New Spark Plugs

[routier1642]

I just had the 120,000 km service done on my beloved Adventra.
For such an important service, I took it to Holden; it was a little pricey but they were very thorough.

They changed the spark plugs, of course.
Since then, I've noticed:
- less visible exhaust
- more torque
- poorer fuel economy (based on observations and the results of one tank)

I expected the first two, but the third was a surprise.
Can I expect that to change as the ECU adjusts?
I noticed that the Long Term Fuel Trim has dropped right down too - it's about -9%.

 

[ozNick]

I just changed my spark plugs yesterday on the Adventra.
When I removed the intake oil dribbled out of it, due to the left side PCV valve spewing oil.
I cleaned the intake tube, inside of the plenum, and the throttle body with Nulon throttle body cleaner.

I suspect the 2 improvements you're seeing is a combination of spark plugs as well as a clean intake and throttle body.
As for the third, maybe it is the ECU getting used to the cleaner intake (or you enjoying the power a bit more).

I just purchased two catch cans for the lines from the PCV valves to capture the nasty oil before it gets into the intake (left side PCV), or the plenum (right side PCV).


Cheers, Nick

 

[routier1642]

Thanks, Nick.

The torque increase is real - I'm getting numbers on DashCommand I haven't seen before.
Even if they're not quite accurate, they're an increase on what I had before.
Power seems to be down a bit, but it probably needs more testing.

Yes, the Alloytec does sometimes/often spew oil through the PCV when revved.
I already have a PCV minicatchcan on the intake side - I wasn't aware of the other side!
Must look into it. What type did you get?

I just changed my spark plugs yesterday on the Adventra.
When I removed the intake oil dribbled out of it, due to the left side PCV valve spewing oil.
I cleaned the intake tube, inside of the plenum, and the throttle body with Nulon throttle body cleaner.

I suspect the 2 improvements you're seeing is a combination of spark plugs as well as a clean intake and throttle body.
As for the third, maybe it is the ECU getting used to the cleaner intake (or you enjoying the power a bit more).

I just purchased two catch cans for the lines from the PCV valves to capture the nasty oil before it gets into the intake (left side PCV), or the plenum (right side PCV).


Cheers, Nick

 

[Smashfist]

That fuel trim sounds way out of whack. Has it got the original oxygen sensors?

 

[routier1642]

Yes, AFAIK, all the oxygen sensors are original.
Hmmm... after the dynotune, the ECU consistently got consistently upset with rear oxygen sensor TOO RICH warnings.
Inspection showed them both to be stuffed. I took it back to the tuner, and his answer to this was to turn them off. (!)

My understanding is that the mixture is (now at least) by default too rich, and the long term fuel trim readings show the ECU's attempt to compensate.
The short term FT readings are reasonable most of the time, but they really move when you put the boot in.
It was similar before the new spark plugs, but not as extreme. LTFT was usually between -6% and -9%

Should I be worried?
Any ideas as to a course of action?

 

[ozNick]

Yes, the Alloytec does sometimes/often spew oil through the PCV when revved.
I already have a PCV minicatchcan on the intake side - I wasn't aware of the other side!
Must look into it. What type did you get?

I just bought some cheapies from eBay and modified them, so the inlet tube went to the bottom of the can and then got filtered through stainless steel mesh before leaving.

I installed them on the weekend staggered on the passenger side of the engine bay.
The front one sits in between the passenger side PCV valve and the intake.
The rear one sits between the drivers side PCV and the T section that feeds the plenum.



Cheers, Nick

 

[routier1642]

I just bought some cheapies from eBay and modified them, so the inlet tube went to the bottom of the can and then got filtered through stainless steel mesh before leaving.

I installed them on the weekend staggered on the passenger side of the engine bay.
The front one sits in between the passenger side PCV valve and the intake.
The rear one sits between the drivers side PCV and the T section that feeds the plenum.

View attachment 181758 View attachment 181759

Cheers, Nick

Neat Job!
I'm envious.

 

[Capsule]

Yes, AFAIK, all the oxygen sensors are original.
Hmmm... after the dynotune, the ECU consistently got consistently upset with rear oxygen sensor TOO RICH warnings.
Inspection showed them both to be stuffed. I took it back to the tuner, and his answer to this was to turn them off. (!)

My understanding is that the mixture is (now at least) by default too rich, and the long term fuel trim readings show the ECU's attempt to compensate.
The short term FT readings are reasonable most of the time, but they really move when you put the boot in.
It was similar before the new spark plugs, but not as extreme. LTFT was usually between -6% and -9%

Should I be worried?
Any ideas as to a course of action?

Hey Routier, any development on the LTFT issue? Mine are getting worse, I was around -7 and -9 but now it's gone to -17 and -14. Not sure if it's the OTR + a lot of highway driving I've done recently or if my O2 are letting go. Strangely enough, the car has never run so well. I'm a bit hesitant to change them as they are definitely not cheap!

Any input would be appreciated, thanks!

 

[routier1642]

Hey Routier, any development on the LTFT issue? Mine are getting worse, I was around -7 and -9 but now it's gone to -17 and -14. Not sure if it's the OTR + a lot of highway driving I've done recently or if my O2 are letting go. Strangely enough, the car has never run so well. I'm a bit hesitant to change them as they are definitely not cheap!

Any input would be appreciated, thanks!

Hmmm... the ECU is trying to compensate for running rich. Possible causes:

* Leaky fuel injector
* Excessive fuel pressure due to bad fuel pressure regulator or restricted fuel return line
* Extremely dirty air filter or restrictions in air intake system
* Exhaust restrictions (clogged converter, crushed exhaust pipe or plugged muffler)
* Bad O2 sensor (output shorted to voltage so it reads RICH all the time)

Most of these items would cause other performance issues, so it's a puzzle.
If the O2 sensor was really bad, it would be throwing a code.

My own LTFT readings have never got below -10%. They normally vary between -9% and -6%.
-17% is getting near serious

You say the car is running well. Has the fuel economy improved?
Maybe it's just magically become more efficient!

 

[Capsule]

Hmmm... the ECU is trying to compensate for running rich. Possible causes:

* Leaky fuel injector
* Excessive fuel pressure due to bad fuel pressure regulator or restricted fuel return line
* Extremely dirty air filter or restrictions in air intake system
* Exhaust restrictions (clogged converter, crushed exhaust pipe or plugged muffler)
* Bad O2 sensor (output shorted to voltage so it reads RICH all the time)

Most of these items would cause other performance issues, so it's a puzzle.
If the O2 sensor was really bad, it would be throwing a code.

My own LTFT readings have never got below -10%. They normally vary between -9% and -6%.
-17% is getting near serious

You say the car is running well. Has the fuel economy improved?
Maybe it's just magically become more efficient!

Lol, I guess it is. Fuel economy hasn't drastically changed, if it changed at all. It's better because I do more highway, that's all.

My theory is the OTR is working "too well" and the ECU thinks it's getting more air than it actually does, so it adds more fuel. Since there's in fact not enough air, the O2 sensors catch the rich mixture and ask the ECU to lean the mixture. But I may be completely wrong. Air velocity inside after the filter can't be that great.

I also noticed the LTFT get a bit better when city driving.

I'll keep an eye on it an eventually change the O2 sensors as they might have been contaminated by since I fitted the extractors around a year ago, but as we say, don't fix it if it ain't broken.