Author Topic: Fuel pressure regulator? (Read 8986 times)

BlitzenGruv · « **on:** August 15, 2018, 05:18:10 PM »

Had some leakage so I replaced all fuel lines and sent my injectors off for cleaning. New intake bushings and O-rings too.
Put it all back and now she don't start. Pulled off the fuel return line at the fuel rail, no fuel. Cranked the engine with the side-stand switch shorted, no fuel.
So, today I removed the air box so I could get to the back of the fuel rail. Took off the feed line to the regulator and cranked the engine, good stream of fuel. Put that back and removed the feed line at the fuel rail, nothing.
Vacuum line to the regulator was not replaced, but it was working two weeks ago. Can the regulator take a dump just sitting there?

BTW: What is that manifold on the back of the throttle bodies? Manual calls it "Fuel distributor" but the only connection is to the air box.

BlitzenGruv · « **Reply #1 on:** August 16, 2018, 12:06:59 AM »

All right, let's try another tack. Will lower than normal pressure from the fuel pump cause the regulator to cut off fuel flow?
Grasping at strays here, I just wanna know why I have fuel to the input of the regulator but not at the output.
Just to be sure, the input is at the rear, and the output is at the side? Doesn't make sense to have it any other way due to the routing of the hoses but "engineers" have been known to make stoopid design decisions.

daveson · « **Reply #2 on:** August 17, 2018, 05:59:38 AM »

just guessing, replace the vacuum line.
your bike was working, then you removed the vacuum line but didnt replace it, now it doesnt work.
also if you remove the fuel return line from the regulator you should be able to blow air through it into the tank, if you cant it is possibly blocked, this happened to one of my bikes the return valve was blocked with rust and just needed scraping out

BlitzenGruv · « **Reply #3 on:** August 19, 2018, 04:43:58 PM »

Replaced the vacuum line, still no joy.
You might be onto something though. I blew into the line from the fuel rail to the regulator. High resistance and I heard no bubbles in the fuel tank. Maybe the thing decided to take a crap while I had the whole thing off the bike. Can't see how it would get rust in it, it's an aluminum fuel tank.
I came upon a page somewhere which listed possible replacements for less than BMW charges. If I can only find it again.

Laitch · « **Reply #4 on:** August 19, 2018, 05:54:24 PM »

Are you certain you've connected to the hoses to the correct ports on the left side of the tank?

rbm · « **Reply #5 on:** August 19, 2018, 06:31:42 PM »

Any of the universal adjustable fuel pressure regulators from Ebay / Amazon should work. I've seen them used on a K1100 with success. They are adjustable with a set screw / hex screw to the pressure that suits the application and most are rated to 140 PSI / 4 Kg/cm3.

daveson · « **Reply #6 on:** August 20, 2018, 06:48:45 AM »

You might not hear bubbles if the return pipe in the tank is higher than the fuel level.
Although the tank is aluminium the return valve, on my bike at least, is steel.
The fuel pump is mostly steel as is the fuel level gauge
The previous owner of my k75 said he never used ethanol blend fuel and the was no rust in the tank (and the rubbers perfect)but i had to bog the low points, the opposite was the case in the other k's
So i will now use one tank of ethanol blend per year on a long trip to absorb water accumulated without remaining

BlitzenGruv · « **Reply #7 on:** August 21, 2018, 12:11:07 AM »

Quote from: Laitch on August 19, 2018, 05:54:24 PM

Are you certain you've connected to the hoses to the correct ports on the left side of the tank?

As stated in my original post, I have a good stream of fuel from the tank to the regulator.
I double checked inside the tank in order to connect the lines to the proper spigots (feed rear, return front.)
Don't have a pressure gauge, but I got a good stream of fuel while cranking the engine.
Who knows, maybe the regulator just rusted shut sitting in humid air for two weeks while my injectors got cleaned?

The Mighty Gryphon · « **Reply #8 on:** August 21, 2018, 08:04:09 AM »

I would guess that your fuel pump is not giving you the pressure it should. What could be happening is that the pump is able to pump lots of fuel with no back pressure, but can't build enough pressure(approximately 35 psi) to open the pressure regulator. With low pressure there won't be enough fuel injected to start a cold engine.

You mention cleaning the injectors. I would guess that the reason you did that may have been to fix problems caused by a failing pump.

There are pumps available on eBay for not much money. Along with a new fuel pressure regulator I would get one to make sure the pump is not the problem.

Laitch · « **Reply #9 on:** August 21, 2018, 08:08:13 AM »

Quote from: BlitzenGruv on August 15, 2018, 05:18:10 PM

Pulled off the fuel return line at the fuel rail, no fuel. Cranked the engine with the side-stand switch shorted, no fuel.

As Gryph has alluded, if you disconnected the hose indicated by the red arrow and fuel didn't exit at pressure with the engine cranking, the fuel pressure regulator isn't part of that problem. The green arrow indicates the delivery side.

The Mighty Gryphon · « **Reply #10 on:** August 21, 2018, 08:18:51 AM »

Quote from: BlitzenGruv on August 15, 2018, 05:18:10 PM

Had some leakage so I replaced all fuel lines and sent my injectors off for cleaning. New intake bushings and O-rings too.
Put it all back and now she don't start. Pulled off the fuel return line at the fuel rail, no fuel. Cranked the engine with the side-stand switch shorted, no fuel.
So, today I removed the air box so I could get to the back of the fuel rail. Took off the feed line to the regulator and cranked the engine, good stream of fuel. Put that back and removed the feed line at the fuel rail, nothing.

I just went back and slowly read your original post. It sounds like you have the fuel lines mixed up. The "feed" line goes directly to the rail, not to the regulator. I am pretty sure that putting fuel into the regulator output is not going to let fuel get to the engine. The regulator is supposed to be in the return line to the tank.

The correct plumbing as I see it on my bike is as follows. Rear spigot goes directly to the rear of fuel rail. The front end of the rail goes to the side of the fuel pressure regulator, and the end of the fuel pressure regulator goes to the forward spigot.

rbm · « **Reply #11 on:** August 21, 2018, 06:47:48 PM »

Fuel hose routing for K100 16V engine from the OEM manual:

#2 from tank supply spigot to rail
#14 from rail to FPR side inlet
#4 from FPR outlet to tank return spigot
#7 from FPR vacuum connection to Cylinder #1 vacuum spigot

BlitzenGruv · « **Reply #12 on:** August 21, 2018, 06:50:20 PM »

DOH!
So, the regulator is in the return line after the fuel rail?
Just the sort of screw up which happens when the assembly is off for two weeks and I rely on the shop manual for illustration. Which is not at all clear, showing the front of the tank and the reverse of the fuel rail assembly. Both lines are simply called "fuel line."

BTW: I only sent the injectors to be cleaned from my own sense of doing a thorough job. Might as well get it done while I have them off. Probably a waste of time and money, only one injector show marginal improvement after cleaning.

rbm · « **Reply #13 on:** August 21, 2018, 08:17:42 PM »

Whether in the 2V or 4V k-bikes, the FPR is always after the fuel rail. The difference is whether the fuel from the tank is injected into the rail from the left side (2V) or right side (4V).

BlitzenGruv · « **Reply #14 on:** August 21, 2018, 08:45:22 PM »

Just seems counter-intuitive to me, like putting the voltage regulator after the battery.
So much for that stupid fluid-pressure to voltage analogy.

johnny · « **Reply #15 on:** August 21, 2018, 10:34:50 PM »

greetings...

the voltage regulator is after the battery...

j o

bizzaro · « **Reply #16 on:** August 22, 2018, 10:04:23 AM »

FPR's do not work in reverse.............Not even a little.

BlitzenGruv · « **Reply #17 on:** August 23, 2018, 02:48:39 AM »

Quote from: johnny on August 21, 2018, 10:34:50 PM

greetings...

the voltage regulator is after the battery...

j o

In whose universe? The voltage regulator MUST bleed off excess current BEFORE it gets to the battery. Perhaps series regulation can work on either side of the "load." Shunt regulation must be before the battery.
I'm thankful that I haven't had to learn how der Deutch do it, at least not since I owned an old VW, but the rest of the world uses either a Zener diode to turn excess current into heat or some sort of interrupter BEFORE the battery.
Perhaps you're thinking electron flow here? In which case everything should be common positive, as per British practice.
The is no "ground" in a DC system.

The Mighty Gryphon · « **Reply #18 on:** August 23, 2018, 01:07:19 PM »

So, is it running now?

alexg · « **Reply #19 on:** August 23, 2018, 02:25:23 PM »

The voltage regulator monitors the battery/system voltage and modifies the alternator field excitation to maintain a constant system voltage. It does not bleed anything. In other words, it manages the supply, not the demand. Same as our national electrical grid.

The fuel regulator damps the excess fuel that has not been squirted into the ports back to the tank. My interpretation is that the fuel pump runs at a constant flow, set to be able to supply enough fuel at enough pressure during max engine demand. Thus, to avoid pressure fluctuations under variable intermediate demand, the regulator modulates the flow back to maintain the pressure on the rail.

So, did the bike start?

Laitch · « **Reply #20 on:** August 23, 2018, 04:10:03 PM »

Think of it this way.

The fuel regulator is like a floodgate in a dam. It keeps the water at a safe level in the dam by releasing water back into the river, although in our case, the river flows back uphill and then downhill to the dam again—over and over until the rains come when the gates must open further, unlike our fuel pressure regulator which has little fluctuation but that doesn't matter either.

Eventually, during the rainy season, the gates will be unable to maintain a safe level at the wall of the dam. Occasionally, somebody comes along to predict this then starts building a seaworthy vessel that will hold a male and female every animal species and a sample of each specie of flora. Sometimes an extra male or female of the vessel builder's preference will be brought along just for variety. Then onlookers will be exhorted to change their bad behavior, and the vessel will sail away on the flood.

We don't have that option. We are stuck in the roadway. We need to know how our regulators work because it is obvious BMW enjoys keeping us in ignorance and hearing us scream impotently for mercy.

Is the moto running well now?

News:

Author Topic: Fuel pressure regulator? (Read 8986 times)