454 help

[Snorider]

This motor is really getting to me - any help would be appreciated.
The stock 1997 454 Mag MPI (merc) started burning oil (after 327 hours), and needed a rebuild.
So, we punched it 40 over, added some J.E. ultra light pistons, and a lunati hyd. roller camshaft (240° int, 245° exh, .612" lift), with lunati roller rockers.
When we first put the motor back in, it would barely idle - kept throwing map sensor codes with the stock ECM (which was expected). At high rpm's, it ran good, although only gained 2-3mph.
But, at idle it would load up so bad that you had to put the boat in neutral and clear it out otherwise it wouldnt plane off.
Sent the ECM out to arizona speed & marine for a reprogram. Came back, and it seems like the thing is even more rich at idle than before, and had no change in top end rpm.
Tried installing an MSD 6M-2 box and an MSD HEI Coil - no difference.
Compression ratio is around 10.3:1, running 93 octane; 8° base timing, ~36° @ WOT, only taching to 5150 with a 23p 3-blade (same as old motor). (~68-69mph)
Motor is solid to 5600, but we cant get it there... Any thoughts to help the idle (at this point that is more important than top end).
So bad that you cant start it up and idle out of the docks without fouling a plug or putting it in neutral and clearing it out.
It has the merc MPI manifold, stock injectors, all of which are working fine - no leaks.
At this point, i am tempted to throw away the MPI, and put a good intake, 750cfm carb, and an new distributor, but really dont want to dump any more money in this P.O.S.!
[ August 13, 2003, 06:54 PM: Message edited by: Snorider ]

[HammerDown]

"At this point, i am tempted to throw away the MPI, and put a good intake, 750cfm carb, and an new distributor, but really dont want to dump any more money in this P.O.S.!"
Sounds like a plan to me!

[ColeTR1]

Check this out SDS injection systems (http://www.sdsefi.com/) or call these guys. I think it will run your EFI system. I have put this system on two cars, you can tune everything and it is under $1000. and you donÂ’t need a lap top, to tune it ! Plus good customer support.

[gnarley]

Just a thought but how does your factory spark arrestor look? Is it clean or has it been cleaned since the rebuild? If it isn't then that would explain the situation, but lets rule out that one first.

[Havasu Hangin']

That's a pretty big cam...you're gonna sacrafice some idle. Did you do any head work? Stock manifolds?

[DogHouse]

Sounds like the bigger cam dropped your idle vacuum so that now the ECM thinks the engine is under a load when it really isn't. Reprogramming the ECU is the key but I don't know how much flexibility the stock Merc unit has. That's probably more of a question for AZ Speed & Marine. The ECU that I run (Electromotive) allows you to blend the MAP and TPS sensors at low rpm to compensate for the big cam and provide a stable signal.

[Snorider]

It has an eddie marine high performance spark arrestor;
They did some mild port work to the heads, nothing major.
Yea, the MAP voltage is all over the place at idle if you use the DDT to look at it. That is probably the problem.
Its got the stainless marine torquer 1 manifolds on it.
[ August 14, 2003, 11:41 AM: Message edited by: Snorider ]

[h2oski2fast]

Check out this system, it's designed to re-map the the EFI and timing. One of my customers is a distributor for them. You can change the settings via a PC.
Go-Tech MFI (http://www.gotech.co.za/)

[Dennis Moore]

Who suggested that outrageous camshaft? That thing is a total mismatch for a 454 MPI. I wouldn't use that on anything smaller than a 540 for a marine application.
Good Luck!
Sincerely
Dennis Moore

[Snorider]

We got the thing almost all the way fixed. Turns out, the IAC count was too low at idle - AZ S&M wanted it at 33, it was at 0. We asked them - they do blend the TPS & MAP sensor to get idle quality.
We got it to 20 before the screw bottomed out, so once we get it to 33 it will be good.
Doesnt load up at idle anymore, just a slight problem at a speed just off idle (around 1100-1400rpm), other than that it runs strong.
The cam is big yea, seems too big for the exhaust, but nontheless, it works. At idle, its very lopey, sounds nasty, and at 3500rpm you can feel the cam coming in, and the motor has all kinds of power between 4000 and 4800rpm, right now its only taching 5400, spinning a 21 3-blade to 69mph currently. Would like to get it up around 5600-5700 though. 1 more mph and I will be happy...
Thanks for everyone's input.

[bigkatboat]

Where can I find hard/ software to reprogram Mercruiser EFIs? I would like to be able to do all three types, and I could then help all of you out! I know how it works ( I work with it every day) and I know I can help, if I can get the proper programs. Thanks in advance for any help.