4.3 fuel pump not operation while cranking

I have spent hours and hours researching and troubleshooting this issue. I a tried a couple of forums and recieved some good advice but I am still having the problem. I have '98 Mercruiser 4.3 LX Gen + (Carb) engine.

I cannot get the fuel pump to run while the engine is cranking. If I jump the fuel pump with 12V it will run. I can then start the boat and it will run fine. A week or two later and I have to do it again.

I found that the fuel pump post on the solenoid was only putting out 8 volts. I changed the solenoid on the starter and it jumped to 9. Not enough for the fuel pump to start. It becch tests at 10. I took the soleoind off and bech tested it. It was putting out 11.28V.

The new starter is only putting out 8 volts. It bech tests at 9v.


I am not sure what else to do. I already started to throw money at it (starter). I am thinking of replacing the battery cables tomorrow. Maybe fuel pump next week???

What voltage should the fuel pump be able to run on? Any other ideas?

This is a quick list of what I have done...
Charged the battery
Cleaned the wire terminals
Had starter tested
Had starter tested again - replaced solenoid
Had battery tested
Had battery tested again
Tried another battery
Tried it with jumper cables.
Bypassed the oil sensor
I bought a new starter (cheap one)
I used jumper cables and connected a second battery directly to the starter.
Bunch of other stuff

you are saying that all these components like the starter, and solenoid are "putting out volts" so there's some suspicion about the testing.

The only thing on your boat that produces voltage while cranking is the battery. Check the voltage at the battery while cranking (red meter lead on pos. post, black lead on neg post- not the terminal, not the clamp, the lead post). It should stay above 10V.
If the voltage is 11 or more and the engine cranking speed is slow, you most likely have a wiring problem.

If voltage drops to 9 or less on the batt, you need a new battery, or your starter is drawing way too much current.

For all other voltage testing on your engine components. leave the black meter lead on the battery neg. post. Never move it. Always reference all voltage readings to the neg. post.

Then, you can move it to do voltage drop tests on particular parts of the system during cranking, especially the ground cabling and block connection, There are some youtube videos that show how to properly do V drop tests. It takes 2 people, but will reveal exactly where the problem is, rather than stabbing all over trying this and that random thing.

Welcome aboard !

You already surmised throwing parts at a problem doesn't solve it. What would i do if this were my boat ?

I would start at the battery. Disconnect it. Follow the the pos cable and clean as you go while closely examining every end. Look for green, might be under the coating. If it is brittle that will be a clue.

The base of the slav is sometimes the ground...speaking of grounds the main ground to the block will be a major area to look for a drop in voltage. Most forget without a good main ground there is problems. So remove the main ground look at the end and clean the bolt and inner part of the cable end.

The main barrel plug may have corrosion in it take it apart take a look and maybe shoot it with some dielectric grease.

Here is one more the new starters use alot less current then the original oem starters.

Not that i would recommend it, some have fresh wired the the fuel pump to a switch at the helm marked and flip it before cranking the engine to start then when they want to shut off the engine they flip the switch. Others have wired the ignition key with fresh wire straight to the pump. Again i do not recommend this.

hystat said:

The only thing on your boat that produces voltage while cranking is the battery. Check the voltage at the battery while cranking (red meter lead on pos. post, black lead on neg post- not the terminal, not the clamp, the lead post). It should stay above 10V.
If the voltage is 11 or more and the engine cranking speed is slow, you most likely have a wiring problem.

If voltage drops to 9 or less on the batt, you need a new battery, or your starter is drawing way too much current.

For all other voltage testing on your engine components. leave the black meter lead on the battery neg. post. Never move it. Always reference all voltage readings to the neg. post.

Then, you can move it to do voltage drop tests on particular parts of the system during cranking, especially the ground cabling and block connection, There are some youtube videos that show how to properly do V drop tests. It takes 2 people, but will reveal exactly where the problem is, rather than stabbing all over trying this and that random thing.

Click to expand...

This may sound ridiculous but how do I keep the meeter on the negative post when checking for voltage on the opposite side of the block? All my testing had been done to the block or a spare factory ground wire.


I'll check the battery voltage while cranking this morning. I think I did but cannot remember what the result was.

I thought about the switch but I am going to try and avoid it if at all possible.

Master mechanic said:

1. Here is one more the new starters use alot less current then the original oem starters.

2. Not that i would recommend it, some have fresh wired the the fuel pump to a switch at the helm marked and flip it before cranking the engine to start then when they want to shut off the engine they flip the switch. Others have wired the ignition key with fresh wire straight to the pump. Again i do not recommend this.

Click to expand...

1. I believe that his 1998 Merc should already be equipped with the newer style HTGR/PMGR starter motor.
If not, and if you were to replace this, use one of the above.

2. Agreed! This must be a "Momentary" switch in order to remain within the USCG regulations. The regs require that the electric fuel pump power becomes terminated or interrupted in the absense of engine oil pressure.
Advantages: the fuel pump can be activated right from the helm, and prior to any engine cranking.
Saves starter motor and battery cycles, usually extending their life.


Hystat is correct. Voltage and Amperage are derived from the battery source.
Items such as starter motors, relays, etc, consume voltage and may lower voltage readings due to the amp draw of the component.
Example: a starter motor may pull 170-180 amps. While pulling 170-180 amps, voltage is lowered momentarily.... and will also be seen elsewhere in the 12 volt system.
Similar to car headlights dimming somewhat during cranking.



By-passing the low oil pressure switch and/or relay will let you know if the pump itself is OK.

While cranking, oil pressure is too low to activate the relay via the NO oil pressure switch.
The relay will then be triggered by the starter motor by-pass circuit.
Once running, the NO oil pressure switch closes and holds the relay circuit closed for pump operation.

Since you say that once up and running it continues to run, your NO oil pressure switch and relay are apparently working.


I'd look towards the start-by-pass circuit, and correct what's wrong......... or circumvent this circuit via a momentary helm switch.
This can be a momentary single pole toggle switch, or it can be a push button switch.... as long as it's momentary.

Keep the relay in the loop.


.

Trace the purple 12 volt wire from the fuel pump to a junction...check it for corrosion but clean the connectors thoroughly.

Ok, while cranking the battery measured 10.80

I made an attempt to check for resistance on the battery cables. I switched the meeter to 20K on the ohm scale (not sure if it is the right one). I checked both ends of the positive cable. It went to 0.0. Same for the negative post on the battery to the block.

Even with both started out and on a bench I only get 8 or 9V to the fuel pump post. It's still not enough to start the fuel pump, right?

My fuel pump is original. Is it possible that it needs a full 12V to start but a new one would start with less? Any way to test. They are not cheap.

Use the 100 ohm scale for more difinitive resistance measurements.

I have a 200 scale.
When I used that setting the positive lead from the battery to the starter was 1.3 and the negative cable is 1.4.
The positive lead is 5-6 feet the negative is 3 feet in length.

I didn't want to cut the tape off all the wires so I connected a jumper wire from the solenoid post the the fuel pump.

I should mention that someone cut off a slice of insulation on the purple/yellow wire just before the connection to the fuel pump. I owned the boat since it was two years old. I only had it in the shop twice. Not sure when or why it was cut. I can say that is has been convenient.

Two methods for trouble shooting:

• Haphazardly throwing parts at a problem in hopes that one or two of them correct it.
• The P of E (process of elimination).

The Haphazard method eventually works. You may not know which part fixed what.... but you'll get it.

The P of E is tried and proven to work when we do one item, and one item only at a time.
When used systematically and mothodically, the P of E won't let you down!
You will find the problem, and you'll be better equipped for future problems.


.

Trace the purple 12 volt wire from the fuel pump to a junction...check it for corrosion but clean the connectors thoroughly. If that is good continue tracing the wires to their origins...starter circuit and oil pressure switch.

I put on a new negative cable. It did help a little. The voltage at the fuel pump post is now up to 10.20 when cranking. I would have replaced the positive cable but could not find one long enough (any idea where to get a 5 ft cable?). I did add a set of jumper cables from the battery to the battery post on the starter.

The battery is measuring 10.80 when cranking. So 10.20 isn't too bad.
I dont see how it will ever get 12V when cranking.

You will not get a full 12 volts when cranking.

there is a voltage drop due to the starter draw,

If i am not mistaken the start draws like 60 - 80 amps when cranking over.

As stated in an earlier post, you will see a voltage drop. I think 10.5 volts is acceptable.

What does your battery measure with no wires attached. Red to + and black to -


Any good battery should read (6 cells at 2.1 volts per cell) or 12.6 volts. STATIC!

Of course the larger the amp capacity of a given battery will have an impact. If you are using anything less than a 500 CCA battery then this could be marginal.

Also if changing the ground wire made a positive impact then replacing the positive cable may also.
Any marine store will have this or going to a auto parts store may also. Make sure it is at least the same wire guage size or larger and if possible make sure it has copper end terminal.!! Make sure the battery connections are very clean also!!

Kghost nails it!

As said earlier, the entire 12vdc system will see this voltage drop during cranking. I'd say that during cranking, 10.8 volts is very acceptable.

The 12.6 volts would be a very healthy battery reading.
These readings will be more meaningful after a battery has been at rest for 6 hours or so.


.

Ok, I changed the positive battery wire tonight.
The reading on the fuel pump post jumped a little. When cranking it is now between 10.3 and 10.4. When I stop cranking it slowly climbs to about 11 before it shuts off about 5 seconds later..

Still not enough to start the pump.

Is there any kind of back flow valve?

So, whats left?
Fuel pump?

Could it be something not related to the starting system that is drawing down the power?

I have the pump disconnected from the carb so that it pumps into water bottle.

Could this be the issue?
For anyone that may have found this thread, I wanted to add that I have located my problem.

Had some co-workers come into town from KC this week and I told them I'd take them up the river for gator spotting and lunch. I hadnt had the boat out for 2 weeks so I dropped it off the lift the evening before and started her up. Same symptoms. She started and ran great for 20 seconds, then stumbled and died and wouldn't restart. Obvious fuel issue. I decided to get my tools and testers to see if I could locate the problem.

Disconnected the fuel tubing from the Fuel pump outlet, and cranked the engine over a few times. No fuel, and my oil pressure gauge looks fine. So, I pulled the fuel pump power connector and checked for voltage while cranking. It was there! So, I rigged up a momentary push button to 12V and bypassed the low oil pressure relay and hot-wired the fuel pump. Nothing but a click! Aha!

I pulled the fuel pump and bench tested it at 12V 2A, backwards and forwards. Nothing but a click. I soaked the fuel pump in PB Blaster for an hour, then tested it again. It started to come to life, upchucking rust particles. Once I got it freed up, I used my momentary push button test rig to run it backwards and forwards directly on a battery, while feeding it oil. Eventually it cleaned out and ran super, even at 2A.

I re-installed everything and the engine whirred to life with a blip of the key.

I can only surmise that my fuel pump has been on it's way out for the last several months, and seizes while sitting due to internal rusting. I guess the continued cranking eventually freed it up before.


It's not serviceable and there doesnt appear to be an aftermarket equivalent that I can find, so I will order a new one next week to replace mine.

Dont be to hasty,

I believe there may be aftermarket ones available BUT they MUST be marine rated.

I always recommed OEM so you can not go wrong with a factory replacement!! That is what I would do and be done with it!!

But if you want to reasearch it do a google search for marine electric fuel pump, Carburated!! No more than 6-8 psi!!

So in retrospect the voltage drop was caused by the pump......................It was asked if you could here the pump running was it not???

Here is the latest...
Based on the information above. I took out the fuel pump. When I connect it to a battery it runs for about 10 seconds but slows until it stops. I tried it on three batteries. It did the same thing.
On one attempt I connect the leads backwards and it continued to run.

It was connected directly to the "+" and "-" terminal of the battery but it was on a bench with no fuel pumping through it.

Is there any reason why it should run like that?

KGhost,

It doesn't run at when cranking. My thought is that it needs the full 12 volts to run. When the engine is cranking it there isn't enough juice. Thats just a theory. I have no way to prove it.

If I bypass the the oil pressure switch it will run once I stop cranking.

This may be a standard Carter Electric rotary vane pump with another name on it.
If it looks like this, it's the Carter brand, and will be easy to find.




Here's the same pump with no name on it.


Here it is again with a two pin harness attached.


.

Actually it looks like this

However the web page lists it as 93-96. I have a 98.
This is what they show for a '98



Here is the site
http://www.ebasicpower.com/c/MERELECFP/Electric+Fuel+Pumps+for+Mercruiser

The schematic shows the purple wire from the strarter solenoid when cranking, should have the 12 volts on it and it should be going to the fuel pump only when cranking. Once the engine starts and you release the key to the run position then the oil pressure switch takes over.


Do not watse time and put any faith on the old one.........testing it gets you no where now that you know it is bad.

To be honest I have never bench tested on to see how long it will run when power is applied directly to it.
My guess it that it will run until it burns up....see the fuel keeps it cool............dont forget this...........

See schematic below...
The purple with yellow stripe wire goes from the starter solenoid to one side of the oil pressure switch (and has 12 volts when cranking but the pressure switch is OPEN) it also goes to the electric choke, (additional voltage drop). the connection or junction is in the wiring harness under the wrap somewhere..........

So to check wether or not you have cranking voltage get a test light and hold it on the fuel pump connector + when cranking. if the bulb lights bright it works......

I know that it is close. When cranking the battery is at 10.8 but the fuel pump is at 10.4 to 10.5. I assume that would be close enough. As you mention there is the draw of the choke and the oil pressure switch.

If I wanted to rule out the oil pressure switch would I disconnect the wires and leave them hanging or disconnect them and use a jumper?

The post about the rust in the fuel pump was not mine. I found it on the internet.
I went back and read though and found I wasn't clear.

Mine does run for a few seconds and stops but as you pointed out it may be because nothing is running through it. I don't remember it happening in the boat and once the boat is running it's fine.

To by pass the oil pressure switch you jump the two connectors together.

When we use to start new boats with this back in the early 90's we used to do this on initial first time starting. This was done to make sure the dry carb had fuel before attemping to crank it over.

The pump should run all the time that power is applied to it......I do not think there is a pressure "shut off" ability (when fuel is running thru it). Not like efi type fuel pumps which are controled by a relay which is controlled by a feul pressure sensor/regulator of some kind.

What color is the connector that pluges into the feul pump.

there was at least one maybe more recalls/service bullitens on this. Dont remember the issues but what they did was change the color to identify the newer version.... Although you say you are bench testing with no connector so.......it should work. I would also say if it runs for a long period of time clockwise and not when power is reversed counterclockwise then I would agree it is toast.

A dc motor does not care what direction it typically runs as long as all the internals are good. Example, cordless drill........

The connector on the pump is white. The one I bought is black.

I received a call back from Mercruiser today. He said the pumps are rated for 4 PSI at 7 Volts. Mine will not run on less than 12v so it further proves the pump is bad.

I ordered one this morning. Hope to have it Thursday. It would be nice to get this thing finished!.

The pump must be between 4-7 psi no more no less verify before installing !

Over 7 psi will overpower the float !

Understand ?

............................

kghost said:

When we use to start new boats with this back in the early 90's we used to do this on initial first time starting. This was done to make sure the dry carb had fuel before attemping to crank it over.
And a great explanation as to why the momentary helm switch works well for an engine that has been sitting for a while.


The pump should run all the time that power is applied to it......I do not think there is a pressure "shut off" ability (when fuel is running thru it). Not like efi type fuel pumps which are controled by a relay which is controlled by a feul pressure sensor/regulator of some kind.
I believe that is correct.

A dc motor does not care what direction it typically runs as long as all the internals are good. Example, cordless drill........
I agree, the motor should not care which direction it's being operated during a test only.
However, these are rotory vane pumps. I doubt that operating in reverse would be good for the actual vane side of the pump itself.

Click to expand...

Looking forward to getting the pump in. It was a problem two years ago but I limped through the season. I thought I fixed it over the winter but a few weeks in the problem came back. At first I was using a test light and struggled with that then spent weeks trying to figure out the voltage issue (it may not have been an issue at all).

In September I started to fix what I thought was a minor floor issue. Three months later I replaced about two thirds of the floor, all the foam, a bulkhead, the seam boxes and the carpet.

I can't wait to get it out of the garage and stored for the winter!

Sump'n is fishy here.
In post #1, first paragraph, third sentence, the OP says this; I have '98 Mercruiser 4.3 LX Gen + (Carb) engine.

Now we're talking about an electric fuel pump that is considered "high pressure" and is for use with FI engines.

High pressure Electric Fuel Pump Fits a GM V-6 & V-8 (305, 350, 377, 454, 496 & 502 cid) EFI engine. This item replaces Merc. # 861156A1.


If this is a carbureted engine, then the carburetor needle/seat are designed for 5-7 psi.
This lower and pretty much standard 5-7 psi is required in order for the float to close the needle/seat.
Excessive pressure would over-power the needle/seat.


Kaw550, are you by chance mistaking a TBI for a Carburetor?????




.