1995 Infiniti Q45 Missing heated oxygen sensors

[gescho]

Good morning Infiniti gurus,

I have an interesting one for you. I happen to be a guy who has been a Datsun/Nissan enthusiast for decades and like to tamper with machinery like the magnificent 1996 Q45. I have recently came upon one at a used car dealership and could'n believe my luck. It is one of only a very few here in South Africa. Have downloaded the service manual, and am sorting out things as I go along. There is however one problem I cannot solve by myself and I need your advice.

The heated oxygen sensors on the exhaust manifold on both banks are simply missing and the holes plugged solid. The connector that is supposed to connect it to the ECM is just hanging loose in the engine compartment. I am not going to be able to fit new ones as the holes are blocked, so my thinking is to fool the computer calculating the right amount of fuel to inject by putting a voltage on the connector, around 1 Volt is what I think will make the engine run lean, and alternating it with 0 Volt to make it run rich.

Any ideas are very welcome!!

gescho

[sx moneypit]

First off,welcome to NICO!
I think the best thing for you to do is to replace the O2 sensors, it will be a whole lot easier than what you want to do.






-Ben

[Rex]

Moved to Q45 sub-forum

[gescho]

Thanx sx moneypit, you are of course right and that is my thinking as well. Problem is the holes where the O2 sensors are to go into are welded with no more thread to screw the sensors in. So that is asking for two new manifolds as well, which in turn is asking for an engine pull and all that goes with it. And as I intend to use the lady for sunday afternoon drives only, I figured that if I can concoct a pulse width modulation job with a potentiometer somewhere on the dashboard to vary the pulse width, I can alter the mixture manually like an old time manual choke. I understand the risk of running the engine too lean of course, but that is another problem. Currently it runs way too rich. I'm willing to experiment with it to satisfy my curiosity.

What I don't know is if this is a mod from the factory and if so, has the computers's program been modified as well to NOT read the O2 sensors at all. Or was there an innovative mechanic on the job who figured "what is this??" and tried to run the car without it, and once being able to start the engine without the sensors, decided to eliminate them altogether. In Africa anything is possible.

Plan B would be to drill and tap a hole somewhere else in the exhaust line and install the sensors there.

So please help think ! Plan C??

gescho

[Q451990]

to NICO gescho!

The manifolds have threaded ports for the sensors, but there is a spacer between those threads and the sensor. This works out nicely if you strip out the threads for the sensor, because you just unscrew the spacer and replace it instead of the whole manifold... Can you tell if they removed the spacer and plugged the entire hole, or just plugged the hole in the spacer? The spacer has hex edges on it so that you can twist it out with a wrench or socket.

In terms of managing the fuel mixture, I think it would be difficult to do with a manual control like a choke. When working properly the sensors are sending a lean or rich pulse to the ECU 5 times per second.

You can read up on them in the factory service manual available at http://www.nicoclub.com/FSM/

Also, your title says you have a '95 Q45, but you say it's a '96 in the first sentence of your first post. Do you know for sure which one you have? Was it a US market Q? The only reason I ask is that there are major differences in the engine controls between those two cars...

Good luck!

Heath

[gescho]

Thanks Heath/Q451990, much appreciated.

First off, it is a 1995 model, the 1996 was a regrettable typo!

The news about the spacer is welcomed, if that be the case and it is removable and replaceble, the problem is solved. I will have time next week to find out what the situation is.

I have the FSM, and had a look at a cross section of the O2 sensor on EF&EC-14 and how it works, providing either a 0 Volt or 1 Volt signal, but I couldn't figure out if there is any electronics on board the sensor to send a signal to the ECM as you have mentioned. Maybe the ECM samples (polls) the sensor 5 times per second? There is a difference because only one of the two must be the active partner in this signal communication.

Your mentioning of the 5 times per second is also valuable info, thanks, because should I be forced into fabricating a sort of "choke" with the PWM idea as a last resort, at least one knows what cycle time should more or less be used. One question though, how quickly does the sensor react on changes in the oxygen concentration in the exhaust gas?

Take care,

Gescho

[gescho]

Hi,

Just FYI, I have successfully installed a PWM to fool the ECM into thinking it is actually measuring the O2 in the exhaust gas, so now I have manual control over the mixture ratio. AND it makes a HUGE difference to the Q45's fuel consumption. However, if you try this yourself, please be aware that you can burn your exhaust valves if you run a too lean mixture, as you might already know.

Gescho

[Q451990]

However, if you try this yourself, please be aware that you can burn your exhaust valves if you run a too lean mixture, as you might already know.

That would be my concern too.

Here are some pictures of the spacer that I'm assuming was welded shut on your car...

[gescho]

Hi Q451990,

You are a star. Thanks for the trouble you have taken with the photos, very helpful. I will certainly try to replace the "modified" spacers. The space available to unscrew them is pretty limited though....

Meanwhile my makeshift manual electronic "choke" is working pretty efficiently, so I can get around quite nicely. Should anybody be interested in the circuitry, just let me know and I'll post it here.

[maxnix]

I would put the O2 sensors on there immediately. Should make you wonder what other detrimental modifications were made?