Keeping Engine Warm??

[Nut Kracker]

Well, the place I took it to couldn't access the ECU with their test equipment.
May be due to the Kalmaker tune.....I dunno. It didn't play up for them when they took it for a test drive, nor did it for me when I picked it up this afternoon.
They checked the engine for vacuum leaks, binding linkages and throttle cable etc.
and that was all ok.

It did play up a bit this morning though, before I took it to the Mechanics, as it wouldn't return to idle while driving.
Cold start idle seemed ok at first, but then slowly crept up to around 1500 rpm.
I stopped the engine and restarted it and the idle was ok.

One thing I have found though, is that when the idle was high when driving this morning,
it would suddenly drop back to normal idle, as if the IAC was closing and then return to high idle, then back down again.
All this was in the space of about 10 - 15 minutes.
I did replace the IAC about 12 months ago, but it was non genuine and I'm wondering if it is playing up.
It seems to me that this is an intermittent fault and associated with the IAC.

Opinions.......?

If it was a fault with the tune, wouldn't the high idle be there all the time?

Also, the temperature gauge seems to be reading lower than normal.
It has always sat half way between quarter and half, whether it's -5 or 45 degrees.
But it is now it sits just above quarter.
I know the IAC (amongst other things) depends on readings from the temp sensor.
So I am also wondering if this is also associated with the problem.

They are not an expensive...."lets see what happens if I replace them" option.
I might replace the temp sensor first, as that's the least expensive of the two.
And I will be going genuine on both, if I need both.

 

[Nut Kracker]

Also.....Couldn't the temp sensor also effect the cold start idle, as well as what I mentioned above?
As the ECU would be reading a lower engine temperature than what it actually is?
Remember I said it wouldn't hold idle until it got to about 40 degrees C.

So what I'm trying to say is, that the engine is hotter than the ECU thinks it is.

 

[Brett_jjj]

The ECU uses the IAT (intake air temp) sensor as well as the CTS (coolant temp sensor)to adjust the fuel/air mixture so the vehicle starts instantly and runs perfectly from dead cold. This is the beauty of EFI/engine management systems.. Not like in the old days where you'd have to crank them heaps just to get them to fire up, and then warm them up for a few minutes before driving off or they'd stall etc. Theres a few variables that the ECU uses in the tune to adjust itself for cold starts , Id reckon its most likely gonna be a problem with the tune itself, or whoever did it did a bad job.

 

[Nut Kracker]

Thanks Brett.
But can a tune go out of tune?
If so, what can cause that to happen?
Because it's not always acted this way.

 

[Brett_jjj]

No, It cant change unless someone changes it. The long and short fuel trims can change a lot through (they constantly change as the engine runs) if things aren't set right in the tune, and this will upset how it runs if the trims are maxed out..

 

[Immortality]

Cold start is fairly basic.

When you crank the engine the PCM injects a set amount of fuel based on a table- fuel pulse width Vs ECT(engine coolant temp) and also has a modifier based on TPS (in case you have your foot on the loud pedal). Once the engine fires and starts the PCM then runs in open loop mode.During cranking there is also another table that sets the IAC stepper motor position which is also dependent on the ECT. Once the engine starts the IAC stepper motor closes up (decay rate) based on another table to achieve a set rpm target which is also ECT based, at the same time the AFR's come up to an open loop target AFR and the rate of change in the AFR is dependent on another table that is based on ECT. In old term speak, the PCM is deciding how quickly the choke comes off

To give a graphical representation of the above check out the data monitors below. This particular example is from a VX SC V6 but what happens with yours will be fairly similar.

If you have a look at the top display starting at (22 seconds) the engine is started, if you follow the dark blue line which indicates commanded AFR, it starts off at about 10:1 and then continues to step up about every 2.5 seconds and by end of the graph is above 13:1. If the data continued you would see this would keep increasing till the open loop AFR target Vs ECT was achieved.

If you look at the lower data monitor you can see what the IAC stepper motor is doing (the green line). You can see the stepper motor is at 160 steps once the engine cranks and starts (@ 22 seconds) it drops fairly quickly as the engine rpms come up (dark blue line at the bottom), it then increases slightly as the actual RPM drops below the desired idle RPM temporarily and then continues down until the engine settles at the desired idle rpm.

All of this occurs in open loop mode. Basically put the PCM isn't using any extra sensor input for the O2 sensors to control the AFR's. It's simply injecting the correct amount of fuel based on the amount of air been used by the engine been measured by the MAF.

Now, the interesting part is when it reaches it's set temperature to go to closed loop operation which I believe is 44° C, then it starts to use the input from the O2 sensors and start to trim the fuel to achieve the actual desired closed loop AFR target which is 14.7:1

I really don't know Tas. That's what I'm thinking.
May be the computer HAS learnt new settings.
Perhaps some one can confirm this.
....I'm not complaining though.

Yes, once your engine goes into closed loop mode it is learning and trimming the fuel injected to achieve it's closed loop AFR target.

does it have knock sensors?

Yes, there is a knock sensor but if it were to pull out and timing it would only be momentarily.

There is a bit more to all of this as there are other scalers which can influence things like ignition timing Vs air intake temps but it covers what is happening during a cold start.

 

[Immortality]

Thanks Brett.
But can a tune go out of tune?
If so, what can cause that to happen?
Because it's not always acted this way.

Yes it can, if a sensor is faulty and sending false data then it can screw with the tune.

Some of the more common are faulty O2 sensors (effecting the fuel trims) or engine coolant temp sensor which can effect the target AFR or prevent the engine going into closed loop mode.

 

[Nut Kracker]

Yes it can, if a sensor is faulty and sending false data then it can screw with the tune.

Some of the more common are faulty O2 sensors (effecting the fuel trims) or engine coolant temp sensor which can effect the target AFR or prevent the engine going into closed loop mode.

The temp sensor you guys have mentioned effecting the tune is leading me more and more into
thinking it may have something to do with the problem.
As I mentioned before, the temp gauge is giving a lower reading than what it used to. While the after market one I have on the car
is still reading the same (two different sensors fitted).

Now, the interesting part is when it reaches it's set temperature to go to closed loop operation which I believe is 44° C, then it starts to use the input from the O2 sensors and start to trim the fuel to achieve the actual desired closed loop AFR target which is 14.7:1

Funny you should say "44 degrees C", as this is the temperature when the cold start idle becomes stable :hmmm:

By the way.......Everyone has gone out of there way to help so much.
I really appreciate it guys.

 

[delcowizzid]

was this mailorder tuned? the map tunes work better with the IAT sensor in the manifold vn style .the coolant temp sensor for the ecu could be getting tired or if its read different on the gauge ever since the tune conversion it may be scaled wrong in the tune.it could also just be kalmaker wouldnt be the first time kal code has been broken and not picked up through testing before release.

 

[Nut Kracker]

was this mailorder tuned? the map tunes work better with the IAT sensor in the manifold vn style .the coolant temp sensor for the ecu could be getting tired or if its read different on the gauge ever since the tune conversion it may be scaled wrong in the tune.it could also just be kalmaker wouldnt be the first time kal code has been broken and not picked up through testing before release.

No, it's not a mail order tune.
It was done when I had the mods done on the engine.
When the custom manifold was made and due to not having room for a MAF with the OTR, Scott, the guy who owned Chip Control,
had a custom mafless tune done by Kalmaker.
This tune (W72 he thinks), is apparently the first of it's kind for the VT sequential 5 litre.

The temp sensor was fine when the tune was done.
It's only been recently that it's reading lower on the gauge.
Coincidence???????

When you say; "the map tunes work better with the IAT sensor in the manifold vn style" and this engine being map tuned,
Would you say this is the spot the VN's had their IAT sensor? (See picture below).
As I recall posting something along the lines of this ages ago.