pro max issue

[largecar91]

I have a 98 225 Pro Max. Bought it 2 seasons ago. It ran great the 1st season. Pushed my 380 ray around 90. Last year it cooked #5 piston. Didn't hurt the wall so I replaced piston. Couldn't really find any reason. Ran it for a week or so and I cooked #5 again. Sent block out and had it sleeved. Rebuilt engine. Had Brucato do the injectors. Went out yesterday and broke it in. At end of day I decided to make a high speed pass. Only ran it to about 6500 for maybe 10-15 seconds. (Normally run 7000). Ran good then lost power. Put it back on trailer and no compression in #5. It is burning the outside of piston by exhaust. Motor is .44 over with forged Wisecos. It is on a Land and Sea 1 pc plate. Im lost. Could this be an electrical problem?

[myron]

yes it could or it could be fuel also, I would check the timing on that that cylinder

[largecar91]

Timing is good.

[TEXAS20225]

who put th sleeve in , do you know if it was a oversize sleeve to insure heat transfer

[largecar91]

Ruck machine. The issue is it did it twice before so I'm sure it's not a sleeve issue. Also the 1 pc plate was on it and it ran awesome for a year then #5 cooked. I just replaced trigger so I know that is not it. Same stator and ecu. I was kinda leaning towards ecu???

[TEXAS20225]

well if it was Ruck and not Ron i would feel good:rolleyes: but anyway drivers fire in pairs any problems with sister hole for #5 im a stickler for no heat transfers troubles never found many of the to be fuel how about double firing swichboxs they cause lean out still

[Dave Strong]

Just thinking the Land&Sea plate is pretty much a Merc one piece plate with a tuner cast in. All the correct cooling system mods done to run a one piece plate?

Dave

[largecar91]

No cooling mods done to plate. Ron did block and has done several with no issues. The big thing is this motor ran perf6 for a year with absolutely no cha ges before #5 we t 1st time. Piston melts right at exhaust port right thru to ring grooves. The cylinder is still in good shape but gotta figure this out before I put another piston in. Thanks for all the help and ideas

[Dave Strong]

Might want to give what TEXAS20225 said could explain things, double fire on 5.

Dave

[Dave Strong]

Another thing worth a real close check is the injector harness, if I remember Bobby had motor drive him nuts and replacing the harness was the fix. Sometimes baisic tests show them Ok but running under load and engine vibration can cause failures.

Dave

[largecar91]

Thanks guys. I'm looking for answers a little outside the box. All the simple stuff seems to lead to a deadend.

[tlwjkw]

44 is to big for tha basic fuel curve of a PM.......

[largecar91]

I'm going to send my ecu to Tony to check out. I don't know if ecu had been recalibrated or not but it spins 7000 with no problem. My big thing is something had to change somewhere. Other than maintenance, I never laid a wrench on this engine the 1 st year and I ran the hell out of it and it ran great. Now all of a sudden in a matter of a day I can burn the side right out of #5. I pulled the head last night and the cylinder is still in good shape except a little bit of alum deposit at top of sleeve. . It will clean up easy with acid but I got to find the problem before I do it again.The piston is gone down thru the ring grooves right at the exhaust port . I will change out switch boxes and have ecu checked. Could a ECU lean out just 1 cyl?