7.4L EFI Surging/Stalling Under Load

Ramblin' Guy said:
PS - I guess this is the vapor separator, not the fuel pump. I guess I might be back to the mechanical one unless I can locate the electric fuel pump. Do you know where it would be on the motor if it had one?

View attachment 119259
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Yes, that's your VST. It sounds like you have the same setup as me: both the mechanical water/fuel pump assembly that share a pulley and the EFI pump that's part of the VST assembly.

The side to the left/aft is the tank itself - it looks like a giant rectangular carburetor bowl. The right side is cylindrical and it contains the EFI fuel pump. Last year I had what turned-out to a bad o-ring in the VST, but troubleshooting led me down the path of replacing the mechanical pump diaphragm (routine maintenance) and considering replacing the EFI pump. The latter is STUPID expensive - even by boating standards. ($800) That stopped me in my tracks and I hired a mechanic to find the actual issue.

I suppose you could swap pumps with the other engine, but I'm also in the camp of not ignoring what the EMC is telling you...
 
RollerCoastr said:
Yes, that's your VST. It sounds like you have the same setup as me: both the mechanical water/fuel pump assembly that share a pulley and the EFI pump that's part of the VST assembly.

The side to the left/aft is the tank itself - it looks like a giant rectangular carburetor bowl. The right side is cylindrical and it contains the EFI fuel pump. Last year I had what turned-out to a bad o-ring in the VST, but troubleshooting led me down the path of replacing the mechanical pump diaphragm (routine maintenance) and considering replacing the EFI pump. The latter is STUPID expensive - even by boating standards. ($800) That stopped me in my tracks and I hired a mechanic to find the actual issue.

I suppose you could swap pumps with the other engine, but I'm also in the camp of not ignoring what the EMC is telling you...
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Thanks for the info. I tend to agree with the consensus on here - if it's telling you something electrical isn't working, it's probably electrical. I thought that with a MPI engine that all the spark/advance stuff was controlled by the fancy ECM. With now it won't advance much above 3200ish, it does seem like that's a point where something electrical should do something. If it were truly fuel, it seems like it would start losing power on the way up before that point. I think we'll start with a tune-up, etc. and replace the distributor cap/wires to see what effect that has. Then if we get past all the electrical/ignition stuff it could be, we can try the 'bypass the fuel system method' and pull some good gas out of a can to that motor as close to the fuel pump as possible. That will eliminate some whole other paths of problems in the fuel system.

with any luck, I won't have to replace the EFI pump. That's ridiculous.
 
Sounds like the RINDA is bitching about this thing. 1 minute to swap from Stbd to Port.
30-80 bucks to replace if that's it.
 

Attachments

  • IC and the ECM.pdf
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370Dancer said:
Sounds like the RINDA is bitching about this thing. 1 minute to swap from Stbd to Port.
30-80 bucks to replace if that's it.[/QUOTE

it’s Spring and I’m headed toward the water soon, so it’s time to revisit this thought. Quick question for you - where is the IC module that I’m swapping? I thought I knew, but I’m not sure. I was looking on the web for an actual picture on the engine but couldn’t.

Another thought/question for you: my sync isn’t working. Does it get its signal for engine RPM from this thing? That would explain several things that are occurring.

Sorry for all the questions, but I think you’re on the right track here.
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The IC module is on the distributor. Has 3 plugs. One from the distributor pickup.
Looks like this:
IC module.PNG
 
ttmott said:
I suspect an intermittent loose or bad ground connection.
First things first - check all of the electrical connectors; take apart, inspect, clean, lubricate, and reassemble.
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370Dancer said:
The IC module is on the distributor. Has 3 plugs. One from the distributor pickup.
Click to expand...

Ramblin, FWIW, in the past few seasons I've experienced both a faulty module and faulty connections on a module. (the harness fitted only loosely on the replacement module, so it's now soldered-on)

This seems like a solid direction to go in: it's a frequent trouble-spot and matches what your MEFI is saying.

It's also not at all pricey. If a new and securely-connected module doesn't help, you'll be out very little and have a spare.
 
RollerCoastr said:
Ramblin, FWIW, in the past few seasons I've experienced both a faulty module and faulty connections on a module. (the harness fitted only loosely on the replacement module, so it's now soldered-on)

This seems like a solid direction to go in: it's a frequent trouble-spot and matches what your MEFI is saying.

It's also not at all pricey. If a new and securely-connected module doesn't help, you'll be out very little and have a spare.
Click to expand...

I’m hoping so much that this is the issue, it isn’t even funny. I’m gonna buy @370Dancer a case of Miller High Life if it is. He’s the man.
 
Ok, this is weird. I switched the ICMs before I drove the boat on a short run from storage to my slip (10.5 nm pier to pier - 1.5 hrs total run time with the channels), and it appears the problem didn’t move to the port engine as hoped, it seems to have completely gone away. Now I’m confused because it appears to be a healing. Not sure what to make of it.
 
I just realized I never closed the loop on this thread, but this problem was ultimately solved with a … tune up. New plugs, rotors, wires, and caps. Runs like it’s new. Kind of embarrassing, but also very relieved it’s something simple and relatively inexpensive. Thanks to all for your advice and hope this helps a future friend.
 
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