E38 Economy techniques

[macca_779]

Ok guys I'm after some tips from people that have got some good ideas to improve economy on E38 ECM equiped cars. From what I can see and the little experience I have with tuning these computers (only tuned 1 E38 car), there isn't much available for us to tweak. Things like DFCO which are only touched on in the cal. I don't see anywhere where I can alter TPS and mainly MAP activate point. Also is there a planed update to include a lean cruise or some other way to alter cruising AFR's, in a semi open loop fasion. I know I could do a work around by forcing OL and tricking the ECM to going lean while cruising, but I don't really want to go down this route. So far the only way I've been able to improve economy on these cars is to optimise timing. It works but there is better gains to be had if I could alter fueling.

[The Alchemist]

I sympathise, I feel your pain macca
I've done 2 E38's with another 2 booked in this week. Having good results with timing, as you do, but fuel is another story. What I have found is that the MAF low is slightly lean resulting in positive fuel trims. Following the logic with the LS1's regarding fuel trims applied to full load fueling, I trim the low MAF until I get slightly negative fuel trims. Not sure if this actually helps though. Perhaps someone else would care to comment.

Mike

[macca_779]

I noticed the same trends with positive trims. I scaled both MAF tables up 1% to improve it slightly as it was consistently hoping around 3% LTFT. It didn't get it down to zero but as it was a street tune I didn't want to screw with the tables too much without a wideband on board. Plus I was hoping economy wouldn't get worse even with more accurate MAF tables.

[GMPX]

I don't know the answers for you guys, but it's a bit dissapointing they have gone from mid 12L/100 (LS1) to 14L/100 (L76).

Cheers,
Ross

[The Alchemist]

I was rescaling the MAF today on a Caprice and found that even when the MAF HZ stayed constant the LTFT would change from 0.8% to 3.9% on a MAP cross over point at 45KPA while cruising at 1100rpm ( Auto).
I guess the VE constants are having an effect as well.....food for thought?
Also was doing full load runs (knock sensors turned off by setting the "disable rpm" to 1000rpm)with knock phones and a tech watching the exhuast for detonation and tuned the full load timing. Those knock sensors can now be detuned to register real knock.
This particular car was getting about 11 to 12 l/100km on the instant readout at 100km/hr.
Mike

[macca_779]

I was rescaling the MAF today on a Caprice and found that even when the MAF HZ stayed constant the LTFT would change from 0.8% to 3.9% on a MAP cross over point at 45KPA while cruising at 1100rpm ( Auto).
I guess the VE constants are having an effect as well.....food for thought?
Also was doing full load runs with knock phones and a tech watching the exhuast for detonation and tuned the full load timing. Those knock sensors can now be detuned to register real knock.
This particular car was getting about 11 to 12 l/100km on the instant readout at 100km/hr.
Mike

Don't suppose it would be too much to ask to get a look at those knock settings would it. I've de-sensitised mine by scaling up the tables to be pretty much a factor of 8 where they were a factor of 2 which follows on from the lower mg cells (BTW what the hell does mg stand for), this was under the advice given to me from a mate. Alas I have no real data or long term testing to back this up, so something more solid would be great.

[The Alchemist]

basically I set up a log to scan all the knock sensors individually, rpm, TPS, load in g/s , knock retard and load up the car either on the dyno or on the road after full load tuning has been completed and I am satisfied that the engine is not knocking. When the scan tool logs knock you check the knock data to see which sensor is playing up. I have found that 1 or 2 sensors are always a bit twitchy which pulls timing for the whole engine ruining on road performance. The way I interpret those 8 knock tables is as follows:
Say the knock occurs at a load of 0.5g/s at 3200rpm on knock sensor "c" I go to the "c" knock map at the closest rpm to 3200 and go to the load point of 500mg/s. I'm assuming this is meant to be 0.5g/s. Now say this sensitivity is set at 2.399, I have found that tweaking this to as little as 2.6 or 2.8 is enough to shut the offending sensor up and stop false knock. Its a bit of a process as you can have noisey knock sensors at different rpms or loads and I find that once you've got rid of most of the false knock this way you get a much better on road throttle response and torque which is what you want the customer to notice. I'm on to my 4th E38 so far and the results have all been the same although the knock sensors that need tweaking vary from car to car, this process seems to work well.
The Caprice gained a solid 15rwkw and about 7% torque across the entire rpm range It was bog standard with no alterations. An amazing car to drive!!!

[macca_779]

Thanks for the tip mate. I'll have a go at working on that. Appears that I may have detuned them a bit too much going by your experiences. Although in saying that, I've found that they still remain quite active when I tried my first spark map in one. They certainly don't like anywhere near the kind of timing that has worked well for me on LS1's.

[The Alchemist]

well I have found that they like 2 or 3 degrees more timing than the typical LS1 engine at all rpm points during a full load run, infact at 6200rpm I run 26 to 27 degrees and the engine loves it. With an LS1 22 or 23 degrees is the limit on our fuel at 6200rpm. Of course the knock sensors at this rpm go nuts regardless if its knocking or not which is why I check first then adjust knock sensors later. Works a treat.


Mike

[oztracktuning]

It would be good to be able to somehow change the AFRs at cruise to something in the 15s. I played with the 02 voltage switch points today, I sent them right down to 0.2V and it didnt make any difference.

Are there any other possibilities?