Possible oxygen sensor and Catalytic converter problem.

[RobMinhas]

Hey guys,
I've got a '95 MX3, 4cylinder and I'm the fourth owner of it. The last two owners(who including me owned the car from about 100,000KM to 229,000KM) have never had very good mileage with it, and neither have I. I'm receiving about 380KM on one tank right now, and I know it's less then I should be getting. I changed the oil and and the spark plugs about a month ago, and I did get a bit more mileage, about 20 more KM out of a tank(before I was getting about 360). I have a serpentine(i believe) belt that is very squeaky, and I can't quite figure out when and why it squeaks but it doesn't seem to have some kind of definitive pattern so far. The car also warms up fairly quick and it's maximum reached temperature is a little past half of the temperature gauge. For the most part it usually only squeaks when I turn the car on and if I (ever, usually it's when someone else drives it) stall and then turn it back on. Another thing is that once the vehicle warms up and I press my brake down to stop, the RPM will pulse and I can feel it from the car as well. It usually pulses between 800-1300 RPM, and only when the brake pedal is held down all of the way. For example if I'm waiting at a light, if the brake pedal is down my rpm pulses but if I'm in neutral or gear with the handbrake up the RPM will stay, although it is a bit high(anywhere between 1300-1800RPM) until it will finally settle down. Also the idle seems to be rough.

I've narrowed it down by getting advice from the reddit r/cars forum and it seems that my oxygen sensor is whack and causing for the car to burn rich, which in turn caused my catalytic converter to get plugged or full of all kinds of filth. This seems reasonable to me, but I was hoping to get some advice from people who know the car better. What i want to know is wheat's wrong with the car? Where is there a problem? Are these symptoms of something else? Any info is helpful.

For some reference, I'm running the stock engine, stock intake, everything under the hood is stock at this point. i did have my exhaust gasket worn out and then replaced at carline muffler when they welded my muffler back together(my sister managed to break off the muffler somehow). Thanks in advance guys.

[Ryan]

Okay, welcome here.

The idle surging is very common. Start by taking off the accordion intake tube and examining it thoroughly for any hairline cracks. Any intake leaks after the air flow meter will cause the idle to be unsteady, and the milage to drop.

-The hose that connects your brake booster to your intake manifold - disconnect it from the booster, it should be quite difficult, and when it comes, make a loud hiss as air enters the booster. If it doesn't hiss, put the hose back on, and take it off the manifold end this time, and suck on it. It should hold vacuum. If it does not, your booster (or the hose) may be defective, causing an intake leak again.

-The belt squeaking is the alternator belt, this is fairly common. Check the voltage across the battery terminals at idle, it should be 14.4V. If it is closer to 12V, your alternator is tired and could use a rebuild. An alternator rebuilding shop should do this for around $100. You could also purchase a new one for more than that.

-Remove the distributor cap and inspect the cap and rotor for oxidization (crusty white build up). For free you can scratch any of it off, but the metal itself looses its conductivity as it carries current for long times (like 100k km) and could probably be replaced.

-You should set your ignition timing using a timing light. You might be able to rent or borrow one. At the same time you should adjust the idle, and the TPS. There are FAQ's on this in the FAQ section.

-You can remove your coolant sensor and check it using a pot of boiling water, a thermometer, and an ohmmeter (multimeter). The engine relies heavily on this sensor, and if its not in spec it won't ever be running optimally.

I also happen to know that this car runs in open loop if you travel 110km/h, but closed loop at 109. Try driving a bit slower.



...Start there.

[RobMinhas]

You sir, are a scholar and a gentleman. Thank you very much for that information Ryan. I'm currently half into exams right now so I won't be able to get right into all of this right I way, but I will post updates for when I do!

I also happen to know that this car runs in open loop if you travel 110km/h, but closed loop at 109. Try driving a bit slower.

Can you elaborate on this please? I don't understand what you mean by open loop? As for the speed, I haven't hit over 110 more then twice since I moved to Calgary for university in September, however as recent as early summer I had pushed this thing as far as speed goes over 110 very often as I lived in a rural area surrounded by highways.

[Daninski]

Go to You Tube and type in Sea Foam and watch. Buy a can at Walmark and pour 1/3 into your PVC hose while having someone throttle your engine so it won't stall. Once it's in let the engine stall by removing your thumb from the PVC hose. 10 mins later start the car and watch the white smoke work it's magic. Drive away happy. Oh and what Ryan said too.

One side note, your cat could be partially blocked. Only way to check is to remove and look at it.

[RobMinhas]

Go to You Tube and type in Sea Foam and watch. Buy a can at Walmark and pour 1/3 into your PVC hose while having someone throttle your engine so it won't stall. Once it's in let the engine stall by removing your thumb from the PVC hose. 10 mins later start the car and watch the white smoke work it's magic. Drive away happy. .

I've heard some info about cars engines going six months or so after, any idea on that? I was considering it before.

One side note, your cat could be partially blocked. Only way to check is to remove and look at it.

Is there anything specifically I should look out for when I remove my cat?

[Ryan]

you should be able to see daylight through it easily.

Good cat:

http://www.nissansonly.com/gallery/albu ... verter.jpg


Bad cat:

http://forums.trailvoy.com/attachment.p ... 1251460479

Or worse.

If you put your hand by the exhaust does it pulse like a motor does, or does it feel perfectly smooth?



Seafoam shouldn't let the last wind out of your motor. If it does... it was about to happen anyway. Like removing a blood clot to save your leg so a chunk can get stuck in your brain and give you a stroke.




One more thing to check is your compression. You should be able to rent or borrow a gauge. There's a FAQ for it too. If your motor is extremely tired, you'll get poor mileage as well.


About the open loop, I mean it ignores the oxygen sensors and just runs from a hard coded base fuel map.
closed loop means it heeds the O2's and adjusts the fuel mix accordingly, which will be a leaner mixture than the base map.

[RobMinhas]

If you put your hand by the exhaust does it pulse like a motor does, or does it feel perfectly smooth?


One more thing to check is your compression. You should be able to rent or borrow a gauge. There's a FAQ for it too. If your motor is extremely tired, you'll get poor mileage as well.


About the open loop, I mean it ignores the oxygen sensors and just runs from a hard coded base fuel map.
closed loop means it heeds the O2's and adjusts the fuel mix accordingly, which will be a leaner mixture than the base map.

Ahh okay, I gottcha on the open loop.

I'm gonna try to see if my exhaust pulses, the problem is I need the car to be running fairly hot and the brake needs to be held down so I'll need to get a buddy to help me out. And I'll see what I can do about the compression.

I'm not driving the car this week as I removed my front bumper to put in some angel eyes headlights and haven't put it back in yet, so some of the things will have to wait till next week.

Once again thanks Ryan.

[Ryan]

Well the exhaust would feel funny at any idle. You may not be able to tell if it idles over 1k though. Just imagine what the difference is, if the cat is free, the exhaust will come out in pulses, but if its all being jammed up behind the cat, its being choked and will come out in a continuous stream.

[RobMinhas]

Well the exhaust would feel funny at any idle. You may not be able to tell if it idles over 1k though. Just imagine what the difference is, if the cat is free, the exhaust will come out in pulses, but if its all being jammed up behind the cat, its being choked and will come out in a continuous stream.

Okay, I will try this when i get the chance!

[Evo_Spec]

if you need help with the seafoam i can help you out as i've done it before, fun stuff XD

[RobMinhas]

if you need help with the seafoam i can help you out as i've done it before, fun stuff XD

Thanks man, I'm actually a little excited to do it, but exams are a priority and I just changed the oil so I might wait till it's time for the next oil change.

[RobMinhas]

Okay, welcome here.

The idle surging is very common. Start by taking off the accordion intake tube and examining it thoroughly for any hairline cracks. Any intake leaks after the air flow meter will cause the idle to be unsteady, and the milage to drop.

So I took a look at my intake and I even took some pics(gonna try photo bucket this time).


This is my stock intake here, I always thought it was a bit strange that the clamps were so new and clean in comparison to the actual intake, but I never looked into it. upon closer inspection I saw that they seemed to be covering certain parts of the intake.

There seem to be two bits damaged here.

this one here and another one


So Ryan, what do you think? The actual piping in the inner part of the intake seems to be fine and there are no holes or cracks that are at least visible here. Could this be the cause? And if it is, what do you recommend I should do as far as replacing the intake goes? Should I go with a CAI or maybe just find a stock intake from another MX3?

[RS_OBD'oh_2]

just get a cheap CAI.

Easy fix

[RobMinhas]

just get a cheap CAI.

Easy fix

I'm sold.

Haha it's my main idea but if it won't make a difference throwing another stock one in I could probably find one for decently cheap and no delivery waiting time.

[RS_OBD'oh_2]

To be honest, I think you'll be able to get an after market CAI for cheaper than a good condition OE intake.

I do believe there are some OE's in the WTB section.

You could probably hit up Mopac (off 16 ave NW) they could probably get you something that will work. There is a year of prelude (??) that will work. And I believe a KL 3 nipple intake will work (probe or mx6). Won't get the coolest air as it's a short system.

Just make sure that you get the correct couplers to mate to the intake manifold and MAF.