Fuel Injection Injector Fuel Pressure

[Rednaxs60]

This will be my second small follow on project regarding the OEM ECU Replacement/Upgrade Project. Fuel system integrity is needed, but so is regulating fuel pressure in the fuel system fuel rail.

The fuel injectors have been cleaned and flow/leak tested. The injector fuel flow is done at a fuel pressure of ~45 PSI and is 284 cc/min (~27 lbs/hr). The static fuel system pressure is ~36 PSI, and dynamic - engine started is between 28 to 32 PSI. The operation of these injectors at 28 to 32 PSI (used the middle pressure of 30 PSI is ~236 cc/min (22.5 lbs/hr). To set the base fuel pressure you disconnect the vacuum hose to the fuel pressure regulator (FPR) valve and set the pressure needed. I have done this with a fuel pressure gauge attached to the fuel rail, and noticed that the fuel pressure increased to ~36 PSI. This is the base fuel system pressure I will set the fuel at.

This brings into question the injector fuel size in fuel flow for the new ECU programming. The programming uses a Required Fuel setting based on four settings:

This setting is one of the parameters that affect the fuelling of the engine. Another setting that affects fuelling of the engine is the injector duty cycle which is being set at 80/85 percent.

I will be researching the various aspects of the injectors, and the fuel system pressure to aid in my tuning the new ECU.

As usual, comments appreciated. More to follow.

 

[Rednaxs60]

More research done and a bit more understanding of why the fuel system pressure is important. This applies to old and new. Not to make myself a designer, but it will be good for my ECU project.

The injectors are peak and hold low impedance (~3 OHM rating). The injector size is quite large, but for a reason. Peak and hold injectors apparently function better in the higher RPM and power range than saturated/high impedance injectors. Most of us will ride in the lower RPM range, and not have to worry about this possible design aspect.

There is a reference fuel pressure for the CFI system. This fuel pressure is set with the engine operating and the vacuum hose disconnected. When you disconnect the vacuum hose the engine RPM will increase. I have noticed this setting to be ~36 PSI that translates into a fuel flow of ~247 cc/min. This fuel pressure can be adjusted if you have an adjustable FPR valve to further tune the fuelling of your engine, but you need to have a baseline to adjust from.

To throw a wrench into the mix is the fuel pump. What it can flow, and what is the maximum pressure it produces. This is for a future (maybe) thread.

When you connect the vacuum hose to the FPR valve, engine RPM will decrease. The fuel system pressure reduces to ~30 PSI (28 to 32 PSI - let's use the median) which takes us to a fuel flow requirement of ~236 cc/min at idle.

The FPR valve is required to keep the pressure across the fuel injector consistent and delivering the same amount of fuel to the engine cylinders throughout the RPM range.

The vacuum as we know it affects the FPR valve, but this is actually a pressure, less the atmospheric. This manifold pressure acts against the fuel injector fuel flow reducing fuel flow. Connecting this "pressure" to the FPR valve compensates for the manifold pressure exerted on the fuel injector tip.

Fuel system pressure is 30 psi, vacuum exerted against the injector at idle say 9 in of HG - equates to a pressure of 4.4 PSI. This pressure acts on the FPR valve diaphragm and in conjunction with the FPR valve spring, raises the fuel system pressure to ~34 PSI. This pressure minus the manifold pressure of ~4 PSI maintains a pressure across the injector of ~30 PSI maintaining a consistent fuel flow through the injector throughout the engine operating range.

Why is this important, changing out the OEM injectors for an aftermarket set can affect the engine fuelling - considering we have no way of adjusting the ECU tune to compensate this. Using injectors that are smaller or larger can affect the engine operation. Larger injectors can flow more fuel for the same amount of time than the injectors designed for the system resulting in a fuel smell from the exhaust, bad for emissions, potential for unburnt fuel in the exhaust causing the fuel to ignite in the exhaust, and fuel economy can be affected to mention a few issues that could occur. Smaller injectors not enough fuel for effective engine operation - possible lean operating condition.

These numbers may be off, but it is the theory that is important. Not to say that we cannot use aftermarket fuel injectors (make sure these are low impedance) - I have, but nice to know what we are doing to the engine.

My interest regarding this subject is because of my ECU project. I mention in my first post about the Required Fuel setting and how the injector flow rate is required. Adjusting this flow rate changes the RF number that is used to determine appropriate engine fuelling to match the estimated air mass considered to achieve the wanted AFR.

I need to determine what base fuel pressure to use, and hopefully determine an appropriate injector flow rate that will be beneficial to tuning. More research using the oracle (Google) is required.

Cheers

 

[joedrum]

I agree the oldwing FI INFO IS LIKE NON EXISTANT ...HOW DOES IT DETERMIN MASS AIR FLOW ...IT HAS A THROTTLE POSITION SENSOR ...BUT IT TAKES MORE THAN THAT TO DO ANYTHING CLOSE TO RIGHT ...AND SEEM TOTALLY NON ADJUSTABLE ...
ON FARM TRACTORS GOVENORS OR RPM LIMITERS CONTROL.INJECTION RATE AND THROTTLE POSITION CONTROLS LOAD MOTOR IS IN ...I JUST DONT SEE HOW THIS IS DONE ON OLDWINGS FI ....
I FOUND THIS TO BE TRUE IN VETTES INFO OUT THERE IS ALL ABOUT STOCK SET UP NOTHING MORE ....GOOD LUCK ON YOUR RESERCH IT PROBABLY WONT BE EASY ...

 

[Rednaxs60]

Thanks for the comment. The Gold Wing CFI components are everything needed for FI operation. The only component missing is an O2 sensor and Honda worked around that issue.

Load versus RPM. The MAP (PB) sensors provide the load aspect, as does the TPS. The OEM ECU calculates the amount of air by mass that is entering the engine from PB sensor signals, adjust with the air inlet and coolant temperature sensors and comes to a an air mass calculation, then determines from the various maps, fuel/spark, and possibly some form of AFR type table, how much fuel is required. The maps/tables were quite small, read on the CX500 forum that these tables are 4X4 or so. Injector timing, pulse width, and such would have been calculated and form part of the ECU programming.

All the ingredients for engine operation are there, just no information on the settings Honda used to bake the cake so to speak.

 

[Rednaxs60]

Review the various forum threads regarding these older FI Gold Wing models. The oEM original injectors are Denso 195500-1070 low impedance. Socrace on the NGW forum operates his fuel system pressure at 3 bar - ~43 PSI to maintain the tested/advertised flow rate. Irishcarbomb on the NGW forum mentions these injectors 195500-1300 high impedance - similar fuel flow. It would appear from ICB's research that most 195500 style injectors will work, just need to match fuel flow. If starting from scratch with a new aftermarket ECU, more flexibility. Suffice it to say the reference/base fuel pressure will be set to 3 bar/~43 PSI.

 

[Rednaxs60]

Posted info on my ECU replacement thread regarding fuel pressure relief (FPR) valve stats. The OEM original FPR tested to about 36 PSI. The Delhi FPR valve rated for 3 bar relieved at approximately 30 PSI. Tested the adjustable FPR valve and set it for approximately 43 PSI. Setting at approximately 43 PSI because the injectors are flow rated at 43 PSI.

Found an article regarding FI systems and the components/parts. The fellow mentioned that every FI system is different and the parts/components are chosen specifically for the system in question. It also mentioned that because of this, and with a non-tuneable FI system, changing out parts with non-OEM parts can affect the operation of the system even when the parts are supposed to be OEM equivalent, not always the same.

For us mortals, this is probably not an issue, but if you have a performance requirement, maybe better to stay with OEM even if it more expensive, or use better quality parts/components in your FI system.

The main consideration is that when we make a change to the '85/'86 CFI system, there may be performance/CFI system operation issues that are affected - maybe not noticeable by us when riding but still happening, and we should be aware of this - there is no free lunch.

Cheers

 

[Rednaxs60]

Using the AN and ORB fittings for my fuel system modernization. Had to go look for info on these, and what the acronym means.

AN stands for Army-Navy. The name is derived from a standardized joint agreement between the Army and Navy during World War II regarding the size specification of the fitting.

Also have ORB fittings - o-ring boss fittings (SAE Straight Thread O-ring Boss). These incorporate a port connection as recommended by the National Fire Protection Association (N.F.P.A.) for leak prevention in medium and high pressure hydraulic systems.

Both work well.

 

[Rednaxs60]

Have been progressing the work. Injector information is vague, but with enough perusing you can piece together a picture of what you are looking for.

Injector pressure is quite specific. It's the pressure across the injector and maintaining this pressure that is important.

For my application, I want to maintain an injector pressure differential of 43 PSI across the injector(s). This is based on the fact that the injectors are flow tested at 43 PSI resulting in a flow rate of 280 cc/min. This flow rate is used to determine the required fuel in milliseconds for each rotation cycle of 720 degrees.

The OEM fuel system pressure was designed to use these injectors at reduced fuel pressure and flow rate. This is a key element in what fuel pressure you use in your FI system.

The OEM fuel injectors will work well with the new Speeduino ECU, but the VE (volumetric efficiency) table must be adjusted to ensure the proper amount of fuel is injected to meet the estimated air mass admitted to the cylinder.

I have installed an adjustable FPR and upgraded the fuel system. Only issue is that I have found that these adjustable FPR may leak pressure at the lower fuel rail pressures. This is not an isolated issue with inexpensive FPRs.

This is my plan to date. More to follow.

 

[pidjones]

What is the average cylinder pressure throughout the injection pulse? Would that be the d/p to maintain?

 

[Rednaxs60]

Think I understand your question. Researched this as well and learned something very interesting.

We tend to look at the fuel pressure regulator as having either vacuum or boost applied to it. The actuality is that we are applying a pressure at all times. Vacuum is a pressure less than atmospheric, but still a pressure measured in inches of HG.

If this were not the case, the pressure in the fuel rail would decrease every time more vacuum is applied, sort of like sucking air out of the FPR spring chamber allowing fuel to be returned to the fuel tank. Instead of this happening, more vacuum equates to a higher vacuum/boost pressure being applied to the FPR spring chamber raising the fuel pressure to the injectors to compensate for the vacuum/boost pressure being applied to the injector spray tip maintaining the fuel pressure across the injector. Similarly for a reduction in vacuum/boost pressure.

There is a formula for this conversion. Pressure to inches of HG multiply by 2.036, to go the other way divide by 2.036. If you have say 10" of HG, then there is a pressure of 4.911 PSI. This added to the FPR setting of say 43 PSI equals ~48 PSI of fuel rail pressure. The pressure at the injector spray tip is 4.9 PSI, and the system maintains a fuel pressure across the injector of 43 PSI and the requisite flow rate. Takes a few minutes to accept this concept

If you have 10 PSI of vacuum/boost acting on the injector spray tip, the 10 PSI is acting on the FPR diaphragm as well, changing the fuel rail fuel pressure to 53 PSI, but the 10 PSI vacuum/boost is negated and you still have 43 PSI across the fuel injector.

Every day riders and vehicles without turbo boost actually have fluctuating fuel system pressure much like the Gold Wing CFI system that operates between 28 and 34ish PSI fuel system pressure. The change in injector fuel flow is not enough to worry about with this pressure swing.

Having mentioned the above, the better the cylinder compression the more accurate the engine vacuum/boost pressure, the better the fuel system reacts and keeps the fuel pressure across the injector more constant and at the pressure you want for the engine performance. This is also why you do not see, or should not see, a fuel pressure fluctuation if you have a fuel pressure gauge installed.

You can calculate the estimated fuel flow at various pressures for the injector in question. The equation is:
(Intended Fuel Pressure/Injector flow test pressure) = "X"
Square root of "X" = "Y"
Injector test flow rate X "Y" = new flow rate

I could use a lower injector flow rate and use the calculation for the Required Fuel setting, and have the FPR set to regulate the fuel pressure at the appropriate pressure.

Thinking Honda used this size of injector, 280 cc/min, for a couple of reasons. To have a fuel flow that provides a fuel flow that ensures the engine operates in a "rich" condition to safeguard the engine and safeguard it from us. The second reason is that environmental legislation was not applicable to the '80s GWs and as such, did not have to tune the engine to suit. An unknown is what the duty cycle for these injectors is, probably in the 80% range. I get to specify this with the new ECU.

The FPR issue is that with all tools/parts and such that are designed for a specific range of settings, the closer you are to the midrange the more accurate the setting. The FPR that I have installed mentions an adjustable range from 0 to 160 PSI. This is probably not as accurate as specified, but think the 43 PSI range is good for the installed spring. Mind you, I have found reference that these less expensive FPRs will leak pressure at the lower settings. This makes sense in that the FPR setting say of 100 PSI would prevent fuel pressure leakage better than at the 43 PSI setting.

I'm on the lookout for a suitable FPR that will better suit my requirement. Have found a couple that have a pressure range from 14 to 36 PSI (AEM 25-302BK), 15 to 65 PSI range (Earl's FPR - Holley FPR) and a PQY that starts at 20 to max offload of fuel pump - not too specific.

Long dissertation but hope it makes sense.

 

[pidjones]

MPI being so much different from direct injection - I forgot that. Diesels have to inject against (not full, but still high) cylinder pressure on the compression stroke. MPI and TBI need much less pressure - but still have a bit of vaiable pressure on the intake (I worked on particle accelerators - it's all pressure to me). Injecting while the intake is at low pressure has the advantage of vaporizing fuel faster, but the disadvantage that there are fewer air molecules to slow the fuel droplets, decreasing mixing and increasing the chance of hitting and running laminar flow along the intake walls. When just a teen, some neighbors were top engine builders for dirt track and drag cars. They kept intake runners and ports rough to discourage laminar flow, yet exhausts smooth to get the gases out. I believe their knowledge was 98% empirical, but it seemed correct as their work was in high demand.

 

[Rednaxs60]

Working on a particle accelerator would be very interesting, nice job. A lot of the old ways using empirical (trial and error) methods is quickly becoming a lost art and going the way of the dodo bird. Hopefully a lot of this experience is enshrined in the methodologies used today.

When I read and thought about vacuum and pressure it started to make sense why I should be thinking pressure regardless of what I was measuring, and the units being used. Fuel pressure across the injector and the fuel flow related to the fuel pressure across the injector are joined at the hip so to speak. Using the correct fuel flow setting based on the fuel pressure across the injector for the Required Fuel (RF) calculation is needed to be as accurate as possible so the RF will be as optimal as possible to start initial tuning.

I have the FPR set at approximately 43 PSI without the vacuum/boost hose attached so I'm thinking there could be a drop to approximately 35/36 PSI when connected to the vacuum/boost hose. This corresponds to approximately 252 cc/min fuel flow. Not a huge difference, but more accurate then using the injector flow rate at 43 PSI. Will be adjusting the settings to suit at next trial, hopefully this week.

The RF setting using 252 cc/min results in 8.0 ms of fuel delivery per engine cycle - 720 degrees. 4.0 ms of fuel delivery will be done every 360 degrees.

There are other tuning aspects that rely on the correct injector fuel flow data such as after start fuel enrichment, warm up enrichment, initial VE table settings, and a few others.

Still learning and trundling on.

 

[joedrum]

What you discribe is exactly how a carb works ...wot NO vacuum max gas feed and advance ...part throttle big vacuum pulls timing advance downto match fuel flow ...and of course choke to enrich fuel during warm up ..FI is just a different form of a carb ...period
I have used the caveman apporch of trial and error on FI ...as maintinence on modded motor on stock specs simply does not work ...obviously I am no tech geek ..so I think about what causes what and modify from there ..my vette motors are twice the horse power over stock ..some sensors are not capable to adjust in such enviroment ..so you do things to where you can control things other ways ...anyway you look at it computer timing and fuel control is base on 100 yr old tech of internal combustion ..a well dialed in carb and distributor will run with any thing FI ...ESPECIALLY WOT ...TAMING THINGS BELOW THAT LEVEL IS JUST AS HARD AS CARBS CAN BE ...IF MODDED FROM STOCK IMO...I AM GLAD I FINALLY GETTING A HANDLE ON THIS WITH MY EARLY EFI TPI VETTE ..WITCH HAS OLD SCHOOL DISTRIBUTOR ..TPS...MAF...ALL MODDED AND TUNED BY HAND ..I THINK YOUR OLDWING IS MUCH HARDER TO DO ...FUEL PRESSURE IS A BIG ONE ...VACUUM CERTAINLY IS TOO ...AND TIMING TO MATCH ALL THIS ...

 

[Rednaxs60]

Thanks for the comment. Agree that the FI system is a replacement for the carb system, but it is not quite that simple. Principles are the same with regards to timing and fluid flow, but that is about it. WWII was a significant contributor to the carb/FI issue. Superchargers/turbos required for high altitude flying. Fighter plane engine systems had to be changed to allow for dogfighting antics. I'm also a fan of the tuning software specific to the ECU in question. Like to see what has been going on and what I can do to make things better, or not.

Carb engines requires RPM and fuel. Fuel is drawn into the air stream in the carb using Bernoulli's principle. The more RPM, the faster air is drawn into the engine intake manifold to be mixed with fuel for combustion. Simple actually.

Timing is used to have the fuel/air mixture drawn into the appropriate cylinder at the appropriate time for combustion. How basic can you get.

We can go further with a carb system. Change the OEM camshaft to change the timing of the cylinder valving, you can swap out the carb jets and do a as you say "caveman" approach. Shave the heads to reduce the volume of the cylinder(s) and increase the cylinder bore to get more compression, pistons as well. Can do this with an FI system, but you get to adjust the system much easier and faster to suit.

A lot can be done to mimic FI, Honda did this on the 1500. There are 5 engine circuits on the 1500 engine that operate the 1500 engine as if it were an FI engine.

FI and the ability to tune the engine depending on the FI system, reduces the guess work in engine tuning. Change the fuel injectors to ones that flow more or less fuel. Update the VE table to suit. Change up the engine cam shaft, adjust the spark, VE and AFR tables to suit. Add turbo boost as a project, have to do more tuning. The days of finding someone knowledgeable in old school engine tuning with carbs is quickly becoming a search in futility, unless you are the inquiring type that will delve into this.

Carbs are going to be a specialty item for vintage car/motorcycle owners alone. Carbs are the same as 8-track tape players, never coming back. First 8-track tape player we had had a small lever on the side that raised a wheel into the tape body to turn the tape, kind of neat. Carbureted engines cannot meet the environmental legislative requirements for emission standards without significant add-on components/parts. I read forum threads regarding carbs, carb tuning, timing - should I upgrade or not.

Carbs do not allow you to do the really interesting stuff. Change driving/riding modes on the fly. Engine and transmission changes are done automatically because of the ECU. Speciality modes using old school technology are case specific, and even area specific.

I submit that if you had two identical cars with similar HP engines, one with carbs the other with a tuneable FI system, and do similar changes to the engines to determine what performance improvements were achieved, the tuneable FI system would win hands down especially if time was a factor.

I will concede that if you have an FI system that you cannot tune, and you do make changes hoping for an engine improvement, it's a lot of guesswork, but in these cases - carb or FI, you try to stay as close to the OEM design specs as possible so you don't have any surprises.

You might have noticed I have a preference for an FI system, same as you do for the venerable carb system. I won't get any better fuel economy than a well tuned carb system. Power will be the same. What I do get is an easier way to tune the engine system for optimal performance. Learning curve is a bit steep, but well worth it.

Lots of vintage cars up here in Victoria, and whenever I follow one, I can tell whether it is a carb model and just how well it is tuned.

Getting back on track, fuel pressure is an interesting topic. carb engines need pressure just as much as an FI engine. We used to remove the mechanical fuel pumps back in the day for electric fuel pumps whenever we started upgrading an engine. Stock cars were routinely upgraded to electric fuel pumps. Had to be careful doing this because we could flood the engine easily depending on what we were doing.

One other comment I will make is that you mention MAF sensor(s), and TPS. Carbs do not use a TPS or MAF sensors, if so, only for ignition. I have mentioned in other posts that you can control ignition and fuel separately, or control ignition and fuel at the same time. You can adjust a TPS sensor to hopefully achieve an engine improvement, but nothing more. All other sensors are fixed and cannot be adjusted, only replaced. If you have a vehicle with injectors, you are now in the FI world with fuel and ignition - maybe the transmission as well, being controlled by an ECU, and carbs are becoming a fond memory that is going the way of the dodo bird.

I think I've strayed off topic a bit, but we must not loose sight of the topic. Fuel pressure is an integral component of an FI or a carb system. Honda fitted mechanical and electric low pressure fuel pumps on the GW carb models because of where the fuel tank is situated and the fact that at the lower fuel tank levels a fuel pump of sorts is required to successfully keep the carbs loaded with fuel for engine operation. There are lots of threads regarding fuel pumps for carb model GWs.

Most every car driven today is an FI model of sorts, EVs excluded. We get in the driver's seat, start the engine, put it in "D" for ditch and go. Never questioning that this won't happen. When something goes awry, into the shop hoping there are technicians capable of getting to the problem quickly without bleeding us dry of cash.

I'm not trying to second guess the Honda Gold Wing design team. It did a fantastic job with the FI system of the day. Fast forward some 38 years, technology has changed and there are owners such as myself that want to use this modern technology to improve (hopefully) the engine operation of our ride, as do others with their cars/trucks. Young gaffers and street racers have been on this band wagon for some time now.

It's back to work on the ECU project of which this topic is part of.

Cheers

 

[joedrum]

Hmmm you missed my point ..I'm not advocating carbs over EFI.AND ALL THINGS INVOLVED ...I've been dealing with EFI ...a few years now ..EFI has one thing more than carbs do it has a fuel map and other computer controls to change fuel fuel map time of open injectors for given inputs ...O2 sensors are very heat sensitive requires big heat to operate and this is not really good for motor ..they have to have knock sensors for this same reason running to hot so it ******* ignition timing to prevent this ...so does running your motor at the optimum temperature ...so in this aspect a motor set up right in safe running temps with no O2 sensor and knock sensor will out run a running hot motor with O2 and knock sensors every time ...as the motor is in its most powerful state running cooler and allowed to use the fuel map to the fullest ...
I like this about the c4 vette it's has old school tuning devices to go along with the EFI making it one of the most user friendly set up out there ...most motors today are not mechanically capabil to run on its own ...no ecu no run ..I love the set up of the early true EFI TUNED PORT INJECTION my cars have like a carb on every cylinder ...fuel injection been around since the diesil motor mechanically operated ..I was a farmer with thousands of hrs operating big tractors and other stuff ...so nothing new here what so ever ..turbos super chargers and so on ..my personam tractor will run indefinitely as long as you keep fuel in it ..it doesn't even need a battery once running ..and it's set up and tuned to run like that ..RUNS cool and pinches fuel to the up most of economy ..some of the newer stuff computer control cost a fortune to run right ...there's is no guess work in my tractor it does what it's suppose to and it's FI no better type motor period in my opinion ...my tractor is 35yrs old never a problem with it ..that's what you call good engineering
As far as carbs go there's no doubt a smart carb could be made easy ... There is no way I would put a carb set up on my VETTES ..but I could it's a complete motor ...very nice set up as the 1200 FI is capable also ...like you I work hard to figure things out for my wants
I just did a ride in the vette it was exciting super fast ride that's up there in the highest levels of running capable cars of today ...it's 30+years old ...

 

[Rednaxs60]

We are on the same page! Apologies for missing your point. Think we have covered everything possible. Cheers

 

[Rednaxs60]

Joe - we have the same view regarding FI, just a different way of expressing our thoughts. Still searching using the "oracle" (google) and finding out more information.

 

[Rednaxs60]

Researching an EFI system, how it operates and what you should be considering is always a learning experience. based on the premise that the fuel injection system is designed specifically to control the fuel delivery to the engine. Nothing more, nothing less. The CFI system does this by using the appropriate sensor inputs to the ECU. Having mentioned this, the key element in achieving this aim is the fuel injector.

I have read that above all else, ensuring the correct fuel injector characteristics are in the tuning software and consequently in the ECU programming is paramount. The fuel injector characteristics will probably need to be tweaked for optimum performance, but starting with the appropriate and correct data simplifies the process, and ensures a better engine tune.

There is a lot of information on the internet regarding fuel injector characteristics; however, it is recommended that if you are starting with fuel injectors of an unknown quantity, it may be best to have these injectors cleaned, flow and leak tested as well as having the injector data determined for you to use.

This is in line with the Honda CFI fuel system design in that the fuel pump is installed to meet the operating requirements of the engine, and since fitted with a non-return valve that may or may not be effective today, there should always be pressure in the fuel system - keeps air out of the fuel system. This can be further complicated when using an FPR valve that is aged as well.

I have additional notes regarding this.

Just a few thoughts to ponder in this on going saga.

 

[Rednaxs60]

As mentioned, upgraded the fuel system, installed an aftermarket fuel pump that I had bought and used previously, new fuel filter, non-return valve, adjustable fuel pressure regulator, and fuel pressure gauge. The FPR is an inexpensive one but should do the job. I noticed on initial install that the fuel system pressure went to "0" PSI quickly, disappointed. Researched some of the more expensive models, but these were a hit and miss as well.

Took the FPR off, disassembled and inspected. Not much to these units. Put back together but used Honda Bond 4 on the diaphragm. Tested, fuel pressure has dropped to and holding at 15 PSI after some 16 hours. I can live with this, indicates that the fuel system is still full of fuel, not air. Better for engine starts.

Will monitor as this project progresses.

This FPR is connected to the vacuum system. pidjones asked about the vacuum connection to the FPR if it was an average or not. It is not at this time, but have a vacuum mixing block where I connect the four engine cylinder vacuum ports to. It is possible to connect the FPR to this vacuum mixing back. Something to be considered.

 

[joedrum]

Seems it would have to be vacuum. From all cylinders to be consistent on FPR...