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cuts out at 2000 rpm

capemaydiamond

Contributing Member
I have a 454 tbi with a mefi 1 system. When I accelerate to 2000 rpm the motor cuts out and drops to 1000 rpm and pops through the throttle body. Once it drops to 1000 rpm I can then accelerate again but cannot pass the 2000 rpm threshold. The motor runs great at 1900 rpm just not any higher. I have replaced the coil and the ignition module checks out fine. What could possibly be causing this as I do not want to get into throwing parts at it that are not neaded. Thanks.
 
I'd be inclined to start with a fuel pressure test.

And I'd pretty sure you will need an adapter as there is no test port on the GM TBI units.
 
Thanks Mark,the people at marine power engines recommended the same thing. All the filters are new as both the high and low pressure fuel pumps but they said it might be the pressure regulator in the throttle body. Does that seem possible?
 
Yes, its possible....same for the injectors themselves being clogged up...

Just to help set expectations, those TBI units have no OEM support as the parts are almost all NLA....that said, most good injector rebuilders can rework the TBI units as well....

Finally, on the adapter - you can buy one or make one - nothing magic about them..
 
I bought the pressure tester and will try it Saturday. Someone suggested it might be the fuel pressure regulator in the throttle body. Thanks I'll let you know.
 
Well I have good fuel pressure up to the throttle body and changed the regulator with no change to the problem. A good friend who is a good tech looked at it and thinks it might be a throttle position sensor crapping out but not showing a code so we are gonna borrow a scan tool to throw on it to check all the live data. I gotta get it figured out soon, striper season is just around the corner.
 
Well the scan tool we borrowed did not come with the right connection so we couldn't use that. I have a solid 20 psi at the throttle body but I don't think that's enough from what I've read. It seems that gm bumped up the psi to a minimum of 30 psi for tbi models around the time when my system was made. So my question is how do I know which pump to use for my tbi and can this be the cause of my problem?
 
The wrong fuel pump could be an issue, especially if you are shorta bit on fuel pressure...

As far as the "right" spec, I can't help as I have no OEM data for the TBI units (i do have some Merc pubs though and most of it comes verbatim from GM). As choice one, I'd suggest calling MP's tech dept and talk to an old boy who has actually touched a few TBI units. For a second choice, I could dig thru the merc specs and share anything relevant...a final option would be to approach an injector shop who deals with TBI units.

As far as the right part number, I'd verify the parts catalog against the serial number of the engine...
 
I checked the MCM big block book for the first gen systems - 36 psi for multiports and 30 psi (+/-2 psi) for the TBI units so I'd agree with your target values.

It could very well be a restriction on the suction side...an outboard tank and some care will allow you to isolate the vacuum side of the pump back to the tank...

As I'm sure you are aware, insufficent fuel pressure will limit the rpm you can obtain, under load, and can also results in a lean condition which shouldn't be maintained...

keep us posted with what you find..
 
Ok. I found it. There is a fuel line that comes out of the high pressure pump that goes into a can fuel filter. It seems it was never attached properly and the high pressure line which is rubber in the center was kinked and broke down internally, probably from ethanol. There is also another line that comes out the other side of the filter which also feels soft in some spots, probably breaking down internally as well. The question is where can I find these fuel lines so I can replace them? I've tried several parts marinas and they don't even have a listing for them.
 
Marine Power distributors/dealers?

If you have no local dealers, then I'd suggest four options: 1) contact marine power directly, 2) try a mail order vendor, or 3) contact a local hydraulic shop and see what they can fabricate for you....this only concern would be to ensure you use an "approved" hose material. The last option would be to fabricate them on your own...

There's rarely anything critical beyond the rated flow (diameter) and the aforementioned USCG type rating...
 
Thanks Mark, marine power no longer makes those hoses so I got my local hydraulics shop to fabricate new ones using the original stainless ends and 2500 psi hydraulic hose which hopefully will never fail. I'll be installing them this weekend just in time for striped season. I'll let you know how it goes.
 
I'd check and make sure the hose part will tolerate ethanol....and that the hose maker has put that statement in writing....just to ensure sleeping at night is easy...gasoline is one thing not commonly used in the hydraulics service area....
 
You indicated you only saw 20 PSI not the +/- 35 PSI...

I believe I read new pumps so I'd say check for a restriction on the suction side....I'd be inclined to get an outboard tank and plumb it into the suction port on the pump...if that's good, then the issue could be the anti-syphon valve, the shutoff valve leeaking air, etc...

Also, a vacuum gauge in the suction line can be helpful in debugging - air leaks will show as hardly any vacuum and restrictions will show high vacuum (like more than 5 in Hg)...how much is too much is up to the OEM/pump maker...
 
Problem solved. I had a marine tech come out and take a look at it and he found that we had the timing set for a standard rotation engine when it's a counter rotating engine. We thought we had it set right but I guess not. We were so focused on something else that we missed something so obvious and should have gone back to the basics. You live and learn. Thanks for all your help.
 
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