RPM for 3.0L project... Falling on face ??

[Champdshull]

OTO19231... Question Don?? I put a set of cut Heads the Jay did at 63cc they were 250 EFI heads he cut... Motor runs real strong with stock 225 boxes... got another set of boxes reflashed by Eric Simon. 300ING/250xb fuel... motor launches out of hole great but hits a wall around 5200 and falls flat and starts to surge... so I eased back. to. landing. Put stock boxes back on and runs super... Right up to 5900 and pulls real strong... figured it must be in the boxes... So I order a brand new set of 250XB boxes.. guess what does exactly the same thing... runs up strong to 4800 and starts the surging again... hits a wall at 5200rpms... What is missing with this application... Need some imput please... runs perfect with stock boxes

[EuropeanAM]

What's the fuel pressure running at WOT when this occurs?

Have you run redundant GROUNDS (2) for the rear electrical plate, and verified the IAT is good?

[Champdshull]

Thanks

[Champdshull]

I will look at fuel pressure....what is idle vs through the rpm curve I should be looking for ??? I will look to run another ground to the other side...Should I look to run a ground to the top box as well For the last question ??? IAT....Air temp sensor??? I did adjust the TPS to 1.02 to hold off lean sneeze from occuring.....What ohm it the IAT , Is that on the side of the intake box???

Thanks DSHULL

[EuropeanAM]

Darrell- do you have a Service Manual?

Also- did you recheck the TPS setting when you had the "new" ECU's installed?

[Champdshull]

No service manual , guess I need to get one....my tps is sitting at 1.02 turning the key on in the shop, Pressing hot foot all the way down and it went to 3.78 I believe with the new ecu boxes installed

[Gamblinman]

Been there done that. So have several others. When you find the right boxes that work together, you'll know it. For whatever reason, some boxes won't work together, or wont work on a specific motor. I can find no rhyme or reason, and I've been through dozen of box combinations to find the right set.

[EuropeanAM]

Darrell: Another thing often overlooked is the condition of the flywheel and the GAP for the CPS. Make sure the gap is right at .050".

[lpugh]

Darrell I went thru what you are doing now run the stock fuel box, and have Eric reflash the ignition box to raise the limiter. Higher compression requires the same air fuel ratio as lower compression and those motors ran on the rich side anyway. If you change airflow then fuel requirements need to be made. I did a lot of mods that Killerbee and Don gave me some tips on. That boat I sold about tens years ago and that EFI is still running today with no motor failures. I found the 250 fuel control to be all wrong for that motor unless you ran wide open all the time
I did not get the symptom of low rpm and surging from the 250 box, which makes me wonder due to the increased fuel flow, it might be running the VST out fuel due to a restriction causing low volume with a increased demand. Might want to look into that possibility
Just thinking out loud

Don also advised me of some earlier 3.0 L that had a more restricted midsection that may require a lower TPS setting in some situations. Maybe he will comment on if this applies to your serial number

[EuropeanAM]

This engine "shouldn't" have the smaller tuner. That being said... I would certainly inspect the tuner for blockage in the Idle Relief areas: Poor Performance- 3L EFI or Optimax, PLUGGED EXHAUST TUNER

[Champdshull]

All tuner and idle reliefs are good, clean and open....Plus I always run your cocktail in non-ethanol 91 octane, I even did the cowling mod as well to ensure we are getting enough air....I will check the clearance on the flywheel...TPS is set at 1.01 What ohm reading should I be on the temp sensor on the intake box....I need to find out the best way to check my fuel pressure and make sure VST is super clean and not running out of fuel......Guess I could just drop it off If I cant figure it out as well Don....I work the Greenville market area every two weeks for my company.

[lpugh]

Did you pull the powerhead off to inspect the relief ports or just the lower unit. Really cant see the top side or very many with the lower unit off. When Don first brought this my attention I checked from bottom and said to myself this does not tell me much. Pulled the power head and was amazed at how bad they really were, Cleaning made a huge improvement in the holeshot
This is not out of a Mercury Manuel, maybe Don can verify application
One of the charts should be close

about 2002 and later

Thru about 2001 anolog

[Gamblinman]

Have you ever done a full throttle chop to check plugs and top of pistons? It can give real insight as to what is happening at full throttle in the combustion cylinders.

[EuropeanAM]

Maybe I missed it, but did you measure the gap on the Crank Sensor?

These really like to be up around .050".

[kllr bee]

If you have cut heads 91 octane is not enough with 250 or 300 ignition. 93 minimum. You also need to check harness plugs for broken pins. One may be broke off in stock computers.
Richard

[Champdshull]

Richard, Did you say you had some extra harnesses laying around ??? Thanks