VPelliccia

Hello All;
I have a 2006 Chaparral signature 350 with twin 496 MAGs.

The PORT engine has always started rough needing some throttle to settle down. Once warm its seems fine with some minor symptoms. After warming up, there is a delay to throttle before the engine revs. And it seems strong once at steady cruise power levels.
The dealer has checked it twice and said its "not throwing any new codes" but they did see a CAM Position Sensor error from 20 hours back. They do not know what to do next.
Heres what I have found and done so far.

1) New plugs : They old ones were in terrible shape but no real improvement.
2) Confirmed low fuel pressure (PORT) and noisy reading vs the STBD engine :: Tried a new regulator and got rid of the needle bouncing but had to rebuild/ replace the fuel pump / filters to get it back to 43 psi. :: Result Slight Improvement.
3) Cleaned the Intake and IAC Muffler and also checked the Flame Arrestor - none of it was tat dirty except the IAC Muffler. :: Result - no change.
4) Replaced the (PORT) IAC :: Slight Improvement.
5) Added Vessel-View so I can get some data. ( Cool Stuff)

But still the (PORT) engine has some trouble starting, less pronounced and at low RPMs, may stall. Advancing the throttle helps to calm it down. Once warm this issue goes away but its still lagging the application of Throttle.
I ordered replacement IAC Mufflers for both engines. I'm thinking to test the Throttle Position Sensor or just swap them STBR to PORT. In any case if you have any ideas for where to look next your help is appreciated.

Thanks
Vince

Keith Atlanta

How many hours are on each engine?

Sydwayz

iTrader: (1)

Have you swapped the IAC from side to side?
IACs can and do go bad without throwing codes.

VPelliccia

Hi and Thanks.
Both show about 371 hours.
Vince

VPelliccia

The PORT IAC is new as of yesterday and thanks as I did read the notes on IACs going bad. I plan to change out STBD too as its was only about $80 and and hour of my labor.
I also order new IAC Mufflers as they are cheep..
Thanks
Vince

Keith Atlanta

Yeah, buy 2, put them in. I live in a salt environment and they go bad almost yearly.

BUP

iTrader: (9)

you have to report at what RPM the cam sensor threw a code. A cam sensor will throw a code if the engine stales or stumbles to a very very low rpm and trys to catch itself to raise RPM. This will throw a cam sensor code and or even a crank sensor code along with it.

What is the PWM % of the IAC - that will tell alot - especially with a fully warmed up engine(s). There is alot more to it than just changing an IAC plus there is more parts involved to keep IAC longevity and working properly.

I have customers with 15 year old IAC with 300 to 800 hours on their engines still using the same IAC from day one.

belt dust and heat and resistance and higher than normal duty cycles for the IAC is mainly the killers in short order. But will add yes IAC for ECM / PCM 555 can be a huge problem child as well.

catman01

Pull the fuel rails and look for rust internally and in the injector screens. Common problem for the inside of the fuel rails to rust and fill the injectors with rust. If you see any rust at all send the injectors out to be cleaned and flow

BUP

iTrader: (9)

Will agree about all that. Also aluminum oxide ( white or yellowish tint powder is another problem) --- but even if you do not see rust or aluminum oxide - the injectors still need to be checked. Its part of maintenance for marine apps.

Fuel samples and examine fuel filters closely will tell you alot. If Gen 2 cool fuel, there is 2 filters that you can cut open to examine. Gen 3 cool fuel you can check those filters and the fuel cell internally plus the pull out basket. The pull out basket one can check for water. Water is not good for fuel injectors nor the fuel rails nor the fuel pumps. If you need help with the fuel injectors let me know. Thanks and good luck.

VPelliccia

Thanks to all..
Im responding to the last three responses.

I do not have any way of getting the IAC Pulse Width data that I know of. While I have "vessel view mobile" and can see error codes, I do not have a full read capability for all data. (Or am i missing something?)
I will check the fuel rails for rust/ oxides and still have the injectors in mind for a cleaning. This would be the time to look for rust. However the engines run well at high RPMs and as a result I had stopped thinking about fuel as a source of issues.
I had pulled the tank pickup and its in fine shape. Sealed the joints with a seal compound.
I have clean fuel filters in both engines and missed the chance to dissect the old filters.
Since changing the IAC (PORT) the cold start issue is less pronounced. It still takes some throttle for the first 10 seconds for a high RPM idle. After that it idles fine. Strikes me that the engines are not heating up or at lease not by much in the short time.

I still plan to check the TPS for a dead spot - I may just swap PORT and STBD - TPS. I also am taking the advice of you all and changing the IAC for STBD.

Again thank to all for the advice and constant ideas.
Al the Best;
Vince