Re: 92 f150 exhaust question
Shoe Salesman wrote:
> I think you got it backwards, can't pump air into the manifold above the O2
> in closed loop, it would read too much O2. It will go upstream when cold,
> then downstream when hot. Sounds like it could be a CA only thing too. I
> think I would have a muffler shop weld the pipe on it, or better yet, get
> the correct part.
Jim has it right. The air is diverted to the cats during warmup to help light off
the cats quicker, then diverted to the manifolds to help burn off unburned HCs before
the exhaust reaches the cats.
For a long time 3\4 ton and up trucks were exempt from some emissions regs.(It was
that way in the 70s, through at least much of the 80s and possibly very early 90s).
It's likely that his pipe was intended for an F-250 or better vehicle without the
Thermactor system. I've seen the 300CID\4.9L in F-250s many times, not sure about
heavier duty trucks. (Thus the melding of aftermarket part numbers)
Take care of that motor in your truck and you will own it for quite a while. The
hose you are referring to was probably steel down to the cat originally. They tend to
rust off just above the converter. Someone probably "repaired" it with hose.(hopefully
silicone). To do it "right" you would have to have someone weld a nipple into it to
attach a replacement steel pipe to (Pipe is about $30). You could do the nipple and
existing hose also, but the hose usually burns off at the cat in a short while.
If you're in an area that doesn't do emissions testing, you could remove the
Thermactor pump and related plumbing, but on a 92 it would probably cause codes to be
set in the ECM and the EEC_IV system to default into "limp" mode. (Mr Warman can
likely elaborate on that if it's true, I don't remember).
On a personal note, it's a shame that Ford had to stop producing the 300\4.9. I'm told
that they couldn't make it meet emissions in later years. That motor was a real
workhorse. Given a choice between a 300 and a 302 (4.9 and 5.0L) in a pickup truck, I
would take the 300 hands down. (And I'm a big fan of V-8 Ford motors).
You could just about drag your house down the street for 200K miles, give the motor
a valve job, and drag it another 200K, with an F-150 equipped with a 300cid\4.9L six
and a 3 speed manual trans. That's stretching it a bit I know, but it conveys the
reliability and torque of that motor. They were tough little suckers with lots of
torque that would run for miles and miles..
Hope this helps, Tom Adkins