Caish

Hey all,
Been all over the net chasing my mpg 12mpg sucks.
87 Renix, 4.0 AX15, 255/75/17 3" swapped 3.07 to 3.55 to account fo the larger tires. Speedo dead on accurate after gear swap. (GPS)
Replace O2 with Bosch new unit,
Multi-tester shows 7ohms between a/b (12v and ground) plus add power to it and starts to heat up. So heater is good.

Cleaned C101 twice, after first time IAC went wide open, so those hunting a high idle issue consider the C101 connection. Second time settled right into a nice idle.

Hook multi-tester to 02, key on, voltage on 02 spikes up, .15 to .2v so its getting power.
Start it up and o2 reads .350 to 3.60 till it runs a bit then settles down and floats around .310 to .360 reading between B and C.

Some youtube videos show voltages surging from 1.5 to 4 volts every few seconds.
I'm using a quailty multi-tester. not a HF one.

REading the RenixFI manual it gives only options testing heater circuit.
Of course schematic for the o2, 5v- set resistor- reads V- O2 - ground.
Now what I can't find for certain, is whats the post voltage others get when you turn the key on at the O2 on the C wire, B ground A is 12v from relay.
THen does yours actually show 1-4v spike instead of millivolt reading?

Just trying to compare to others.
of course its hard to tell its actually any different till I buy gas again and its 12mpg....
Use to get 17mpg even with the larger tires.
Been to Lund XJ site, Been to cruisers site, many forums, and many YT videos.
Learned a lot about O2 sensors and operation of them and actually generating voltage in use.
Also using old sensor, with MM on ohms, read between C and B, (signal and ground) it read about 750ohms, and if you would blow through the small hole in the end, it would start to drop in ohms, down to about 690, so they're reading a drop in oxygen levels.
Lastly also checked IAT intake was warm to the touch, about 100*F read 1667 ohms right where it should be for about that temp...

Next thing i know to do is actually pull the ECM and check wire continuity, but since its showing a post voltage when i turn the key on its getting power from the o2 circuit.

Narrowband o2 sensor charts show 3.2 is right at about 14.7:1 ratio.

cruiser54

Your O2 sensor should switch from .1 to 4.9 quite rapidly.

Use only NTK replacements.

Caish

A wideband o2 has a wide flux like that. But no Place anyone anywhere say renix o2 is a wideband.
Here is a Yt I just uploaded of mine.
https://youtu.be/zS3fDVN7cYI
.

cruiser54

I'm telling you what I see with my factory tester and the REM..........

Caish

show me a part number that corresponds with a wideband o2 for renix.
What's your o2 show on a multimeter at connector.
Because to get that high a voltage it absolutely has to be a wideband.
I've got to find the schematic for c101 so know what v wire is signal from o2 and check it there too
Be great to have a labeled test port in place of c101,

cruiser54

I'm at work now. There has to be a pin or two in one of the diagnostic plugs.....

Caish

I wish there was.
Diagnostic port only has has a pin for 12v to o2 sensor and ground.
It's pin 9 and 7 the o2 information has to come from the serial data.
I was actually thinking wiring up a serial port on a laptop and just plug it into the data pins and see what kind of data it pipes out.
Actually assume it's just hexadecimal data so not much info to be gleamed there without piping it through a program to convert to ASCII but then again it's a bit trial and error decipher the data...
Thanks.

cruiser54

Check out this link. http://cruiser54.com/?p=568

Caish

Yep seen that the other day.
Not really on my wish so few things can't be checked on renix not sure it would help.
But picked up new o2 sensor today, was using old one with out of spec heater circuit.
With new Bosch 12009 post voltage was 1.25v
Then starting and letting run started at .65x v varied a little but no large spikes on the fluke.
Then as it warmed a little more dropped to .59x then varied to .61x
These are Lambda Narrowband o2 sensors.
So it reads higher voltage with Rich condition and lean with lower voltage from .1 to .9v typically,
I think I'll order one of these plotting multi-tester/scopes this weekend.
Be good addition to the shop for testing many things.
https://www.ebay.com/itm/Digital-Han...r/362207390143

Also a set of 4 hole bosch injectors will be on the order.
THanks. for advice cruiser.
There is some missing data on Renix diagnostics in this area that needs to be worked out.
i think being able to plot out the waveform of/at the o2 sensor will go a long ways.
Addition of a wideband o2 and readout to know the stoic ratio would be helpful too.
Not real sure the antique Bendix ECM would like a wideband swinging voltage spikes.

cruiser54

I've had poor luck with Bosch O2 sensors on Renix. I prefer NTK.

werewolf19

Where would one purchase NTK?

cruiser54

It's part number 23553.

http://www.rockauto.com/en/parts/ntk...2)+sensor,5132

Also available on Amazon and O'Reilly's.

werewolf19

Thanks. I was told that you should change the o2 sensor every 50,000 miles. If so, it's time.

cruiser54

67,500 miles to be exact......

PatHenry

Is NTK the preferred brand for later years as well? (95 to be specific )

Also is there a trick or technique for getting the old one(s) out?