MFI Pump - Open Heart Surgery

[dicklague]

yup......now I am confused too....will have to think about it when I am less harried....

[jeffc280sl]

I agree. Sorry about that. Think of it as positive and negative (vacuum) pressure. As you open the throttle body the engine takes a big gulp of air to mix with fuel. That gulp of air reduces the air pressure in the intake manifold. On an acceleration air pressure will drop as rpms increase because the engine is demanding air and fuel. MAP drops. We want to know what happens to the afr as we start and end the acceleration phase. It will come to you, I had trouble with this also.

[Mr Beau]

Try doing a log before the engine starts. AFR should be 14.7 and your vacuum reading should be equal to atmospheric pressure. As you crank the engine and it starts, you will see the AFR change and the MAP decrease. The voltage reading you have before the engine cranks will be close to what you should see at WOT.

Hopefully this will help makes sense of the readings.

[dicklague]

I just did a bit more research. On a GM product that uses the same MAP sensor, I found that the voltage is low at idle say 2 volts and increases to 4.7 when the vacuum increases. which makes sense and fits your observations.

[jeffc280sl]

I found some 1-Bar GM MAP specs.

0 inHg = .3 volts
29.5 inHg = 4.9 volts

You should be able to set these limit values in your data logger which will calculate everything in between.

[dicklague]

thanks for the information - will use those numbers.

[jeffc280sl]

Let us know how your testing is going.

[dicklague]

Jeff and all......have not had much time this week to do additional testing. I did do some freeway running on Wednesday that gave me the opportunity to do some steady throttle running.

I also tried taking one sample per second rather than one every half second. This makes the RPM less erratic. I also tried upping the "debounce" on the charts which also smooths them out a bit. I get the impression that the fast sampling make the charts look pretty erratic.

Philosophically do we need this much information?

Remember I am a new user to wideband sensors with data logging, so I don't know the answer.

[al lkosmal]

If your Open Office spreadsheet is like Excel, you can generate a trendline from your data, which will "smooth" out the short term spikes and may provide you with better idea of what's going on.

[jeffc280sl]

My LogWorks software has the capability to smooth data so that you see trends with fewer spikes. Whatever you end up using I would try and use the same smoothing technique for all rums so that you have an apples to apples comparison. I was interested to see what happens to the afr when you mash the accelerator at 3k rpms in 3rd or 4th gear. This is full load throttle response and it can be fine tuned if off. By off I mean fuel is behind (lean) WOT as viewed by map or afr rises or falls during WOT
Here is a sample. Black is rpm and it rises from 3 to 4.5k. As I mashed the accelerator you can see map pressure fall. You should have seen some of my before tuning runs. I think this is what you want to see. Responsive afr at the correct mixture.

[911st]

I guess I am late to the party.

If it has not been said, the difference between the low and high points on the space cam relate to the torque range a space cam can support.

A 2.4T space cam can support say 10-150 lbs of TQ (just guessing).

A 2.7RS has deeper cuts into it and support between say 10 and 200 lbs of TQ.

If you put a 2.4T space cam in a motor that it going pull 200lbs of TQ and adjust the rack so it is delivers enough fuel to support 200lbs of TQ, it will be to rich at idle and part throttle as it will then be on be able to support a TQ range of something like 60-200 lbs.

The springs and weights determine the rate the sensor stylist moves across the space cam with changes in RPM. Adjusting these only effect how fast the space cam stylist moves from low rpm to high rpm operation points. The space cam delivers more fuel as the rpm increases up to the RPM point of TQ peak so playing with the spring tensions gives the impression it is adding fuel if it gets you to a deeper part of the space cam faster.

The deepest point on the space cam and the point where the most relative fuel delivery will be had should be at WOT (space cam fully rotated) and at the rpm where TQ peaks. Fuel delivery should then reduce after that point to red line.

The spring tensions can not add any extended fuel delivery capacity or range per say. They just let you advance to a higher delivery part of the space cam faster or slower.

Only playing with the racks position with the adjustment screw, the thermostat pin depth, and or altitude pot depth can add more gross fuel delivery capacity. (Larger pump plungers can also extend the TQ range.)

I have used a black felt pen to mark the space cam so I could identify the point of operation where I was having issues. The stylist would then leave marks at that point if that is where I limited my operation to. If I needed more fuel I would then carve at the space cam in that location.

I really do not suggest trying this but increasing the depth of the cuts into the space cam can extend the supportable TQ range of a space cam. I would guess that if taking this approach it might be better to get the low load idle and cruse AFR's working correctly first. Then work to add more fuel at increased load points by carving the space cam. Not for the faint at heart.

Best to send your or a representative TQ curve to Gus and have him figure out which cam and plunger/piston size combination and what spring and weight settings might fit it.

Not an expert just what I have found.

[jeffc280sl]

I think your comments are excellent. As for expert opinion I'd say anyone who has carved on a space cam has a very good understanding of the flyweights, springs and levers inside the fip. Either that or they have extra space cams lying around.

How did you know what area was limiting your operation. Did you use a dynomometer or portable afr device? Were you trying to meet an afr spec? My afr meter and data logger will accept an accelerometer input. I've just begun to tinker with it but I'm led to believe you can calculate/estimate hp and torque.

[911st]

AFR gauge. This was some 8-10 years ago on a 2.8 twin plug w cams and we did not have the cool AFR monitoring stuff we have now.

Again, one can adjust the rack for more fuel to support a higher level of peak TQ, but there will not be any increase in 'range' of fuel delivery unless the range of depths on the space cam are increased, or - larger plungers are swapped out which is probably beyond most of us. JMO.

I love Turbo CIS and MFI.

[jeffc280sl]

Even with an afr meter, map sensor, tps, rpm input and accelerometer tuning the MFI is challenging. Can't imagine the difficulty and trial and error you must have gone through. Amazing work which few others would even think of attempting.

Did you try tuning by just moving the bc or altitude pot as you call it? I think its the easiest change to make for a novice who has a rich or lean overall condition.

[356RS]

Keith explains the space cams function very well. I have used the black marking pen method on a space cam before and documented throttle positions at every 10 degrees to 80 degree full throttle and rpm's at every 500 up to 3500 pump rpm. Below is a crud photo of this. The lower right corner of the space cam is the starting point. Up is RPM and to the left is throttle.

[jeffc280sl]

Very cool. Its very clear from your marks that great precision must be used when adjusting the white, black and rack screws. When adjusted perfectly the stylus will read the correct indentation/spot for the throttle position as shown in your vertical marks and the correct rpm indentation/spot as indicated by the horizontal marks. The horozontal position being determined by engine rpms as tension is adjusted on the flyweights via the white and black screws. Simply amazing. Those dots represent the setup table for a modern computer controlled system.

[911st]

Originally Posted by jeffc280sl

Did you try tuning by just moving the bc or altitude pot as you call it? I think its the easiest change to make for a novice who has a rich or lean overall condition.

No, that is the same as adjusting the screw on the rack. The just change the relative position of the rack.

Again, moving the relative position of the rack increases the fuel being delivered but dose nothing to increase the 'range' of fuel delivery.

[911st]

Originally Posted by 356RS

Keith explains the space cams function very well. I have used the black marking pen method on a space cam before and documented throttle positions at every 10 degrees to 80 degree full throttle and rpm's at every 500 up to 3500 pump rpm. Below is a crud photo of this. The lower right corner of the space cam is the starting point. Up is RPM and to the left is throttle.

Mark,

I think we talked about the felt pen in a thread when you were started your test bench. I spend much of my time on the 930 board talking up how to trick CIS so I missed this wonderful thread. Seeing it used is so cool and I love what you did.

I had to pull my pump, drain it, and take it apart every time I wanted to check a point on the space cam. Having a bench must make this much easier. With your info you are basically one step away from pulling the programing code from the MFI space cam. Now you just need to measure the depth of each point.

MFI relates to TQ, not to HP per say. It actually should deliver less fuel per stroke at HP peak than at TQ peak.

Having said that, MFI is probably not going to be totally accurate under all conditions and if we can get with in a point of goal AFR at points other than at the WOT power band, we are probably pretty lucky. However, we should be able to nail the WOT power band area petty well. It is the part throttle positions that can be a challenge.

The effect on fuel deliver with changes in stylist height is probably liner, we would just need to input the expected TQ at every say 250rpm and set a reference point or two on the space cam for setting the spring tensions. It is just a 2 axis injection map with RPM on one axes, throttle position on the other, and the cell or stylist height is how much fuel we want delivered per stroke.

We need someone that can translate or program our space cam needs on a 3d mill of some type.

We could even cut out the map area out of the space cam so the map section could just be milled and replaced.

Dam this is exciting stuff!

[911st]

Originally Posted by jeffc280sl

...Those dots represent the setup table for a modern computer controlled system.

Well said!

[911st]

It might simplify things to start by thinking of the space cam as three different space cams. One for low rpm (where TQ is increasing) one for mid range RPM, (where TQ is flat and or peaking) and one for high rpm (where TQ is falling).

We can then use the three stage spring sets to determine when each section of the space cam will be used and at what rpm.

Again, we do not care about HP, just TQ. TQ is the weak line on the following chart.

It this case the low rpm 100% throttle angle might be set for something like 125# TQ, the TQ peak section for 175 lbs, and the high rpm section for 150#.

There will be transitions between each slice of the space cam to sooth the transitions between them.

The space cam values or stylist heights will basically mirror the motors VE table at all RPM and throttle angle operating points.

This is all just a thought.

Originally Posted by Jeff Higgins