BUP

iTrader: (9)

On your boat title as a lot of issued titling states posted the serial #s of drives and engines on the paper work and or titles or registrations. Just saying to help

Brandonb_05

It sounds like you possibly have two different issues going on, water temp and lack of power/hesitation. You can verify water temp with a temporary water temp gauge I would use a mercury filled tube style gauge. You can get one for cheap, like a autometer. As far as the hesitation it could be any number of things. I would start with checking the basics fuel, fuel delivery, timing and spark. I don't know how the fuel is calculated for the TBI system, if it runs off a MAP sensor or if it is a closed loop system. Maybe someone here with more knowledge of the TBI setup will chime in.

BUP

iTrader: (9)

FYI Mercruiser did have a TBI 454 in 1996 and 1997 as the OP stated. Anyways there was just a 2 year run but a serial # run of OF820000 thru OK999999. Throttle body injection with GEN II cool fuel system

You need to scan the engine and do fuel pressure testing.

Also did you change the whole impeller housing out when you changed to the new impeller ? I would bet your housing and wear plate was scared. Really waste of time just doing an impeller only with these black housings. even the impeller housing wear plate scaring hurts water flow volume output thru the engine.

Next possible restricted / bad electric fuel pump(s) also there is a screen under the fuel pressure regulator in the gen II cool fuel that could be restricted.

phragle

iTrader: (3)

Most definitly NOT TBI. And has VST system


/

BUP

iTrader: (9)

Thanks for posting YOUR app 7.4 LX MPI and Mercruiser had also a 7.4 LX TBI a totally different app than yours as well 1996 thru 1997 and the serial # range that I posted and used cool fuel GEN II.

Yours 7.4 LX MPI had split serial # runs were earlier engine serial # runs used the VST and the later engine serial # runs used cool fuel GEN II..

I am 1000 % of this and will put my money were my mouth is. Anyone want to bet and I will give you 5 to 1 odds. Anyone ???

BUP

iTrader: (9)

No takers here is the proof anyways and you can click on the parts lists to see the set up. Anyways surprise no takers at some great March madness 5 to 1 odds in your favor.

http://www.mercruiserparts.com/selec...D8+1996%2D1997

phragle

iTrader: (3)

Merc did some weird crap around that time. Trying to look up parts by my serial number gets pretty tricky. My VST also had a fuel cooler when I got it too,,

Griff

I believed you. LOL!!!!
Just never seen one or heard of them. I knew Merc did TBI on some small blocks, but never knew they did it on any 454's.


My guess is its a gauge or sender issue on then temp since the alarm isn't going off.
My guess is the hesitation is probably a fuel delivery/injector issue.

BUP

iTrader: (9)

The deal was what Merc could buy a lot of this stuff from GM as in big discounts to make more profits.

EFI / TBI and MPI in the 90's for marine apps was still somewhat new for the boat owner but for the auto world was old hat.

keep in mind GM in the truck world got rid of TBI arouind 1994 or 1995 used on the 350 5.7 and then the 5.7 350 went away for GM to.in the truck / auto side apps. Also the 454 was gone early for GM in the truck world to. Hence a lot of stuff to sell to get rid of to Merc. TBI really is a poor efi system and down the road can be very unreliable especially for marine apps.

Nick454

I have not tested fuel pressure as merc uses different fittings than the automotive tbi, the same reason why I have not had it scanned, I guess maybe I should get the fuel pressure fitting for it and start there, any one in west Michigan have a scanner that's cheaper than 80$ to hook it up??