DMM

2004 CTS-V with an Edelbrock Eforce, cam, heads, etc. I've had the tune nailed down for a while and just noticed this yesterday while logging. I have the BE set up for fueling under boost (high load low rpm etc) and the PE set a bit more aggressive for max performance. At an airport now and do not have the tune handy, but figured I would ask this now since I don't remember this issue when I dialed the tune in.

I found that when the BE kicks in under light boost (outside of the PE parameters) the ST/LT trims reign the AFR back to stoich. Example, fourth gear up hill at 1800 RPM I crack the throttle a bit and get about 2-3 lbs of boost. The BE richen the mixture and I can watch the fuel trims ramp negative incredibly fast to lean the AFR back to stoich. This does not happen in PE, just BE.

Anyone ever seen this? I don't remember this being the case last time I tuned it. I cannot turn off the fuel trims as this is mainly a street driven car.

With the fuel trims leaning out the BE fueling, it kinda makes the BE pointless.

Anyone have any ideas?

rpturbo

iTrader: (47)

I thought BE was a secondary, requiring PE first?

DMM

It may not always act as fast as PE, however it is independent. I am still seeing the enrichment, however the fuel trims are not locked as they are with PE so the trims lean back to stoich. Don't recall seeing this before.

Russ K

iTrader: (1)

As mentioned by rpturbo, the PE has to be enabled before BE. I would change the PE enable TPS to 0% at all RPM's, then raise the PE enable Map to 95 KPA. This way you will hit PE any time the Map is 95 KPA or higher, then your BE will stay in open loop.

Russ Kemp

DMM

Thanks for the explanation. The PCM will default to the richest of the tables, correct? So PE and BE can still be independent values? If I enable PE and flatline the enrichment table, it would fuel directly from the BE tables as long as the enable criteria is present, correct?

Thanks to both of you.

Russ K

iTrader: (1)

I wouldn't 0 the PE enrich table as even a value of 1.00 would command stoich (but would be in open loop) I would set it to 1.13 (13.0 AFR), then set the BE to come in at ~105 KPA. Yes, if your already in PE, then once BE is enabled, the PCM will default to the richest table.

One thing to watch out for is that the BE can be delayed on some OS's. In those cases, just set the PE enable to 95 KPA and set the enrichment to 1.13 until the RPM that your over ~105 KPA, then set the enrichment as desired.

Russ Kemp

NicD

iTrader: (7)

Do NOT rely on BE, it operates in a slower area of the code and there is a delay on the Gen 3 PCMs. BE should be setup so that PE always comes in first even though they are indepedent and I really only use BE as a fail safe for a boost spike, etc.

rockoosi1

iTrader: (1)

Not sure if this is directly related, but I changed my PE to 100KPA and 25% TPS and the car would fall on its face during the burn out. It would also stumble very badily on the launch until I went into boost (or above 105 KPA where the BE kicks in).

My guess is I satisfied one of the criteria (TPS) and not the other (KPA). I lowered the KPA back down to 15 and left the TPS setting at 25% and now it seems to do much better. I'm still not sure if I using the correct approach because I'm basically in PE the entire the car is running as long as I'm above 25% TPS correct?

rockoosi1

iTrader: (1)

Russ, are you saying that there is a scenario where you can be in BE and not be in open loop? In other words, the last part of what you said has me wondering just a little. Thanks!

rockoosi1

iTrader: (1)

Just out of curiosity, how can you relay solely on PE if it only goes up to 105 KPA? I understand your theory I'm just not sure how you set things up once in boost? Thanks!

Russ K

iTrader: (1)

Yes, if you don't enter PE you will be in closed loop. All the BE does is command a richer AFR, and the car will be in closed loop causing the fuel trims to go negative trying to keep the fueling at stoich.

Russ Kemp

rockoosi1

iTrader: (1)

So with my TPS set at 25% and KPA 15 for PE, this should ensure I'm in open loop once I go above 105 KPA correct? Also what do you think about those settings? They seem to work well at the track but might not be the best for the street huh?

To be honest I didn't even relaize you could get into BE without going into PE 1st.

Russ K

iTrader: (1)

I would raise the enable KPA to at least 80-85, as you don't need to be in PE at 15 KPA.

Russ Kemp

rockoosi1

iTrader: (1)

I posted this earlier in thread "but I changed my PE to 100KPA and 25% TPS and the car would fall on its face during the burn out. It would also stumble very badily on the launch until I went into boost (or above 105 KPA where the BE kicks in). "

Do you think the PE & BE thresholds were too close and I was dealing with the delay of the BE that others were talking about?

NicD

iTrader: (7)

That's something else, you could make the PE and BE match and it wouldn't cause that issue.

edge04

iTrader: (9)

I've started looking into these settings. If I understand correctly, I won't enter PE until the TPS setting is met: example TPS needs to be above 29% and above 4k RPM and if not it is running in closed loop? Or am I entering PE above 15kpa? I wouldn't think not as I disable PE it by setting the TPS 100%.

Once in PE I am running stoich which is 14.5 then it seems like it is using the richer of the two, PE vs BE and dividing by 1.24 for 11.69

This all sound about right or am I missing something?

Realcanuk

Also running an eforce and I don't use the BE. I don't see any need for it and with some saying it has a delay, why bother.

A quote from Chris at HPT...

the issue is it does not activate as fast as PE does, there is a longer delay due to the processing loop the code is in.

For any kind of engine driven supercharger just use PE.

BE was intended for use as a safety mechanism on turbocharged vehicles when the turbo could spool for some reason below the PE threshold and run lean. This generally happens if the turbocharger is not sized correctly for the engine (too big or too small). When i had twin turbo's on my car i used PE only and had BE set to enable at the same enrichment as PE when boost exceeded 110kPa. Usually if the turbo is unexpectedly spooling it is not at a high load situation anyway (your TPS is below PE threshold).

rockoosi1

iTrader: (1)

So once again just ot be clear. If for any reason you enter the BE but haven't gotten into PE, you will be in closed loop and the NB O2s /STFT/ LTFT will be fighting against you BE tables anyway correct?

Realcanuk

I haven't played enough with it to confirm that, but from the descriptions above, it seems that's the case.

danieloneil01

A 2 bar OS goes way past 105kPa, it doubles actually.