I picked up an 89 F250 with a 5.0/5spd. Failed TX emissions, so I took a look.

No cat, no O2 sensor. Plug for the O2 is dangling. Local genius at the gas station says some HD trucks came sans cat and sans O2. I can believe no cat, but I don't believe this truck came without an O2 sensor.

BUT- I have been sure of things in the past and been wrong- so before I go any further, I want to make sure- This truck needs an O2 sensor hooked up or it will not run right, correct?

I know a thing or two about EFI, but this is my first Ford truck. The only doubt I have is that there's no trouble code for O2 in the computer- it is reading bad MAP and bad ECT, both of which were verified with a meter and are being replaced this week sometime. I have never seen a non-antique fuel injection system without an O2 sensor. Please confirm.

 

If its EFI and has the O2 sensor wiring dangling there, then definitely hook it back up.

I bet the exhaust has been redone, and someone didn't put it back in.

 

EFI without O2 sensor = open loop. The computer is guessing as best it can but will never get close enough to pass emissions.

 

All Ford EFI trucks have O2 sensors.. and every other brand does too as far as I know.

 

I had an 04' Yamaha R1 that didn't have an o2 sensor and it was fuel injected. I'm guessing that they ran it off of a set map with TPS, RPM and inlet air temp data. It might of had a MAP sensor too but i'm not sure......

 

You need to cut a hole in the pipe & weld in a bung & put a new sensor in & hook it up , and don't take it to the local genius , like above , you will only be running in open loop , very rich.....Lew

 

Thanks for the confirmation. I was 99% sure.

Anybody know for sure about the cat?

 

Ford trucks had cats long before they were EFI so your "local genius" is batting 0 for 2 on this one.

 

Can I say "You have EFI, just not w/ ECU assisted fuel trim"?

 

If the ECU isn't going into closed loop function, courtesy of a bad ECT sensor, would it even know they (o2's) were missing? Also, "If a tree falls in a forest & no one's there to hear it .........(sorry, wrong Forum!)

Your mileage must suck! If you had Cat's, they'd probably be pooched as a result anyway! You be running rich, dude!

All this & a bad MAP to boot, & it still want's to keeps running? Either put a bullet in it, or help it out! This is gettin hard to watch! Just kiddin!

I thought prev. owners had to supply a smog cert. to transfer ownership in CA.?

 

Ah, yes, the ECU may not be looking at the O2 if the ECT is bad.... that explains no fault code for O2. Thank you!

Yes, the truck runs. Surprisingly well. I know what cats and O2 sensors do- the question was "did Ford ever make a truck without them?' and "why do I not have an O2 fault code?" The answers so far are "no" and "ECT failure". I'm satisfied. If it's hard to watch, I'm sorry.

TX is short for Texas, not California.

 

Thanks Paul..... were there no exceptions for HD trucks?

 

Both Mercedes and VW sold cars with mechanical and semi-electronic fuel injection. I know VW was doing it up until 1990 or so, not sure about Merc. However, I don't know of any domestics selling anything other than full EFI recently. My 88 VW Fox had a big circular metal plate (about 6" across) that moved an arm up and down depending on how much air was going past it into the engine. The other end of the arm moved a window that changed how much fuel flowed through slits to the injectors (can't remember if it was single point or multi point). It also had an electrical widget on the side but I can't remember what it did. It wasn't a full ECU but it did some extra tuning for the fuel trim with the help of an O2 sensor. The O2 sensor version was only sold for a couple of years before they went full electronic.

 

Oh, "that" TX!

I just said that because bad Map's can sometimes be pretty tough on driveability! Once again, not entering closed loop may have been a blessing! I think that keeps you in perpetual warm up mode!

I'm wonderin if someone could "temporarily" set aside some drivability problems, (like if they cropped up in the middle of a trip), by disconnecting the ECT, forceing/ keeping the ECU out of closed loop function. Sure, your mpg would take a hit, but you'd get home! That would be a great trick wouldn't it? Comments?

 

No.. not on domestic gasoline powered EFI vehicles.