GMPP E38 crate engine ECU - speed density

[efnfast]

I have a gmpp crate engine controller package (ls3/525) and a n/a 427 LS3. Using the as-provided tune and the MAF plugged in, the car starts fine, idles fine and drives fine. The only problem is ultimately I need to go to speed density because I am using an ITB intake manifold (Harrop LS3 DBW ITB manifold). I would like to go in baby steps - make sure the as-provided tune works with the stock intake manifold (check), get it into speed density mode and get the car to just idle on its own and drive up/down the driveway, and then put on the ITBs and cross my fingers (with final tuning being done on the dyno ....I would be thrilled if the car could start and move forward/back on its own with the ITBs)


My understanding is that to get the ecu into speed density mode I want to set the MAF frequency fail high and low to 0hz and P101, 102 and 103 to 'ses off', 'error mode no MIL'. However, what I don't understand:

(1) How do I determine if the default parameters in the ECU are 'okay' for speed density (okay meaning it can idle on its own and move forward/back on the driveway) ... I have no idea what to look for

(2) How do i determine what bar MAP sensor I need to use - the engine came with a camaro 3 bar MAP sensor but if the ECU is setup to only use the MAF maybe they just stick on any MAP sensor they have? This one is doubling confusing because under 'VCM enhancements' there's options to upgrade to 1/2/3 bar speed density (but 1 and 3 are greyed out, only 2 is available). so I don't understand why this exists if failing the MAF causes it to go into sd mode. do I want to upgrade to 2 bar SD (and then replace my 3bar map sensor with a 2 bar, or would this impact my base MAF tune)

(3) Since the air temperature sensor is built into the MAF my understanding is you can fail the MAF and the temperature sender will still read using it. How critical is it it gets an exact reading of air temp? is more-or-less okay? I was thinking about relocating it somewhere around the engine bay away from heat.

I've attached my base tune file hoping to get some guidance about the speed density - i.e., if i fail the MAF will the ECU go into speed ensity mode, are the current parameters 'okay' to get it to idle, what bar sensor should i be using with the given file, do I want to upgrade my OS to 2bar speed density?

917_STOCK_tune.hpt

[schpenxel]

Yes, basically set the MAF fail high to 1hz. I would recommend first setting the p101/2/3 to "MIL on first error" AT FIRST to make sure you are getting the code that means the MAF has "failed". You can turn the light off later.. right now you just want to make sure everything is working so leave the light on so you have some sort of feedback on whether it error'ing out or not.

1. E38's use a system called virtual VE which is an equation based VE system. Instead of just having a VE "Table" they have a bunch of coefficients and a long as hell equation that is used to figure out different VE values for different RPM's / MAP readings. The equations are way too complex to even think about understanding. The 2.24 version of VCM Editor can't really edit these very well either..

Your options are basically to keep virtual VE and to use the new beta version of VCM Editor (2.25-->email HPTuners support and request access to it) which includes an editor built specifically for virtual VE, OR you can upgrade to HPT custom OS that basically switches you back to a "regular" VE table. Either will work, but I'd probably go with door #2 personally.

If you do go with the 2 bar OS route you'll need a VE table to get you started. Here's what you need to do.

Go to OS-->VCM enhancements and hit 2 bar MAP speed density. It will want you to save the file.. save it. Now close VCM editor and then open up the file you just saved.

Post a copy of the new file here and I'll give you a VE table to use that fits the format of your new file.

2. Post the part number for the MAP sensor and I should be able to give you the values you need. What you have in there already is probably fine. Keep in mind that when you upgrade OS's the upgrade process oftentimes updates your MAP sensor values even though it really shouldn't be changed... so you may have to switch these back to your original values (if they end up being changed)

3. Once you're not using the MAF there will basically be two wires left in the "MAF" harness that you can run to an IAT temp sensor somewhere else. I don't know anything about the intake you're trying to use, but anything is better than nothing. As long as it's fairly consistent I wouldn't worry too terribly much about it. I'm using the WT382 sensor from Borg Warner and mine is screwed right into the side of the intake manifold.

[efnfast]

If i wanted to use a 3 bar map sensor (e.g., 12592525 or 55573248) would i stick with the virtual VE table? The custom OS option only lets me upgrade to a 2bar, but the problem is, when I'm looking at 2 bar map sensors, i don't think any of them would install properly into my intake manifold (it requires an LS3 style one with the bolt hole for a screw)

[schpenxel]

You can use whatever MAP sensor you want up to about 5 bar

Don't get confused by the 2 bar OS name. That's just saying the VE table will go up to 2 bars

The MAP sensor is totally separate and independent. You can use a 1 bar, 2 bar, 3 bar, 4 bar, doesn't matter as long as you have the settings for it so the ECM knows what it's reading.

[efnfast]

I started to do more reading to try to educate myself.

(1)
Under MAP sensor, my linear & offset is 128.13kpa and -0.31kpa. I ~think~ this is correct for my MAP sensor - #55573248. this part number apparently goes to LS3 and a ZL1 camaro.

(2)
I don't understand the difference between loading the tune as is from the computer and failing the MAF to get into SD mode versus selecting the 'custom 2 bar os' under 'vcm enhancements'. Shouldn't failing the maf put it into SD mode? For a n/a application is it necessary to use the custom os? The reason I ask is because when I select that option and review the new file it makes, it seems like everything changes, even simple stuff like when cooling fans come on, and I'm not ready for that level of detailed change yet.

(3)
After failing the maf, do I want to adjust the high rpm disable/re-enable under dynamic air flow? Right now disable is set at 100rpm and re-enable is at 50rpm. According to the description, it will use filter maf airmass for its calculations. I've read some posts indicating to set these values high to make sure they're not used (e.g., 9000 disable, 8900 re-enable), and others indicating the opposite.

[schpenxel]

1. I think that's right

2. Yes, failing the MAF will put it in SD mode whether it's the stock OS or HPT upgraded OS. The difference is in what you have to work with as far as a VE table goes. With the original OS all you have to work with are some pretty crazy coefficients (goes under airflow-->speed density and open up some of those tables). With the upgraded OS you'll have a conventional VE table that is easy to edit. This can all easily be un-done, so if you don't like it you can just go back to the original tune/OS no problem. Just keep a copy of your original .hpt file. It doesn't matter if you're running boost or not.. you'll just not use portions of the VE table that are for boost. This is the easier route. Updating some cooling fans settings is easy so don't worry about that.

3. Doesn't matter. If MAF is failed then you can set dynamic airflow whatever you want, but it won't matter