MSefi.com read only forum (Jan.15,2018)

Hi all. After a couple of month of gathering parts and plotting and planning everything, and then a couple of weekends of installing everything, I have completely converted over from a Holley 390cfm 4brl carb and distributor, to a 500cfm 2brl GM TBI and Ford EDIS-6 under MSII control.
The engine has a "medium" street cam (no idea what the specs are on it), stock 8:1 compression ratio, ported heads, and a Weiand single plane 4brl intake (I got an adapter plate for the TBI).

I am only running with a NB O2 right now. I have a WB on the way.

Without changing anything on the base VE table, I have gotten it to start up and idle at 1000 rpm (for now) at around 0.8v on the NB O2 *without* the MAP vacuum hose connected!! As soon as I connect the MAP vacuum line, it goes lean and dies.

Just looking at the 1000rpm column in the VE table, at 100kPa (no vac line connected) the VE is 86, where it is currently idling a bit rich but quite happily.
But at my manifold vacuum of around 50kPa (15" hg), the VE table says 43.

If I understand correctly, I need to almost double the VE table (or the Req_fuel which was calculated to 7.3) to get things within range to just idle??
My 2x injectors are suppose to be 55lb/hr each (GM 5.7L TBI). But the engine is idling as tho its VE is way high at 1000rpm, or the injectors are really WAY lower flow rate than rated!
Am I going about this right? I have attached my most resent .msq file for anyone to look at.
Any ideas??

Thanks-
Colin

Check your fuel pressure. If it's too low, the injectors will behave like they are considerably smaller than they are.

Here's some info so you can verify your injectors, too. If the injector size or fuel pressure isn't right those errors proliferate thru everything.

http://home.earthlink.net/~jcgebhart/msindex.html

4.3 45 lb/hr 5235203
5.0 40 lb/hr 5235279
5.7 pickup 55 lb/hr 5235206
5.7 copcar 65 lb/hr 17084327

From what I recall the fuel pressure gauge was showing about 12.5 to 13 psi.

Thanks for the link.
I don't remember seeing any color coding on the injectors, but I will look for the part #.
Unfortunately the car is in another city and I only get to work on it about one weekend a month.
So I have to do all the research I can to be prepared when I do work on it.

My Req_fuel is calculated to be 7.3.
I am running 3 injections per cycle and set to simultaneous.
My pulsewidth at "idle" (currently 1000rpm) is 4.12ms, and 5.10ms at 5500rpm.
Should I lower the injections per cycle and/or change from simultaneous to alternating?
Seems like the pulse-width is really low in the range-- doesn't this limit accuracy?

I like the idea of running a flow test as outlined here: http://www.megamanual.com/ms2/injectortest.htm
That will tell me for sure what my injectors are running, and how close they are matched to each other.
I have a bad feeling that the injectors are flowing much less than what I am thinking.
Otherwise, by the numbers, the engine would be getting 70-80% VE at 1000rpm!
When I adjust to get it within range, should I alter the Req_fuel number or change the values in the VE table?

Thanks again for the help!

nicad,

VE numbers can be very high at idle when you start tuning. However, as you start aiming to achieve the minimum MAP kPa value, you may well find that the VE decreases substantially. So if this was mine, I wouldn't worry too much about the actual VE numbers at first, I would just tune the fuel and timing and then see if there is an anomalies.

I have seen many engines idle with a VE of 60+%. This does NOT mean the engine is using 60% of the fuel it uses at wide-open-throttle because the fuel pulse width is also scaled by the MAP, and rpm has an effect too. So if the VE=70%, and the MAP is 35 kPa, then the fuel pulse width is 0.70*0.35 = 24.5% of what it would be at 100 kPa and 100% VE - per cycle (ignoring opening time). Also the engine is also going much slower, and there are a lot fewer fuel pulses, so if these example was 600 rpm at idle and 6000 rpm WOT, then the fuel would be 600/6000*24.5 = 2.45% fuel use. And WOT VE may well be over 100% (depending on the other settings).

Finally, because of the short pulse widths, the VE at idle depends a lot on the value you have chosen for your opening time setting in the tuning software. If the value you set is shorter than the actual opening time, you will have to up the VE table to provide the longer pulse widths. So in your case, you might need to increase the opening time a bit. Finally, this error is amplified by having more squirts, so you might also want to switch to 2/alternating, which will reduce the effect of any mis-judgment of the opening time.

Lance.

I bought some flow-tested and matched pair of "61" lb/hr injectors. I will be working on it this weekend. This is my plan:

- Run an injector flow test in Megatune starting with aprox 1ms pulse width and tweak to find the exact opening time of the injectors.
- Configure Megatune with the actual open time number and Req_Fuel based on the data from the flow-testing print-out and my fuel PSI.
- Switch the pulse strategy from 3/per and simult, to 2/per and simult, or even 2/per and alternating. (3/per and simult is too short of pulses, but the 2/per and alt might be too rough idling.)
- Adjust VE table cells at idle with vacuum connected to get the highest manifold vac. (Is it normal to get the highest vac at idle but still be too rich or lean according to the O2?)
- Adjust the remaining VE table cells based on the WB O2 data.

I currently have the EDIS system set to 15* BTDC for idle. I have read that the Buick V6, with its low compression (8:1) and head characteristics, can take a lot of advance. I think 15* is where it idled with the highest vacuum before with a distributor setup. From there I am only guessing for the advance curve up to 3000rpm going to 36*.

Also, correct me if I am wrong, but is this how the AFR and VE tables relate to each other?-- When using a WB O2, the AFR table is a reference table for the WB O2 readings to be compared to, and if there are changes to be made (either automatically EGO or manually) they are made to the VE table? Is the AFR table only edited if you want the engine to hit different AFRs under different conditions, and so the "base" AFR table should be fine for most engine applications and setups?

Thanks-
Colin

Well, I got it running OK over the weekend and test drove a few times, letting the Autotune start to do its thing on a WB O2 sensor.

But I am still very confused about how much fuel this thing is requiring compared to the basic calcs.
For my injector flow at my fuel pressure (2x TBI injectors each rated ~60lb/hr @ 11.5psi), the MegaTune calcs Required Fuel at 6.7ms (231 ci, 6 cylinders, 60lb/hr, 14.7:1 ratio).
However, to get it running within range according to the WB O2 (and to confirm the O2 readings, it seems to be running pretty well), I ended up having to up the Required Fuel to 18.0 and increase the entire VE table by at least another 50%!!

I know they always say give an engine what it wants, but Is it normal to end up at almost 4x the amount of fuel than the base VE and Req_fuel started at?
How is this possible???

Colin--
Not that I'm any expert, but I seem to need a lot more fuel than the calculations suggest. I'm running E85, but even calculating for that I've already gone to more than 50% more req_fuel and the VE table is in the high 50's around idle. One thing I would mention is to verify that your fuel pressure gauge is indeed reading correctly, with a stock TBI you are right, it should regulate to 13 psi +/- 1 psi or so. I believe your understanding of the AFR and VE tables are correct.