EML Code 45 Oxygen circuit - voltage high (rich mixture)

[Skara]

Hi everyone, I had the EML on for quite some time now and I just can't seem to get rid of it not matter what I do. I'll try and describe my problem as thorough as I can hoping some of you could help me or at least give me some good advice. The engine is 1.6 (C16NZ), the problem is code 45 as stated in the subject, the car idles poorly, sometimes it revs to 2000 -2500 rpm for 5-10 seconds then settles, when standing near rear end of the car you can hear it missfire also when you put your hand on the rear exhaust you can feel that missfire every 2-3 seconds, also you can smell gasoline in the exhaust. Now for the things I tried and replaced: two O2 sensors (first one was NGK second one was Bosch) same thing with both, idle control valve also new, replaced gaskets on throttle body all 3 of them they were not in a bad shape although the car is almost 30 years old, also cleaned the whole intake manifold as well as throttle body, cleaned the injector, new exhaust and intake gaskets, new spark plugs, new air filter, new intake pipe between throttle body cap and air filter, new spark plug leads, new cap and rotor, new fuel pump, new fuel filter, EGR valve is blanked. After all of this the problem persists the car has 250000 km, about 35000 km ago the timing belt and pump were replaced so don't know if the timing could be off alittle bit nor do I know how to check that. The only thing I can tell is maybe the problem is worse when the gas tank is full and a bit better when it's near empty but that could be placebo I don't know, the car is really messing with my head. If anyone has any good advice please do let me know. Sorry for the long post and thanks for reading it.

[Cavalier342]

Hmm that is very strange indeed. I think you've covered pretty much everything there, these engines don't have much to go wrong. Short of the ECU having a fault inside it, the only other thing I can think of, IF the C16NZ has the MAP sensor just like the C18NZ, tucked under the scuttle panel flap, if that's faulty or the outlets for the vacuum hoses are blocked, maybe that could cause issues?

Regards.

[Skara]

Thanks for the reply, forgot to mention the MAP it indeed has one but I doubt it's the culprit, the hoses are fine I tried disconnecting it while the engine is runing and the engine almost immediately cuts off and MAP being disconnected the engine can't start whatsoever. That being said I ruled out MAP but I might be wrong.

[Robsey]

As Andrei reported, you have covered all the obvious stuff.

Rich mixture eh?
IF it is anything like the C16NZ2 or C18NZ, then the most common issue is a sluggish or dribbling injector valve.

I see you have had it "cleaned", but was that done professionally or "the best that you could do yourself".?
No slur against you or your abilities by the way.

As said, when these central injectors get worn, tired or dirty, they begin to run very rich.

Have you checked for a loud crisp ticking noise from the injector as it is running to ensure that it is operating efficiently and smoothly.?
You would need an automotive stethoscope for this.

Also - obvious, but I read you fitted new gaskets... what about new injector seals?

I am struggling to look for an alternative cause.
From memory, the main culprets were the injector valve, the MAP sensor, possibly dirty idle control valve or a snapped vacuum pipe elbow.

Don't recall any issue with the fuel pressure regulator...

Again all of which, you have covered.

That just leaves the ECU, which is in the driver's footwell.
Have you checked this for clean and dry connector pins.?
In recent cold, damp weather or ambient condensation, moisture could cause a few issues.
This sure is a head scratcher.
I am certain it will be something obvious when you finally suss it out.

[Skara]

Thanks Robsey for your reply. The injector has been cleaned professionaly as you can see in a picture below, as for the ECU I'll try to unplug it and see if there is anything strange about it, wires, connectors etc. One more thing to mention and I dont know if it has to do anything with this problem, when the engine is cold it wont start at the first turn of the key it needs slightly more cranking but if it's warm it starts at the first turn of the key.

[Cavalier342]

That almost sounds like the autochoke not working properly, but don't quote me on that. I think that's probably controlled by the ECU.

[Skara]

Now since you mentioned it, what exactly are you considering under ''autochoke'' ?

[Cavalier342]

I'm not sure how it works, but they have an auto-choke system which acts like a normal choke basically, adjusting the fuel/air mixture in different temperatures. I think it's electronically controlled as I said before, so would be down to the ECU.

[Robsey]

Looking at the Haynes, it does appear that the C16NZ is the same Multec set up as the C16NZ2 and C18NZ.

On these units, I can see that there is an air bypass valve on the EGR side of the throttle body, and also a fuel pressure regulator on the front.

Items to consider would be -
Throttle position sensor.
Fuel Pressure Regulator.
Air Bypass Stepper Motor.

If any of these are faulty, then I would suspect that the fuelling would be affected.

I think that the air bypass unit is the enrichment / choke unit that Andrei refers to.

[Skara]

That's idle air control valve or a stepper motor you are refering to ?

[Robsey]

Look at these

[Skara]

Yep, looked at all these parts, I will try and find replacement for the diaphragm in the fuel pressure regulator if I manage to find one anyway, who knows after 250000 km and almost 30 years a membrane is more likely to fail.

[Robsey]

Sounds like you have indeed covered every single part.

If all parts check out as okay,
this brings us back to the ECU, connectors or the wiring.

As you indicate 30 years of hot and cold, condensation and vibration...

[Skara]

Just a minor update, I managed to disconnect the ECU and check the connectors. There was no indication of water ingress nowhere around ECU, although I won't yet rule out the ECU until I get my hands on a second hand one. Also I ordered new ignition module which will arrive in a week or two, but will probably rule that one out too because I doubt it will be that easy.