7.4L EFI Surging/Stalling Under Load

Ramblin' Guy said:
All right - lots of good thinking going on in this thread. I appreciate all of the great input. I'll try to answer all the questions, but I've been working all day at my real job (ha!), so I can pay for repairs and upgrades on this beast.

The engine serial numbers are OK144591 and OK144594. They are the original engines, and I have no idea when or if they were tuned up last. My bet is that the owner wanted to sell the boat and wasn't interested in PM's toward the end. Fortunately, this was the original owner of the boat, so I think he was invested in keeping it mechanically sound.

I did the oil change and fuel separator change after my ill-fated trip across on Halloween. There's two fuel separators on each engine, and I didn't see any water when emptying them into the bucket. When I took the boat later that week up to Muskegon, it was still pretty much doing the same thing, maybe ever so slightly better, but that could be wishful thinking.

My engines look a lot like Stee6043's, which makes sense b/c they're the same year. I've attached some photos of what I think is that fuel pump. I think it might be a good idea if they are mechanical and attached to the water pump, to remove them, replace the impellers, and rebuild the fuel pump if that's possible. I have no idea when the impellers were done last. I'm definitely going to make sure the fuel is OK in that tank, too (I guess by running off the other tank if the valves will allow. I'm wondering if I should put electric fuel pumps on, or stick with the mechanicals.

Thanks again to everyone - maybe we'll get this figured out.

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That pump looks like it is pretty new. Teflon tape? take a look at the other engine and see if it looks new. Maybe a issue the old owner was trying to fix.
 
Bad Cap and rotor (moisture in the cap) will cause that exact issue. Id start with full tune-ups before i did anything else, especially on a new to you boat. Then you know where youre at.
 
I’m sorry my gut from here says you are barking up the wrong tree.
Timing (ECM if you have one)
Tune up complete wires plugs if you have a cap. These thing need to be done anyway.

I’m sorry, it’s just a feeling I have.
 
dwna1a said:
I’m sorry my gut from here says you are barking up the wrong tree.
Timing (ECM if you have one)
Tune up complete wires plugs if you have a cap. These thing need to be done anyway.

I’m sorry, it’s just a feeling I have.
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I have an ECM-1 I believe since it's a 1st generation. It is throwing the code for ELECTRONIC TIMING SPARK MALFUNCTION when you plug into it. I'll get it tuned up for sure, but what could that be indicating? I thought the ECM was supposed to correct timing automatically.
 
The ECM controls the timing, as you advance the throttle it advances the spark. There are many great gear heads on this site, maybe one will chime it with a better explanation.

From idle to 3000 or so it will run great above that it will fall flat. It’s your comment about the backfire that has me going with the timing.
 
Ramblin' Guy said:
I have an ECM-1 I believe since it's a 1st generation. It is throwing the code for ELECTRONIC TIMING SPARK MALFUNCTION when you plug into it. I'll get it tuned up for sure, but what could that be indicating? I thought the ECM was supposed to correct timing automatically.
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MEFI-1 is your ECM. Your Rinda is yelling at you. If you really want to swap a part from one engine to the other, swap the ignition module that is bolted to the distributor. See if the problem moves. #9
distributor.PNG
 
Stee6043 said:
Well...I don't have a very impressive resume to share with the forum but I can tell you that my 1997 7.4L fuel injected engines do in fact have mechanical fuel pumps, OEM. I can also tell you there are a bunch of us here that have the same configuration in this vintage motor. No clue what years...but....this post was about 1997's so I took a shot based on my direct
experience. Though the OP has horizons which may not have the mechanical pumps I suppose.

I'm also just tickled pink that my engines have stickers on the top that tell me what MPI stands for. Otherwise...I never would have known until just now ;)

50966046812_428d3ad744_h.jpg
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Searay must have changed fuel pump set up on this year engine.
My 97 370 Sundancer had 7.4 MPI engines.
Serial no OK 189574 and OK 189579. It was a late 1996 production run badged and sold as a 1997. It had electric fuel pumps. I had to change one in 2017 that’s how I know. Mine was surging just like yours and and caused a fuse to blowout it was a 10amp fuse If I remember correctly on the ECM. Panel. It just stopped running while traveling on lake Mich. Not Fun!!! I limped it in to Pentwater and a Mechanic figured it out for me.
 
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Nauti 97 said:
Searay must have changed fuel pump set up on this year engine.
My 97 370 Sundancer had 7.4 MPI engines.
Serial no OK 189574 and OK 189579. It was a late 1996 production run badged and sold as a 1997. It had electric fuel pumps. I had to change one in 2017 that’s how I know. Mine was surging just like yours and and caused a fuse to blowout it was a 10amp fuse If I remember correctly on the ECM. Panel. It just stopped running while traveling on lake Mich. Not Fun!!! I limped it in to Pentwater and a Mechanic figured it out for me.
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Well, for those playing along at home I went out to the boat Friday and looked over the fuel system. I believe I do have an electronic fuel pump. The attached picture is the pump I found behind the engine (toward the bow of the boat with a v drive). I'm wondering how you test such a device.

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?

IMG_2555.jpg
 
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techmitch said:
Without reading the entire thread, what are you losing, spark or fuel/pressure? That is the first step.
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it feels like a fuel issue, but I don't have a tremendous amount of experience with that. the motor seems to run fairly well other than the surging issue. If you want to hear how it sounds/looks, there's a video in the first post in this thread.
 
If you have an electric fuel pump, you should hear it "whine" for a few seconds when you first arm the ignition after it has sat for a few days.

I'm a bit confused about the direction this thread turned. A lot of emphasis on fuel where your ECM is screaming "ELECTRONIC TIMING SPARK MALFUNCTION". That coupled with back-fires would have me looking at the distributer.

That said, if you are absolutely convinced this is a fuel issue, I'd buy or rent a fuel pressure gage and see what's what.
 
Ramblin' Guy said:
Well, for those playing along at home I went out to the boat Friday and looked over the fuel system. I believe I do have an electronic fuel pump. The attached picture is the pump I found behind the engine (toward the bow of the boat with a v drive). I'm wondering how you test such a device.

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?

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You posted a photo previously that looked exactly like the fuel portion of the mechanical fuel/raw water pump combo. It's possible that pump has been disabled but the photo you shared surely looks like it's still fully hooked up?
 
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