but I also remember the fuel sending unit appearing to work correctly at the dash when I posted this. I usually leave the overhead display on MPG rather than outside temp, so it's not something I frequently notice. I just went outside to check, and it appears to be displaying the correct temperature. That being said, it was below freezing, so having the a/c on would not have been an issue. The engine was also off.

I do not know if having the a/c on affects it. I also don't remember if I actually did anything to fix it - I may find next summer that it's off by 20 degrees again. At least I have one data point. If it is off, I probably won't spend the effort tracking down why, at least not anytime soon.

What I can tell you is that if you're also having the dashboard fuel level always indicating empty, then yes, they are related, and you'll need to replace the fuel sending unit (I think I found one at a junkyard). Do that first, then see if it fixes your temperature reading. I think I also had some symptoms where the fuel level indicator was not necessarily ALWAYS showing empty, but I could tell it was jittery at times. Treat empty and jittery as the same symptom, checking for electrical continuity as well.

You can drop the tank to access the unit using car jacks (I definitely recommend doing that with an empty tank - a syphon can help here), you can remove the bed, or you can do a little bit of both where you drop the tank a little and lift up that corner of the bed, which saves you some alignment difficulty when reattaching the tank. I'm not mechanic, but I was still able to do it myself with maybe 1 other person helping as a spotter.

I think I also remember trying to fix my sender with epoxy putty, having it work for a bit, then the fix starting to fail, and replacing it with the junkyard part, so that may have been the storyline. Sorry my memory on this issue isn't better.

Good luck.

 

FWIW,
I have noticed IAT is always way lower than the true Ambient.

have not looked into the why, suspicion it has to do with where the sensor is placed, Venturi effect? causing a Temperature drop?

I have one snapshop showing it close to Ambient, but this was on a 100*F day and I was pushing hard pulling 8k trailer load.


100*F outside temp




an average day, don't recall the exact outside temp, but wasn't wearing any jackets for sure. Just a T-Shirt

 

Thank you for the replies to this older thread.

@mattm_ my fuel gauge is definitely intermittent and it is correlated with my OAT reading incorrectly low. When the OAT reads correctly, the fuel gauge is working. When I notice the OAT suddenly drop about 20Fish the fuel gauge drops out soon after….then at some point it all starts working again. The early thought that it’s possibly a grounding issue seemed like the best hypothesis. I was hoping you may have proven that one way or another.

You mention the sending unit having a fault and dragging down the OAT with it. I suppose there is a delay in the fuel gauge reading like the computer is sampling so it’s not all over the place. That might account for the lag between what I see with the OAT and the fuel gauge. So you think you replaced the sending unit and it fixed everything? Just wanted to confirm before I go that route. Mine was replaced about 7 years ago when I got bad fuel that clogged everything and detonated my fuel pump.

Thanks so much for your time!

Doug

p.s. My rig is a stock 2002 f350 7.3 crew cab SRW