Logo
FULL SITE MENU

2000 7.4 MPI Throttle Body Gasket. Why 2 types?

B

Bodyshot

New member
Hello all I’m new here but I’m learning quite a bit.

I actually have 2 questions the first being, why there are 2 different TB gaskets for these engines.

One has a cut off at the bottom of the TB opening reducing the TB diameter and the other without that restriction. I have no idea why they would want to restrict a BB GM like that so let me know if you’ve figured that out. My engine is SN 0L691360 so what one should I have installed?

The second question is… I don’t think the fuel pressure regulator on the fuel rail dose a damn thing. It’s a non-return system so why even have it there just to possibly create vacuum leaks?

or does it somehow do something? The return fitting is plugged so?

thank anyone who has answers in advance.
 
o2batsea said:
The parts breakdown shows only one gasket:
https://www.marineengine.com/parts/mercury_marine_parts/sn/0L691360/4542067N1/2705_100

The fuel pressure regulator is doing its thing, so unless that has specifically been targeted as a source of trouble, don't mess with it. It's a $600 part.
Click to expand...

Well I’m chasing a misfire and installed the Bosch injections from Five O Motorsports. I used the Gasket without the restriction in it and the thing won’t idle well nor will it run properly at lower RPM as it surges significantly. It either doesn’t like these injectors or it really does need that restriction in the TB opening. I’ll be slapping the old in just to check.
 
o2batsea said:
If you're using automotive parts and not the original marine parts, well, you're on your own there.
Click to expand...

it doesn’t like the injectors. Well that was a waste of money.

the injectors I bought where the wrong ones as it seems the merc 7.4 is calibrated for 24lb injectors. I’ll pick them up.

has anyone had luck with the Codemate reader?
 
Update:

The boat will run well for a short bit then starts the misfire. This began last year but was barely noticeable and has gotten to the point where cruising speed is no longer attainable.

The engine is throwing no codes only code 12. A few plugs (one or 2 on each side) look fouled up and bit darker. The plugs are new as of last year. Same with the cap, rotor, wires, intake plenum gasket. The cap is getting a copper oxidation build up already and when taking off one plug wire at a time it barely has any affect. Not sure why this is as it only has about 30 hours on it. Ohm out the injectors when they where warmed up and read 12 ohms on all 8. Took them out and cleaned them. No change, going to check fuel pressure next. I need to check timing as well it is my understanding that these are set at 8 degrees base?

I have a very hard time understanding how the fuel rail pressure regulator can be doing anything, its completely blocked off from elevating pressure like it would in the trucks it was designed for. The trucks are return fuel systems these are not.
 
Back
Top