Accessing the fuel pump on a 4.3 EFI

[AlboranC]

I have a non running Mercruiser 4.3 EFI from 2001 - the engine turns over fine, there is spark, but no fuel, so it seems like a fuel pump problem.

I have checked all the fuses and tried swapping the relays (which I can hear clicking) but I can't hear the fuel pump running.

Next step is to check the pump is getting power, but I can't get to the pump. Am I right in thinking the pump is inside the fuel cooler underneath the port manifold and that removing the riser and manifold will give access?

Any other suggestions for things to check before starting to dismantle everything?

Thanks for your comments and suggestions.

 

[alldodge]

The FP is located where you say. To gain access, the plastic cover comes straight off away from the motor. On the middle of the top and bottom of the cover, push in on both side and pull away.

The electrical connector powering the pump is on the outside of the box on the edge facing the front pulley

How about a motor serial number?
When cranking the motor do you see the tachometer moving up to at least 300 rpm?

 

[AlboranC]

Thank you AllDodge - the description of the cool fuel box is very useful. There is no way that i can get to the fuel pump from the side except by touch because there is a bulkhead in the way. I think I am going to have to take the riser and manifold off and anything else that is in the way.

To answer your question, yes I'm sure it's getting to 300 rpm on the key - the starter sounds very healthy and the battery is fully charged - it sounds no different to when it was working. What is the significance of 300 rpm?

I can't hear the fuel pump working when the ignition is turned on and there is power on both sides of all three of the fuses by the ECM - I haven't checked which one is for the fuel pump, but I think I am right that one of them is for the pump.

I will get the engine serial number and post it here.


Thanks again for your comments.

edited to add a photo of the what I think is the fuel pump - the front of the engine is to the right.

 

[achris]

Very common. The engine mounts obscure access to the fuel pump. I have the same on my boat, and every EFI/MPI boat I have worked on. The only option, and I know it's harsh, is to pull the engine... So yes, you want to be real sure it's a fuel pump problem before going there.

Chris.........

 

[alldodge]

Your looking for the tach to show 300 rpm. If the tach does not come up and show 300 rpm then signal from the distributor is not making it to the ECM. If the ECM does not know the distributor is firing then the fuel injectors will not pulse

 

[AlboranC]

Your looking for the tach to show 300 rpm. If the tach does not come up and show 300 rpm then signal from the distributor is not making it to the ECM. If the ECM does not know the distributor is firing then the fuel injectors will not pulse

Ok, thanks. Does the fuel pump not run as soon as the ignition is turned on to prime the system? I could be misremembering, but can't you hear the pump immediately?

I will do some more checks with a multimeter before I do anything else.

 

[AlboranC]

Very common. The engine mounts obscure access to the fuel pump. I have the same on my boat, and every EFI/MPI boat I have worked on. The only option, and I know it's harsh, is to pull the engine... So yes, you want to be real sure it's a fuel pump problem before going there.

Chris.........

Thanks for the good news, lol.

I managed to get my hand down and pulled the cover off.

I think I will try removing the riser and power steering pump to see if that gives any better access. From the diagrams it looks like I can at least unbolt the hose fitting from the front of the pump and then maybe unscrew it from the fitting that goes to the cooler - worth looking at at least.

​​​If I have to pull the engine it would be an opportunity to clean and paint the underside of the motor and replace hoses etc as the engine is 18 years old now. The outdrive needs to come off anyway for a service and I wouldn't mind the opportunity to paint the shield inside the engine compartment.

 

[alldodge]

Ok, thanks. Does the fuel pump not run as soon as the ignition is turned on to prime the system? I could be misremembering, but can't you hear the pump immediately?

When key is first turned to ON, the pump will run for 1 second then shut off.

 

[Lou C]

Engine pull to change a fuel pump? Was there a good reason why they put it there or is that just Merc wanting more money from you? The old school ones take about a half hr to change depending on how cooperative the fuel pump pushrod is. And the OE one lasted ah about 30 years.

 

[alldodge]

All cool fuel cells where installed with EFI/MPI motors. The reason for mounting them low and having raw water cool the fuel was to try to keep the motor from vapor locking in hot weather. None of the cool fuel systems always keep from vapor lock happening, but they do help

 

[achris]

Engine pull to change a fuel pump? Was there a good reason why they put it there or is that just Merc wanting more money from you? The old school ones take about a half hr to change depending on how cooperative the fuel pump pushrod is. And the OE one lasted ah about 30 years.

Tiny little fuel pump to feed a carburettor versus a high pressure, regulated cooled fuel delivery for a fuel injection system... I see your logic. :facepalm:

Chris...

 

[Pzilly]

Pulling riser will help, hardest part after 18 years might be freeing the water inlet line off the back of the cooler, be careful just pulling the fuel pump blind, there are several o rings in it and one comes off easy, luckily I put a new oil absorber mat down prior to starting or I wouldn't have noticed mine fell off.

if you have to pull the ex manifold I used 2 bolts 3/8 by6" with the heads cut off and thread them into two of the bolt holes before removing the rest, now if your bulkhead is there this probably won't help or if you have 1 piece manifolds this won't work, if you have 18 year old 1 piece manifolds turn those into anchors and get new 2 pc. If you haven't seen your flappers in 18 year pulling riser and give them a look too

 

[Lou C]

My logic is carbs work like they still work on thousands of boats and hot rods across the USA. And tell me just how easy it is to explain Mercs logic to your customer. Even Volvo puts the efi fuel pump assembly in a better place for access! I saw the tech at my boat yard working on one of these abominations on a 95* degree day. Not a happy camper!

 

[AlboranC]

My logic is carbs work like they still work on thousands of boats and hot rods across the USA. And tell me just how easy it is to explain Mercs logic to your customer. Even Volvo puts the efi fuel pump assembly in a better place for access! I saw the tech at my boat yard working on one of these abominations on a 95* degree day. Not a happy camper!

Yep, on my boat there is plenty of room either side of the engine to put both the water separating filter and the cool fuel assembly, there is zero reason to have it buried under the engine. Really the filter should be easily accessible to make it easier to regularly check it.

Its just one more PITA from having an outdrive boat.

 

[alldodge]

The pump low because an electric fuel pump doesn't create much suction, it just moves fuel. There can still be better places, but its all done to try and stop vapor lock.

In your case the boat manufacture makes it worst by placing a bulkhead next to the motor

 

[Lou C]

Just looking at it, one would get the impression that Merc wanted to put it in a standard location that would work with any boat installation without modifications, however that is until something goes wrong! As I said, Volvo does not put their pumps in a location like that and their system works too. As far as vapor lock, maybe it just does not get hot enough here (but it does top out in the high '90s in summer) or because we are at sea level but I've never experienced it with the 4.3/Quadrajet carbed engine.

My point is simply this:
Manufacturers both engine companies and boat companies are making it harder and harder for customers to justify to continue to buy sterndrives. Once someone gets hit with what they feel are unreasonable repair costs (and pulling an engine just to replace a poorly located fuel pump IS unreasonable, I don't accept the logic that it must be done that way) eventually they turn to outboards. Enough already between $800 EFI pumps, Cat Converter Exhaust ($6000 parts cost to replace, look it up if you don't believe it), buried starters in some installations that require an engine pull to replace (mostly boat companies fault though) etc.

 

[AlboranC]

The pump low because an electric fuel pump doesn't create much suction, it just moves fuel. There can still be better places, but its all done to try and stop vapor lock.

In your case the boat manufacture makes it worst by placing a bulkhead next to the motor

Agreed there is a bulkhead in the way, but even without one, the cool fuel unit is always going to be under an engine mount and whatever that is bolted to.

On my boat the whole thing including the fuel filter could have gone not much further up next to where the trim pump is located. It's just a lazy design choice.

 

[AlboranC]

Pulling riser will help, hardest part after 18 years might be freeing the water inlet line off the back of the cooler, be careful just pulling the fuel pump blind, there are several o rings in it and one comes off easy, luckily I put a new oil absorber mat down prior to starting or I wouldn't have noticed mine fell off.

if you have to pull the ex manifold I used 2 bolts 3/8 by6" with the heads cut off and thread them into two of the bolt holes before removing the rest, now if your bulkhead is there this probably won't help or if you have 1 piece manifolds this won't work, if you have 18 year old 1 piece manifolds turn those into anchors and get new 2 pc. If you haven't seen your flappers in 18 year pulling riser and give them a look too

Thanks for the tips. There is plenty of room to get to the manifolds - they can be slid off/on as you suggest - I'll take a photo to show the layout.

I'm just wondering now if it is possible to add a second fuel pump elsewhere and bypass the one at the bottom of the boat.

 

[alldodge]

I'm just wondering now if it is possible to add a second fuel pump elsewhere and bypass the one at the bottom of the boat.

The pump is on the motor so it can be dropped in, hook up and go

Another pump can be mounted about anywhere, but should be mounted low. Others have replaced cool fuel with Aeromotive, Weldon and others. If the return is routed back to the tank then no VP. Can also use another pump and not route back to the tank and just keep current setup. The regulator is what controls ther pressure.

Note: If a high output pump like Weldon or Aeromotive is used the return needs to go back to the tank. The high output pumps will push way more fuel then the motor will use so it can build more heat

 

[kenny nunez]

After removing the Cool fuel system to check the screen filter and replacing it on my 18’ Donzi my old arms looked like they are covered with tattoos from the blood just below the surface.
Pulling the manifold will make it a lot easier if their is room to get it off.
Since GM engines do not have provisions for a mechanical pump, Mercruiser had to make an adapter for the mechanical pump to be belt driven on the raw water pump. This was used on the carbureted and early fuel injected models.