Emisisons high could it be faulty cat

[scoobydo123]

Helping out someone with a Nissan 2.4 4 cyl petrol engine car. Car had major running issue that I have solved. At some stage a HG job had been done by a previous owner (front cover had not been machined with the head so oil leak as there was a 28 thou difference) cam timing had not been done correctly, also the IGN timing was too far retarded, had arcing plug leads and also a faulty knock sensor casing even further retarded ign and also the wrong injectors and faulty o2 probe (only has a single wire before cat). During the fixing of all these issues also found evidence of mechanic in a bottle that had been used that had sludged the heater matrix and also the IACV that has a wax stat in it for mechanical idle advance before warm up. So have gone through the car with as fine a tooth comb as can manage. Hopefully that has set the scene.

Have took the car to local garage and HC is 234 and CO 2.2 lamda was around 1 haven't got exact figures to hand is this indicative of failed CAT? I stuck a wideband up the exhaust and was sitting at 14.7:1.

Thoughts are given the history of head gasket failure and the extreme overfuelling (engine would cut out after 5 mins due to sooted plugs)and ign retarded to ATDC do we think the CAT is kaput? It would have had high EGT and fuel in the exhaust. The onboard narrowband voltage at 2000 rpm goes between 0.2v and 0.8v cycling around once a second. Got 19psi of vac at idle, performance seems ok and idle quality is good.

[kambites]

It it's been over-fueling, there's a very good chance that's killed the cat, yes. They don't like coming into contact with petrol.

[scoobydo123]

Thanks i dont know of any test other than putting a probe in the exhaust stream prior to the cat to confirm i guess. Given the number i am seeing is that indicative to what would spew oiut of an engine with no cat?

[stevemcs]

Any air leaks or leaks on the exhaust ?

[stevieturbo]

scoobydo123 said:

Have took the car to local garage and HC is 234 and CO 2.2 lamda was around 1 haven't got exact figures to hand is this indicative of failed CAT? I stuck a wideband up the exhaust and was sitting at 14.7:1.

Exact numbers matter.

Widebands do not give a proper full picture.

CO of 2.2 is very rich for a car equipped car.

A wideband cycling once per second is too slow, although does at least suggest the system is in closed loop, even if it is not working correctly.
Although single wire, not heated....wont be much use until well warmed up, so that might be why it's slow.

Take an emissions reading from before the cat and after the cat for comparison.

[stevemcs]

stevieturbo said:

Exact numbers matter.

Widebands do not give a proper full picture.

CO of 2.2 is very rich for a car equipped car.

A wideband cycling once per second is too slow, although does at least suggest the system is in closed loop, even if it is not working correctly.
Although single wire, not heated....wont be much use until well warmed up, so that might be why it's slow.

Take an emissions reading from before the cat and after the cat for comparison.

We had an Audi petrol last week average 3.5 but at some points hit 4.0

[scoobydo123]

Ok only way i can see of getting a before cat test is to remove the narrowband but not sure the local garage will have an adapter or even want me to attempt that with their probe.

So on a non cat equipped car running well would you expecr a CO lower than what I am getting.

I smoke tested the car and found leaking injector cushions that i have replaced before the test.

Thanks

[scoobydo123]

Thought I had read somewhere that you can test with an infrared thermometer if the CAT is working the exit temp should be greater than the input if it is working. So will give that a go

[stevieturbo]

scoobydo123 said:

Ok only way i can see of getting a before cat test is to remove the narrowband but not sure the local garage will have an adapter or even want me to attempt that with their probe.

So on a non cat equipped car running well would you expecr a CO lower than what I am getting.

I smoke tested the car and found leaking injector cushions that i have replaced before the test.

Thanks

My own car runs around 1.5-2.0 %CO which is far from standard and big yukky injectors, and will easily pass MOT at that ( sub 3.5% CO etc etc or whatever old car st is...might even be 4..5% )

So yes, any standard car with a lambda sensor, which when all is working correctly should ensure you're close to stioch...should be well under 2%

Whilst this is theoretical, it's a rough guide. Air leaks, misfire and all sorts can screw up a wideband reading hence why they are not always reliable for this sort of thing compared to a proper gas analyser. As what they report as AFR, will not always correspond to CO on a chart like the below. ( nor what they report as Lambda, will be same as what a proper gas analyser reports as lambda )
So if you were running at stioch and all was well, in theory you should be around 0.1% CO

[scoobydo123]

Thanks Stevieturbo. So it would seem something is up somewhere with this. The car does not go into closed loop at idle if what i have found on the internet is true by design. I have put on my home made smoke machine and cannot find a vac leak. Maf sensor seems to respond ok. One thing that does bother me is that when i corrected the cam timing someone had for some reason timed the cams at 15 degree rather than tdc, i dont have the cam tining events to see how much the skim has affected cam timing.

Coming back to vac leaks I tested at tdc on cylinder 1 and rotated engine 180 degree and left the smoke machine on then rinse and repeat. I had the o2 sensor out but bunged and also blocked the air intake before the maf so as not to contaminate that with my smoke medium whichbis baby oil.

I also have diagnostics available for the vehicle and AF alpha is showing 90pc on the nissan datascan which although was not written for this model of Nissan it is picking up the sensors.

[stevieturbo]

I would find it almost impossible to believe the car is not supposed to be in closed loop at a warm idle.

What age is the vehicle ?

A gas analyser before and after the cat would at least tell you if the cat is doing anything, or very little. In early/older cat cars, there used to be a takeoff port for this purpose, although isn't something I've seen for a very long time.

[scoobydo123]

Thanks Stevieturbo. It is a JDM Nissan Largo ka24de 1997 this model came to market 1993 iirc. I have looked at similar equupped vehicles of that era i am sure i have read that it isnt in closed loop at idle but could be wrong. There is unfortunatley no FSM available for the car so bit stuck. Waiting on hearing from the friendly garage near to me when i can take it to them to put on the gas analyser again and this time i will make sure that I have the laptop with me to make sure that it is fully up to temperature. On the day in question it is only a 2 mile drive amd it takes a long time to warm up especially if the summer winter switch was not on winter as it was a cold day. With the laptop i will be able to confirm coolant temp when the probe is in place.

[GreenV8S]

scoobydo123 said:

On the day in question it is only a 2 mile drive

I think you're wasting your time trying to diagnose emission problems on an engine which isn't fully up to temperature, especially given the crude spark/IAC control mechanisms you described.

[scoobydo123]

Yes agreed, didnt manage to get the go ahead to have it tested again today. Will report back my findings when i go there with the winter switch acrivated. To confirm it has pwm idle control as well as the wax stat. This mechanic in a bottle garbage had also gunged up the small water ways that are inside the throttle body nasty stuff that. Found that out when sorting the issue of coolant flow as when the water got up to temp and it took full control electrically of the IACV it would stumble. However now we have the water flow through the IACV it doesnt stumble onnthe transition :-)

[scoobydo123]

Sorry for the slow updates, been ultra busy with work and havent managed to get it back to the garage to go on the emission machine. What I found was that the engine wqs being over cooled for certain so as you guys mentioned pointless on trying to get emissions anywhere near on an early model vehicle when enrichment was active. I syspect the cay may be kaput or maybe my testing is not good. At an extended length idle then output of cat is cooler then input, but unsure if cat works at idle when it hasnt actually been driven? Couldnt drive on the road as no insurance but that is now active so will retest. The cat is a good 2 half foot from exhaust ports.

https://drive.google.com/file/d/1INOgSUgLnarCxTage...

https://drive.google.com/file/d/1IQEZ9s0qZ5c19bXEW...


https://drive.google.com/file/d/1IQNr8G7KgJ32iz1PU...

[scoobydo123]

Ok so the latest update is that there appears to be an issue after a rev of the engine. What appears to happen is that the injector duty cycle remains high as a result of the MAF reporting higher than can be possible airflow. Please see the attached log. This log was took during engine warm up. I had a start from cold that had a stumble as per below highlighted

https://docs.google.com/spreadsheets/d/1wpkxV_Uk7s...

I stopped the log and continued the log below dont worry about the temperature drop that was me moving the summer winter switch to make sure that was working. Now in this log is a rev up that seem to have a lag on the MAF when going back to idle. Injector duty cycle goes up even though revs are going down as does the MAF voltage. Row 1976 onwards

https://docs.google.com/spreadsheets/d/1Jti9axR8Uw...

Would you call the MAF out? The Maf on these is £600!

[scoobydo123]

Ok so new MAF is on and also cooling system now does dont have the summer bypass open. Took car back to the machine and have the following readings. Drove it the last mile in 2nd gear (automatic) but it didnt get on the machine for a good 15 mins so lost the advantage there.

CO 0.25
HC 251
Lambda 1.064
CO2 14.4
02 1.72

So is a pass if you use the no passenger vehicle option( 8 seater) and not listed on the database (which it isnt) and before 2002

Do we call the CAT out with these figures, remembering that it has a history of over fuelling from the previous owner and has had a headgasket at some stage as well so maybe CAT suffered then as well.

In the FSM for cars with the same engine and the same year it states vehicle doesnt go into closed loop at IDLE. It has one CAT that is at least 500mm from the closest port

If it is the CAT there are aftermarkets ones for the Nissan Skyline on Ebay for £104 would these even work at that price point.

Tks for any pointers.

BTW it is very lively now the guy at the garage went to pull away and ended up wheel spinning it caught him by surprise and he said whats going on there :-)

Edited by scoobydo123 on Monday 6th December 15:49

Edited by scoobydo123 on Monday 6th December 19:00

[scoobydo123]

Just a update. I noticed that during my testing that the IGn timing at IDLE was pegged at 15 degree which is the base setting when synchronising engine to ECU. I found the reason for that is that the IACV adjuster screw was too far in (not enough air bypasing). The duty cycle was 40pc at idle. However there must be a logic inside the ecu that says if above x then dont use ignition to control idle speed. Unscrewed the bypass and now the ecu controls ign timing during idle. The knock on effect with this is that the engine now runs hotter (fan now cuts in after long idle period even though ambient is much cooler where it wasnt before). Hopefully this is a result of the extra fuel now being burned at idle and the ecu getting more near optimal?

[scoobydo123]

Just a update. I noticed that during my testing that the IGn timing at IDLE was pegged at 15 degree which is the base setting when synchronising engine to ECU. I found the reason for that is that the IACV adjuster screw was too far in (not enough air bypasing). The duty cycle was 40pc at idle. However there must be a logic inside the ecu that says if above x then dont use ignition to control idle speed. Unscrewed the bypass and now the ecu controls ign timing during idle. The knock on effect with this is that the engine now runs hotter (fan now cuts in after long idle period even though ambient is much cooler where it wasnt before). Hopefully this is a result of the extra fuel now being burned at idle and the ecu getting more near optimal?

[scoobydo123]

Ordered the ebay CAT. Was greeted with an empty shell inside.. Hopefully now will pass the emissions test without using the non passenger vehicle 8 seater not in database gag. Also done an airport run in it yesterday, 120 miles round trip with 12 of that being local roads got 30mpg with 4 adults and large suitcases that don't seem to bad for a 2.4 maybe because I was effectively running a de-cat :-) Hopefully get it on the emission machine next week and will report back

Edited by scoobydo123 on Sunday 13th February 17:06