Low Fuel Pressure Reading

[CliffA]

BT has more experience than me with these diagnostics so I won't get in the way that. But something I've learned from dealing with electrical problems... always check battery cables (both ends), both pos and neg. If they're loose, corroded (corrosion can work it's way under the sheathing, too), etc, it can create nightmares trying to track down what feels like a "ghost" problem. Be sure to follow the battery cables (pos and neg) everywhere they go and clean each connection (battery switch, alt, starter, etc).

This may not be your problem, but I've been bitten enough times by this bug to have learned to always check.

Dennis offered excellent advise here...i had the exact same thing happen to my mother-in-law's car....it was very sluggish to start even with a new battery....i cleaned the battery cable terminals and still had the issue...since she lives out of town i did not know what weight of engine oil had been put in the engine during the last oil change so i changed the oil to the proper 10W-30 weight...this was during the winter time so i thought that heavy weight oil could become very viscous in cold temps and drag the engine during cranking....well, this did not help either.....i went as far as repacing the starter because i thought the starter must be dragging...you guessed it, the new starter did not help...i finally decided to replace the battery cables even though there was no obvious signs of problems.... low and behold the engine started like new....i peeled back the insulation cover of the old positive battery cable and there was corrosion all the way up and down the cable under the insulation cover....

cliff

 

[ardeprint]

I will check all connecting points, but that does not reflect on the fact I have low fuel pressure and a significant drop after pump ignites and primes. Also, after shut down it drops slowly to about ten and then holds.

 

[CliffA]

I will check all connecting points, but that does not reflect on the fact I have low fuel pressure and a significant drop after pump ignites and primes. Also, after shut down it drops slowly to about ten and then holds.

we were just offering suggestions related to your earlier statement that the engine struggles to start with symptoms of a weak battery.....your are correct that this would not have anything to do with low fuel pressure.....good luck

cliff

 

[Lazy Daze]

I would wonder, though, that if the fuel pump is NOT getting good, clean power... could that cause it to act weird? But... I do not know how finicky the pump is to say for sure whether or not this would cause it. Just that I've come across this before. Besides, it's always good to check the easy (free) things first!

Good luck - I hope you get it figured out.

 

[Fun Times]

Ardeprint, Both Dennis and Cliff have definitely offered you some really sound advice that always needs to be taken into consideration anytime you have an engine runnability issue of any kind, It's the thing you will read over and over again once you start to use the service manual to help you out. Some of the issues you describe would fall into their advice, So thank you guys for your input & Dennis you're never in the way with your sound advice, so please always feel free to put your input behind anything I try to help out with.:thumbsup:

Ardeprint, Your fuel pressure specifications for engine serial number 0M310001 MIE 350 MAG MPI 630V 2:1 RWC 3"R is definitely 43 psi, So you are definitely low on fuel pressure.

The pressure regulator on top of the engine is only used as a fuel rail pulse damper, So in this case it wouldn't have helped with your low fuel pressure reading.

There are a couple of test in mercruiser service manual part number 90-864573001 ECM 555 DIAGNOSTIC SERVICE MANUAL #36 "Section 2A - Troubleshooting" to test if your fuel Pressure regulator is leaking past or maybe your fuel injectors are leaking down. Below is an example,

Disconnect both battery cables from the battery. Install fuel pressure gauge. Connect the battery cables to the battery. Turn ignition to "ON."Fuel pump will operate for 3–5 seconds. Note the fuel pressure while the pump is operating. The pressure may drop after the pump stops, but should not drop immediately to 0 kPa (0 PSI). Turn ignition to "OFF."​

Was the fuel pressure within specification when the pump was operating? Y or N?

Does the system establish fuel pressure and then quickly decrease to 0 kPa (0 PSI)?​

Go to step 8. Turn ignition to "OFF."Block fuel pressure line between the fuel pump and the fuel rail. Turn ignition to "ON."​

Does fuel pressure remain steady? if yes then​

Locate and repair leaking fuel injectors or fuel line connections. if no then Go to step 9.
Turn ignition to "OFF."Block fuel return line using the fuel shut off valve tool part number 91-805918A1. Turn ignition to "ON."​

Does fuel pressure remain steady? if yes then​

Replace faulty fuel pressure regulator. If no then Install a known good fuel pump.​

Retest system.

The "suspected" not definite fuel pressure regulator part number for your engine is 861126A1.

If you end up changing the fuel pressure regulator you may need some dielectric grease for the fuel pump retaining bracket 92-8235061.

The fuel pump needs good B+ power to work correctly. B+ is usually your 12.6 + volts of power from your battery or alternator, Make sure your battery & alternator are within specifications. The fuel pump would run with a little less power but if you know the sound of the pump at key up then you can usually tell if it's not right.

I hope this will help you out a little, Good luck to you Ardeprint.:smt001

 

[ardeprint]

Thanks Boat Tech, Dennis and Cliff. All suggestions are valid and appreciated. This problem has been lingering too long to ignore the advice of those who have been around boats longer than I have.

I will implement all suggestions and follow up with an update.

Once again... THANK YOU!

 

[Great lakes pirate]

Ardeprint, Both Dennis and Cliff have definitely offered you some really sound advice that always needs to be taken into consideration anytime you have an engine runnability issue of any kind, It's the thing you will read over and over again once you start to use the service manual to help you out. Some of the issues you describe would fall into their advice, So thank you guys for your input & Dennis you're never in the way with your sound advice, so please always feel free to put your input behind anything I try to help out with.:thumbsup:

Ardeprint, Your fuel pressure specifications for engine serial number 0M310001 MIE 350 MAG MPI 630V 2:1 RWC 3"R is definitely 43 psi, So you are definitely low on fuel pressure.

The pressure regulator on top of the engine is only used as a fuel rail pulse damper, So in this case it wouldn't have helped with your low fuel pressure reading.

There are a couple of test in mercruiser service manual part number 90-864573001 ECM 555 DIAGNOSTIC SERVICE MANUAL #36 "Section 2A - Troubleshooting" to test if your fuel Pressure regulator is leaking past or maybe your fuel injectors are leaking down. Below is an example,

Disconnect both battery cables from the battery. Install fuel pressure gauge. Connect the battery cables to the battery. Turn ignition to "ON."Fuel pump will operate for 3–5 seconds. Note the fuel pressure while the pump is operating. The pressure may drop after the pump stops, but should not drop immediately to 0 kPa (0 PSI). Turn ignition to "OFF."​

Was the fuel pressure within specification when the pump was operating? Y or N?

Does the system establish fuel pressure and then quickly decrease to 0 kPa (0 PSI)?​

Go to step 8. Turn ignition to "OFF."Block fuel pressure line between the fuel pump and the fuel rail. Turn ignition to "ON."​

Does fuel pressure remain steady? if yes then​

Locate and repair leaking fuel injectors or fuel line connections. if no then Go to step 9.
Turn ignition to "OFF."Block fuel return line using the fuel shut off valve tool part number 91-805918A1. Turn ignition to "ON."​

Does fuel pressure remain steady? if yes then​

Replace faulty fuel pressure regulator. If no then Install a known good fuel pump.​

Retest system.

The "suspected" not definite fuel pressure regulator part number for your engine is 861126A1.

If you end up changing the fuel pressure regulator you may need some dielectric grease for the fuel pump retaining bracket 92-8235061.

The fuel pump needs good B+ power to work correctly. B+ is usually your 12.6 + volts of power from your battery or alternator, Make sure your battery & alternator are within specifications. The fuel pump would run with a little less power but if you know the sound of the pump at key up then you can usually tell if it's not right.

I hope this will help you out a little, Good luck to you Ardeprint.:smt001

Nice write up BT! If the troubleshooting points toward a leaking injector, what is the next step to isolate the leaker? Would it make any sense to pull all 8 of them and have them cleaned/repaired by a injector shop?

 

[ardeprint]

Whta do you guys think of Mallory Fuel pumps?

 

[Fun Times]

Nice write up BT! If the troubleshooting points toward a leaking injector, what is the next step to isolate the leaker? Would it make any sense to pull all 8 of them and have them cleaned/repaired by a injector shop?

If the injectors do turn out to be leaking, then there are now a few options available for him to consider doing depending on what the situation would be for everyone involved such as time frame, location of boat, $$$, Or the if Mercruiser dealer he's using has the newer $500.00+ fuel injector cleaning kit made for their engines, to sending them out to be cleaned using the ultrasonic fuel injector cleaner machine, or of course replacement.

Merc part number 92-8M0062765, $11.65 each, This fluid restores injectors to their original spray pattern, helps prevent recurring problems, and reduces intake and port deposits. Used in canister‑type cleaning devices. Note: Not for use as a fuel additive; do not pour into fuel tank. For professional use only. Use in Mercury pressurized injector cleaner tool 91‑898263A01. Consult Instruction sheet (comes with tool) 90‑898266 for proper use.
http://marinepartsexpress.com/Merc_...ng Tool 91 898263A01 Bulletin No. 2008-12.pdf

When the marine manufacturers (Merc) started using electronic fuel injection as a whole in 1993 it was real simple, we were trained in service school that if you had a bad injector you just replace it. Cleaning them would do you no help and a waste of time even though the auto division was cleaning them already with kind of the same system merc has out now :huh: $$$:huh:. You need to remember the marine industry is or should i say was at least 12+ years behind the auto industry, But nowadays it appears as if their starting to catch up a little in technology in their own way.:smt001

Now that there's more options to choose from today i'm more in favor for trying to clean them while their still on the engine if possible because it would be quicker to know if it's going to work or not before removing and sending them out for testing/cleaning.

If you do find the need to remove them from the engine after cleaning while on the engine then I do believe in they all should be tested & cleaned due to the fact that if any should continue to fail then you're going to need to replace the bad one's anyway, So that should help save some money so your not just replacing them all.

Usually the companies that test/clean them may not charge you for some of the injectors should they fail their before and after inspection test, so that helps as well.:thumbsup:

Another way to help isolate a bad injector would be to do a injector balance test.
The injector balance tester is a tool used to turn the injector ON for a precise amount of time, thus spraying a measured amount of fuel into the manifold. This causes a drop in fuel rail pressure that we can record and compare between each injector. All injectors should have the same amount of pressure drop. Any injector with a pressure drop that is 1.5 PSI (or more) greater or less than the average drop of the other injectors should be considered faulty and replaced. Injector testers are available for Injector testers are available for various manufacturers. For 7.4L / 454 and 502 engines: the tester must be capable of selecting an injector pulse width in the range of 200-400 milliseconds (m sec). The recommended starting point for these engines is approximately 300 m sec. In any case a pulse width that drops the fuel rail pressure to half the normal operating pressure, should be used.

The Fuel Injector Quick Probe is a pretty cool must have "cool tool" to test fuel injectors as well, see video below.:thumbsup:
http://www.youtube.com/watch?v=UrqyrI5aNl0&feature=related

 

[ardeprint]

Boat Tech do you think that a computer diagnosis would have picked up bad injectors? I had two done in the last six months and on both occasions there were no faults related to injectors. I also performed my own "homemade test".

1- I secured the boat well
2- Ran my engine in gear at 1500 RPM
3- Disconnected each injector to check for a drop in power. They all checked out. In other words each one had a small drop pretty similar in feel.

 

[Fun Times]

Boat Tech do you think that a computer diagnosis would have picked up bad injectors? I had two done in the last six months and on both occasions there were no faults related to injectors. I also performed my own "homemade test".

1- I secured the boat well
2- Ran my engine in gear at 1500 RPM
3- Disconnected each injector to check for a drop in power. They all checked out. In other words each one had a small drop pretty similar in feel.

With an engine/ECM system such as yours, It's pretty unlikely to set a fault if you just had leaking injectors.

Usually to set an injector fault, there would be more of an electrical problem versus a minor fuel flow problem.

The electrical problem could be the electrical part of the injector itself, the wiring between the injector and ECM, or the ECM itself.

The fault would set if for some reason the ECM sensed an out of range pre programmed value form one of the sensors, injectors, or wiring.

If you did set a fault, it would have looked something like this,
Fault # 59, CDS Fault Message would read, Fuel Injector #1, has Open Circuit.
DDT Fault Status Message would read, FINJ1, OPEN.
♠=System View Icon, ♥= Horn Icon, ♦= Guardian %, If you had a bad injector would read, ♠‑Bell ♥‑Warning or Caution ♦‑100% available power.
Fault Explanation would read, Insufficient current draw on fuel injector circuit.
Possible Root Cause would read, Open connection to injector on harness. Bad fuel injector.

Fault # 60, CDS Fault Message would read Fuel Injector 1, has Shorted Circuit.
DDT Fault Status Message would read, FINJ1 SHORT.
♠=System View Icon, ♥= Horn Icon, ♦= Guardian % would read , ♠‑Bell ♥‑Warning or Caution ♦‑100% available power.
Fault Explanation would read, Current draw of fuel injector has exceeded its limit.
Possible Root Cause would read, Shorted connection to injector on harness. Bad fuel injector.

And it would read the same for all 8 injectors.

I know we're talking a lot about fuel injectors here but don't get to hung up on having an injector problems sence there are other obvious symptoms of other issues to contend to first, Like why is the fuel pressure low?:wink:

Good luck.:smt001

 

[ardeprint]

Thanks Boat Tech!

I agree with your quoted comment. I have ordered the Fuel Pressure regulator (lower) and should get it Tuesday. In the mean time I am just trying to learn how I can apply all the info to my experiences or to what I might face.

You have been VERY helpful and I hope I can help you someday.

 

[ardeprint]

Boat Tech... You where right! It was the lower FPR. I immediately got 40+ PSI and it held. It also stared like it should. Just wanted to let you know your diagnosis was spot on. Thank you!

This problem seems to be resolved. Now I'm dealing with a few others not regarding this thread. Thank you to all who chimed in with helpful comments.

 

[psubill78]

How were you testing your fuel pressure? Is this easy to do? Had a stalling issue at the end of last season that I suspect will creep up when we splash in 2 weeks?

I am thinking of replacing the anti-siphons first too. Sea ray actually recommended bypassing the fuel crossover system, said my year boat had issues with that.

 

[skolbe]

Glad to see it is fixed!

 

[ardeprint]

How were you testing your fuel pressure? Is this easy to do? Had a stalling issue at the end of last season that I suspect will creep up when we splash in 2 weeks?

I am thinking of replacing the anti-siphons first too. Sea ray actually recommended bypassing the fuel crossover system, said my year boat had issues with that.

Checking the fuel pressure is very easy. You will need a fuel pressure gauge. These are available at any Auto Parts Store for around $30-$40. On the fuel rail right below the spark Arrestor there is a Shredder valve a little larger than a tire's stem valve. Screw in your Fuel Pressure Gauge here and check the pressure. It should be at 40+ PSI when your fuel pump primes or is on (when engine is running). A light drop of about 3-4PSI after prime or shut down is normal. It should not drop down to zero PSI right after you shut-down or after it primes. A very, very slow and gradual drop is ok.

By the way I learned all this from the helpful folks on this forum, so I'm sure there is more info someone can supply us with or may correct me.

Based on your post, I feel it may be your IAC valve.

 

[psubill78]

Checking the fuel pressure is very easy. You will need a fuel pressure gauge. These are available at any Auto Parts Store for around $30-$40. On the fuel rail right below the spark Arrestor there is a Shredder valve a little larger than a tire's stem valve. Screw in your Fuel Pressure Gauge here and check the pressure. It should be at 40+ PSI when your fuel pump primes or is on (when engine is running). A light drop of about 3-4PSI after prime or shut down is normal. It should not drop down to zero PSI right after you shut-down or after it primes. A very, very slow and gradual drop is ok.

By the way I learned all this from the helpful folks on this forum, so I'm sure there is more info someone can supply us with or may correct me.

Based on your post, I feel it may be your IAC valve.

Been there, done that on the IAC valve.... it isn't that... I'm going to have to check out the area you speak of tomorrow.

Is anyone else not getting the notifications from here anymore when a new post is posted? hmmmm