duballstar

What's up guys?

I recently purchased a 1991 Lexus LS400 and it was hesitating at low partial throttle and vibrating at higher highway speeds. There was no check engine light at the time of purchase, but I did not realize that it would not come on at start up either. After pulling the cluster and confirming a burnt bulb, it was replaced and I pulled codes:

Code #28 - Primary Oxygen Sensor (right bank)

Code #55 - Knock Sensor (number two)

I will be replacing the oxygen sensor first to see if by any chance it will fix both codes. I assume the knock sensor itself is probably fine, but the wiring is most likely brittle from engine heat and probably damaged. The higher speed vibration is most likely tire balancing and/or transmission mount. I can literally see the gear selector rattling when the vibration get worse (I can make it happen very severely if I try).

Few questions:

1. Right bank would be passenger side, correct?

2. Knock sensor two would be left (drivers) or right (passenger) bank?

3. You guys will probably hate this, but if you don't want to answer or want to tell me how bad of an idea it is please keep it to your self. I know this isn't the proper fix, but I've done this with older 7M motors before (no sure how the LS will react because it relies heavily on these sensors for timing adjustment). To "quick fix" the knock sensor wiring until I do my timing belt maintenance etc, could I jump the working knock sensor signal into the non working sensor wiring so the ECU input sees the working voltage for both pins? Basically splice the two ecu input together and pull signal from the working sensor.

I know it is not correct and could cause severe engine damage, but hypothetically speaking both banks should see the same knock to change timing so I would assume it will "work". If you want to let me know how dangerous and stupid of an idea it is then your an internet genius.

Thanks for the help guys and hopefully I should have some results in the upcoming weekends.

Here are some pictures for fun. I haven't posted any up yet. Exterior is pristine and the interior was good to go after replacing a few window switches, the rear drivers window motor, drivers seat belt assembly, and a few trim pieces. I also added front 6.5" Kicker speakers with Kicker cross over and tweeter and rear 6.5" Clarion 2-way speakers. All I need now is to install the new Pioneer deck I have.

duballstar

P.S. Yes that is a Jimmy hat on the ground in front of the car. I think hookers get taken to that parking lot to get wrecked. Make your guess.

duballstar

I haven't had the time to install a new oxygen sensor yet, but I've decided to go with Denso Part # 2344211 (upstream). Hopefully I will get some time this weekend to change the oil, install the new sensor, and replace the transmission mount bushing. Will update accordingly.

I also found a diagram on this site that references the engine layout / piston orientation. For the record, this would tell me CODE 55 calls for Knock Sensor Two, which would be Bank two (Passenger Side).

python

iTrader: (4)

you can tell which bank is #1 by standing on the side of ur car and looking to see which cylinder is furthest forward.
you cant just fix the wiring on the knock sensor..u cant get to it....u will need to buy both sensors...both wiring harnesses/connectors and u might as well replace ur starter while ur in there with a denso. good luck its a big job
btw ur timing belt has nothing to do with this job...so dont bother

Yamae

I suggest you to check the voltage of the O2 sensor first. This is a fairly easy job. You can check it at the diag connector.

As far as I knew, the simultaneous code #28 and #55 was caused by other reasons.

duballstar

This method doesn't make much sense to me. Standing on what side of the car? Furthest away from where you stand? Anyway, I'm sure the diagram is correct.

I wouldn't fix the wiring at the sensor, I would do it at the ECU.

The timing belt is normal maintenance that needs to be done anyway. I would be removing the intake and other accessories anyway so doing it all at once would not only give me more room to work and less stuff to remove twice. I understand the timing belt is not related.

Thanks for the help though.

duballstar

I was thinking the same thing considering both codes relate to bank two. Any resources on this manor? I've done some research and haven't come up with any similar scenarios.

LScowboyLS

keep in mind the following about O2 sensors:
(I realize some of y'all already know this)

each cylinder bank has a pre-cat and a post-cat O2 sensor

the ECU is only interested in data from the pre-cat sensors, as far as making fine adjustments to how the car runs.

the post-cat sensors are really only there so that your state or city can check emissions compliance without having to go to the expense of actually testing the exhaust fumes, which was the case back in the 1990's, you could affectionately refer to the post-cat O2 sensors as the "tattletales"

so if you don't care about the environment, and you don't live in an area with mandatory emissions testing, and you don't care that your Lexus isn't running exactly right (or that your cat is working right) then the post-cat O2 sensors are meaningless in your case.

LScowboyLS

and yes, you can cheat the signal coming from the knock sensors at the ECU input, with a little bit of thought and mimic a hardwired "no-knock" state, in order to avoid this huge job of replacing them, but keep in mind, Lexus put the knock sensors in there so that the ECU can retard you timing and make other adjustments when you are in a situation of pre-ignition, in order to protect your engine, so bypass this at your own peril!

rather than doing this, I would recommend Tom & Ray's recommended fix of some black tape on the cluster!

duballstar

In my case CODE 28 signifies it is a primary (upstream) sensor so this would not relate to my issue. I believe the secondary oxygen sensors are diagnosed as CODE 27 and 29.

It is nice to have the ability to see a "new" check engine light if one does occur. Driving around with a CEL "knowing/thinking" the code is for secondary sensor wouldn't let allow you to see a new problem arise, unless codes are pulled (ie. no prompt light).

You can also use oxygen simulators with adjustable jets for applications like this to avoid check engine lights. They work as a "spacer" or "J-bung(another option)" to direct LESS air to the sensor which in turn will produce the same resistance as gas flowing through a cat (assuming the sensor is working). NEVER use these fixes on a primary oxygen sensor, which heavily relies on a proper signal to create fuel trims.

Or you could always just wire the proper resistor in-line.

Thanks for the great info!

duballstar

The same peril of driving around with a secondary oxygen sensor CEL light on...... not as bad, but you know


Also for the record here is the diagnostic code sheet I have been referencing:

http://www.lexls.com/tutorials/intro/codereading.html

Yamae

My resources are the service manual, my actual experience and some what I heard from shop owners. In my experience, multiple codes are often caused by different reasons such as the unbalanced injections, ignition timings, half dead sensors, wiring problems, connector problems, clogged filters, too old gasoline, clogged engine oil, and sometimes the ECU itself. Lately the ratio of the ECU is getting higher due to the bad capacitors as LScowboyLS has written.

I am not a mechanic but I'm sometimes called by shop owners to come when they encounter some complicated electrical or electronics related problems. I am not good at handling mechanical tools but I have different electric/electronics related equipments and these are certainly useful to help them as a volunteer. Sometimes a spectrum analyzer is needed to find the root cause.

Anyway, if I were you, I would check those sensors first to judge they are working properly or not. A O2 sensor generates DC voltage swinging between almost 0 to nearly 1V.The cycle time is more than 1 second at the idle and you can check it using a simple circuit tester very easily. To check the knock sensor precisely you need an oscilloscope but without it, you can cheat the ECU by the method you have written at your 1st post.

Inform me the results above and I will give you a next step to be done as I do for shop owners.

duballstar

Thanks for the response. I appreciate the offer, but I think I've got it under control. I'm mainly posting this thread to provide knowledge of this specific code set for future reference. Like I stated, I didn't see many similar scenarios during my research.

I'm going to replace the transmission bushing and change the oil this service time regardless. While I'm in there I will remove the oxygen sensor, check resistance and proceed from there.

If the resistance is out of spec I will replace the sensor, clear the codes and see what comes back. Hopefully this will take care of both codes, but I doubt it. If the knock codes continues to register I will jump the ECU inputs.

If the sensor tests to be good I will return the new sensor and most likely start trouble shooting the fuel system. Come to think of it I will probably replace the fuel filter while I'm in there. I've also heard the fuel filter in the tank (strainer) could need replacing. I've owned many old cars where this strainer gets clogged due to bad gas sitting in a tank for extended periods of time.

Will report back with updates. Thanks for all the input and advice.

LScowboyLS

if you haven't done the ECU capacitors, you are kind of pissing in the wind, as this is a known problem, kind of like the first thing you should have already done!

It really does correct 80-90% of driveability and intermittent problems - and you *will* be doing them, they are dying due to a design flaw - I had to learn this myself the hard way, after wasting months chasing issues and codes around the car!!

duballstar

What were the symptoms you experienced when these units failed?

Where can I source the capacitors? I have a tuner that sockets ecu (like Hondata and Nistune) that could most likely source commercially.

The proper diagnostic would be a visual inspection I assume and replace accordinlgy? I would most likely do all of them while I'm in there.

Did your ECU throw the same codes (28, 55)?

Why would I be pissing in the wind if I pulled the oxygen sensor to confirm if it is faulty or not? That seems like a good first step to me.

Thank you for the help.