rvtransport

I was told fuel pressure should be min 43 psi with vac line disconnected under load. 43-45 is target numbers? 40 seems low.

Sydwayz

iTrader: (1)

Replaced:
Spark Plugs
F/W Separator
Inline Fuel Filter
Crankshaft Position Sensor

I did not test individually after every swap, but I can tell you that this afternoon's test run seemed to have cleared all issues. I even picked up a few ticks on the GPS speedo by re-syncing my throttles/cables with the TPS measurements via the Rinda.

My money is on the CPS being the main culprit.

But I will tell you this, it was BlTCH to replace. They are not terribly difficult to get to; but getting it out was awful. Once I starting getting it out, I was committed to replacing it as I could hear and feel the plastic starting to crack. It has been in there since 2003 sometime, and it liked being there! I ordered a second one for the other engine as well. I will likely replace it soon just to make certain I don't have that issue of it trying to fall apart on me, when I am short on time (before an event).

Again, many thanks everyone, especially T-RAV as I replaced the CPS after reading your post.

T-RAV

iTrader: (1)

I learned taking the oil pressure sender off and twisting the crank position sensor while pulling it up makes it come out easier. Just for future search efforts. Glad your problem got solved sydwayz!!

Sydwayz

iTrader: (1)

I was able to twist it about 125 degrees back and forth while pulling up on it, but it was REALLY in there. The new/replacement Crankshaft Position Sender has a fluted design to it vs. mostly solid shaft. I do feel as though the new design is better and will easier to pull if ever needed.

BUP

iTrader: (9)

There is normal resistance testing you can do on your old camshaft PS with a volt meter. Testing the sensor, A to B is 24.04 mohms and B to C 24.05 mohms values is a good sensor, if out of those specs it is bad. Test it to see.

Also Merc has had problems with the connectors as well and some even hold moisture in which can set a fault code. They offer connector kits for the past 2 years for sensors like this and IAC, and others - they have a service bulletin about it and new part #'s so you can splice in new connectors / connections to the sensors that is needed.

The Cam PS and Crank PS supply the PCM with timing and rpm inputs. More times than not the engine will stall while running at any rpm level or run very rough or no start issues if either one of these sensors fail or a failed connection or shorted.

No start issues for a PCM engine if no tach is showing its the crank PS, if tach is showing with no start, it very well can be the Cam PS. FYI

Sydwayz

iTrader: (1)

Update:
Ran the boat in a ROUGH poker run in Norfolk, VA this weekend and the engine ran great!

Actually, the other engine through a Crank Position Sensor and Cam Position Sensor code at one point, and both cleared on their own.

I will be replacing the Crank Sensor on the other engine, and Cam Sensor on both engines.

Again, many thanks everyone, except TomTBone.

Sydwayz

iTrader: (1)

One more update for future reference:

I replaced the Crankshaft Position Sensor in my other 496HO last night.
BUP is RIGHT ON THE MONEY with removing the Oil Pressure Sender. It spins right out and provides a lot more access. I got this Crank Position Sensor out with only one scrape on my arm when it popped out faster than I expected due to more leverage; as opposed to several busted knuckles and 4x more effort on the first one.

New CPS on left vs. Old CPS on right.
You can see how the new one is better designed for strength and ease of removal.

[ATTACH=CONFIG]525953[/ATTACH]

I spent over $200 on that CPS from a Mercury dealer.
http://www.rockauto.com/ sells it for just over $50 bucks. It's the exact same part that Mercury sells; listed as 8.1L / 496 HO.

It seems as though RockAuto has done the research and has parts listed well to pretty easily to determine which GM/Ford parts plug right into the Mercury common points of failure.

BUP

iTrader: (9)

I just PM you for a heads up. On the crank sensor you have to watch out because (especially in saltwater apps) they can get stuck from corrosion and when you try like to pull them out - they can break off. anyways. FYI.

BUP

iTrader: (9)

200 dollars Merc shows retail for 170 bucks part # 892617. Unless another new part # just came out. Everytime these OEM engines have a part # change, they raise the price as well. Jeepers keep boaters in boating not make them broke so they can't afford boating anymore. even 170 dollars retail is very high for that. If you only knew what merc buys them for

BUP

iTrader: (9)

Last post always look at the bottom tip of your crank sensor to see if any of the raised portion is worn, chipped or completely flat, if so you have a problem and the crank reluctor back to the crank sensor can not read (output) correctly. It should not be flat and should have raised portions lines on the bottom tip of it.