Volvo RWD 700 Forum

INDEX FOR 10/2025(CURRENT) INDEX FOR 7/2008 700 INDEX

[<<]  [>>]


THREADED THREADED EXPANDED FLAT PRINT ALL
MESSAGES IN THIS THREAD




  REPLY TO THIS MESSAGE Replies to this message will be emailed.    PRINT   SAVE 

O2 Sensor stuck at ~0.85v and failing for NOx (long) 700 1989

posted by  Bean on  Thu Oct 14 17:41 CST 2004
Author: [PROFILE] [EVERY POST] [THREADS] [BEST POSTS] RSS Feed     [IGNORE ALL POSTS]
last visit: Mon Aug 30 03:53 CST 2010
[RELATED]

1989 765T, w/69k mile '94 B230FT engine, LH2.2

Took the car for it's safety/emissions check today and it failed for high Nox.

HC Read: 1.75 Limit: 2.25
CO Read: 21.08 Limit: 23.74
Nox Read: 5.72 Limit: 3.25

I understand that NOx is formed when combustion temperatures are too high, the Nitrogen in the air combines with unused Oxygen to form the NOx.

Some background:
Car has 130k miles on chassis, the old engine cooked itself from loss of coolant through, I believe, the heater valve...bad enough that piston #1 melted. Passed emissions (old engine) in MAY 2004. Assumption: cat converter is/was doing its job in recent history. How long can an untuned engine run before killing the cat converter?

I recently finished the engine transplant (500 miles ago) and the car runs like a champ now. Upon reassembly I was very meticulous with regards to putting everything back together properly, timing is spot on. Also replaced all the vacuum hoses with Volvo hose ($$ but very high quality). I checked for vacuum leaks around the intake and most all other connections, no change in idle speed. Assuming no leaks but will dig alot deeper over the weekend.

The O2 sensor that I am currently running with was the original that was involved with the overheat, could be contaminated with coolant and oil...I should assume that it is. Anyhow, I figured since the car was running well with mileage that is comparable to my wife's '94 945T (same driving conditions) the O2 sensor was doing its job.

Today I checked the O2 sensor voltage:
* Took the car for a good 10 min highway drive
* Immediately measured sensor output voltage at home.
* Voltage reading a constant 0.85 - 0.90 volts
* Pulled and plugged vac hose from FPR (rich), no real response.
* Introduced vac leak from intake, no real response (I don't remember the numbers as they were far from what it should be.)

Now my theory/question:
If the O2 sensor voltage is at a constant ~0.85v (rich reading) this should instruct the ECU to reduce the amount of gas to be injected? Yet, the same amount of air would still be entering the engine which would make the system lean therefore causing the high NOx. Is my logic correct?

One line in the FAQ that caught my attention, the "no-switching" part describes what my sensor is doing:

"Leaking fuel pressure regulators or leaking vacuum hoses and intake gaskets often will cause a "no-switching" condition at the oxygen sensor."

I don't think that any of the above is bad but will check all of these things over the weekend as well as replace the O2 sensor with a universal Bosch (#13913 or 13953) for the Ford 5.0 V8, cheap enough for peace of mind.

What do ya'll think?

Thanks in advance for your help.
Bean
--
'80 242GT 93k, '94 945T 142k, '89 765T 69k (new '94 B230FT)








  •   REPLY TO THIS MESSAGE    PRINT   SAVE 

    O2 Sensor stuck at ~0.85v and failing for NOx (long) 700 1989

    posted by  740ATL on  Fri Oct 15 10:56 CST 2004
    Author: [PROFILE] [EVERY POST] [THREADS] [BEST POSTS] RSS Feed     [IGNORE ALL POSTS]
    last visit: Wed Nov 14 12:40 CST 2007
    [RELATED]

    Have you tried checking the O2 voltage while yanking the AMM plug connection? I know this will simulate a rich condition and force the O2 reading to the 0.8-.9 range.

    Mike








  •   REPLY TO THIS MESSAGE Replies to this message will be emailed.    PRINT   SAVE 

    O2 Sensor stuck at ~0.85v and failing for NOx (long) 700 1989

    uid 18083's pic
    posted by  lucid on  Fri Oct 15 02:24 CST 2004
    Author: [PROFILE] [EVERY POST] [THREADS] [BEST POSTS] RSS Feed     [IGNORE ALL POSTS]
    last visit: Fri Oct 24 12:31 CST 2014
    [RELATED]

    * Pulled and plugged vac hose from FPR (rich), no real response.
    * Introduced vac leak from intake, no real response (I don't remember the numbers as they were far from what it should be.)

    I know those tests are probably valid, but pulling the FPR hose only simulates (forces) a rise in pressure as with accelleration. The forced lean test is also rather "delicate", IMO.

    After you've got the new O2 sensor in, you mught want to try the following version of the same tests:

    A test of O2 sensor/ECU interaction can be made by sending simulated Full RICH and Full LEAN O2 sensor signals to the ECU, and watching for appropriate responses from the O2 sensor. This is done "Open Loop", (i.e., with the O2 sensor signal unplugged), and with Voltmeter on the O2 sensor lead. The engine and O2 sensor should be fully warmed up for this test.

    Full Rich Test: Apply a + voltage potential to the ECU Green wire. Use either the + terminal of a grounded 1.5 volt (Flashlight) battery. Or, if you have Orangutan arms, hold the ECU (green wire) terminal with one hand and put the other hand on the Battery Positive terminal. The ECU should see this as a "Rich" O2 signal and set a very lean fuel mixture. The Idle should worsen (may even stall), and the O2 sensor should respond with a correspondingly low output (.1 to .2 volts).

    Full Lean Test: Ground the Green wire going to the ECU (I use the braided ground on the valve cover). This simulated "O2 Lean" signal should result in very rich setting from the ECU . The RPMs should increase, and the O2 sensor output should rise to nearly a full 1.0 volt.

    These tests are described in the the Bosch FI & Engine Management manual (p 6-22, "Rich stop" and "Lean Stop"), for Continuous Injection (CI) K-jet, but are equally applicable to LH injection.

    --
    Bruce Young
    '93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.








    •   REPLY TO THIS MESSAGE    PRINT   SAVE 

      O2 Sensor stuck at ~0.85v and failing for NOx (long) 700 1989

      posted by  someone claiming to be swede4 on  Fri Oct 15 16:01 CST 2004 [RELATED]

      A simple way to test the O2 sensor only is to put it in a vise , hook up a voltmeter and heat it to dull red with a propane torch. By sweeping the torch back and forth across the sensor you should see the voltage generated by the sensor instantly change. If not, replace.







<< < > >>



©Jarrod Stenberg 1997-2022. All material except where indicated.


All participants agree to these terms.

Brickboard.com is not affiliated with nor sponsored by AB Volvo, Volvo Car Corporation, Volvo Cars of North America, Inc. or Ford Motor Company. Brickboard.com is a Volvo owner/enthusiast site, similar to a club, and does not intend to pose as an official Volvo site. The official Volvo site can be found here.