Triple Blown 47

I have a pair of 525 efi's in a 30' Eliminator which are stock except for Whipple PCM tunes. All of a sudden one engine started running 10percent less RPM through the whole range and stays that way at WOT...one at 5500, other at 5000. We switched the computers and the problem stayed with the motor. We bought a Rinda and everything checks the same between the two motors. We did the Induced Misfire test with each motor in gear at 1500 RPM while on my lift and each cylinder dropped 100 RPM on both motors which tells me that we have spark and fuel and each cylinder is contributing pretty much equally. It almost seems like a timing issue as the power loss is through the whole RPM range. Could the crankshaft position sensor be giving a false reading? There are no prop, drive or trim issues. Anyone have any ideas as to what might be causing this? Your help is appreciated...thanks!

Young Performance

What yr engines/boat? I would start with a leak down test, especially if it's a pre 2006 engine. The head gaskets in those engines suck and are famous for pushing out between the cylinders. I would also lift the valve covers to be sure that it didn't lose a rocker arm. They are also known for taking a dump.

If the crank sensor was either not working or not working correctly, it would not only have a code for it, but it would go into power reduction mode and would not turn 5000 rpm. Since you did the misfire test, I assume you scanned it for codes?

Let me know what yr it is and how many hours it has.
Eddie

BUP

iTrader: (9)

Look into history of the scan and see if anything shows up there. Also look at available power to see if it shows 90 % or 100 % or what ever. If it shows 100 % available power - you are not in any form of guardian mode. Also Whipple recal the stock tune ? You would have to call him to see how well or how much Diacom will read the scan. I use diacom almost a daily bases but for all the OEM stock tunes and CAT engines,

Added info FWIW - with some retune ECM's / PCM's by whomever Diacom will not even communicate or will on a limited basis and of course the possibility reading a full scan. It just depends. You can call Diacom as well to verify what I am talking about and He might can lead you into more about the scan and or retune of it. Just saying.

I agree with a comp test and leakdown. test. and of course possible Valve springs getting weak ? I would also compare fuel pressure readings and make sure your throttle cable is working correctly and throttle plate fully opening.

Sydwayz

iTrader: (1)

On my 496HOs, I had a power loss issue I could not diagnose.
No alarms.
No Guardian
No physical issues.
One engine was just consistently down 300-500 RPM across the range.

Turned out I had a bad crank sensor, and it was not throwing a a code. I own a Rinda too.

You likely won't be able to switch them if original. They can be a bear to remove. I cracked one of mine coming out. I don't know if I'd trust to R&R used parts side to side.

If it were me, knowing what I went through; I'd buy at least one, probably 2 Crank Sensors.

Good luck.

Triple Blown 47

Boat is MY2007 built in mid-06. Engines have 294 hours.

BUP

iTrader: (9)

depending on serial number HP 525 - the crank sensor is set up a bit differently, but . thru out all the years its location bvasically is down by the timing cover. Earlier years had a sensing wheel mounted and is a different sensor - . They are still available thru Merc no matter which ones he needs. I am not saying he needs a crank sensor but of course you can swap them out with the good running engine side to see if anything changes.

yours Bryan is like a long pogo stick mounted top side rear of engine (496). And they can get stuck very easily and break off.

It is wise to post your engine serial number as that how the set up and parts list goes.

Triple Blown 47

No codes, no guardian, both engines read the same on the Rinda. Power loss is 10% through rpm range...3300vs3000, 2200vs2000, 4400vs4000 etc. Everything sounds fine, no misses, popping or mechanical noises. It just seems like the timing is retarded, but Rinda shows both engines the same.

Young Performance

It is certainly possible that you may have 2005 engines. Easiest way, beside serial numbers, is to look at the head bolts. If the tops of the head bolts are flat and say ARP, then they are 2006. If they have a slight recess and there is a plus sign (+) on top of the bolt, then they are 2005's. If they are 05's, they will also have the composite head gaskets that are known to fail, especially with the time you have. Have the top ends been done? If not, you certainly want to do them sooner instead of later.
Eddie

BUP

iTrader: (9)

Look back in your scan and possible knock detection - possible bad knock sensor or its connection or knock circuit. - Knock detecting / knock faults how many times / seconds. Also whats timing advance in the scan any retarding timing going or is spark advance the same with both motors (depending on RPM) - anything there ??? Possible for the 10 % lose

Triple Blown 47

I believe that these 2006 engines do not have active knock sensors??? The spark advance is the same for both motors when checked at the same RPM. Could the crank position sensor be giving a false reading to the PCM to where the PCM thinks the timing is OK but really ins't because the "home" position is off?...and thank you all for the replies.