Fuel Pressure Regulator

[Guest ratchethack]

Sorry if I beat the shit out of this topic.

Frustratin', ain't it -- eh, Dan?

 

Nicely beaten though -- and far better you than me.

 

Trust me on this one from hard experience -- The bigger, nastier, and more gruesome the delusions, the harder they are to kill.

 

 

The necessary final step is always a great relief to all concerned -- and highly appreciated.

 

By all means, leave us now resume "normal" programming. . .

[badmotogoozer]

I have dial cutoffs that I added to my Twin Max and they work great. If I dial them too loose, I get too much pulsing, but if I dial them too tight, I get a lack of instantaneous response.

 

Once again reading through all the useless crap yields an interesting tidbit.

 

What are you using for your cutoffs? I keep meaning to bring home my collection of flow restrictors and find a permanent solution to this problem. In the beginning I just balanced to the center of the bounce. Now I just stick a clothes pin on the tubes. Works quite well. Interested in what you are using - inline valve?

 

cheers,

[dlaing]

Once again reading through all the useless crap yields an interesting tidbit.

 

What are you using for your cutoffs? I keep meaning to bring home my collection of flow restrictors and find a permanent solution to this problem. In the beginning I just balanced to the center of the bounce. Now I just stick a clothes pin on the tubes. Works quite well. Interested in what you are using - inline valve?

 

cheers,

I am using little plastic (nylon?) inline screw valves.

I had bought a crappy set of vacuum dial gauges from "Cycle Gear"

I could never get the gauges to stay in synch with themselves despite the umpteen calibrations.

But the gauge kit came with screw valves, which worked great at damping the pulses, once I bought the Twin Max.

Something like this could probably do the trick but the short quarter turn is not ideal. A thumbscrew valve is more precise.

http://item.express.ebay.com/Home-Garden_O...cmdZExpressItem

EDIT, Never mind that valve, this might do the trick

http://item.express.ebay.com/PART-IN-LINE-...cmdZExpressItem

Assuming 1/4" is right size

Maybe a carburetor jet with a small orifice would nicely dampen the pulses????

[dlaing]

You are missing something. Other than the threshold for overcoming the regulator spring, fluctuations in manifold vacuum have no effect on the pressure in the fuel lines. The regulator is just using vacuum to mechanically switch the regulator. Think of it as a regulator with a manual lever to throw to switch from low pressure to high. the "lever" that is getting thrown is the vacuum diaphragm. The regulator can be considered as on or off. "On" with vacuum applied allowing fuel to pass back to the tank at a lower pressure than "off". The fuel pressure is in the fuel circuit (pump, lines, injectors, and finally regulator) atmospheric pressure and manifold vacuum do not alter it.

The regulator is the last component in the circuit, it blocks the flow back to the tank causing pressure in the system. When vacuum is applied to the port, it overcomes one of the springs via the diaphragm and allows fuel to pass more easily back to the tank reducing pressure. It only has two values, with or without vacuum applied, high or low, if you will. If there was a mechanical switch instead of a vacuum diaphragm there still would only be two values, how hard you pushed the switch would have no effect.

When you apply vacuum, nothing changes until you get to the threshold when the vacuum overcomes the spring. Then the change is made and it remains that way until sufficient vacuum is released for the spring to relax.

 

Whew. Pretty redundant here. Sorry if I beat the shit out of this topic.

Thanks. Redundancy helps. I am not sure I believe you, but I'll take your word for it until I see further evidence.

For now since the fuel pressure doesn't need it as a reference, I think I'll cap off the vent since it is useless and the ozone exposure is slowly eating at the diaphragm.

[Ryland3210]

One more thing. There seems to be some confusion about the relationship between vacuum and fuel pressure. There is none. Vacuum is just used to trigger a regulator at a specific value. Fuel pressure is governed by the regulator at two preset values. Let's say for the sake of agrument that the regulator applies at 15"Hg. and the fuel pressure spec is 35psi with the regulator applied and 40psi with it not applied. Vacuum is just the switching device. If the engine is producing less than 15" vacuum the fuel pressure in this model will be 40psi. If the engine is producing more than 15" vacuum the fuel pressure will be 35psi. The idea is high load = low vacuum ~ low load = high vacuum. This is why vacuum is a handy means of actuation. Make sense?

 

Thanks for the clarification. As I understand it, the switchover occurs around 13"Hg, and has a hysterisis of 1-2"Hg.

 

I think Dave missed my point that I was speaking of instantaneous RPM. Of course, as soon as that changes, even at fixed throttle position, airflow will change.

 

I do not understand how a map sensor can sense load, nor how load changes airflow at a particular combination of throttle opening and RPM. The only difference load makes is how fast RPM changes for that combination.

 

On the other hand, I maintain that a smart enough (and fast enough) ECU could calculate load without an map sensor, provided it has the other inputs I mentioned before with a suitable model of the bike's power output and mass, by sensing the rate of change of RPM. F=m*a. That would assume a known rider mass, however, so maybe a sensor under the seat would be needed for better accuracy! Either that, or the ECU would need to be user programmable for rider weight.

[Ryland3210]

Seeking knowledge for it's own sake, with or without practical application, is a joy for some.

Every so often, some finding which seems useless at the time, becomes valuable later on.

[Dan M]

Thanks for the clarification. As I understand it, the switchover occurs around 13"Hg, and has a hysterisis of 1-2"Hg.

 

I think Dave missed my point that I was speaking of instantaneous RPM. Of course, as soon as that changes, even at fixed throttle position, airflow will change.

 

Uh huh.

 

I do not understand how a map sensor can sense load, nor how load changes airflow at a particular combination of throttle opening and RPM. The only difference load makes is how fast RPM changes for that combination.

 

On the other hand, I maintain that a smart enough (and fast enough) ECU could calculate load without an map sensor, provided it has the other inputs I mentioned before with a suitable model of the bike's power output and mass, by sensing the rate of change of RPM. F=m*a. That would assume a known rider mass, however, so maybe a sensor under the seat would be needed for better accuracy! Either that, or the ECU would need to be user programmable for rider weight.

 

MAP (manifold absolute pressure) doesn't tell load all by itself. It is a calculation made by the computer considering throttle position, rpm and map. Likewise, with an airflow meter, the inputs with from the crank sensor (RPM) and the TPS (throttle position) are used in conjunction with airflow to calculate the load.

Either way it is easy to comprehend if you think about an engine under an extreme load as you would have with low rpm a high gear and a high throttle opening. If you open the throttle wide the vacuum drops to near zero, stays there and the rpm doesn't change quickly. If with an air meter, under the same circumstances the air flow stays low even with a wide throttle opening because the rpm does not rise quickly. In a low load situation RPM rises faster, vacuum recovers faster and air flow increases faster. The computer considers all of this. In both situations the computer needs to know what is flowing through the manifold measured either as vacuum (after the throttle plate) or airflow (before the throttle plate). Without that info the computer can only estimate the load.

Systems like ours do not use MAP or MAF sensors and it works but it is not nearly as accurate.

If the computer adds fuel at the same rate under high load as it does under low load the mix will be too rich. (less air flow needs less fuel to maintain the proper mix)

In the modern emission conscious world it is all about accuracy. Manufacturers can no longer dump fuel to cover inaccurate delivery. This is why systems are getting more complicated.

 

 

 

Again, sorry to all who find reading through all of this minutiae boring or a waste of time. Ryland is bringing up valid points and I feel like giving him valid answers is what a technical discussion board is all about.

I do after all have some qualifications even if Dave doesn't believe me.

[Guest ratchethack]

Again, sorry to all who find reading through all of this minutiae boring or a waste of time. Ryland is bringing up valid points and I feel like giving him valid answers is what a technical discussion board is all about.

I do after all have some qualifications even if Dave doesn't believe me.

No need for apologies, Dan. You're exactly right. Somebody will certainly "correct me" if they b'lieve this is wrong, but I b'lieve hashing such stuff as this out as has been done here is the entire intent, purpose, and value of the Technical Topics Forum.

 

This has been most enlightening, even as distractions abound -- as has always been the nature of any such Forum. Would anyone attempt to claim otherwise??

 

Speaking for myself, I'm grateful to you and John for taking my understanding considerably beyond where it was previously, even though it hasn't changed anything I'll do to tune the Guzzi. Knowledge for knowledge's sake, as John pointed out.

 

There will always be the whiners who complain about stuff they're not interested in reading, let alone not capable of comprehending. Please don't let those bringing nothing of value to the table deter the discussion here.

[jtucker]

Please don't let those bringing nothing of value to the table deter the discussion here. <_>

 

Great... I've found this thread interesting, but now due to this comment, I feel compelled to contribute. So here goes....

 

Umm....

 

... I got nuthin'. Sorry.

 

__Jason

[raz]

Either way it is easy to comprehend if you think about an engine under an extreme load as you would have with low rpm a high gear and a high throttle opening. If you open the throttle wide the vacuum drops to near zero, stays there and the rpm doesn't change quickly. If with an air meter, under the same circumstances the air flow stays low even with a wide throttle opening because the rpm does not rise quickly. In a low load situation RPM rises faster, vacuum recovers faster and air flow increases faster. The computer considers all of this. In both situations the computer needs to know what is flowing through the manifold measured either as vacuum (after the throttle plate) or airflow (before the throttle plate). Without that info the computer can only estimate the load.

But why do the ECU need to know the load? In a freeze frame, we have a given throttle and a given rpm. Just throw in the correct amount of fuel. I'm not arguing here, I'm just trying to understand. Is it because the ECU will be too slow without knowing load, always using the pulsewidth that was needed the previous revolution? Or should we aim for a different A/F ratio under different loads? If so, why?

 

I'm sure anyone not enjoying this thread has left us long ago so I'm not apologising

[Dan M]

But why do the ECU need to know the load? In a freeze frame, we have a given throttle and a given rpm. Just throw in the correct amount of fuel. I'm not arguing here, I'm just trying to understand. Is it because the ECU will be too slow without knowing load, always using the pulsewidth that was needed the previous revolution? Or should we aim for a different A/F ratio under different loads? If so, why?

 

I'm sure anyone not enjoying this thread has left us long ago so I'm not apologising

 

 

How would it know if the pulse-width on the previous revolution was right? It is not about needing different A/F ratios under different loads, it's about maintaining proper A/F ratio under different loads. The correct amount of fuel requires the knowledge of the amount of air. Load limits the speed at which the engine accelerates. That speed of acceleration governs how much air can be pumped in. To be accurate, fuel has to be matched to air flow. This was the beauty of carburetors, load (vacuum / airflow past the venturi) governed how much fuel was drawn into the intake. While fuel injection is far more precise, it needs to know airflow to get it right.

As I've said, our bikes do it without knowing load. The value (compensated for by temperature) is governed by RPM and TP alone. It is just not accurate. This is why there are so many of us using PC3s or other devices to modify our fueling. If we had a system that considered load and to take it a step further, an O2 sensor to monitor what was coming out for further fine tuning, no one would need a PC3. The mix would be right at all times.

[Guest ratchethack]

To be accurate, fuel has to be matched to air flow. This was the beauty of carburetors, load (vacuum / airflow past the venturi) governed how much fuel was drawn into the intake. While fuel injection is far more precise, it needs to know airflow to get it right.

Aye. Hence the invention of the heated filament air mass meter, wot we ain't got.

 

But this thing's a bit of a stone axe in a field o' razor blades anyway, and how much of an edge d'you really need on a stone axe to make it work as well as it's ever gonna work??

 

Enquiring minds. . . (well, you know).

[Dan M]

Aye. Hence the invention of the heated filament air mass meter, wot we ain't got.

 

Si.

 

But this thing's a bit of a stone axe in a field o' razor blades anyway, and how much of an edge d'you really need on a stone axe to make it work as well as it's ever gonna work??

Yes, Yes, The cleaver on a table of surgical tools. But this is what we love about them. If they did everything precisely we'd have nothing to do or talk about.

Well, that's not true there are always hooters to look at.

[Skeeve]

If we had a system that considered load and to take it a step further, an O2 sensor to monitor what was coming out for further fine tuning, no one would need a PC3. The mix would be right at all times.

 

Well, it would if the govt. would let the manufacturers tune for efficiency, that is! But in this bureaucracy-driven instance, it would just mean that they were constantly running too lean for good power...

[raz]

How would it know if the pulse-width on the previous revolution was right? It is not about needing different A/F ratios under different loads, it's about maintaining proper A/F ratio under different loads. The correct amount of fuel requires the knowledge of the amount of air. Load limits the speed at which the engine accelerates. That speed of acceleration governs how much air can be pumped in. To be accurate, fuel has to be matched to air flow. This was the beauty of carburetors, load (vacuum / airflow past the venturi) governed how much fuel was drawn into the intake. While fuel injection is far more precise, it needs to know airflow to get it right.

As I've said, our bikes do it without knowing load. The value (compensated for by temperature) is governed by RPM and TP alone. It is just not accurate. This is why there are so many of us using PC3s or other devices to modify our fueling. If we had a system that considered load and to take it a step further, an O2 sensor to monitor what was coming out for further fine tuning, no one would need a PC3. The mix would be right at all times.

Yes, it needs to know airflow to get it right. Not load. What I am trying to say is this: Provided we have a perfect map value for each cell, according to Rylands post below the pulse-width of each cell will be right at high load AND low load at that cell. So the answer to your question is; it will know the previous pulse-width was right because it looked it up, and compensated it correct. Furthermore, it does not need to know whether it was wrong or right because it doesn't have to use any data from the previous revolution.

 

I'm thinking just one four-stroke cycle at a time, freeze framed. On high load, yes rpm will raise quickly but that just means that for the next very cycle we use another map cell that is accurate for that exact rpm and throttle. Likewise for low load.

 

This however assumes a perfect interpolation between map cells. It also assumes that the ECU is fast enough to not lag in it's perception of rpm, and fast enough to perform said interpolation in almost no time. But hey, this is a theoretical discussion. It also assumes that Ryland is correct in saying:

 

Whether you are in one gear or another has no effect on manifold pressure. It will only affect the bike's rate of acceleration/deceleration. Of course, that will change RPM.

 

To say it another way: the engine is a fixed displacement vacuum pump as far as its suction of the air/fuel mixture is concerned. Setting aside the effects of valve timing, resonance effects in the intake passage, etc., for the moment, the rate of suction from the engine is proportional to its RPM. The atmosphere is supplying air at 29.92 inches of Mercury through the filter and throttle body to the intake passage . The manifold pressure is 29.92 minus the air filter restriction, minus the throttle body restriction. So for a given RPM, the intake manifold pressure is determined by those restrictions alone, not the load on the engine, as it is affected by the grade or whichever gear one is in.

So unless you manage to explain to me why load should affect instantaneous pulse-width, I'm still not following. How much air mass is being sucked (pushed) into the engine is built into each map cell. The ECU must compensate the map value for air pressure and temperature but it does not have to compensate it for load. Load will always be handled by the map cell used for the next revolution...