225 promax failure diagnosis

**billybob** · 04-15-2020, 04:18 PM

I would send ECM out to have fuel mix fattened. Also on TPS, increase voltage reading,well above .250 volt to make mix richer. And of course run nothing but premium fuel, the best you can find. Make sure the tag on ECM says 225 PROMAX on it. someone could have switched it.

**Merc 2.5** · 04-15-2020, 04:23 PM

Originally Posted by tlwjkw

.020 normally equals wiseco's (what they look like) that usually equals sticky if not done exactly right with clearance's and temp break-in with tha v6 merc... jmo

think a lot of tha a17's (mighta been tha a12 though?) were recalled and fixed/replaced but not all...

I'm with tommy on this especially with new found info and almost confirms the piston sticking. If u have weiscos in that motor , then it really needs to b changed back to a cast piston or have sumone very very experienced go over all 6 cyl , weiscos needs lots and lots of clearance. just not real suitable for steel cyl unless racing

**Promaxin** · 04-15-2020, 04:45 PM

Originally Posted by Merc 2.5

I'm with tommy on this especially with new found info and almost confirms the piston sticking. If u have weiscos in that motor , then it really needs to b changed back to a cast piston or have sumone very very experienced go over all 6 cyl , weiscos needs lots and lots of clearance. just not real suitable for steel cyl unless racing

They are just wsm pistons think they are cast, but will make sure everything is remeasured before it goes back together. Is there anyway to fatten up the factory ecus? What would happen if you increased the fuel pressure a few psi using an adjustable fuel reg? Will look at potentially down the track going for a brucato but the weak Australian dollar makes that pretty expensive at the moment.

**tlwjkw** · 04-15-2020, 04:54 PM

oversized ina PM jus never set good with me.. 15 over yes but larger ina "lake" motor jus never had trust in it.. merc only offered a 15 over on any efi production motor but went well past that on carb motors.. i figured they know tha carb can be upped but ya stuck with whatever tha ecu puts out.. if ya got an ecu thats border line (thanks to their fine QC in mexico) ya got trouble.. jmo

**Merc 2.5** · 04-15-2020, 05:04 PM

But your pistons look nice and fat?? I haven't ever ordered 20wsm. I have 015 over tho , if they r for sure wsm. Just make damn sure your bores r in spec , if all that is good. ECU b my next thing since rest fuel system clean. I'm no ecu/efi guy either. just goin by top of piston. How many hrs did those pistons have on em?

Do you know all the lectrics r in gud shape? Stator,trigger,switch boxes?

**Promaxin** · 04-15-2020, 06:25 PM

Originally Posted by tlwjkw

oversized ina PM jus never set good with me.. 15 over yes but larger ina "lake" motor jus never had trust in it.. merc only offered a 15 over on any efi production motor but went well past that on carb motors.. i figured they know tha carb can be upped but ya stuck with whatever tha ecu puts out.. if ya got an ecu thats border line (thanks to their fine QC in mexico) ya got trouble.. jmo

Do they not like going oversize in fear of leaning out?

**Promaxin** · 04-15-2020, 06:28 PM

Originally Posted by Merc 2.5

But your pistons look nice and fat?? I haven't ever ordered 20wsm. I have 015 over tho , if they r for sure wsm. Just make damn sure your bores r in spec , if all that is good. ECU b my next thing since rest fuel system clean. I'm no ecu/efi guy either. just goin by top of piston. How many hrs did those pistons have on em?

Do you know all the lectrics r in gud shape? Stator,trigger,switch boxes?

Definately wsm have done about 20hours on the pistons so think it’s just rubbed that black coating off the sides. Stator and trigger are 2 years old, was running really nice for about 1.5hrs before this happened. Might send the ecu away to be tested. I appreciate the help

**tlwjkw** · 04-15-2020, 06:35 PM

Originally Posted by Promaxin

Do they not like going oversize in fear of leaning out?

only reason i can justify when carbs can go bigger.. tha carb motors are "naturally" fat from production anyway.......

**JR IN JAX** · 04-15-2020, 07:49 PM

My Promax failures were due to flaking VST outlet hoses clogging the screens on the injectors.

**TEXAS20225** · 04-15-2020, 09:04 PM

Tommy the super twerked 225 on my bullet now is .015 over and i have limbered this thing many ,many times with no problems it also has some major port work by James and i know Merc does not list a bigger then .015 piston for pmax we both read that

if its wiescos more commonly known in rebuild circles as siezcos ,but it could be other brands as well there are two more mfg of ..020 pistons now, but wiescos need different clearance to live maybe not as much now as it used to be but more, this 200 i just started building today had 6 new .020 weiscos put in by the Grand parrie mafia one hole popped after only a weeks running it seized up . i had James put 6 new sleeves in it( any one need some wiescos in good cond cheap). but this issue we are talking about who did what last is bad now to many dont know so much guys are trying to save money by building in unknown territory especially when most people just bore out!!! i learned the hard way some bored out cylinders wont run again because of no heat transfer. So i put 6 new sleeves in every time from then on my come backs went to none but idid not have many any way but eating 2000 bucks in machine work and new guts is not tasty either good luck mister

**Promaxin** · 04-15-2020, 09:30 PM

Originally Posted by TEXAS20225

Tommy the super twerked 225 on my bullet now is .015 over and i have limbered this thing many ,many times with no problems it also has some major port work by James and i know Merc does not list a bigger then .015 piston for pmax we both read that

if its wiescos more commonly known in rebuild circles as siezcos ,but it could be other brands as well there are two more mfg of ..020 pistons now, but wiescos need different clearance to live maybe not as much now as it used to be but more, this 200 i just started building today had 6 new .020 weiscos put in by the Grand parrie mafia one hole popped after only a weeks running it seized up . i had James put 6 new sleeves in it( any one need some wiescos in good cond cheap). but this issue we are talking about who did what last is bad now to many dont know so much guys are trying to save money by building in unknown territory especially when most people just bore out!!! i learned the hard way some bored out cylinders wont run again because of no heat transfer. So i put 6 new sleeves in every time from then on my come backs went to none but idid not have many any way but eating 2000 bucks in machine work and new guts is not tasty either good luck mister

thanks Texas, yeah sleeves installed aren’t cheap this just had 3 brand new sleeves put in it. The originals were damaged from when it was “rebuilt” with the pistons in the wrong banks previously, found some cowboy stuff inside this thing unfortunately. The hole them went this time though was an original bored .20. Using wsm pistons.

Went through and removed the casting marks from the front efi manifold, reed plate and rod slots. Did some blending in the exhaust chest and tried to port match the sandwhich plate to tuner. Any other tips while it’s apart? Worth putting a slight chamfer on the rod slots to face the ports?

**Dave Strong** · 04-16-2020, 12:08 PM

Might just have been the pics but port chamfers did not look the best in those pics.

Dave

**PanRonnie** · 04-16-2020, 01:05 PM

the bulletins

**PanRonnie** · 04-16-2020, 01:11 PM

guides

**Cervelo777** · 04-16-2020, 02:20 PM

sounds like you are getting most of the info that is most likely for this motor. I will just add from my experience. Number 6 cylinder is always the hottest, it also is the lowest injector, or said differently the first in line to get any contaminates in the screens. I run an adjustable regulator and fuel pressure gauge at the dash, so I can rule out the possibility of fuel pressure issues. You can turn it up a couple pounds and see the pyrometer readings go down. It has already been said those motors have a known lean spot in the curve, between 4000-5000 rpm. One thing I have not seen mentioned is to check the heads, if someone has machined on them and changed the squish or who knows what somebody may have done. verify each camber is correct and the same size. Last, I would set timing on all six spark plugs, I have heard that it is possible for the switch boxes through different advance on different cylinders (I don't understand how that could happen, but I have heard that it is possible). One last thing to discuss might be the amount of oil you are using during break in. I wouldn't use more than 32:1 as you increase the amount of oil the leaner it will be because the fuel mix is heavier, less of it goes through the injector when it opens. I am sure there have been many people break in on double oil, but just another thing to be aware of if you are fighting problems.