Merc 2.5 EFI

[prboatdoc]

I'm running a 2.5 EFI (stock) @ 5000' elevation. I have it propped to 5800 rpm and have installed a dual Digitron EGT monitor. I put the probes in place of the two center bottom exhaust divider plate bolts. At WOT the temp is SCARY! It climbes quite fast up to and past the 1250 degree alarm setting I entered in to the unit. Doesn't alumunum melt somewhere around 1300 degrees? The engine runs great, it does not show lean on the plugs, the water pump is new. Has ANYONE ELSE tried this and if so what temps could be considered safe/normal? Any thoughts would be appreciated.

[johnboy 88 vegas]

2.5 260 race motor or 2.5 200? In either case it sounds like its starvin for fuel on the top end. Oh yeh what kind of boat and how heavy is it.

[prboatdoc]

It's a stock 2.5 200 with analog ECU (1993) It is bored .020 with Wiseco pistons. Fuel supply to eng is 3/8 with no restrictions, fuel prssure was at spec last ime I checked (at idle) I did not check it under load though, does not feel like starving, no surging etc. Spark plugs look tan and exhaust has normal sooting. The boat is a 180 Sea Ray rated for a 150, runs 62 here @ 5800 to 6000. I just don't want to take out the powerhead again. (I took it in on trade with one bad hole last year) also had Brucato flow the injectors when I built it.

[johnboy 88 vegas]

If the plugs are tan when you pull the kill switch from WOT then sounds like your gauge aint tellin the truth. Tan on idle means nothing. Do the WOT run and see what it looks like. Could be the screen in the VST tank. Check the fuel pressure while runnin wide open.

[prboatdoc]

Thanks, I will try that in the spring. (lakes are getting hard up here in Colorado!) I went through the VST when I did the build too. I'm just not sure about the placement of the EGT probes. Tony @ Brucato told me to put them there and said 1150 degrees was (safe) I had him calibrate his custom ECU for me, I bought the adjustable knob too. If I run his ECU and keep the temp under 1200 @ WOT, the thing is just sick rich and loses several hundred RPM. Gotta do A WOT plug read. Thanks again (hittin the sack now)

[Jay Smith]

Read the piston crowns on the intake side . EGT readings can have you chasing your tail and be DEAD WRONG...They can signal too lean and also too rich. If the motor is not having complete clean combustion ( to rich OR weak ignition ) the flame will travel down the point of where the signal is taken to the EGTS and show lean when its really rich. I don't trust EGT's I trust reading the tops of the pistons after a hard pass and killed clean , if the wash coming across the piston crown at the intake side is wet the size of a quarter or farther across the piston it RICH. If the wettness is the size of a dime or none at all its LEAN , you need something about inbetween to be correct..

Jay

[prboatdoc]

Hi Jay, Thanks for taking the time. How long is a safe hard pass, and when you kill it do you also chop the throttle? I can't do a lake run 'til spring but I do have a dyno. Could I accomplish the piston read withn the dyno? I don't feel comfortable @ WOT for more than 30 seconds. (especially if it is lean) Also, am I to look at the bare aluminum, or carbon deposit, It seems to me the last time I looked there was quite an area of piston dome that was not carboned up. Another note: I discovered yesterday that the detonation/advance module was no good. The max timing just stayed at 19 degrees all the way to 5500. The book says it should go to 25 degrees as long as there is no signal from the knock sensor. Wouldn't late timing @ WOT also carry the burn to the EGT sensors?

Your time is appreciated,
Pat