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  1. #1
    Chief Petty Officer Flargin's Avatar
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    Default EFI Pressure - Bouncing?

    I just attached a fuel pressure gauge on my 89 7.4 with after-market EFI (Commander pro).

    for those of you who know better, should the pressure be constant on the fuel rail?

    I attached the pressure gauge direct (removed Schrader valve and installed pressure gauge) and it bounces between 25 and 55 or so, and averages about 35-40. It bounces very fast (10 times/second) regardless of RPM. I am thinking I may need to replace my pressure regulator because of this bouncing, and because it is supposed to be about 45 lbs. But I don't have anything to compare it to...

    Thanks for the help.

  2. #2

    Default Re: EFI Pressure - Bouncing?

    Quote Originally Posted by Flargin View Post
    I just attached a fuel pressure gauge on my 89 7.4 with after-market EFI (Commander pro).

    for those of you who know better, should the pressure be constant on the fuel rail?

    I attached the pressure gauge direct (removed Schrader valve and installed pressure gauge) and it bounces between 25 and 55 or so, and averages about 35-40. It bounces very fast (10 times/second) regardless of RPM. I am thinking I may need to replace my pressure regulator because of this bouncing, and because it is supposed to be about 45 lbs. But I don't have anything to compare it to...

    Thanks for the help.
    Hi I tryd to help some eles before with bouncing fuel psi, And he came back and said he found too burnt intake valves on a 6.2 engine. Here is the link, Good luck to you on it.http://forums.iboats.com/showthread....hlight=bounces

  3. #3
    Chief Petty Officer Flargin's Avatar
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    Default Re: EFI Pressure - Bouncing?

    Quote Originally Posted by boat teck View Post
    Hi I tryd to help some eles before with bouncing fuel psi, And he came back and said he found too burnt intake valves on a 6.2 engine. Here is the link, Good luck to you on it.http://forums.iboats.com/showthread....hlight=bounces
    Hmm,
    I am running a newly rebuilt motor (30 hrs) could that bring me back to the Regulator..

    Mine, when I turn the key off will slowly float back to 0... takes about 20 seconds or so.

  4. #4
    Chief Petty Officer Mkos1980's Avatar
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    Default Re: EFI Pressure - Bouncing?

    How goods your gauge? Whats the pressure the second you turn the engine off? I've seen a ton of cheapo gauges bounce all over the place. The pressure should increase with more rpm's. When you remove the vac line to the regulator does the psi increase? if you do it at idle the engine should stumble a little.
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  5. #5

    Default Re: EFI Pressure - Bouncing?

    Quote Originally Posted by Flargin View Post
    Hmm,
    I am running a newly rebuilt motor (30 hrs) could that bring me back to the Regulator..

    Mine, when I turn the key off will slowly float back to 0... takes about 20 seconds or so.
    Ok, quick test to see what is happing, Start engine up, unhook power to fuel pump let engine die, try to restart to make sure no fuel is in the rail, Unhook all 8 injector wires at injectors, Hook up power to fuel pump and build psi, try to start engine, If it starts and kind or runs, Then you have a leaking injetors, If it does not run the fuel might be going down to the Regulator, Or you will need to do a fuel injector balance test using a scan tool and a fuel psi gauge, to fire of each injector at a time and recored the fuel psi drop of each injector with in a certin amount of time frame. Also does it take longer to start now?

  6. #6
    Chief Petty Officer Flargin's Avatar
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    Default Re: EFI Pressure - Bouncing?

    Quote Originally Posted by Mkos1980 View Post
    How goods your gauge? Whats the pressure the second you turn the engine off? I've seen a ton of cheapo gauges bounce all over the place. The pressure should increase with more rpm's. When you remove the vac line to the regulator does the psi increase? if you do it at idle the engine should stumble a little.
    I think I have the definition of cheapo gauges... might want to invest in a higher quality one. I did see one that was fluid filled, is that higher quality? other than "Snap On" any suggestions?

    pressure appears to decrease with more RPM's.

    I will have to try out the vac line test.

  7. #7
    Chief Petty Officer Flargin's Avatar
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    Default Re: EFI Pressure - Bouncing?

    Quote Originally Posted by boat teck View Post
    Ok, quick test to see what is happing, Start engine up, unhook power to fuel pump let engine die, try to restart to make sure no fuel is in the rail, Unhook all 8 injector wires at injectors, Hook up power to fuel pump and build psi, try to start engine, If it starts and kind or runs, Then you have a leaking injetors, If it does not run the fuel might be going down to the Regulator, Or you will need to do a fuel injector balance test using a scan tool and a fuel psi gauge, to fire of each injector at a time and recored the fuel psi drop of each injector with in a certin amount of time frame. Also does it take longer to start now?
    I will have to try that test, the boat is away and i will not be able to see it for 2 weeks.

    Starting...
    that is my basic problem, and why I have been researching. cold start. always fine. at most one second crank...

    when I am running, and stop and kill the motor (i.e. skiing pickup etc) it may take 5 - 10 seconds of cranking to get started...

    once and a while, a Lot more (ok once this season) and once and a while flooded out (ok once this season as well) I am trying to find the "phantom" problem....

    even before the re-build the PO reported intermittent 'hard to start' problems and 'flooding'. so I don't think it engine based, but EFI based.

    Remember this is an aftermarket EFI, not Mercruiser, so I doubt anyone has a scan tool.

  8. #8

    Default Re: EFI Pressure - Bouncing?

    Quote Originally Posted by Flargin View Post
    I will have to try that test, the boat is away and i will not be able to see it for 2 weeks.

    Starting...
    that is my basic problem, and why I have been researching. cold start. always fine. at most one second crank...

    when I am running, and stop and kill the motor (i.e. skiing pickup etc) it may take 5 - 10 seconds of cranking to get started...

    once and a while, a Lot more (ok once this season) and once and a while flooded out (ok once this season as well) I am trying to find the "phantom" problem....

    even before the re-build the PO reported intermittent 'hard to start' problems and 'flooding'. so I don't think it engine based, but EFI based.

    Remember this is an aftermarket EFI, not Mercruiser, so I doubt anyone has a scan tool.
    What is the name brand of the EFI system, Can you call them and get some info from them? If it is flooding then maybe you could find out how there system works, because all the big named guys have a system programmed in to there system called [clear flood mode] And if you open the throttle to a certin %%% it will turn off the injectors while cranking so you do not push fuel down to the engine. Problem is knowing where the certin % is because some engines are set at 50%, 75% and 100% give and take a few numbers in between. I hope this helps you some good luck with it. By the way I just thought of that test sitting here. [LOL]

  9. #9
    Chief Petty Officer Mkos1980's Avatar
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    Default Re: EFI Pressure - Bouncing?

    Fluid filled are the good ones. I know some of the cheap ones I use on my EFI cars shake horrible. I basically use those only to check max pressure with the vac line disconnected.
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  10. #10
    Chief Petty Officer Flargin's Avatar
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    Default Re: EFI Pressure - Bouncing?

    Quote Originally Posted by boat teck View Post
    [/B]What is the name brand of the EFI system, Can you call them and get some info from them? If it is flooding then maybe you could find out how there system works, because all the big named guys have a system programmed in to there system called [clear flood mode] And if you open the throttle to a certin %%% it will turn off the injectors while cranking so you do not push fuel down to the engine. Problem is knowing where the certin % is because some engines are set at 50%, 75% and 100% give and take a few numbers in between. I hope this helps you some good luck with it.
    it is a Hirel, which is the predicessor to the "Marine Power Commander". it actually says Marine Power on the EFI, but the manual is all Hirel... so it must have been purchased right after MP purchased them.

    I can give them a ring. never heard of the clear flood mode, I just pull the EFI power fuse... kinda does the same thing

    the problem is I have only had one instance of problem, so in some ways I am fishing for an answer.... because it sucks to be stranded on the water.... I would rather fix it before the next event.

    I have a feeling that if the pressure reg is 'weak' the following problems can happen:
    1. loosing top end speed (i.e. not enough fuel at WOT
    2. When I shut down, I loose pressure, when it is hot, this can result in vapor-lock.. which is why I have to crank hard.

    Flooding, I think might be due to an over-reaction to the vapor lock. Once the vapor is replaced with real fuel, they may have it at a higher throttle and thus flood the cylinders. (I have never been on the boat when it flooded - I would never over-react) but I have been on when the 'really long need to crank' problem was happening. I helped it by running the Pump a few times without cranking (turn on - pump runs 3 seconds - turn off - repeat) and then it started over fine, but it took me 3-5 minutes of playing before that.

    Quote Originally Posted by boat teck View Post
    By the way I just thought of that test sitting here.
    Hey sounds like a good way to isolate some of the possible problems...
    I do know there is no leaking - tested that pre-install, as well as no 'sticking' injectors. nice to have the entire EFI off of the motor for a while... and an electric pump.

    I do need to check the vac advance.

  11. #11
    Cadet ghcoe's Avatar
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    Default Re: EFI Pressure - Bouncing?

    EFI do not vapor lock. The PSI in fuel line is to great for the fuel to turn to vapor. That is why cars with fuel injection do not vapor lock. I do not claim to be a fuel injection expert, but I have read a lot on injection systems (mega squirt, Bosch L). I would like to give some tips though.

    Sounds like you already have a gage in the system now. The quickest way to check if you have a problem is to watch the gage. Start the engine and let the fuel system pressurize. Now turn off the engine and see what the gage does. It should stay steady and not drop off. You may see a loss of pressure over a few hours or overnight, but it should not drop off quickly after you turn off the engine. If you are loosing pressure then there are 3 places that it could be loosing it.

    One-There is a one way valve in or near the pump. I believe most are incorporated in the outlet side of the pump. If this is faulty pressure will leak past it back to the tank.

    Two-The pressure regulator. When you shut off the engine the vacuum to the regulator drops off and closes the valve. If it leaks fuel pressure will bleed off through the return line.

    Three-Injectors can leak when worn, or dirty.

    Any one of these can cause hard starting because the pump has to repressurize the system before it will start. Generally this requires some cranking because the way most fuel injection systems work is that the ignition system has to be operating for the fuel pump to work. This is a safety circuit so that if for some reason the engine quits running that the fuel pump does not keep trying to pump. Usually such as a roll over in a car.

    Being that you are complaining of occasional extreme hard starting I would look at the fuel injectors if you have pressure loss. A rapidly leaking injector can leak a lot of fuel into the intake in a short period of time. Not only does the pump have to repressurize the system you are trying to clear the fuel from the intake. Now if it does not start you let it sit a bit, meanwhile the injector is leaking more raw fuel into the intake compounding the problem.

    To check the injectors take them out and run fuel pump to pressurize system and shut pump off. watch for leaking from the tip.

    On another note. The pressure in the system should stay the about the same pressure at any RPM. You may have a +-2 PSI over what the manufacture stated operating PSI is. You get more fuel from the injector staying open longer not by more PSI.

    Well hope this helps. George.

  12. #12
    Chief Petty Officer Flargin's Avatar
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    Default Re: EFI Pressure - Bouncing?

    George,
    Quote Originally Posted by ghcoe View Post
    EFI do not vapor lock. The PSI in fuel line is to great for the fuel to turn to vapor. ....

    The quickest way to check if you have a problem is to watch the gage. Start the engine and let the fuel system pressurize. Now turn off the engine and see what the gage does. It should stay steady and not drop off. You may see a loss of pressure over a few hours or overnight, but it should not drop off quickly after you turn off the engine.
    That is the problem I have... I loose pressure in less than 1 minute after shut-off. Thus the reason I think it may be vapor locking... the rail is still hot, and the pressure is down to 0 in a matter of minutes.

    Quote Originally Posted by ghcoe View Post
    One-There is a one way valve in or near the pump. I believe most are incorporated in the outlet side of the pump. If this is faulty pressure will leak past it back to the tank.

    Two-The pressure regulator. When you shut off the engine the vacuum to the regulator drops off and closes the valve. If it leaks fuel pressure will bleed off through the return line.

    Three-Injectors can leak when worn, or dirty.
    I can pinch the return line and prevent the pressure drop after it is turned off. this is where I think the pressure reg is shot. this seems to confirm it.

    Injectors appear to be ok, did some testing when they were out of the motor. if/when I replace the pres reg, I may go through and re-check the injectors. The fuel pump is new this spring, I would hope it is not a problem

    Quote Originally Posted by ghcoe View Post
    On another note. The pressure in the system should stay the about the same pressure at any RPM. You may have a +-2 PSI over what the manufacture stated operating PSI is. You get more fuel from the injector staying open longer not by more PSI.
    that is where I am trying to figure out. with the motor not running and the pump going, I have a nice consistent pressure. When running the gauge is bouncing up and down.

    I am beginning to think that my regulator is regulating pressure (have to check the vacuum adjust feature) but it is not capable of holding the pressure after it stops. Do you think the bouncing of the gauge is due to the gauge itself or something in the FI system? and what ?

    Would the post shut-off pressure drop require me to replace the regulator, and do you think it could cause the 'hard starting'?

    thanks for your help.

  13. #13
    Cadet ghcoe's Avatar
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    Default Re: EFI Pressure - Bouncing?

    Quote Originally Posted by Flargin View Post
    George,


    That is the problem I have... I loose pressure in less than 1 minute after shut-off. Thus the reason I think it may be vapor locking... the rail is still hot, and the pressure is down to 0 in a matter of minutes.



    I can pinch the return line and prevent the pressure drop after it is turned off. this is where I think the pressure reg is shot. this seems to confirm it.


    Injectors appear to be ok, did some testing when they were out of the motor. if/when I replace the pres reg, I may go through and re-check the injectors. The fuel pump is new this spring, I would hope it is not a problem



    that is where I am trying to figure out. with the motor not running and the pump going, I have a nice consistent pressure. When running the gauge is bouncing up and down.

    I am beginning to think that my regulator is regulating pressure (have to check the vacuum adjust feature) but it is not capable of holding the pressure after it stops. Do you think the bouncing of the gauge is due to the gauge itself or something in the FI system? and what ?


    Would the post shut-off pressure drop require me to replace the regulator, and do you think it could cause the 'hard starting'?

    thanks for your help.
    Can not figure out how to multi quote so forgive me.

    I would say if you pinch your return line and the pressure stays constant with the engine off then the pressure regulator is at least leaking. It may not be able to regulate pressure too. This would also indicate that the pump and injectors are holding pressure, although, I do not know how long you pinched of the return line. The regulators are usually pretty simple units so you might take it off and look through the ports and see if anything is lodged in the seat.

    If the gage is mounted to the engine or anything else that can vibrate when the engine is running it could be. Try and mount it where engine vibration does not interfere with it. If it is still bouncing I would put a vacuum gage on the intake manifold and see if you are getting erratic vacuum. As said earlier burnt intake valves can cause intake manifold vacuum fluctuations. Since the regulator is operated by the intake vacuum it could interfere with it's performance.

    As I said before. If the system is depressurized then the pump has to re-pressurize the system to get the injectors injecting again. If the lines are hot and there is no pressure in them then you would get vaporization of the fuel but the pump will purge that out as well as the pressurizing of the system. I would imagine that it would take a few seconds to purge out the vapor and re-pressurize the system which would cause hard starting.

  14. #14

    Default Re: EFI Pressure - Bouncing?

    [ghcoe] If it is still bouncing I would put a vacuum gage on the intake manifold and see if you are getting erratic vacuum. As said earlier burnt intake valves can cause intake manifold vacuum fluctuations. Since the regulator is operated by the intake vacuum it could interfere with it's performance.Quote] You Could try hooking up a vacuum gauge to the little hose going to the fuel regulator to see if it is bouncing also, Normaly when you unhook the vacuum hose off the regulator with the engine on, The psi will go up 4-6 psi that would tell you the fuel regulator is doing it's job as you give it more throttle It should go up. When you un hook the vacuum line off the regulator does it still bounce? if yes it does bounce then I would think the fuel pump is making it bounce by pulsing, Or the regulator is cloged up or something, But normaly a cloged regulator could give you hi fuel psi, And I think you have that also. Or the injectors are not pulsing right and making it bounce would be my guess on that part of it. If it stops bouncing when unhooked then it sounds like a burnt valve, or something in that area of the engine itself.

  15. #15
    Cadet ghcoe's Avatar
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    Default Re: EFI Pressure - Bouncing?

    Quote Originally Posted by Flargin View Post
    I just attached a fuel pressure gauge on my 89 7.4 with after-market EFI (Commander pro).

    for those of you who know better, should the pressure be constant on the fuel rail?

    I attached the pressure gauge direct (removed Schrader valve and installed pressure gauge) and it bounces between 25 and 55 or so, and averages about 35-40. It bounces very fast (10 times/second) regardless of RPM. I am thinking I may need to replace my pressure regulator because of this bouncing, and because it is supposed to be about 45 lbs. But I don't have anything to compare it to...

    Thanks for the help.
    Just noticed that you attached the pressure gauge to the schrader valve. I would guess this is mounted to the engine. Engine vibration will make guages bounce if they are not designed for a vibration environment.

  16. #16
    Chief Petty Officer Flargin's Avatar
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    Default Re: EFI Pressure - Bouncing?

    These forums are great.

    Here is my next steps... when I get her home, (end of next week)

    1. Yes it is mounted directly to the block so vibration may well be the problem. I will try to re-mount it with rubber hoses to see if that eliminates the bouncing problem.

    2. confirm the pinch holds up the pressure post engine shut off for a long time (not just a few minutes)

    3. this fall when I am not going to be boating, I will pull the rails, check the injectors for leaking again and look at the regulator to see if anything is stuck, replace if needed.

    Thanks.

    BTW, now I understand how burnt valves can create bouncing. thanks. I don't think it is in this situation due to the speed of the bouncing, way to fast for that....

  17. #17
    Cadet ghcoe's Avatar
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    Default Re: EFI Pressure - Bouncing?

    Quote Originally Posted by Flargin View Post

    BTW, now I understand how burnt valves can create bouncing. thanks. I don't think it is in this situation due to the speed of the bouncing, way to fast for that....
    That would depend on how many valves are burnt!

    A vacuum gauge can tell you a lot about a engine.

    http://www.centuryperformance.com/tu...e-spg-148.html

    Glad to be of help, George.

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