Testing your boats fuel system.....

[powbmps]

Followed the procedures outlined here in the [FONT=&quot]HOW TO: Testing your boats fuel system [/FONT]thread and have a question about the results.

First test for airbound/leaky system - no leaks.
Second test for vacuum testingt the fuel system - 0 in. Hg, so no obstructions/restrictions.
Third test for testing the fuel pumps ability to create a vacuum - failed this one. Started at 5 and slowly dropped. In the thread, it says that if the pump can not generate 6 to 9 Hg of vacum over 10 seconds then it needs to be replaced. Is this true for a low pressure fuel pump on an inboard motor?

I have a reman 5.7l Vortec with new 600 cfm Edelbrock 1409 carb, new Carter 6-9 psi pump (72 gph) and new Holley 4.5-9 psi fpr set at 5.5 psi (recommended setting for the carb). Even unrestricted, I don't think this pump will get close to 9 psi. I originally had a Carter 4-6 psi pump, but I was only getting 3 psi at the carb.
Thanks!

 

[Fishermark]

Are you having running problems with the engine, or are you simply trying to set up your new engine and accessories? You generally do not need a pressure regulator with a mechanical pump and carb set up.

 

[Bondo]

Ayuh,.... Put yer tests into context,.... Where, 'n how ya testin',..??

 

[powbmps]

Sorry. I left out some details.

The reman motor that I bought does not have a mechanical fuel pump. I had to add an electric pump when I installed the motor. It came with the 4-6 PSI Carter and I replaced it with a 6-9 PSI version to get the recommended 5.5 PSI at the carb. I'm just going through everything to be sure it is working and set up properly. I have always experienced an initial lag when going WOT, but recently have been experiencing some issues at higher rpm's where the boat will cut out. Just trying to rule things out. It's really starting to aggravate me.

Original Thunderbolt V ignition with new plugs, rotor, plug wires (checked resistance), new distributor sensor, distributor gear does not appear to be worn, timing is set at 10 degrees in base mode, but won't advance fully to 28 unless I set it at about 13 in base mode, Carb is new, checked floats and anything else that can be adjusted, compression is good, checked engine vacuum which seems good (at idle it wanders from about 16.5 to 19).

Planning on going out tomorrow and checking the knock module and sensor (per the manual) to see if that could possibly be an issue.

 

[alldodge]

. I had to add an electric pump when I installed the motor. It came with the 4-6 PSI Carter and I replaced it with a 6-9 PSI version to get the recommended 5.5 PSI at the carb.

You have a restriction or leak somewhere. In your first post you said the pump was unable to create a vacuum, this being the case means you have a leak. Need to install a clear line and check for bubbles

I have always experienced an initial lag when going WOT, but recently have been experiencing some issues at higher rpm's where the boat will cut out. Just trying to rule things out. It's really starting to aggravate me.

The lag in many cases is the accelerator pump either does not have the correct stroke or the pump needs replaced. This can also be the power valve.

Original Thunderbolt V ignition with new plugs, rotor, plug wires (checked resistance), new distributor sensor, distributor gear does not appear to be worn, timing is set at 10 degrees in base mode, but won't advance fully to 28 unless I set it at about 13 in base mode, Carb is new, checked floats and anything else that can be adjusted, compression is good, checked engine vacuum which seems good (at idle it wanders from about 16.5 to 19).
.

From a previous thread you stated this is a 1995 model. The advance on the TB5 is determined on which module you have and this is +/- a few. Timing is set using base timing mode at 10 degrees. Once out of base timing the module takes over. In the curve below the mean timing is 25 degrees, and the TB5 can add more only during acceleration and this is determined as to how hard the acceleration is.

The wandering vacuum gauge is either incorrect carb adjustment (most probable) or plug gap is incorrect

 

[JustJason]

I wrote that test many many years ago. Testing the pumps ability to create positive vacuum only works with mechanical (or electrical) diaphragm type pumps, it will not yield a result on an electric impeller style fuel pumps.

 

[alldodge]

That doesn't make since, all pumps have to be able to draw a suction (vacuum) to pull the fuel up to the pump. May not be able to draw as much :noidea: have not tested, but has to be able to draw something

 

[powbmps]

I appreciate the responses. No air bubbles in the fuel lines, so I don't believe I have any leaks. I Spent some time adjusting the idle air/fuel ratio and the vacuum gauge now jumps around between 18 and 20 at idle. I couldn't get it any better than that. Plugs have about 60 hours on them and are gapped at .045. Can't find any leaks around the manifold or carb.

http://vid1218.photobucket.com/albums/dd415/powbmps/20160924_092513.mp4

Instead of starting another thread, I will just throw this question in here. With the key in the on position, I am getting 12 volts at the coil. At idle the volt readings are all over the place. Is this normal?

http://vid1218.photobucket.com/albums/dd415/powbmps/20160924_091713.mp4

Thanks again!

 

[alldodge]

With the key in the on position, I am getting 12 volts at the coil. At idle the volt readings are all over the place. Is this normal?

No this is not normal, it should be good and steady. So either your meter is defective, its connections are the issue, or (more then likely) you have corrosions issue. Start with the battery cables, 10 pin connector, and block ground connections.

Could also have an alternator going out and the diodes are bad causing a AC sine wave type signal

 

[powbmps]

The meter is cheap, but seems to be working properly. I've had pretty much everything apart on the motor, so the connections are pretty good. Battery charges fine, but alternater is 21 years old, so maybe it's on its way out. I'm assuming that could affect the way the motor runs?

 

[alldodge]

Something isn't right with the meter going to this, note 18.86V and another time it shows -1xxxx. Voltage should not be above 14.5 volts

 

[NHGuy]

When the voltage moves like that it's probably in the alternator's voltage regulator.

I'd recommend don't run it much that way, the voltage spikes can be tough on light filaments and electronic bits.

Many auto parts stores have a device to test the alternator. Of course they want to condemn the one you bring in.

Most folks buy an alternator, but a few old school types, keep it oe types, and cheapskates like me prefer to repair the existing alternator.
If you decide to fix it you can get the bearings and electric parts on the internet.

A complete instruction (on how to do the tests and changes of parts) is in the Mercruiser manual. Or just buy an alternator and go boating.

 

[powbmps]

I just snagged an open box Sierra alternator on Amazon for $55, so minimal investment involved with replacing it. Any idea what it would take to replace the Thunderbolt V with another option?

Thanks! Chris

When the voltage moves like that it's probably in the alternator's voltage regulator.

I'd recommend don't run it much that way, the voltage spikes can be tough on light filaments and electronic bits.

Many auto parts stores have a device to test the alternator. Of course they want to condemn the one you bring in.

Most folks buy an alternator, but a few old school types, keep it oe types, and cheapskates like me prefer to repair the existing alternator.
If you decide to fix it you can get the bearings and electric parts on the internet.

A complete instruction (on how to do the tests and changes of parts) is in the Mercruiser manual. Or just buy an alternator and go boating.

 

[NHGuy]

I kept the TB V, it's good stuff. Sturdy and much more modern than the plain style ignitions you could replace it with.
If you still get that weird vacuum try using the vac gauge to set your warm idle mixture. And if that does not work pull the valve covers and set the valve lash to half or 2/3 turn from zero lash instead of the Mercruiser full turn.
If it's a flat tappet setup you should do a cam & lifter run in with break in oil.

 

[powbmps]

double post

 

[powbmps]

Adjusted my valves (with the engine running). Only went about 1/8th turn after they stopped tapping. Tried adjusting the idle mixture, but vacuum reading is about the same.

Installed the new alternator, but the voltage did not change. Wondering if this is just normal??? Not sure what else I could replace to fix it. The new one is so quiet, it was worth it just for that reason. Replaced the knock sensor with a legit Mercruiser piece and put in some new plugs (just because I like throwing money at it). Hopefully taking it out in the morning for a test run.

 

[alldodge]

Suggest get back to basics. Start with your grounds, I'm leaning toward there is a loose connection.

What is your serial number?

 

[powbmps]

Suggest get back to basics. Start with your grounds, I'm leaning toward there is a loose connection.

What is your serial number?

It's a re-manufactured motor, so the serial number is not correct. The serial number for the motor that I took out was F349262. I believe this is a wiring diagram for my setup:

http://i1218.photobucket.com/albums/dd415/powbmps/Scan0008.jpg

Not sure I quite understand the flow of electricity. Does it go from the wiring harness to the alternator (branching off to the coil), or vice versa? Also, when you refer to grounds, do I need to worry about up front, behind the gauge cluster, or am I primarily worried about the grounds on and around the engine? I have had all the gauges out, and cleaned those connections up, so they should be good. Replaced the circuit breakers as well (the originals were all corroded). Alternator and starter connections are all clean. Main harness connector looks good as well. I have spread the pins a bit.

Thanks!

 

[alldodge]

I have always experienced an initial lag when going WOT, but recently have been experiencing some issues at higher rpm's where the boat will cut out.

The above quote is from the initial issues I'm thinking the issues is about. The there was discussion about it not getting enough advance (28) but turns out the TBV gives 25 degrees.

Now there is erratic 12V measurement which leads me to a bad ground. Suggest start with the battery to engine ground, then work toward the 10 pin engine connector

 

[powbmps]

The above quote is from the initial issues I'm thinking the issues is about. The there was discussion about it not getting enough advance (28) but turns out the TBV gives 25 degrees.

Now there is erratic 12V measurement which leads me to a bad ground. Suggest start with the battery to engine ground, then work toward the 10 pin engine connector

Thank you AllDodge. I will take a look before I head out.