E38 idle tuning

[hymey]

I fixed the error! cheers!

[The Alchemist]

Basically the engine should start dead cold with minimum time required for warm up before the car can be driven away with no sluggish or surging behaviour.

now that you mention it, since we have some good fuel numbers HOT in this V8 we are doing, supercharged, cammed new engine VE Ute, I did a cold start yesterday and found it going to 10%+ STFT at idle and had a really doughy throttle response ie not enough fuel.
Is Table B0141 & B0146 the tables to alter to increase fueling during warmup? And why does it appear that its fuel trimming even when under 55degs and been running for about 60seconds from dead cold. Also as the temp went past 80deg the fuel trims went from +10% and quickly went down to a nice -2% (yet the actual AFR richened up (see log)) which is where I had it set hot running from the day before.
Cheers,
Mike

[swingtan]

Do not under any circumstances relay on fuel trims for cold start corrections, always use a good WB sensor.

The E38 has different tables for CL control and for NB O2 "ready". in the stock setup, this means that LTFT's can be applied before the O2 sensors are enabled for "true" CL operation. The LTFT data is learned from previous drive cycles, but of course, if the O2's are yet to be enabled, the LTFT data is not actually correct for the current engine conditions. you will also find that both LTFT's and STFT's will change as the engine warms up, IE. the trim amounts will vary until full operating temp is achieved. This is due to engine efficiency changing as the combustion chamber heats.

{B0141}: This is the base OL fueling table. It's a bit weird the way it's set up, as in theory, IVT can never be much lower than ECT. So if you keep this in mind you can set up the table fairly quickly. Remember that it's only a "commanded fueling" table and should be used try and get the desired fueling, it has no effect on the actual AFR's measured with a WB. Personally, I use this for controlling initial cold start and the first few minutes after that. Once IVT is up to 64'C I have all cells set to Stoich. I have a theory it can be used to help hot starts as well though.

{B0146}: This is used to fine tune the commanded fueling, for engine load and IVT. Again, it's only a commanded table, it's not used to "correct" a BEN difference when cold. I use this to add fuel when cold, and the load varies. Sometimes an engine will want more fuel when idling cold than when driving, so you can you this table to add more fuel in the idle cells, less when cruising. Once the engine approaches normal temps, all cells should be set to "1"

Remember that for both of these tables, they only take effect when the NB O2 sensors are not used. If you have STFT data occurring, these tables are not used at all.


Simon.

Edit: I should have commented on the trim issue....

{B1501} & {B1502} Set the enabling of full CL mode. These settings will control when the STFT's become active.
{B1503} & {B1504} Set the enabling of O2 Ready. These settings will control when the LTFT's become active.

In the stock calibrations, the second two table enable the LTFT's well before the first two tables enable CL mode. So you end up with LTFT's being applied with no O2 correction. I set these table to be the same ( {B1501} = {B1503} & {B1502} = {B1504} ) so all trims occur at the same time. Actually, to be truthful, I don't run LTFT's in my car at all. When I did run them, I set the tables to be equal.

[hymey]

I was waiting for Simon to reply The IVT tables should be used more so for cold start and can be used for lean start up issues which occur when going mafless on hot start. It is the best way to go about adding more fuel cold. It is just a multiplier of the vve or maf scale. And IVT will equal ECT until full running temp there after IVT will increase gradually over time until it roughly doubles ECT. You don't want your O2s coming on cold not until around 60 degrees.

cheers

[The Alchemist]

I was waiting for Simon to reply The IVT tables should be used more so for cold start and can be used for lean start up issues which occur when going mafless on hot start. It is the best way to go about adding more fuel cold. It is just a multiplier of the vve or maf scale. And IVT will equal ECT until full running temp there after IVT will increase gradually over time until it roughly doubles ECT. You don't want your O2s coming on cold not until around 60 degrees.

cheers

So in my case, the o2's were working from very cold at the factory temp setting B1502/04 is -40 and the runtime 10secs, once I see STFT activity these tables do sweet nothing! I will raise the temp settings to 60degC as you have suggested.
mmmmm
SOooooooo why was the commanded 14.68 yet the measured AFR was slightly lean at 15.2 when I was free revving at 2000rpm (was measuring at the tail pipe with reversion) then at 14:16.33 in my log the STFT suddenly changed from +10s to -3's when the ECT crossed over 80degC and the actual AFR changed to? What suddenly changes at 80degC to cause this?
AND when you reach 60degC and the STFT's are working is there no ECT enrichment table as such to adjust, its all just done by the VVT and STFT's???

BTW that idle stuff was awesume thanks got this car idling with zero swing sounding almost stock lolol !!!!! Couldn't believe the difference!

[hymey]

So in my case, the o2's were working from very cold at the factory temp setting B1502/04 is -40 and the runtime 10secs, once I see STFT activity these tables do sweet nothing! I will raise the temp settings to 60degC as you have suggested.
mmmmm
SOooooooo why was the commanded 14.68 yet the measured AFR was slightly lean at 15.2 when I was free revving at 2000rpm (was measuring at the tail pipe with reversion) then at 14:16.33 in my log the STFT suddenly changed from +10s to -3's when the ECT crossed over 80degC and the actual AFR changed to? What suddenly changes at 80degC to cause this?
AND when you reach 60degC and the STFT's are working is there no ECT enrichment table as such to adjust, its all just done by the VVT and STFT's???

BTW that idle stuff was awesume thanks got this car idling with zero swing sounding almost stock lolol !!!!! Couldn't believe the difference!

Set them to 60 degrees C, the stft changes rapidly by the sounds of it, I will look at the log tonight, But the open loop tables are the only tables that have an effect on commanded afr, the engine will want more fuel cold aswell. Once the ects are hot and oil temps right up the IVT should be around 160 degrees and afrs will stabilise at this time IATs will have increased aswell from heatsoak in the manifold/blower. Also commanded idle rpm and TP%, idle vacuum changes can all alter afr suddenly if it drops to a different cell in the vve. Especially with the vve where individual cells cannot be changed so easily without affecting other areas. The IVT table multiplier changes commanded afr, If the afr changes by 13% and the commanded afr is still 14.68:1 it is most likely IAT and vve related, open loop alterations will show a difference in commanded afr.

I'm glad the idle instructions worked out for you, The e38 really eats the early pcm for controlling big cams once you get the hang of it. Once you nail min idle air,(which is basically desired airflow) you can raise max idle air back to factory values. min idle air is very sensitive and the easiest way to get it right is how I outlined it, by getting max idle area to the correct value, then lowering min idle air gradually until you can see the throttle blade trimming slightly when the throttle closes. 1 g/s to far and the trimming will be overactive and overcompensating, in which the first thing people do is start to make proportion and integral correction less aggressive, which does not need to happen. If you sneak up on min idle air by dropping it gradually you can get it spot on and the trims will only move plus or - 0.4%. Say if its idling at 18.0% it may go 17.6% on decel and recover idle with 18.4% before settling to 18.0% with 100% stock proportion and integral values. In which case I am very happy with as only the critical tables are altered. Once this outcome is reached see how the car feels to drive and work on getting coast down timing and idle timing correction right. After a bit of driving the idle gets even better as you may of noticed the e38 can really trim nicely and accurately if min idle air is right. The next morning I add 0.08 to max idle air and make sure I have enoguh air cold. If the engine is lagging behind commanded rpm and timing is high I basically keep bumping max idle air until the idle timing is around 15 degrees. I have found they cold start and drive cold a lot better by using more air rather then timing to get them starting and driving smoothly. I also suggest zeroing out cold noise reduction timing. This creates a lot of problems with a cammed car. The factory os adds timing cold in ect correction and then removes it in cold noise reduction? I just zero out both and run same timing cold to hot, I found it is the easiest way to do it.

[The Alchemist]

added screenshot for you to my last post
RPM Vacuum, TPS are all constant when this happens, the only thing I could see that changed was engine temp rolled over 80degC which could be completely unrelated anyways seems like a huge swing in trims when the commanded remains unchanged AT 14.68:1

<<For those reading thru this post and my ramblings the problem was that LTFT stored in the E38 were affecting logged AFR's even when in full open loop and during a cold start as well!. Morale of the story hit the fuel trim reset button under Bi-rectional control before commencing any VVT tuning in open loop>>

[swingtan]

As I've said before, if you work on an E38, you MUST log IVT. It can tell a different story to what ECT says....

As you would guess, there is a change in the engine efficiency that is causing the resultant change in trims. Assuming a cold start, the 80'C ECT probably relates to about 120' IVT. At this point, Dynamics are usually in a transition state between cold and hot running. I've found that dynamics can have an effect on fueling even when the airflow remains fairly constant, especially in cold start situations ( at least I think that's what it is.... )

Many would know that when going SD on the E38, you seem to end up with a very, very lean cold start. You can "fudge" the AFR's by commanding very rich when cold, or you can mess with dynamics to help reduce the lean condition. those that have looked in to this would know of an aprox. 8 second window after first start. I'm pretty sure this is dynamics related. If you want to rule out dynamics, you could try a cold start and disable all wall wetting in the tune. I might try this just to see what happens....

Simon

[hymey]

Yeah they are sensitive, without looking at the tune its hard to tell as you most likely have dynamics stock. I just finished an e38 then just by changing from dual 2.5inch to dual 3 inch system caused the entire vve to go out of whack also creating a very lean condition at start up at all ects. I would log IVT aswell. You have a blower on to which can change things. With the MAF on all these problems go away and when there setup correct there is hardly any difference in power anyway.

[swingtan]

I did a test today re: dynamics and the lean start condition..... They make little difference :P I turned off wall wetting all together and the AFR's were pretty much the same as when they were turned on ( for the initial 10 second start cycle ). They certainly made a difference when I attempted to move though.....