MEFI 1 Definition File

[Trash]

Kind of a technical question, but here it goes. Currently tuning a MEFI 1 ECM. I'd like to expand the RPM/MAP/BPW table and add some MAP columns and RPM rows.

Can the .xdf file be modified?

Will a MEFI 1 ECM recognize the expanded table?

I'm sure this thread will go viral with a topic like this:D

[Dave Wettlaufer]

I'm thinking no, but I have not played with that setup.

[Trash]

I was able to build the expanded MAP/RPM table, but haven't tried to up load it yet. I know it's probably unlikely it would 'hurt' the ECM but want some feedback before I hit the Upload button.

Then I need to see if the module will 'see' the new table.

[Trash]

Does anybody no how the ECM behaves when you run the motor outside of the MAP/RPM table range, i.e. low map or RPMs higher than 5200?

[Racey]

Call All Seasons Marine in Boulder City and talk to Mike. He's pretty familiar with MEFI stuff. I know that MEFI 1 computers are extremely limited in what can be done with them, in fact i think Mike told me the entire map runs from 1 or 2 tables.

1604 Nevada Hwy
Boulder City, NV 89005-1903
(702) 293-4499

[Trash]

Racey,

Thanks for the reference, I will call them. The MAP/RPM/BPW table on a MEFI 1 is indeed one table. To say they are extremely limited as to what can be done with them is not exactly true. I'm in the middle of a tune right now and the options will make your head spin. True the MEFI 3's and up have more capability, but a MEFI 1 works just dandy for non-boosted applications.

I've received answers from 'pros' out in the field about the MEFI 1 that were so inconsistent it wasn't even funny.

I know the MEFI 1 has the ability to supply BPW information for 'off MAP/RPM' conditions, I'd just like to know exactly what kind of formula is used. For instance on low MAP situations below 40 kPa does it use linear interpolation off the lowest MAP/RPM point or another formula? I'm curious about off the top of the RPM band as well.

[AzGeo]

Buick GNX turbos ran mefi 1 and didn't blow up. I would say that 'map sensor base line (and top voltage readings) VS fuel pressure regulator references' would be the place to start when going with boost on mefi systems. I'm doing a BB chevy truck with 'vortex EFI mefi 1' on a turbo BB pickup truck deal. I will use a 'false coolant reading/resistor' when my boost gets over 5 lbs. But I feel that the original fuel system will keep up until that point, as designed. IMHO "if your fuel pressure regulator is closed (due to boost conditions) you will be getting all of the fuel/enrichment you need under boost. Unless you think you can boost that motor over 5 lbs with that underpowered EFI system! IMHO YOU can't make that system make very much more power than it was designed for. How will it run (how long will it run) with 99% injector pulse at any given RPM? You may be able to 'up size the injectors' but how will it idle ? IMHO there are many ways to 'tune the GM/Merc stuff' but never enough to make it a true high performance system. (on a long term basis) IMHO the '330 hp system' may make '450' hp max, so when you talk about your system can you calculate the fuel curve needed ? I am ready to learn, please teach me on how all this stuff works !!! Look, I read your post above and the 'single area maps' don't give any viable reading below 0.2" of vacuum. What are you actually trying to learn ? Reprograming without any map input? Get a map sensor that 'sees boost' and then come back with questions about "voltages/pulse widths/map numbers" and then maybe we can see what you are trying to do. IMHO "the factory designed MAP is what you seek to improve on" IMHO it only takes personal insite as to where you want to make the changes and how they effect your project.

[STV_Keith]

In the systems I have seen, when you get off the table in any direction (let's use your instance of <40kPa), then it will use the cell value for 40kPa (lowest value) and the true RPM. If you get over the highest RPM value, it will use that RPM value and the true kPa.

[Trash]

Buick GNX turbos ran mefi 1 and didn't blow up. I would say that 'map sensor base line (and top voltage readings) VS fuel pressure regulator references' would be the place to start when going with boost on mefi systems. I'm doing a BB chevy truck with 'vortex EFI mefi 1' on a turbo BB pickup truck deal. I will use a 'false coolant reading/resistor' when my boost gets over 5 lbs. But I feel that the original fuel system will keep up until that point, as designed. IMHO "if your fuel pressure regulator is closed (due to boost conditions) you will be getting all of the fuel/enrichment you need under boost. Unless you think you can boost that motor over 5 lbs with that underpowered EFI system! IMHO YOU can't make that system make very much more power than it was designed for. How will it run (how long will it run) with 99% injector pulse at any given RPM? You may be able to 'up size the injectors' but how will it idle ? IMHO there are many ways to 'tune the GM/Merc stuff' but never enough to make it a true high performance system. (on a long term basis) IMHO the '330 hp system' may make '450' hp max, so when you talk about your system can you calculate the fuel curve needed ? I am ready to learn, please teach me on how all this stuff works !!! Look, I read your post above and the 'single area maps' don't give any viable reading below 0.2" of vacuum. What are you actually trying to learn ? Reprograming without any map input? Get a map sensor that 'sees boost' and then come back with questions about "voltages/pulse widths/map numbers" and then maybe we can see what you are trying to do. IMHO "the factory designed MAP is what you seek to improve on" IMHO it only takes personal insite as to where you want to make the changes and how they effect your project.

For the record this is a N/A application. No boost what so ever. All your references to boost are moot in this application. I would not use a MEFI 1 for a boosted motor, but that's me.

Second, the injectors are not stock. Stock injectors were 24 lb Keihin units. I've installed 42 lb RC injection units. These injectors will be no where near the 80% duty cycle even at full throttle. It idles fine with the bigger injectors after I trimmed about 1.5ms off the pulse width. Idle AFRs are in the 14.0-14.5 range. It will hold a 600 rpm idle even with a fairly stout cam.

Third, the motor has a wide band AFR installed and I data log it. I am also data logging all the MEFI parameters and have the ability to change all of them.

The new motor has the ability to spin well past 5200 rpm, which is the top of the rpm row on the MAP/RPM/BPW table. So my question is what value does the ECM assign to injector pulse width when I exceed that rpm?

I like Keith's response and I have hypothesized that same scenario too, but I'm not convinced that is happening. The system does linear interpolation between cells for all the other regimes. It is conceivable it interpolates "off table" based on previous inter-cell slope or a fixed slope. I'm just not sure. For example the spark table has a slope extension you can assign.

Now the reason I want to know this is it will allow me to tailor edge of table parameters to best suit 'off table' performance. I know that may be confusing.....

As of now I just haven't spun the motor past 5200, but would like to have an idea of how the ECM will behave when I do so that I can best keep the motor in safe operating parameters, specifically the AFR.

Let me also say I am extremely pleased with how the system has responded to the demands of the new motor. This new motor is a significant departure from stock form. In spite of that it immediately starts and holds idle, never stalls going into gear and runs very smoothly in all the tests I've done so far. All I've really played with is the main fuel table. Virtually all other parameters are still stock. As I expand my tuning envelope and start to reach the outer limits of the fuel table I want to be prepared, hence the question.

Keith thanks for response and ideas, I appreciate the feedback.

[STV_Keith]

I like Keith's response and I have hypothesized that same scenario too, but I'm not convinced that is happening. The system does linear interpolation between cells for all the other regimes. It is conceivable it interpolates "off table" based on previous inter-cell slope or a fixed slope. I'm just not sure. For example the spark table has a slope extension you can assign.

Now the reason I want to know this is it will allow me to tailor edge of table parameters to best suit 'off table' performance. I know that may be confusing.....

As of now I just haven't spun the motor past 5200, but would like to have an idea of how the ECM will behave when I do so that I can best keep the motor in safe operating parameters, specifically the AFR.

Let me also say I am extremely pleased with how the system has responded to the demands of the new motor. This new motor is a significant departure from stock form. In spite of that it immediately starts and holds idle, never stalls going into gear and runs very smoothly in all the tests I've done so far. All I've really played with is the main fuel table. Virtually all other parameters are still stock. As I expand my tuning envelope and start to reach the outer limits of the fuel table I want to be prepared, hence the question.

Keith thanks for response and ideas, I appreciate the feedback.

If this MEFI stuff (that I have not used myself) is anything like the GM and Ford stuff that I have seen, then it will take the last known value and run with it. So if you have PW of 10ms at 5200rpm and 100kPa, then go to 5500, but still at 100kPa, it will keep using the 10ms value until the kPa changes...it which case it will then move to whatever cell intersects the highest RPM value and actual kPa.

Think of the "cell trace" feature of many software packages, where a bouncing ball or highlighted cell moves around and following the current operating location...when you fall off the table somewhere, it just sits at that location in one axis direction, and follows the other axis as long as there is resolution to do so.

In your MEFI software, do you have an RPM multiplier that you can change to make it so the RPM stays on the table? I can't see a good scenario where you exceed the limits of the table, with no additional fuel control, and that last value is good for more RPM. Usually, you would be tapering fuel out as you continue on past peak torque towards even less torque (more RPM).

Also, is there a RPM limit in the software that is going to either cut timing or fuel to hold the RPM at a certain point? I'd have to imagine so.

[Trash]

Keith,

I need to look for the RPM multiplier. I'm not sure at this point. It does have a rev limiter. Stock was set to 5080. I currently bumped it up to 5500.

I haven't gone off the top of the RPM band yet, but have gone off the left of the MAP (less than 40 kPa). The MEFI burn people tell me it interpolates off the borders, but who knows.

If it becomes a problem I believe I can redefine/dimension the fuel table to change the top RPM points. That too may involve a little testing.

[DaveH]

something else to consider. If your ECU fuel table will not go above 5400 RPM and you are worrying about running out of fuel as go above that in RPM, that may not necessarily be the case. you may actually go RICH.

what i see on the dyno is once past peak torque, engine RPM can continue to increase, but airflow actually DECREASES. the physical time to fill the cylinder decreases as RPM increases. Unless your cam/intake/porting is specifically designed for very high RPM use, you will actualy need LESS FUEL with increasing RPM past peak torque.

if you arent going to dyno it where you can actually measure torque and horsepower, and do it the "crude way" on the water with a wide-band, DONT BE SUPRISED if you see it getting rich in the fuel MAP and wanting less fuel with increasing RPM. at least you would be safe by setting your VE for X at 5400 and RPM increases but VE is decreasing.

[Trash]

I'll try find out more later this week. I've been too busy and haven't been able to play with it. My wide band O2 sensor took a dump so I just got the new one installed today.

The MEFI 1 doesn't have VE tables, just rpm/map/bpw. I've got a few modified .xdf files I may try as well to see what happens. I've got plenty of head room on my injectors so I can trim the bpw at the top of the rpm band up or down to see what happens with 'off table' rpm parameters.

I've found having the wideband O2 addicting to monitor. I think I'll feel naked without it when the tuning is done.

[AzGeo]

IMHO you must look at what your 'mods to stock programming' are doing to the (what I call) interlocking divices GM has build into their software. I have found that when I modified one area of their program, it effected one or more other functions in other areas. I've worked on a number of motors and reprogramming done by 'well known shops' that ran well at 75%/100% throttle opening, but at the same time had created all kinds of problems with 'cold start, low speeds, back fire at throttle opening, etc....' Since learning about all the 'booby traps' in the MEFI 1's, if I was forced to use one I have since just 'fooled the stock programs'. I think I do remember that MEFI 1's turn full rich at a (80% + ?) TPS value anyway, does your unit show that type of operation now ? I have fooled the stock software by introducing 'variable readings' (modified feedback) on a number of sensors. The 'IAT' has about an 10% variable on pulsewidth and the 'coolant temp sender' has about an 18% variable on pulsewidth. IMHO those two sensors along with your larger injectors and a nice aftermarket fuel pressure regulator, (and pump) should do what you require. If you have an 'early model' you could always use a 6 cyl rev limiter for a little more RPM. IMHO they (all Merc factory stuff GM or Motorola) are very limited as to modification and performance gains. Why not ask Motec on their web site ?

[Trash]

I've worked on a number of motors and reprogramming done by 'well known shops' that ran well at 75%/100% throttle opening, but at the same time had created all kinds of problems with 'cold start, low speeds, back fire at throttle opening, etc....' Since learning about all the 'booby traps' in the MEFI 1's, if I was forced to use one I have since just 'fooled the stock programs'.

I've been really fortunate since I have not had any of the cold start, low speed or back fire issues. In fact the darn thing runs pretty good! My changes to the stock tune have been very deliberate, usually changing only one variable at at time.

Just to be clear, I am not having any problems with the tuning process. I have a boat I can get in right now, fire up, hit the lake, go skiing all day etc. It runs great. I'm trying to learn all the inner workings and slowly modify the parameters and fine tune the entire spectrum of operation. As the motor gets a few break in hours on it and I expand the rpm envelope I would like to have an idea of how the MEFI 1 will behave when I exceed the max rpm on the fuel table, 5200 rpm in this case. If I know how it behaves I can have a plan of attack or at least some controls in place prior to pushing the envelope.

I have not witnessed any booby traps with this MEFI 1. Again I'm dealing with a NA motor. I was actually impressed at how well the bone stock tune handled all the modifications (cam, displacement, stroke, heads, valve train etc). My very first try to start the new motor it lit right off and held idle on it's own. No hiccups, sputtering, back fire...nothing. I've been able to trim out the fuel table, tweak the ignition table, and am getting good AFRs in most of the regimes.

I think I do remember that MEFI 1's turn full rich at a (80% + ?) TPS value anyway, does your unit show that type of operation now ?

No. It does not go full rich at 80% TPS. Nearly all of the TPS inputs are rate of change and not static values. It looks for TPS rate of change and will modify the BPW by a factor to introduce additional fuel much in the same way an accelerator pump on a carb would do.

The 'IAT' has about an 10% variable on pulsewidth and the 'coolant temp sender' has about an 18% variable on pulsewidth. IMHO those two sensors along with your larger injectors and a nice aftermarket fuel pressure regulator, (and pump) should do what you require.

MEFI 1 doesn't use IAT, so I don't have to play with that. I've also found no need to play with the ECT. I have modified the idle speed based on ECT in that specific table however.

If you have an 'early model' you could always use a 6 cyl rev limiter for a little more RPM.

I've got the Merc EST ignition. No need for the 6 cyl rev limiter. I can change the rev limit in the Scalars/Constants section of the program. Stock was 5080, I've bumped it up to 5500 for now. I can also modify the advance in another table. The ignition also has a Mean Best Timing algorithm.

IMHO they (all Merc factory stuff GM or Motorola) are very limited as to modification and performance gains. Why not ask Motec on their web site ?

I'm not using the MEFI program modification to enhance performance per se, rather I'm tuning it so I get the best potential out of the new motor. I let the crank, heads, cam etc. do all the performance work.