Pat McPherson

For those of you that may be interested, I had another long conversation with Mark at Precision. I’m going to try a few more things using the ECU that Mark has loaned me before pulling the plug. Mark as been extremely helpful and I recommend his company to anyone in the performance boating world.
Also, I can use the existing distributor and wire harness as is with a carberator. Mark is just not sure what the advance curve is on the built in IC module.

pslonaker

iTrader: (1)

When you either decide that you have "blown" enough money on the current system or sta around and watch everyone else go out boating...this is all you need to do. I have done this to several of my friends boats here and they all perform flawlessly now.

1. pull the MPI stuff off and toss it in the yard
2. unplug all the knock sensors, this sensor & that sensor. Dont cut them off because some of the plugs loop back. Tape them up or cover them in silicone to water tight them...toss the ECU. (Basically all you want to be connected is the hot wire running from the alternator and your temp wires to the temp senders)
3. install your intake and carb
4. pull the stock distributor out and toss it.
5. Order from Jegs or Summit ...
a. MSD-8560 distributor (install the black bushing inside the distributor and the smallest springs on the weights)
b. MSD-6460 brain box
c. Holley "RED" electric marine fuel pump


You have any questions...holler and I wil help you out...
[email protected]
817-657-5662

SB

iTrader: (1)

No need to. Very dependable and has a spark curve module in it that very good for most performance motors. If you want different timing curves, rev limiter, and stronger ignition it is very easy to modify to hook a Crane HI-6M box into.

It's been a while, but I think the advance is only about 16-20 degrees or so. Just set the total where you want it and the initial will be wherever it ends up.

The swap from the 502MPI to carb is relatively easy. Been done by many.

Pat McPherson

Thanks for all the replys guys.
I found a little time between the rain drops yesterday to change the TS and check the wiring for the 4th time.
Tomorrow I will test run again and hopefully there won't be any error codes in the ECU. I will also double check the fuel pressure under load.
If it doesn't work out, I'll likely be pulling the EFI off next weekend...

IRONMAN

You could use a Mallory marine mag pickup distributor or the ready to run MSD and you would not need any box. Check timing a few times the first year then you won't need to touch it for 10 years.

Pat McPherson

Yup, I also like the DUI ready to run distributors.
The existing EFI distributor does have an IC module with spark/timing control so no box required either.

I ran the boat again last night after changing the TS. The TS error code came back though. The diagnostic procedure now tells me to change the MAP sender and then if that doesn't work change the ECU. I’ll change the MAP sender because it's about 3 min to do it, but???

The engine seems to run so well up to about 80% of the throttle. If I push it farther the engine stumbles.
I can hold the throttle at 80% and trim up and she'll rev from 3800 to 4200+ but as soon as I give it a little more, she dies...

Maybe I should change the throttle position sensor too? Hell, that would be just about everything…

The fuel pressure is a solid 34lbs at all rpm...

Anyone want to buy a Merc EFI system cheap...

Pokher Ace

Change the Throttle Position Sensor I just did on two of my motors. One read it was opening 67% and the other motor only opening 82% After we swapped in new TPS sensors they are both reading around the 94% range. This might help

Gordo

I have a friend, (BigSheesh) in the same situation about to go through the same thing due to intermittant shutdown of one engine I'll try to get him to step in here...

Pat McPherson

I changed the MAP and ran it on the hose with no change. I still have error code 14. Changing the TPS is the only sensor I have yet to change. I have another TPS, but Mark suggested running with it disconnected first. I also have another wire harness I could try but…
The season has maybe 3 weeks to go here so I guess I can debate if I go with a Carb or MEFI-3 all winter. I’m not going to bother changing it now.
Thanks for all the replies.

Pat McPherson

Well guys we changed the TPS and tried disconnecting the dash from the ignition circuit. No change, the engine still idles and runs perfectly to about 4000 rpm and then stumbles like its loosing spark or starving for fuel.

I called my marine EFI engine consultant, Mark Boos @ Precision Marine EFI.
I told him what went down last night and then asked him about what else I can try.

From the fuel delivery side-
Even though my fuel pressure looks good, it does not mean that the fuel is not being aerated by a cavitating pump or a cracked inlet hose or pipe. I need to try running the return line back to the tank directly rather than to the fuel filter block.

From the electrical side-
If I think the ECU or the injectors may be loosing power when the ignition circuit has higher load, I can wire 12VDC directly to the injectors bypassing the relay that normally powers them. The engine will probably not shut off quickly when I turn the key off, but it's a test. He has seen fuses/breakers or relays act funny as the load on the circuit increases.
I can try changing the coil too, but he thought I already did. I can't remember so I'll just change the thing again.
As for changing the ECU wiring harness, sure, but that is a much bigger pain in the azz than the rest so that is a last ditch effort.

Thanks to Mark and the rest of you for all the help.
I plan to keep at it without buying more electronic parts I don't already have in my stockpile. Hell, I've got 2-3 more weeks before the freezing weather hits...

Replies and other ideas are appreciated...