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8.2 litre efi mercruiser problems

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whitelightnin

New member
I own a 1996 8.2 litre with efi. I have owned this for over 20 years and has always run good. This engine had a vs tank as standard equipment. I wanted to get rid of this tank due to many replacement parts are no longer available. I removed the tank and replaced it with a separate electric fuel pump, that is supposed to be rated for the gph and pressure requirements. I have upgraded the spark plugs, cap & rotor new fuel lines and inline filters before and after the new pump. The motor is supposed to run at about 37 to 38 psi. I installed a pressure gauge and the best I get is about 30psi. The boat starts and runs ok up to about 3000 to 3300 rpm, then it appears to be starving for fuel, It falls on its face at those rpms for a few seconds then recovers somewhat, but not completely. In my area there are few Maine techs that know anything about this type boat, so am hoping there is someone out there to help. I am at best an amateur back yard mechanic with basic knowledge. I do not want to aimlessly be replacing parts with no avail. any help will be greatly appreciated. If you respond please remember I have limited understanding, so please speak in layman's language.
 
Have you tried removing the vacuum line to the fuel pressure regulator while the engine is running to see if the fuel pressure goes up roughly 5psi like it should?

Where did you run the fuel return line to? back to the fuel filter or fuel tank?

What brand/part number fuel pump and related parts did you install?

Could you elaborate some more regarding upgraded spark plugs, cap and rotor? I'd believe you'd want to keep these parts OEM (original equipment manufacturer) or not venture out to far from their specifications.

Engine serial number is?
 
Yours is EFI which says it's TBI and use to have a VST which was removed and replaced with just a single fuel pump

ok
As Fun Times mentioned, what pump did you install?
The VST returns excess fuel back to the VSTank. How is the fuel return line installed?
 
Fun Times said:
Have you tried removing the vacuum line to the fuel pressure regulator while the engine is running to see if the fuel pressure goes up roughly 5psi like it should?

Where did you run the fuel return line to? back to the fuel filter or fuel tank?

What brand/part number fuel pump and related parts did you install?

Could you elaborate some more regarding upgraded spark plugs, cap and rotor? I'd believe you'd want to keep these parts OEM (original equipment manufacturer) or not venture out to far from their specifications.

Engine serial number is?
Click to expand...
I have not tried removing the vacuum line, I am just now de-winterizing the boat, hope to have it running on Friday. The return line was brought back to the tank. The pump name is unknown, I am beginning to think this may be the problem, it is not a name brand pump. I am thinking of going to AEM pump. the plus and things were installed prior to any work and the boat ran fine. The serial number is OF 597878. What will removing the vacuum line tell me. The new electric pump is supplied by a mechanical pump, the same as the old vs tank pump was, the difference there is the vs tank always had fuel right there. I will let you know what I see on the pressure guage when I remove the vacuum line. The existing vacuum line has what I will call a small kink in the line, this may or may not be a problem, but I will change the line.
 
AllDodge said:
Yours is EFI which says it's TBI and use to have a VST which was removed and replaced with just a single fuel pump

ok
As Fun Times mentioned, what pump did you install?
The VST returns excess fuel back to the VSTank. How is the fuel return line installed?
Click to expand...
The pump may be the issue, I am thinking of upgrading to an AEM pump. The new return line goes back to the tank. I see you mention a single pump. The vs tank had only one pump and used a mechanical pump for supply, the difference is the vs tank always had a fuel supply in the tank. The new electric pump also is supplied by an updated mechanical pump. I am just now de-winterizing the boat and hope to have it running on Friday, then I can start diagnosing the problem. Any help will be appreciated.
 
whitelightnin said:
The pump may be the issue, I am thinking of upgrading to an AEM pump. The new return line goes back to the tank. I see you mention a single pump. The vs tank had only one pump and used a mechanical pump for supply, The new electric pump also is supplied by an updated mechanical pump. I am just now de-winterizing the boat and hope to have it running on Friday, then I can start diagnosing the problem. Any help will be appreciated.
Click to expand...
I know what you have, it was same VST but mine was a MPI, and I to replaced with different setup. Still have the old VST sitting on a shelf

The new pump may not be able to pump at 50 to 60 psi. The the higher level and the Reg would be set to lower to 30
 
AllDodge said:
I know what you have, it was same VST but mine was a MPI, and I to replaced with different setup. Still have the old VST sitting on a shelf

The new pump may not be able to pump at 50 to 60 psi. The the higher level and the Reg would be set to lower to 30
Click to expand...
I to still have the vs, but parts are almost non existent. I used to have my boat serviced each year, then I found that in 26 years they never cleaned or serviced the vs, that is when I took service over, I have the shop manuals and I love this boat, so I will continue servicing myself. any help you can give is appreciated.
 
AllDodge said:
I know what you have, it was same VST but mine was a MPI, and I to replaced with different setup. Still have the old VST sitting on a shelf

The new pump may not be able to pump at 50 to 60 psi. The the higher level and the Reg would be set to lower to 30
Click to expand...
you said you have the same set up, how did you change yours .
 
whitelightnin said:
you said you have the same set up, how did you change yours .
Click to expand...
Again mine was a MPI so it had a fuel rail.
Connect the pump output to the top port of the rail. The bottom port is after the Reg which returns fuel to the main fuel tank

1779451912048.png
 
whitelightnin said:
I to still have the vs, but parts are almost non existent. I used to have my boat serviced each year, then I found that in 26 years they never cleaned or serviced the vs, that is when I took service over, I have the shop manuals and I love this boat, so I will continue servicing myself. any help you can give is appreciated.
Click to expand...
You posted "but parts are almost non existent"- where are you located?
 
AllDodge said:
I know what you have, it was same VST but mine was a MPI, and I to replaced with different setup. Still have the old VST sitting on a shelf

The new pump may not be able to pump at 50 to 60 psi. The the higher level and the Reg would be set to lower to 30
Click to expand...
what pump did you end up putting on yours. I want to try to find the right one. Thanks
 
You kept saying EFI so I thought TBI
I didn't need cool fuel either but it was cheaper than Aeromotive, and with fuel return to tank, it was a non-issue. Was also converting from MEFI-2 to MEFI-3 and a remap to give me 530HP

The fuel rail was angled cut where the fuel lines went in and re-tapped for AN fittings.

I would suggest Aeromotive 1000 or any other pump which can provide 50 psi

louc said:
wonder if anyone ever made a 4bbl marine intake that would fit those engines. then you could convert to a 4bbl carb.
Click to expand...
Yes many have, just look for BBC rectangular port intake. Will fit 454 or 502
 
Fun Times said:
Have you tried removing the vacuum line to the fuel pressure regulator while the engine is running to see if the fuel pressure goes up roughly 5psi like it should?

Where did you run the fuel return line to? back to the fuel filter or fuel tank?

What brand/part number fuel pump and related parts did you install?

Could you elaborate some more regarding upgraded spark plugs, cap and rotor? I'd believe you'd want to keep these parts OEM (original equipment manufacturer) or not venture out to far from their specifications.

Engine serial number is?
Click to expand...
I am getting back to you after I had a chance to remove the vacuum line to the fpr. The pressure was about 28 psi before removing the line, after removal the pressure went to about 33psi. the was a small kink in the old line, but replacing it made no difference. I have checked to anti-syhfon valve and found it to be clear. I checked the fuel tank vent and also clear. if I have to buy a new pump that is ok, as long as I have some kind of idea that is the problem. I have not put the boat in the water yet, so there is no way of putting a load on the motor to match the load in the water, with drag and propeller action. Any ideas ??
 
The pressure rise when disconnecting the regulator's vacuum reference is a good thing.

It is possible that your new pump is starving (about 3000 RPM )and could be due to the mechanical pump being in front of it, the line from the tank to the pump being too small, or a combination. no installation requirements for the new electric pump

Another option is to Tee in a vacuum pump on the suction side of the pump in question...though you will have to load the engine to get a realistic reading...another option is to use an outboard tank, for testing purposes, to rule out the plumbing from the tank to the engine...but you may have to do more than one test to ID the specific issue.
 
Maybe a long shot but it might be worth it to remove the fuel pick up tube to see if there is screen on the end of it, those can get clogged.
 
makomark said:
The pressure rise when disconnecting the regulator's vacuum reference is a good thing.

It is possible that your new pump is starving (about 3000 RPM )and could be due to the mechanical pump being in front of it, the line from the tank to the pump being too small, or a combination. no installation requirements for the new electric pump

Another option is to Tee in a vacuum pump on the suction side of the pump in question...though you will have to load the engine to get a realistic reading...another option is to use an outboard tank, for testing purposes, to rule out the plumbing from the tank to the engine...but you may have to do more than one test to ID the specific issue.
Click to expand...
Thank you for your reply, the more I get the better. If you read my original post, you will see that I am a novice at this, even though I am 82 years old. I had this boat serviced each year by a marina, only to find out that they never touched the vs tank and knowing that many parts for that are no longer available, I had to get to out. With that said let me tell you what I have done. First, the engine is running. I have checked the vent line to make sure no debris or clogs, clean. I removed the line from the tank and checked the anti syhfon valve, clean & clear. All the fuel lines are new, marine grade lines. Both filters are new as are all the fittings. One thing I have to check is, My pressure gauge is teed off the main supply line before the rain. Getting to the schrader valve on this] rail is very difficult and may require removal of the plenum. As I said, the guage is on a tee from the main supply line but, there is about 2 feet of line from that tee to the guage. I am wondering if this could be part of the low pressure reading. I assume when you said that the rise I n pressure was a good thing, that it means the fpr is functioning properly. The reason for the mechanical pump before the electric pump is this is the set up for the engine with the vs tank. Now I realize this was there to push fuel to the pump in the vs tank and that there was always some fuel in the vs tank. The electric pump is below the level of the fuel tank so it cane gravity fed, do you think this may be part of the problem. As I said any ideas are appreciated. Thank you. PS I am quite mechanically savy. I am a master electrician/ builder and developer, so I am not a complete dummy.
 
louc said:
Maybe a long shot but it might be worth it to remove the fuel pick up tube to see if there is screen on the end of it, those can get clogged.
Click to expand...
Thank you, I have checked all the lines vents and anti-syhfon valve and all are clear. I just responded to makomark, if you can access that post maybe it will give some ideas. Again, thanks for any help.
 
Some fuel pick up tubes have a fine screen on the end of them; these can clog with crud and can cause fuel starvation problems. Some have them, some don’t, but you’d never know unless you check OR run it on a separate outboard tank. Even then the gas in the tank could be bad and no problem with any other component. I thought that was the cause of my fuel starvation issue last year but after checking everything including the pick up tube it was the GAS! I had the tank pumped out this spring.
 
louc said:
Some fuel pick up tubes have a fine screen on the end of them; these can clog with crud and can cause fuel starvation problems. Some have them, some don’t, but you’d never know unless you check OR run it on a separate outboard tank. Even then the gas in the tank could be bad and no problem with any other component. I thought that was the cause of my fuel starvation issue last year but after checking everything including the pick up tube it was the GAS! I had the tank pumped out this spring.
Click to expand...
how do I get to the potential screen, the fitting for my tank fuel shutoff valve appears to be permanently installed in the tank and no visible way of getting to the bottom of it. if all else fails once I get it in the water I can use a separate tank. If you know of any reliable pumps, let me know. Thanks.
 
36 +/- 2 PSI is what Manual 16 calls for with the MPIs...TBIs call for 30 +/- 2 PSI...

THE MPIs went up to 43 PSI in 98...I think they changed the flavor of the MEFI unotd at the time, too.
 
whitelightnin said:
how do I get to the potential screen, the fitting for my tank fuel shutoff valve appears to be permanently installed in the tank and no visible way of getting to the bottom of it. if all else fails once I get it in the water I can use a separate tank. If you know of any reliable pumps, let me know. Thanks.
Click to expand...
maybe post a pic of the fuel tank set up in your boat....
 
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