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Just food for thought and idea ???- fuel pressure accumulator with regulator ???

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schiker

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You know what I have thought about that might be an area for a slight improvement? I have not really heard this discussed on the 6.5 a whole bunch. Might help on an older IP more than new but it might provide some stability and slightly increase metering stability and performance ?????

Adding a fuel pressure regulator and maybe a pressure accumulator to hold inlet fuel pressure as close as possible to say 7 psi all the time no matter the demand or LP delivery.

I know the transfer pump and internal to the IP has this function internal but would it help to balance the inlet too. Might help the IP have a slightly more consistent flush or help dampen the current draw of the LP ???

They use to sell a fuel pressure regulator back in the 70's to help worn carburetors from slobbering and wasting gas. I think it was suppose to help the floats from bouncing or something with gas pressure surge ?????

I have often wondered how a higher pressure lift pump might blow fuel past the seals of the fuel filter element. It might be good to regulate pressure at filter inlet and set accumulator after filter ????? This might stabilize the pressure differential across the filter too ????

I googled some and saw some BMW or Mercedez fuel accumulators iirc around 7 or 9 psi.

Any thoughts or anyone seen this on a modern diesel ?
 
the ford diesel guys use it for when they delete the fuel bowls and add more fuel. look on dieselsite.com and they have pressure regulated fuel systems for sale with aeromotive "diesel safe" fuel pressure regulators. it seems like a great idea actually. have an lp that pumps tons of fuel and let the regulator do the work keeping the pressure down
 
I think the stock LP is electrically regulated to like 4-5 psi or something and there are optional Walbro's with more pressure and flow. I have read some on airdog and Fass being able to regulate down for the 6.5.

I run an electronic fuel pressure guage without a snubber and the pressure dances a fair bit. And a snubber circuit is suppose to dampen the signal and suggested for life of guage. But I would guess the IP still actually sees this pressure dance. Its not excessive but 0.5 psi almost constant and then varies a few psi during fuel demand changes then recovery. This varies 1-3 psi constantly with appreciable changes of the right foot.

Do pressure regulated fuel delivery lines also very slightly with pump/demand surge and still require a snubber for the fuel pressure guage??? The problem being liquid is not compressible and pressure varies instantly with volume or flow and resistance.

Would a fuel pressure accumulator dampen this better and provide a nice steady psi at the IP inlet. Maybe overkill just a thought of mine. Not sure exactly but would think if you balanced an accumulator at 7 psi and a regulator at 7 psi the IP inlet would get a nice steady 7 psi without pulses. Or the pulses would be dampened and have a different frequency maybe. Could this improve transfer pump pressure control a bit ?????

I have only seen a bit on fuel pressure accumulators.
 
Blow past the filter seals is one concern of mine and also just to hold the pressure as steady as possible.

What would be the best settings 10 psi regulated and have the accumulator able to hold 15 psi then it would allow a little give and hold fairly steady at 10 psi and act like a snubber ????

Anyone seen a small pressure accumulator used like this for fuel.
 
people have reported that with a stronger lp and ftb that the truck feels more confident and powerful so i bet if you controlled it so the ip got constant fuel pressure it would help the transfer pump pressure
 
Here is something that came up with an internet search

http://www.mercedessource.com/node/6791

But it doesn't give the accumulator pressure range. Says its suppose to help dampen LP noise. And helps with warm starts but I guess that all depends on how the LP primes and pumps during start. I think its best if the pump runs with glow plug cycle to make sure IP is fueled and ready to go with cranking.

This accumulator fills and holds steady volume but I would think one that can "float" a little bit would be better for holding a steady pressure.
 
I think the IP is happy just to have 9psi and the surging/dancing probably won't matter much. Looking at the IP flow, the spill chamber releases pressure back to the transfer pump inlet. When the fuel solenoid closes it allows pressure to build up in the rotor that sends fuel to the injector, then the fuel solenoid metering valve opens and the pressure from the plunger escapes, some of that goes out the return and some goes back into the inlet. So its a constant surging inside the transfer pump inlet regardless. There is an adjustable screw fitting on the IP inlet that can modify the pressure there, kind of like when pumping higher lift pump pressure.
 
Good point thanks for the discussion. I forgot about the recirculation dump back to inlet loop. But I bet there still might be some merit to an accumulator to dampen surges. Probably won't provide any performance gain over FTB but I still wonder about some long term injector balance performance average. And or when higher fuel delivery is programmed and being injected. I wonder if when the internal fuel accumulators are pushed to their max volume range there could be some transfer pump pressure variation.

The transfer pump meters fuel and pressurizes the filling of plungers. Its pressure build up is based on RPM of pump and somewhat its backpressure (the inlet pressure). I guess it depends on how bad the LP is surging but would expect the surge to follow through the transfer pump somewhat.

Now having said that the variation of 0.5 - 3 psi looking at 9 psi is a fairly large swing and variation but if transfer pump internal IP pressure is much higher I think it was mentioned upwards of 50 or 100 psi ??? 0.5-3 psi is a much smaller variation. Just thinking variation is bad but I guess since fuel is not compressible 0.5-3 psi is not really any volume difference. But does it make very very slight difference if plunger fill balance ????????? Just some thoughts of mine.
 
FWIW - my Autometer mechanical fuel pressure gauge is sensitive enough to really show that pressure fluctuation you're talking about from the type of lift pumps most of us are running. I got most of that attenuated out by putting a brass fitting with significant restriction/orifice into the gauge feed line/branch.

Basically, I brazed the fitting shut internally, then drilled a small hole back thru to limit how quickly the gauge could response to pressure changes. Can't recall what orifice size I wound up at, but it's posted in a thread somewhere on this forum.
 
Its my understanding that is a "snubber". I have read bits and pieces about Autometer won't honor a warranty on their guages for a Diesel application without a snubber inline so the guage doesn't constantly dance.

How much variation did you get before the snubber? I would think the IP is still getting that variation and you just don't see it on the guage anymore.
 
schiker said:
Its my understanding that is a "snubber". I have read bits and pieces about Autometer won't honor a warranty on their guages for a Diesel application without a snubber inline so the guage doesn't constantly dance.

How much variation did you get before the snubber? I would think the IP is still getting that variation and you just don't see it on the guage anymore.
Click to expand...

Anywhere btwn 2 & 4 psi from idle fueling, to coast (non-fueling) when I don't believe the electronic IP is injecting any fuel at all. If your email can accept large files, I can send a few videos showing the gauge under different conditions. The files are ~ 25-30 MB. So too large to post here.

I was going to buy Autometer's snubber they recommend for the Dodge application but kept not getting it ordered. Over time it occured to me it was prolly just a restriction to limit the gauge's exposure to fuel pressure pulsations. So I fab'd in my own restriction & it seems to work fine.

No doubt that degree of pulsation over the course of each lift pump stroke is hitting the IP. Don't know to what affect. Buddy's logic about the other events happening in the IP also causing pulsation makes sense to me. If you've got access to some type of appropriate accumulator, why not try it & see if there's any difference you can detect.

On a mildly related note, I've got injector noise that seems to ride the mechanical coolant temp gauge's copper capillary tube into the cab. Can't see that the line touches an injector line or other obvious source to pick up the inj noise - except the end of the tube is mounted in the passenger side head's temp sensor port. It's mildly annoying in an otherwise reasonably quiet cab. Anybody have any thoughts/suggestions?
 
Like you mentioned, the IP transfer pump pressure is anywhere from 30-130psi, depending on RPM. The metering is done after injection starts. The FS metering valve closes which allows pressure to the rotor to the injector. Then depending on how long the valve is closes is how much fuel is metered. So its injecting then valve opens and lose pressure to the injector. The pressure increase with RPM allows more fuel to get injected faster, so that is part of the metering calculation of pulse width for the metering valve to be closed. The pulse width/angle commanded decreases with RPMs, yet higher fuel rates.
 
Any idea what vintage the Mercedes &/or BMW IP systems w/ accumulators were? Just wondering how similar the Mercedes & BMW injection pumps/systems w/ accumulators are (to our old rotary Roosa-master origin) IP's?
 
Thanks for the offer but I would say its typical to what I see. During acceleration my LP pressure will dip and recover 1-3 psi depending on right foot application. Then consistently flutters just a bit ~ up to 0.5 psi with minimal change in fuelrate.

How about anyone with a true pressure regulated line on a gas or diesel what do they do?

I don't know about the Mercedes IP design but if I gleemed this correctly •MERCEDES BENZ 300CE (1988 and 1989 only)

We are talking about 20 +/- years ago so it probably wasn't common rail and was either a rotary or inline pump mechanically operated I would guess.

4 psi fluctuations at 30 psi would be what ~ 13% variation hmmmm would that make a difference???? I have for a long time had a shudder on launch thats annoying and seems correlatable to fuel quality, lubricity, and or cetane. I think my IP is getting really tired and having problems precisely metering fuel at idle control with varying load.

Often thought about some instances of fishbite and the IP being the problem and wondered about the transfer pump influence.

I haven't seen a little air bladder accumulator for this pressure range ~10 ish psi ??? yet. Still toying with the idea and wonder what others thought. $138 for this Mecredezes seems awful high for a spring with diaphram when it doesn't really float and steady pressure it seems more like a checkvalved pre fueler.
 
If its vibration noise or a knock that the tubing accentuates might try to glue or mold/bend a piece of lead to mechanical sender line or basically add some mass to deaden the energy response absorbtion/transmittal. Easier said than done. From just a bit of sound / noise testing iirc for low frequency noise you deaden with mass and higher frequency you deaden with longer path and direct the sound in a better direction iirc. The main thing I learned about noise is its a lot about frequency. Some frequencies are just annoying and seem louder than thier numerical Db measure if you are looking for sound quality/perception.
 
Arrrgghhh, uhhhh I may have assumed incorrectly. I have been looking for other brands that use accumulators and or for more information and ideas. Apparently in my above link fuel is as in european nomenclature and could be (probably is ) gasoline not Diesel.

Seems fuel injected (gasoline injected) systems have been using accumulators for a while. Probably since those systems are I believe in the range of 70 ish psi gas pressure are they not?????

Still interested in how an accumulator might affect an IP and Diesel system.
 
"I have for a long time had a shudder on launch"
This is from the amount of power the engine has and the load it has to get moving. The real problem is a misaligned driveshaft in regards to the rear end. A driveline shop can get this fixed for you. Other solutions are a poly carrier bearing but that gives you more high speed vibrations from the drive shaft. "launch shudder" would be the correct GM term.
 
Can you explain that a little bit more. I might be wrong but THINK my problem is more fuel metering related. I get some surge when towing and my overall performance has deteriated with age (close to 200K miles OE IP and timing set) the shudder on launch developed over time and I would say is age related (with fuel a strong contributor).
With early onset fuel made a huge difference in smoothness of launch. Now I have to put a quart of Sae 30 oil and some Stanadyne in it with fresh fuel fill to get it smooth. I have over time developed fishbite with varying severity that can also be subtle. I am on my 3rd PMD/FSD and use a fuel pressure guagel so I don't think those are areas of issue. The truck seems normal.

But then too driveline slop has accumulated too.

It stared in reverse gear and reverse is still the worst. I get appreciable shudder or clutch chatter backing up. It then developed in 2nd gear launch and now is starting in 1st gear but much more subtle and varies considerably. Its not all the time and can vary severity. That is why I don't THINK its mechanical driveline in nature. But could be a major contributor. Feel free to educate me here.

I have on another truck replaced ujoints and did not seat centered well enough. I think I bent the Yoke of the Ujoints and experienced driveline out of balance / alignment wobble and it doesn't seem the same for this launch shudder. I fixed that truck with different snap rings and reseated the U joint caps. This truck is otherwise smooth and drives nicely.
 
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