86 Prelude o2 sensor

Love reading the ECU in these things- so easy to find and figure out.
Anyway, after the PGM-FI light comes on my ecu tells me it's a bad
master O2 sensor. I bought one although the Autozone fellow said two
were recommended. I was lookin' around in my Haynes manual and can't
find where the second one IS. Anybody know? I'm thinking the master is
the one right up front sticking out of the exhaust manifold shroud
(which I just tried to take off to give me easier access to the sensor-
rusted bolts made that a screaming nightmare- gotta go buy myself a
deep socket wrench), is that the master? Is it really necessary to
replace them both at the same time?

Thanks,
Bill

 

a 1986 model would be an OBD-I which only used ONE O2 sensor,ahead of the
catalytic(on the manifold).OBD-II and two-sensor use did not begin until
1996,for 4-inline motors.

On OBD-II,the 2nd O2 sensor was to monitor the catalytic's
effectiveness,the front sensor controlled the fuel input to the motor.

 

Please be specific when posting here. Which 1986 Prelude do
you have?

If it has a second one, it should be downstream of the
catalytic converter.
By internet reports, it pays to use /only/ a genuine Honda
sensor. If you have to keep the Autozone one, and it does
not seem to work right, consider buying an OEM one at
https://www.automedicsupply.com .

Try soaking rusty, subject to heat cycling and exhaust gases
bolts with the penetrating oil "PB Blaster." It is amazing
stuff. It costs about $6 a can at Autozone, Wal-Mart, and
the like.

I replaced all those exhaust shroud bolts on my 91 Civic
when I pre-emptively replaced the oxygen sensor.

I trust you borrowed (at no charge) an oxygen sensor wrench
from Autozone.

 

I was thinking along these lines, too. But
www.automedicsupply.com indicates some 86 Preludes have two
sensors. Also, for 1988-1990 Preludes, two sensors are shown
at
http://media.honda.co.uk/car/owner/media/manuals/PreludeManual/62sf100/6-142.pdfandhttp://media.honda.co.uk/car/owner/media/manuals/PreludeManual/62sf100/6-121.pdfNeither of these two sensors are downstream of the catconverter. (So my first post was off on this point.)See also the two sensors (both in the exhaust manifold) inan 89 Prelude athttp://www.hondaautomotiveparts.com/auto/jsp/mws/prddisplay.jsp?inputstate=5&catcgry1=Prelude&catcgry2=1989&catcgry3=2DR+2.0SI&catcgry4=KA4AT&catcgry5=EXHAUST+MANIFOLDThis site provides more ambiguity for the 1986:http://replacement.autopartswarehouse.com/parts/autopartswarehouse/wizard.jsp?year=1986&make=HO&model=PRE-SI-001&part=Oxygen%20Sensor&dp=trueSo I think there's a bit more puzzle to solve here. I am notsure the Autozone guy is wrong yet.At any rate the OP should be able to use the drawings aboveto quickly determine if he needs one or two.

 

I was told a failed emissions test on my last '87 Accord was due to a bad O2
sensor... so I picked up a replacement... and spent an hour trying to figure out
where the thing one. It wasn't where the manual showed it to be. I even got
under the car packing a cordless phone with a local dealership's service manager
on the other end, telling me where to look, to no avail.

I finally stopped in at another dealership, hoping someone could actually look
and find it for me; every source I checked insisted that there HAD to be one...

The first guy I talked to, I explained the steps I'd been through... he said
outright, the 86-89 generation was when Honda just started putting O2 sensors
in, and a lot of those cars, especially the carb'd ones, simply didn't have it.

So it's very possible that despite what every other source says, your '86
Prelude may simply have just the one sensor...

 

You never totally know whats gonna be in a certain car.. They sometimes
change stuff mid year. A 2nd sensor should be fairly easy to spot if he
can
get under the car. Should be back of the cat.. Many/most of the 86-89
carb engines also have the O2 sensor. My 89 with a carb has one. It's
needed for the feedback carb. But like you say, it wouldn't really
surprise
me if his only had one. It could go either way.
MK

 

I have indeed noticed this on occasion.

My links got all mudged. If anyone has the time, take a look
at

http://media.honda.co.uk/car/owner/media/manuals/PreludeManual/62sf100/6-121.pdf
(page 2)

and

http://www.hondaautomotiveparts.com/auto/jsp/mws/prddisplay.jsp?inputstate=5&catcgry1=Prelude&catcgry2=1989&catcgry3=2DR+2.0SI&catcgry4=KA4AT&catcgry5=EXHAUST+MANIFOLD

Note the /two/ O2 sensors are /both/ in the exhaust
manifold.

Dunno why.

 

Thanks for all the excellent information (mine's a 2.0si, for
completeness). I definitely know it's not on the exhaust manifold as I
got a good look at that clambering all over the car trying to get the
last stuck bolt (gotta get that blaster stuff). As soon as I get my
hands on my ramps and creep I'll go looking underneath and see what I
can find.

Thanks,

 

Don't even get me started on mid-model-year changes...

My first car was a 1980 Mazda GLC. When the (dual-solenoid mechanical) voltage
regulator went, I tried to find a new one... all the parts catalogs listed eiter
another mechnanical (single-solenoid) unit, or a replacement electronic unit.
Neither worked properly. An astute dealership parts clerk finally found me the
right one when I brought the old one in... where the others ran around $35, the
proper one could only be had from a dealer, for $110(!!!) Seems it was one of
those infamous mid-model-year changes that ended up in only a few of the 1980s.

I lucked out and found one at a wrecker, from a car that had been recetly
written off. Beauty part is, the regulator was practically brand-new - it had
been replaced only a few weeks before the car was killed. $25!

 

Good deal!
I can't think of any reason why a inline 4 cyl. motor would use a second O2
sensor,prior to OBD-II's monitoring of the catalytic.

I've heard of V-engines using them,one for each bank of cylinders.
They mount them on the exhaust manifold so they heat up quicker and have
less lag than a sensor mounted far down by the catalytic underneath the
car.That's why the Integras had double-walled A pipes,to retain exhaust
heat better for the cat and it's sensors.

 

You don't have one. Dual O2 sensors came along about 1994-1996, with the
advent of OBD-II.

You have only one oxygen sensor, and it's probably a single-wire one at
that.

 

the 88 prelude si has dual sensors, one each side of the upper manifold
casting. both single wire.

http://www.hondaautomotiveparts.com/auto/jsp/mws/catimgs/13sf10_d13.gif

#'s 14 & 15 on the right.

 

The OP's car is an eighty-SIX, not an '88. The '86 has only one sensor.

 

i'm just pointing out that not all two-sensor cars are obdcII. obdcII
is sensor before and /after/ the cat, which is not the configuration
here.