Fuel Pressure Regulator

[Kiwi_Roy]

In a document Raz refered to regarding ECU on the bottom of page 7 talking about the fuel pressure relief valve it mentions connecting the spring case to manifold thus keeping the pressure drop fuel to manifold pressure constant.

I seem to recall recently the subject came up on another thread and we were told it shouldn't be connected.

Which is correct?

I ask because the regulator on my bike is not connected to the manifold and it runs very rich which of course it would with 30% too much fuel pressure ( flow and pressure drop are a square root relationship i.e. to double the flow you need 4 x the pressure)

It seems to make sense that you would want the pressure drop constant and not the pressure to atmosphere.

Thanks

Roy

[fotoguzzi]

I have never seen a Guzzi w/that connection. they always vent to air.. the regulator just has a big spring in it, I don't think manifold pressure would have any effect.

[Kiwi_Roy]

I have never seen a Guzzi w/that connection. they always vent to air.. the regulator just has a big spring in it, I don't think manifold pressure would have any effect.

Yes it would have a huge effect, connecting the spring housing to the manifold would drop the pressure by whatever vacuum the manifold is running. At idle it would be 33-14 psig, at WOT it would be 33 psig. That kind of makes sense in a way the flow thru the nozzle constant and metered by length of Open pulse, I'm trying to find the link

 

With the spring case disconnected the gauge pressure is constant (pressure measured with a pressure gauge)

With the spring case connected the pressure drop is constant (pressure measured with a differential pressure gauge)

 

Raz, would you please attach that link to this thread, I completely lost it.

 

BTW the diagram is a bit confusing because it shows two regulated pressure connections, The bottom one goes back to tank and the top barb connection is the one the text is refering to.

 

Roy

[docc]

I recall at least one fellow experimenting with connecting this and found no real effect. Yet, I'm sure that was based on 'riding impression.'

 

I suppose it should technically be based upon an exhaust gas analysis.

 

Still, this is how the regulators were delivered; open to atmosphere.

 

Interesting, though , the impression of "running rich." I recall reading Greg Field's account of the development of the Sport1100 heads by John Wittner in Moto Guzzi Big Twins, (MBI Publishing Co, 1998) about the use of "fuel cooling" on the Battle Of the Twins motors and how that was considered inappropriate for production leading to the delays developing proper alloys for the heads we have today. (My goodness, but I have paraphrased rather deeply!)

 

It makes me think that wet valves are happy valves and I don't mind the extra fuel. Lean, or ultra lean, conditions are not for air-cooled push-rod big valve motors with broad piston surface. Sorry if your eyes water following me through the mountains on the South'n Spine Raid . . .

[gstallons]

In a document Raz refered to regarding ECU on the bottom of page 7 talking about the fuel pressure relief valve it mentions connecting the spring case to manifold thus keeping the pressure drop fuel to manifold pressure constant.

I seem to recall recently the subject came up on another thread and we were told it shouldn't be connected.

Which is correct?

I ask because the regulator on my bike is not connected to the manifold and it runs very rich which of course it would with 30% too much fuel pressure ( flow and pressure drop are a square root relationship i.e. to double the flow you need 4 x the pressure)

It seems to make sense that you would want the pressure drop constant and not the pressure to atmosphere.

Thanks

Roy

 

 

It would be best to Google "fuel pressure regulators or theory of operation".

This device regulates fuel pressure. When (high)manifold vacuum is applied to the vacuum port on the reg. you will see a desired fuel press.#. when you accelerate and manifold vacuum drops the fuel pressure rises to an established or desired #. This action causes more fuel to be sprayed through the injector.

Evidently MG has mapped their fuel delivery system to not need this activity to take place.

[emry]

I will not read this entire thread. I will post this tid bit. Fuel pressure(relative, that is what matters) is the differnce between the face of the injector(in the manifold, subject to engine vacuum at partial or less throttle) and the fuel rail(determined by the regulator). Our bikes have NO manifold pressure sensor. they are purely Alpha-n, throttle-speed, or any of the other names. The ECU calculates base fuel injection duration based on throttle angle and rpm. Period. It is modified per enviroment variables, temps, altitude, engine temp (that is a whole other thread)....

 

Our system was mapped to a atmosheric relative value. That means the regulator keeps fuel pressure constant, relative to atompheric pressure (NOT connected to any intake ports). Relative pressure will change from idle to WOT, with high pressure differnce at idle then at WOT (atompsheric pressure is in the manifold at WOT). The ECU uses "best guesses" to determine how long to open the injector. Our system will never be close or even very good, in regards to fueling calculations. But it will work.... ok at least.... enough to ride and enjoy.

 

Pressure regulators utilize a spring and diaphram to regulate fuel pressure, rapidly changing levels of vacuuum cause the diamphram to "vibrate" which causes premautre wear of the diaphram and early failure. Manufactours that use a "manifold relative" system join 4 cylinders (only type I am aware of) to the regualtor so that constant vacuum is applied and fuel pressure is constant (relative to the intake manifold pressure). Fuel mapping is done accordingly. Those same manufacturors twin and single cylinder models use no manifold referencing for fuel pressure but use a manifold pressure sensor to calculate "speed-density" also known as D-jetronic fuel based values. Thus the ECU is now compensating for changes in "relative" fuel pressure based on manifold pressures. Ex. at lower throttle settings the realtive pressure is higher so lower fuel injector durations are the result, this is based off of manifold pressure and rpm values. As the engine begins rev higher (throttle opening) the relative pressure across the injector decreases as the manifold pressure get higher (closer to atomoshperic), then ECU adjusts the injector duration based on the known pressure differnce (remember, the pressure in the fuel rail is constant based on atmospheric {which is monitored by the ECU}) so the relative pressure differnece is known to the ECU.

 

We Guzzisiti do not have that option, at least on the older models V11's etc.

 

Any questions? Please no spelling corrections. I have had to much GOOD liquer and am going to bed now.

[fotoguzzi]

I will not read this entire thread. I will post this tid bit. Fuel pressure(relative, that is what matters) is the differnce between the face of the injector(in the manifold, subject to engine vacuum at partial or less throttle) and the fuel rail(determined by the regulator). Our bikes have NO manifold pressure sensor. they are purely Alpha-n, throttle-speed, or any of the other names. The ECU calculates base fuel injection duration based on throttle angle and rpm. Period. It is modified per enviroment variables, temps, altitude, engine temp (that is a whole other thread)....

 

Our system was mapped to a atmosheric relative value. That means the regulator keeps fuel pressure constant, relative to atompheric pressure (NOT connected to any intake ports). Relative pressure will change from idle to WOT, with high pressure differnce at idle then at WOT (atompsheric pressure is in the manifold at WOT). The ECU uses "best guesses" to determine how long to open the injector. Our system will never be close or even very good, in regards to fueling calculations. But it will work.... ok at least.... enough to ride and enjoy.

 

Pressure regulators utilize a spring and diaphram to regulate fuel pressure, rapidly changing levels of vacuuum cause the diamphram to "vibrate" which causes premautre wear of the diaphram and early failure. Manufactours that use a "manifold relative" system join 4 cylinders (only type I am aware of) to the regualtor so that constant vacuum is applied and fuel pressure is constant (relative to the intake manifold pressure). Fuel mapping is done accordingly. Those same manufacturors twin and single cylinder models use no manifold referencing for fuel pressure but use a manifold pressure sensor to calculate "speed-density" also known as D-jetronic fuel based values. Thus the ECU is now compensating for changes in "relative" fuel pressure based on manifold pressures. Ex. at lower throttle settings the realtive pressure is higher so lower fuel injector durations are the result, this is based off of manifold pressure and rpm values. As the engine begins rev higher (throttle opening) the relative pressure across the injector decreases as the manifold pressure get higher (closer to atomoshperic), then ECU adjusts the injector duration based on the known pressure differnce (remember, the pressure in the fuel rail is constant based on atmospheric {which is monitored by the ECU}) so the relative pressure differnece is known to the ECU.

 

We Guzzisiti do not have that option, at least on the older models V11's etc.

 

Any questions? Please no spelling corrections. I have had to much GOOD liquer and am going to bed now.

what he said.... that you ratchet?

[Kiwi_Roy]

I hate to disagree with you guys who have multi year experience

 

This is the document that prompted my question

 

http://www.dpguzzi.com/efiman.pdf

 

On page 7 it talks about the regulator connected to the manifold and why referring to the diagram on top of page 8

 

Also the picture on page 3 clearly shows the regulator connected to the manifold.

 

Could it be that it is talking about an earlier model?

 

I have been searching for a reason why my V11 Sport is running so rich ~ 8L/100 km so I clutched at this straw.

 

BTW I work with and specify regulators all the time. (Process Control Instrumentation)

 

Actually once i took the time to read the whole document it's refering to a Webber ECU of earlier vintage.

 

 

Roy

[raz]

Sorry Roy, we've been over this before and I believe it's no use. I was as enthusiastic as you until I was convinced (from empirical tests made by Dan M, can't find the original thread now but a resume is at http://www.v11lemans...dpost&p=159156) that connecting that hose it will only work as a switch. It will not change the pressure linearly with the intake manifold. I also believe it will break prematurely.

[fotoguzzi]

 

I have been searching for a reason why my V11 Sport is running so rich ~ 8L/100 km so I clutched at this straw.

 

 

Roy

Have you re-set the TPS starting all the way from base line?

[Kiwi_Roy]

Sorry Roy, we've been over this before and I believe it's no use. I was as enthusiastic as you until I was convinced (from empirical tests made by Dan M, can't find the original thread now but a resume is at http://www.v11lemans...dpost&p=159156) that connecting that hose it will only work as a switch. It will not change the pressure linearly with the intake manifold. I also believe it will break prematurely.

OK, I will take your word for it, that document must be an old one, I think you mentioned that.

Please see my next to fotoguzzi.

Thanks

Roy

[Kiwi_Roy]

Have you re-set the TPS starting all the way from base line?

 

Yes I started with the 150 mV with the stops backed off and choke clear.

My idle reading is ~ 460 mV

 

A little history

I purchased the bike late last year. It came with a power commander.

Earlier this year it started to miss badly so I disconnected the power commander and put it back to standard, It runs well but seemed to be using too much gas. 8L/100 km at highway speed

 

I thought to myself OK, I will start from scratch, get it running as well as possible then put the power commander back

After reading all about the TPS (all 100 pages) I re-set this at the same time adding a little black box that allows me to offset the TPS while riding.

I found that even changing the mV by about 250 mV has little effect on performance.

I figured that the bike is so rich that even reducing mV by 250 still doesn't approach lean running.

 

My question

Does the power commander add/ subtract from the map inside the original ECU or does it completely replace it,

In other words even though I am way too rich with the standard map will putting the PC back start me off from scratch?

 

Thanks

 

Roy

[Dan M]

Hey Roy,

 

On the issue of the regulator, it's use in a typical system is to bump fuel pressure when vacuum is removed. So when the throttle is opened fuel pressure gets a bump of between 5&10PSI. It acts as sort of an accelerator pump and provides full pressure for open throttle. Conversely, in high vacuum situations, closed throttle or small steady throttle openings, less fuel pressure is used. It is not variable as some have suggested. It switches from high to low when vacuum (approx 10"Hg) overcomes the internal spring.

It is a great system but it only works with multi-cylinder engines that share a intake manifold as it needs to have relatively smooth vacuum. The trouble with the Guzzi is the big twin makes pulsing vacuum. If you hook a vacuum gauge to it, even if you tee in both cylinders it pulses wildly. This will cause the diaphragm inside the regulator to flutter and not operate as designed. If you apply steady vacuum via a pump, the pressure drops as does idle CO.

We talked about this at great length quite a while ago and theorized this issue was discovered and the fix by Guzzi was to leave it disconnected and run at a fixed pressure.

 

Your PC3 alters the factory map. Did you get the software with it? You start can with a "zero" map and add or subtract. There are off the shelf maps that you can load that have been done to bikes with various mods. Find one close to your bike then tweak from there.

 

edit: oops, just read emry's post. What he said in other words.

[docc]

Roy,

 

You've looked at your CO trim with a software interface?

[raz]

Air filter is clean? Nothing else restricting air flow? You probably have thought of that already. Do you have internal or external fuel pump and regulator? While I've never heard of anyone having an incorrect fuel pressure, it could be something wrong with yours. It's easy enough to measure it, should be 3 bar.

 

If the regulator would just block for whatever reason, you would get about 5 bar due to the internal relief valve in the pump. If I understand the formulas right, 5 bar instead of 3 bar would give you a 29% rich mixture (square root of 5/3). The bike would still run, but very rich. I don't really believe this is it, but maybe you want to check it out.

 

Edit: I would follow Docc's suggestion before thinking of fuel pressure.