7.4L EFI Surging/Stalling Under Load

Ramblin' Guy

Ramblin' Guy

Active Member
Nov 8, 2021
156
Grand Haven, MI
Boat Info
1997 370 Sundancer
Engines
370 hp 7.4 MPI Horizon w/V drives
Hoping that someone on here with a 7.4L Horizon MPI has some experience with this. I bought a new-to-me 1997 Sea Ray 370 DA this fall and took delivery on Halloween. On my way across Lake Michigan, the starboard engine would struggle to make it to 3300 RPM before dropping to <2000 and stumbling/stalling before regaining power and trying to surge back up to set point. Occasional backfires were also noted. I have a video that encapsulates pretty much how the whole trip went, but it's too large to upload. I can send it via e-mail or PM if you're willing (or maybe someone can tell me how to make it smaller to post!). I thought that maybe there was a clogged fuel filter, so I did the oil change/filter change when I arrived at my destination, but the problem is still occurring.

My current thoughts are that it's the fuel pump, but I'd like to defer to those with more engine experience than I have. The engine computer is indicating an ELECTRONIC TIMING SPARK MALFUNCTION, but I'm guessing that could be a million things.

I figured out how to share it! Here's the link

Any advice is much appreciated!

Thanks,

Jim
 
Last edited:
That's got to be a bit unsettling mid-lake in a new to you boat!

If you want to start ruling things out you could swap parts between the motors. Though if you have mechanical fuel pumps that's not the easiest swap.

For kicks you may want to consider new plugs and wires for both motors. That's a nice winter maintenance project that won't break the bank.
 
Agree with @Stee6043, start swapping parts from good engine to bad. Also could be fuel so run off one tank and see if it's better. MPI/EFI backfire is usually a lean issue, restricted air.
 
Stee6043 said:
That's got to be a bit unsettling mid-lake in a new to you boat!

If you want to start ruling things out you could swap parts between the motors. Though if you have mechanical fuel pumps that's not the easiest swap.

For kicks you may want to consider new plugs and wires for both motors. That's a nice winter maintenance project that won't break the bank.
Click to expand...

It was pretty unsettling - the lake was really rough and we were 25 miles out from Winthrop to GH. It was decision time, but turning around meant bashing pretty much into it and my fall window for coming across was closing.

I haven't tried running off of the other tank to see if the gas in the stbd. is bad - seems a somewhat unlikely, but possible. I'm leaning toward the fuel pump. It's mechanical and looks original. It seems like the boat is fuel starved, I thought I should crack the fuel fill to see if the vent line is clogged. The plug wires look pretty new, I'm not sure how good the plugs are. I'd like to know how to check the fuel pressure on that side to see if the pump is failing. It looks like a pain to take it off.

Thanks for your advice - I'll probably have to start swapping parts this spring when it's back in the water.
 
mrsrobinson said:
Agree with @Stee6043, start swapping parts from good engine to bad. Also could be fuel so run off one tank and see if it's better. MPI/EFI backfire is usually a lean issue, restricted air.
Click to expand...

for restricted air I'm guessing I have take off and clean out the intake filter with some solvent? Could it be lean because of no fuel pressure?

Thanks,

Jim
 
If it's the same configuration as my 330DA in those 7.4s the fuel pump was somehow (I forget how) connected to the raw raw water pump, horrible design, I replaced both of mine. Doubtful it's your air intake but worthwhile to clean/replace anyway while you are at it if it's never been.

I'd start with the simple things like replace both fuel water separators (check for water/dirt when you do this and always carry a spare on your boat), then test. If the issue is still there switch to one fuel tank, test. If the issue is still there switch to the other tank, test. Don't do a lot of things at one time and don't start throwing parts at it without a plan to rule things out 1 by 1. Don't underestimate bad fuel on a boat.
 
Ramblin' Guy said:
It was pretty unsettling - the lake was really rough and we were 25 miles out from Winthrop to GH. It was decision time, but turning around meant bashing pretty much into it and my fall window for coming across was closing.

I haven't tried running off of the other tank to see if the gas in the stbd. is bad - seems a somewhat unlikely, but possible. I'm leaning toward the fuel pump. It's mechanical and looks original. It seems like the boat is fuel starved, I thought I should crack the fuel fill to see if the vent line is clogged. The plug wires look pretty new, I'm not sure how good the plugs are. I'd like to know how to check the fuel pressure on that side to see if the pump is failing. It looks like a pain to take it off.

Thanks for your advice - I'll probably have to start swapping parts this spring when it's back in the water.
Click to expand...

A few years back I ran my 400 home from Sturgeon Bay, WI. First trip, jumped right into a lake crossing like you. She ran like a dream but every noise, every creek, everything made me uncomfortable. Even with phones, VHF, EPIRBS, etc nobody wants to be stuck in the middle of Lake Michigan for any period of time.

FWIW on the pumps - since the fuel pump is also your water pump assembly it might not be a bad idea to go ahead and buy a new unit this winter for install in the spring. Then have your exist rig rebuilt for a spare. I consider myself pretty handy with my boat but the combo water/fuel pump is intimidating to work on. I pay to have the impellers changed for fear of really screwing something up. And if yours are original there is an 80% chance there is scoring on the water pump side which will require those "halves" to be replaced when you do the impellers.
 
I would tend to doubt that a 7.4 MPI fuel injected engine has a mechanical fuel pump. (MPI stands for Multi Port Injection)
Search me on this forum, and you will find 20 years worth of troubleshooting every aspect of these engines.
Mine started in 1998 and are now 1999 engines, so I could be talking out of school here for a 1997.
An engine serial number will take a lot of the mystery out of the situation. Assuming these are the original engines?
 
370Dancer said:
I would tend to doubt that a 7.4 MPI fuel injected engine has a mechanical fuel pump. (MPI stands for Multi Port Injection)
Search me on this forum, and you will find 20 years worth of troubleshooting every aspect of these engines.
Mine started in 1998 and are now 1999 engines, so I could be talking out of school here for a 1997.
An engine serial number will take a lot of the mystery out of the situation. Assuming these are the original engines?
Click to expand...

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
 
370, I’m not a gear head so I will ask you, doesn’t this sound more like a timing issue? Does he have ICM’s I’ve read guys going thru the fuel system only to fine it was a timing issue.

ICM fails at around 3000 due to the module not being able to advance the timing. Just a question.

As when was the motor given a good complete tune up?
 
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.

IMG_2489.jpg
IMG_2490.jpg
IMG_2491.jpg
 
Last edited:
I wish I could help you with the fuel pumps but I can't remember what mine looked like. I noticed what looked like gear oil on the stringer. When I did my research I learned that was from the pump, that the mechanical arm uses gear oil animals starting to leak. Which is when I also learned about this miserable horrible design. If I were you I would not rebuild anything, I would replace them with OEM. Replace the water pump housing and impeller, replace the fuel pump at the same time. However this might not be your issue so I wouldn't start there first.

I replaced one of them on my own, I'll never do that job again. You probably have more beam in your engine compartment with your 370 than I did with my 330 though.
 
This is what the mechanical pump looks like off the boat. You can replace the fuel pump side (bottom part of the photo) independently from the water pump side but like I mentioned above that water pump housing is probably toast if original.

I believe there's also oil to maintain on the fuel pump side, as mentioned above. Reason #18.65 I have someone much smarter than me maintaining this gem on my boat...

upload_2022-1-11_8-5-2.png
 
For kicks, in case it isn't clear, circled below is where you'll find your impeller. Accessibility...at least on my setup...is terrible. Enough to make you want to start drinking before the project even starts...

upload_2022-1-11_8-10-22.png
 
Stee6043 said:
This is what the mechanical pump looks like off the boat. You can replace the fuel pump side (bottom part of the photo) independently from the water pump side but like I mentioned above that water pump housing is probably toast if original.

I believe there's also oil to maintain on the fuel pump side, as mentioned above. Reason #18.65 I have someone much smarter than me maintaining this gem on my boat...

View attachment 118258
Click to expand...

Who is that smart guy in Grand Haven? I need to meet him so he can help me with this come spring.
 
Stee6043 said:
I believe there's also oil to maintain on the fuel pump side, as mentioned above. Reason #18.65 I have someone much smarter than me maintaining this gem on my boat...

View attachment 118258
Click to expand...
Yes, gear lube oil.

BTW, when I removed both I sold them on eBay for $25 each, nice rebate :)

Do not spare a $$ if you replace the fuel pump; replace the raw water pump at the same time, go new, not used, not eBay cheapo.
 
And buy yourself a 4" foam topper, if you DIY you will need it to lay across the top of those engines.
 
You must log in or register to reply here.

Forum statistics

Threads
113,175
Messages
1,427,949
Members
61,086
Latest member
MrWebster
Back
Top