Throttle Position Sensor

[CJ]

How did the nct go? Did she pass?

As I expected, it failed on high idle emissions (3300rpm):

lambda: 1.017 - PASS (between 0.97 and 1.03)
CO 0.83 vol % - FAIL (above 0.3)
HC 246ppm - FAIL (above 200)

Mustangs recent results below for comparison:

Lambda 0.825 Pass criteria 0.97 to 1.03
CO 6.6 vol% Pass criteria below 0.3%
HC 243ppm Pass criteria below 200ppm

Everything else was spot on. More investigation required. My thoughts (bearing in mind TPS and IAT errors flagged):

1. Wiring \ earth \ continuity problem
2. Faulty MAF \ IAT
3. TPS out of tolerance (already swapped in second unit)
4. CAT matrix

Further reading re emissions

Interesting excerpt below:

During acceleration, the engine momentarily drops out of closed loop and receives a richer fuel mixture for more power. During this time (depending on the system), the MAP or Airflow Sensor and the TPS sensor play critical roles in controlling the fuel mixture.

Most fuel-injected engines have either a throttle position sensor or switch that indicates when the engine is at idle. When this device indicates that the engine is no longer at idle, the on time of the injectors is increased to temporarily richen the fuel mixture. The same thing happens any time the engine comes under load and manifold vacuum drops. The MAP sensor tells the computer the engine is under load, and the computer responds by adding more fuel.

It is normal to see some spikes in CO during acceleration, but unusually high CO readings indicates that the fuel mixture is too rich. Possible causes might include:

Flooded charcoal canister or a leaky purge valve;

Leaky power valve (older carbureted engines);

Defective mass airflow (MAF) sensor, manifold absolute pressure (MAP) sensor, or vane airflow meter (VAF); or

Defective throttle position sensor.

If the feedback fuel control system is working properly and there are no apparent sensor or purge valve problems, the catalytic converter may be contaminated or not functioning.

Elevated HC readings during acceleration indicate ignition misfire under load. The causes could be:

Defective knock sensor;

Weak ignition coil(s);

Excessive resistance in spark plug wires;

Arcing inside the distributor cap;

Worn, fouled or incorrectly gapped spark plugs;

Over-advanced ignition timing; or

Lean air/fuel mixture

CJ

Edit: Berno, I removed your post so as not to detract from the discussion...

[Mustang]

Mustangs recent results below for comparison:

Lambda 0.825 Pass criteria 0.97 to 1.03
CO 6.6 vol% Pass criteria below 0.3%
HC 243ppm Pass criteria below 200ppm

Some more useful reading here

Carbon Dioxide, is an indication of the completeness of burn, the more complete the burn, the higher the CO2 reading.
Carbon Monoxide, is an indication of the air: fuel ratio, too much fuel results in a high CO reading.
Hydrocarbons, is an indication of unburned fuel exiting the exhaust, the more incomplete the combustion, the higher the HC reading.
Oxygen, is an indication of either incomplete combustion or an air leak. Air: fuel ratio too weak, low combustion efficiency and a pre or post- combustion air leak will cause a high O2 reading.
Oxides of Nitrogen, is an indication of combustion temperature, low compression pressure, retarded ignition timing and rich mixture will all result in lower NO2 readings. When considering carburettor cars or basic injection cars, emission faults are relatively straightforward to diagnose.

With Low Lambda, High CO and high (ish) HC all of my reading point to a rich fuel mixture -they all appear to be consistent

As I expected, it failed on high idle emissions (3300rpm):

lambda: 1.017 - PASS (between 0.97 and 1.03)
CO 0.83 vol % - FAIL (above 0.3)
HC 246ppm - FAIL (above 200)

High lambda =>lean mixture
High CO=> too much fuel i.e rich mixture
High HC=>Incomplete combustion, typical of rich mixture

Maybe we don't have the same problems afterall.
As I said previously, my mechanic seemed convinced it was the cat (I'm not sure that I agree especially as I'm getting IATS and TPS errors) -first step in the process will be to replace that. Next will probably be the lambda sensor.
As an aside he reckoned that some E85 in the tank does wonders for emissions readings -anyone treid this?

[CJ]

As an aside he reckoned that some E85 in the tank does wonders for emissions readings -anyone treid this?

Karl has used cellulose thinners which appears to work for him, not heard of anyone trying an E85 mix.

Re the suggestion of replacing the cat - I'd say its likely to get the car through the test. High HC = high content of unburnt fuel favour being pushed through the a hot catlytic convertor, this is known to shorten the life of the cat and reduce its effectiveness (on a side note, flooding an RX-8 has been known to render the cat useless, not like-for-like but similar concept - unburnet fuel on cat). Replacing the cat is masking the problem but my guess is that we would both get through the NCT if we took this route. On the downside, the life of the new cat would be significantly reduced on the basis of a consistantly high HC mix.

Wanna go halvo on a new cat?

CJ

[TopCat]

As an aside he reckoned that some E85 in the tank does wonders for emissions readings -anyone treid this?

... not heard of anyone trying an E85 mix...

Worked for me.
I didn't go mad on it though, just roughly a 1:10 mix. I've heard of people using much stronger ratios though.

[CJ]

Worked for me.

So it did, forgot about that one.

I noticed you passed on HC first time around, in both Mustangs and my case, we failed which is an indicative of a rich mix.

CJ

[fatboyfat7]

Currently undertaking idle learning procedure on driveway....

CJ

Any idea how long this takes? Currently doing it myself and she's been idling for close on 40mins and the engine tone is still constantly rising and falling. Ive fitted the Lambda and the second hand TPS. Hopefully....

[Dragonheart]

This may be a stupid comment but if the air con is turned on is it going to make a difference to engine tone? I know with mine when the air con is turned on it revs higher at stages cause the air con is using more of the engine power. So if checking this should it be turned off?

[CJ]

Update:

Dropped the GX into this man last week to check things out:



He stuck it on the emmisions tester, NCT results in black, results froms Pauls machine in red:

lambda: 1.017 0.997 - PASS (between 0.97 and 1.03)
CO 0.83 vol % 0.09vol % - FAIL (above 0.3)
HC 246ppm 22ppm- FAIL (above 200)

Big difference I'll think you'll agree. Paul, put it to the test and got me to take the car for a 5 min spin (from cold) around the the industrial estate, the results above were recorded after a short drive.

He recommended not running the car at idle outside the test centre, this actually cools down the cat and will increase emissions readings. I've been telling people to run the car at idle outside the centre on the assumption that it would help - hand up, I was wrong.

He also said that the FTOs cat cools down a lot quicker than many other cars which doesn't help. In other words, if the car is sitting outside the centre for a long period of time, theres a higher chance of failure.

I have the repeat test this evening, I'll report back on the outcome....

CJ

[Dragonheart]

So in other words you would have passed with Pauls figures ya?
Any chance the NCT machine was off, I mean nobody regulates the regulators do they? Whos to say they did it properly first day?

[CJ]

Update, the GX passed this evening

I did a couple of things differently but nothing significant:

Drove the car up the M50 1 gear lower than normal throughout the rev range.
Left the house earlier so as I could take a detour and go for a 'proper' drive.
Didn't let the car idle outside the test centre (the tester had the car running @ idle for about 5 mins before the test, the longer it runs @ idle, the greater the chance of failure it would seem).

Moral or the story - drive the ring out of the car before the test and don't let it idle for a prolonged period outside the test centre.

Updated results below:

Black - original test
Red - Paul Nolans test
Blue - new test

lambda: 1.017 0.997 0.998 - PASS (between 0.97 and 1.03)
CO 0.83 vol % 0.09vol % 0.25 vol% - FAIL (above 0.3)
HC 246ppm 22ppm 63ppm - FAIL (above 200)

CJ

[Bernard]

Good stuff, everyone seems to be passing lately.
I hope the trend continues, not long before it's my turn.

[Dragonheart]

Excellent stuff CJ. Seems like the cure for the emissions has been sort of decided so? I remember mine was very close to the figures you quoted there the last time I went and its going to be out (I think) when I get back so was worried that it would fail and not sure how to go about sorting it. Looks more promising now though!

[fatboyfat7]

Great news, as per Berno, hope the trend continues!

[escu_calin]

Any idea how long this takes? Currently doing it myself and she's been idling for close on 40mins and the engine tone is still constantly rising and falling. Ive fitted the Lambda and the second hand TPS. Hopefully....

After changing the Lambda and TPS the rise and fall revs have stopped? because mine, when is cold ..first 5-10 minutes, goes with this high revs and is very hard to drive, when I change speed it revs like crazy and is very frustrating, when i idle it oscilates between 1000 and 1500 for a couple of times then somehow stabilises at 1300-1400 . at the end of the worming up the rex is at 700-800.

Advices?

[CJ]

Escu, sounds like a stepper motor problem, search the forum for more info.

CJ

[escu_calin]

Escu, sounds like a stepper motor problem, search the forum for more info.

CJ

thanks CJ... i wrote after reading all posts concerning stepper motor. the story is:

while the engine is cold(~25 degrees Celsius) the car starts at 2100-2500 RPM and if acceleration is pressed then released, the engine revs down veery slowly, as a consequence the next step was:

i removed the stepper from the throttle body; i measured the coils and they are around 90 ohm with 50 ohm at mid point.
i disassembled it and reassembled after cleaning with alcohol and WD40
i cleaned its nozzle and connected it while unattached at throttle body !
when i turn the key at last step before engine start, the stepper retracts completely and when i get the key out it expands ... so is a behavior of a sane stepper.
when mounted back in throttle body the behavior did not improved.

that's why i suspect now the lambda sensor and the throttle position, since the exhaust mixture is also quite rich for my nose.

advise?