How do I know if I have carb or fuel injection?

R

RichieRitz

Active Member
Aug 25, 2022
476
Lorain, Ohio
Boat Info
Sea Ray 340
Engines
496 BravoIII
I know sounds dumb, but…. It’s a 1998 5.7 mercruiser on a 215ec. I thought it was MPI but removing flame arrestor I saw two big butterfly valves in what looks like a big carb. Can these still feed injectors or what am I looking at? I do not see injectors like I do on my 2019 v6 Nissan truck. Thanks
 
Back then mercruiser made a TBI and a carb. What does the flame arrester say? Have you looked up the serial number? My bet is on a carb 260 HP.
 
This is what the top view of MPI looks like (plate open). The throttle body has one big plate (at least my 5.0 MPI did). With MPI there won't be a fuel line to it, and you won't see the fuel injectors. They are on the fuel rail closer to the heads/intake. TBI looks like a cross between a throttle body and a carb. Best thing would be to get your engine serial number, then use a site like mercruiserparts.com and they will direct you to the correct parts diagrams for your engine. And post pics!


1694875584426.png
 
If it's truly 260HP then it should be a TBI system. If you don't see the injectors sitting on top of the throttle body squirting fuel as it runs, then it's not 260HP. It would be 250HP.
 
Dxdave said:
No. All the way forward then back to quarter throttle to start.
Click to expand...
That implies a choke is used to help start the cold motor so my guess is carbourated, but the serial number or picture will help us take the guesswork out.
 
So throttle body because it injects the throttle body vs each cylinder I guess? Does it feed each bank of cylinders separately?
 

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"EFI" on your flame arrestor tells the whole story... Electronic Fuel Injection. :)

No, does not feed separately. It simply takes the place of a carb.
 
“Digital Ignition” I never knew you could run an engine with numbers. Must run in dollar increments.
 
It’s like that digital exam for guys they were advertising and my daughter said I should look into it because it must be the latest thing, it’s digital….
 
mrsrobinson said:
I'm curious to learn why he has to do this if it's EFI.
Click to expand...
Agreed, Throttle Body Injection (TBI pictured) “ should compensate for a cold engine then re-evaluate fuel needs as the engine warms. So no need to “pump” the throttles like my 4.3l little girls. If your manual is telling you to do this then there may be another section that says “if you have TBI do this…
 
mrsrobinson said:
I'm curious to learn why he has to do this if it's EFI.
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Me, too.

Dave... have you tried just starting it like you start your car? Or have you always assumed you had a carb'd engine and someone had told you to do that?
 
Lazy Daze said:
Me, too.

Dave... have you tried just starting it like you start your car? Or have you always assumed you had a carb'd engine and someone had told you to do that?
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Dave,

The reason we are all wondering is that in a carb’ed motor, the act of pumping the throttle does two things, it squirts a metered amount of gas into the carb ( accelerator pump) and also allows the choke spring to rotate the choke blade and allow some cams to rotate to allow the throttle stops to keep the idle high until it warms up.

To me in a digital system, there is no accelerator pump so I would expect the engine to start with just a key turn.

I personally have first had experience on the carb’ed version but don’t have first hand experience on the EFI in your picture though.

I guess it doesn’t matter as you have your answer now, I was just explaining whey we might be puzzled.
 
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