Carb to MPI problem 2011 Merc 4.3

[kbryant]

No MPI is very good. 220 hp on your engine vs the 190 hp carbed model.

yes the cap is a common fail point for misfires. Certainly could be other things but if you dont know when it was changed would be a good thing to rule out.

Thank you, Scott, for your help here. I appreciate your time. I will buy a cap and rotor and see. Is changing the injectors out for new ones something a person could do themselves?

 

[Scott06]

Thank you, Scott, for your help here. I appreciate your time. I will buy a cap and rotor and see. Is changing the injectors out for new ones something a person could do themselves?

It is but lets do some diagnostic work first


How about a little more description of the problem ? And what’s your serial number


Have you checked your fuel filter contents for any thing but fresh clean gas?

 

[kbryant]

It is but lets do some diagnostic work first


How about a little more description of the problem ? And what’s your serial number


Have you checked your fuel filter contents for any thing but fresh clean gas?

The problem is starts great , idle is good, all gauges good. Runs great at lower rpms, start putting a load on her and she starts to sputter and backfires a little and then starts to smooth out a little, but you can still fell her struggling.
2011 Tahoe Q51
4.3 Merc Mercrusier MPI Alpha 1
1A035000

 

[kbryant]

The problem is starts great , idle is good, all gauges good. Runs great at lower rpms, start putting a hold on her and she starts to sputter and backfires a little and then starts to smooth out a little, but you can still fell her struggling.
2011 Tahoe Q51
4.3 Merc Mercrusier MPI Alpha 1
1A035000

I did order a new Cap and Rotor

 

[kbryant]

The problem is starts great , idle is good, all gauges good. Runs great at lower rpms, start putting a load on her and she starts to sputter and backfires a little and then starts to smooth out a little, but you can still fell her struggling.
2011 Tahoe Q51
4.3 Merc Mercrusier MPI Alpha 1
1A035000

I put new Fuel Filter on it -- all clear fuel
New Plugs and Wires
New pickup valve
New PVC valve

 

[Scott06]

I put new Fuel Filter on it -- all clear fuel
New Plugs and Wires
New pickup valve
New PVC valve

@alldodge and @QBhoy may have some other ideas given its MPI

 

[kbryant]

@alldodge and @QBhoy may have some other ideas given its MPI

I will give the cap and rotor a roll and see if that helps. Does that seem like a cap issue?

 

[Scott Danforth]

the crab caps fail internally, causing cross-talk on the plugs. some people have luck with them, most people get about 12-15 months out of them.

I would recommend a cap and rotor change like you are planning.

 

[Scott06]

I will give the cap and rotor a roll and see if that helps. Does that seem like a cap issue?

it could be and given how many times you see strange misfire symptoms cured by this you need to rule it out

 

[QBhoy]

@alldodge and @QBhoy may have some other ideas given its MPI

Thanks. Replied to a message sent there.

 

[alldodge]

Changed the title to help others understand what happened

Yes, Cap and rotor
If no change check fuel pressure, should be 43 psi at the rail

S?N doesn't come up (might not be registered) but it is in the last numbers of 4.3 MPI

 

[kbryant]

Changed the title to help others understand what happened

Yes, Cap and rotor
If no change check fuel pressure, should be 43 psi at the rail

S?N doesn't come up (might not be registered) but it is in the last numbers of 4.3 MPI

Thank you for your help. My new Cap and rotor should be here tomorrow. Will install and give it a try. Crossing my fingers this is the fix. Do you think any of the fuel injectors are bad?

 

[QBhoy]

Ok
I like beer so that sounds like a better idea. The only thing is I don’t know how the hell to pull carb off this 4.3 Merc. I can’t find a video about that. Picture attached. Where do I begin

Hi. See that blue main harness plug…take that apart and get electrical cleaner into it. Straighten out the wiring on it there too. Doesn’t look to great there. Make sure nothing is earthing onto the engine block or elsewhere from any un capped unused sensors too. There are an array of unused plugs near there that should have weather caps on them and can end up shorting out causing issues.

 

[alldodge]

Do you think any of the fuel injectors are bad?

No as yet, need testing if cap does not fix

 

[kbryant]

Hi. See that blue main harness plug…take that apart and get electrical cleaner into it. Straighten out the wiring on it there too. Doesn’t look to great there. Make sure nothing is earthing onto the engine block or elsewhere from any un capped unused sensors too. There are an array of unused plugs near there that should have weather caps on them and can end up shorting out causing issues.

That wire harness, is that the one with red wires in front of it you're talking about?

 

[QBhoy]

That wire harness, is that the one with red wires in front of it you're talking about?

The big blue and black main loom plug

 

[kbryant]

The big blue and black main loom plug

Hello
Just getting to the cap and rotor. I noticed nothing is plugged into this on the picture by the rotor. Should something be plugged into that??

 

[alldodge]

Not all motors use the cam sensor and appears yours does not

 

[kbryant]

Ok
I just want sure what that was.

 

[QBhoy]

Yeah. As AD says. Not always utilised. My 2003 v8 mpi doesn’t have anything plugged there either.
On a side note…is that picture taken, showing the new rotor or old rotor in place ?