big blocks
 

I have a 1999 baja h2x recently put a 415hp in it cause motor was busted when we purchased it. It has a air motive aftermarket fuel system on a mpi set up. Should I put a new stock fuel pump and start back like factory! My problem is it loads up in no wake zones and the computer messes with the timming! Next thing you know it wont start for a while!! Just looking for some good advice cause im ready to carb and intake it and be done with it!! Runs great other than the fuel preasure not cutting back at a idle!

Any help would be appreciated! Thanks in advance! !

If it is all factory stock save yourself a lot of time, headaches and money by putting a scan tool on it and find the problem without guessing. At least then you can make informed decision on whether or not to go carb. Been down the same road before and so have many others. Good luck. Ijust saw you have aftermarket fuel system, so my suggestion may not work. Sorry.

I would start by seeing what the fuel pressure is doing at idle. Perhaps it is overrunning the fuel pressure regulator? Fuel pressure is a constant with the ECM and without O2 sensors it does not know if it is injecting too much fuel and will not compensate for it.

It almost sounds like you are experiencing vapor lock. Which year mpi setup is it?

1999 genVI

About 35 psi at end of rail. Im going tobput one where fuel line first goes in and in the manual it says to not use the gm regulator thats factory on rail cap it and use bottom line in. Maybe with this pump not being factory it should go threw the regulator on the rail!

Mefi 2 is the fuel injection

So you're trying to use that Aeromotive pump with a factory regulator ?

Am I reading that correctly?

If so, thats not going to work if its not adjustable.

Why not ?

Pump doesn't create pressure - it pushes against it. Regulator is what stops or restricts flow depending on demand to keep the psi.

If the regulator orifice size, or something else in the system with too small orifice size, that flows less than what the pump can flow, will cause over pressure.

Anyway, the 502MPI ATI procharged set up used a FMU after the factory regulator to add more psi when under boost. Without boost, the factory regulator mainted the fuel psi....which it did fine. These systems had the Aeromotive 1000 fuel pump.

35psi is not too much fuel psi by any stretch.

Sounds like this might have had a Procharged engine in the boat - or something else that needed such a high flowing pump.

By any chance does this have a water crossover in place of the recirculating pump ?

And/or does it have a t-stat ?

What water temp is this running ?

Water temp is very critical to EFI because of cold start programming, ie: fuel enrichment, and etc.

A stock regulator wont have a large enough return line to bleed off the excess fuel pressure, cause too high of fuel pressure and causing the problems he's seeing.

Guess I shouldve wrote that instead of what I did, sorry for the confusion.

I believe donzi matt is spot on

I totally understand. And I'm with it.

It has a big nice regulator on it.

It did have a super charger on it.

That is the pump I got airmotive 1000 with regulator!

Has thermostate runs close to 200 on plane about 50mph!

Feeding the factory cool fuel system?

No cool fuel it and pumps all there just no lines

Loads up so bad the fuel burns your eyes sometimes! And leaves a black film on back of boat from rich fuel!! Made me loose intrest in it ! Love my boat always wanted a big block. I tried to do it right spared no expenses now just the little things I would like to get worked out befor ed the end of season here in ohio!! Coming soon!!

Mefi 3 is my injection just broke out my go to book!! Looks like the regulator on the cool fuel system is def in need of use by running off vacuum! Might try to run that somehow not sure how but some how!! And 41-45 psi of fuel which is where my boat runs its best! So at the idle that fuel relay runs on vacuum from motor speed . Makes good sense to me now!! What we strain are brains for a little fun!! Def appreciate all you guys help! Had boats all my life first fuel injected big block!! Never give up!!

does it have high flow injectors to go with the high flow fuel system?

All Multiport fuel injection has vacuum referenced fuel psi regulators.

Reason is that the injectors are in the intake manifold (thus they 'see' manifold pressure) vs being outside in the atmosphere.

So, yes, at idle without the regulator being vacuum referenced, the injectors will be flowing more fuel then they are supposed to be.

You said the boat had a blower on it, does the computer still have a tune in it from when it was blown?

Thats exactly what I thougt! I got the new pump and I think im going to buy a new regulator to be safe cause not sure if its good.

No its a stock tune the great outdoors marine checked that for me cause that was another worry I had.