Hello. I'm seriously considering purchasing a boat I looked at today. But, I have some questions for you 454 Mag EFI experts. This might be long,but bear with me.

First, the dealer sales rep told me that they replaced the twins with "drop in crate motors" that have between 15 and 20 hours on them. Come to find out today by their mechanic that they actually were long blocks with all new accessories and the intakes, fuel injectors and dizzies were reused. Ok, that explains some of the very light corrosion one would expect on a 1995 Formula's engines. I saw the new high pressure fuel pumps mounted on the left sides of each motor. It doesn't look factory. But I guess the motors are Gen 6 vs Gen 5? Would that make sense?

Second, the motors were started "cold" (relatively speaking, lol. It was 78 degrees). The 1995 vintage Formula VDO gauges all seemed to work properly. However, the Port motor showed like 25psi of oil pressure cold and the Starboard motor registered like 38psi. FYI, I heard no bad engine noises on either at startup. We proceeded to take the boat out and run it at varying speeds. The Port motor oil PSI was still around 30ish and the Starboard motor was 40ish. Water temps read around 165-170 the whole time. Should those oil psi reading be a concern?
At all speeds the engines seemed to run smooth and fast (to me). Idle to WFO.

Third, the motors each had a PCV vent (like you'd see on a car). Each one looked like a mini K&N style conical air filter on end. Looking at the Starboard one, you could see little bubbles of oil popping out but not spilling over. The port one was a little better but the same.
Of course, the sales guy told the mechanic that we ran it hard. Hmmmm, a few hole shots, some mid range cruising (2500-4000rpm) and a one WFO run to 4800rpm for about 20-30 seconds tops..

Fourth, both of the motors seemed to stumble a bit from off idle. Kinda what I would expect from an old carb motor that hasn't been run very much. But, the mechanic said all the 454 Mag EFI's and 502 Mag EFI's have a "stumble". I have never heard that but then again, I haven't
driven a boat with old big block EFI's in it. Does that sound right? If not, what would cause the slight stumble. Once the motors "clear their throats" the run perfect.

That is all I can think of now. Any input would be appreciated!

Merc remans ? And they shouldnt stumble , even cold.

1. & 4., aftermarket. Fuel pumps? Possibly not tuned for them and/or not running the proper fuel pressure. If the pumps are aftermarket the OE non adjustable fuel pressure regulator needs to be replaced with an adjustable unit on each engine. Also 4. My non-mag. 454's of 1996 Vintage are completely OE and do not stumble EVER. Possible causes can also be ignition related.

2. Merc. Manuals require 7psi as min. Oil pressure. My non-mag. Port engine runs a top psi of 30 with SAE 40 fill and I'm not worrying about it......yet with 247 hrs. On the clock.

3. No experience to comment on the amount you are experiencing but I'm sure you know too much blow by equals similiar issues. Most here will tell you to do a compression test at minimum and prefer to add a leak down test as well, I agree.

Hmmmm....fuel pumps & regulators. Good point. Would timing cause this too? They seemed a little harder to start initially when they were cold out of the boatel.

My old Formula 292 with carbed 454 mags always started (after a couple setting the choke and moving the throttle forward twice) the first time every time. Never stumbled. Oil PSI when cold was 50+ ish.both sides.

You should not have to pump a merc efi.. and it should fire right off and run smooth..thats the beauty of EFI

Don't like those oil psi readings. Must be verified with mechanical gauge before proceeding forward with further diagnostics if needed.

And what 'Crate Motors' ? Everybody and their mother offers 'Crate Motors.'


It would like me selling a Truck and just listing it as a Chevy with no other info.

I agree, its one thing to have a hot idle around those numbers but at a cold start should be 60ish, and over 40 when the engine is over 1k rpms no matter what.

The internal bypass i believe is just over 50 (?) So cold start should be over this number.

Electical gauges can be suspect but both are reading low would have me worried. The 7 psi minimum might be the minimum spec, but thats crazy low.

That's what I would have figured. I "pumped" my carb motors years ago, but I thought EFI eliminated this step.

+1. That's what I was thinking...

+1. Exactly the numbers I was expecting, but since I didn't hear any audible noise at startup, idle or under load, I suspected that maybe the gauges could be off.

Just a quick question, would old oil cause a lower oil pressure reading? I mean, could the oil have lost some of its viscosity or something? Kind of a reach, maybe, just wondering.

anyone?