700 SCI Problems
 

Boat was running good came off plane and port motor did not want to run right started running rough. Then the beeping started 5 beeps 3 seconds long. Looked in my Mercury book and it said. Coil pack failure,Fuel Injector failure,Fuel pump failure,Idle air control failure. Got the boat home plugged it into scan tool coil failure number 2. Replaced coil still ran bad changed mechanical fuel pump,replaced IAC, replaced Map sensor, checked fuel injectors, replaced fuel filters and replaced spark plugs. Took PCM off bad motor put it on good motor it ran great. The only fault code I get is 17 Map Sensor Idle Fault. Looking at the scan tool while running it seems to think it is under boost at Idle. IAC is at 44.6% and Spark advances is at 19.0 degrees Manifold pressure 14.6 psi and fuel pressure is 67 to 70 psi. Good motor at Idle, IAC 0.0 % spark advance is 0.0 manifold pressure 10.1 psi and fuel pressure is 59 to 61. I am thinking maybe a sensor is bad, not sure any help would be greatly appreciated. There is nobody local that works on these motor so trying to figure it out on my own.

Thanks Jack

Not really familiar with that eng but does the MAP sensor have a vacuum hose? If so, I'd check that. May be cracked.

Just an idea as I have no knowledge for 700's does it have spark at #2, check with putting coil wire on spare plug grounded?
compression check
can the scanner read live data from sensors
I have rinda PC version which can record data

It does not have a vacuum line attached to it. It is electric.

All the coils are good check them all have spark. Compression is good. All it tells me is I have 5 volts to sensors.

certainly sounds like a sensor issue, or wiring to the sensor connector, you've ruled out the pcm

Yes I took the Pcm of the bad motor and installed it on my good motor and it runs great. I was thinking sensor also or boost control valve.

Map sensor reads atmospheric pressure key on engine off. So 14.6 psi is correct. 0 is gauge pressure

Barometric Pressure was 14.8 and the manifold pressure at idle was 14.6 my mechanical boost gauge is bouncing all over the place at idle.

is the engine surging ? like a poorly tuned carbed roots blower.......:cool-smiley-011:

Intake manifold press bouncing= intake/exh valve issue or maybe some oddball blower issue.
I would remove blower belt and see if the press keeps bouncing at idle. If it does, you can rule out the blower.

Compression test would be a good idea too.

I'm assuming the other eng has a steady intake manifold press at idle using mechanical gauge.

That was going to be my next step is to pull blower belt and see what it does. Other motor gauges all good nice and steady. Is there a boost relief valve somewhere i am missing?

Did you ever get this figured out? I have a 700 stg 2 that is running rich at idle and it's a dog when first getting on it from a dig I am sure it's from being so full of fuel. Very short time out back of boat was getting black. Ordered scan tool today.
Thanks

Yes the boat is surging when up and running i can see the boost gauge moving up and down at the same beat the boat is surging.
I get a boost valve error on my vessel view also but not all the time. Some times i get it if the motor i just idling and also get it some time up on plane.

picked this from my Whipple install PDF,

Supercharger By-pass system. The supercharger is installed with a by-pass system. This allows the supercharger to operate at higher efficiency under vacuum operation. It is advised to verify the operation of the bypass valve. At idle and low engine loads, the bypass will be open. At higher loads (engine in boost) the bypass will be closed. As the throttle is opened quickly the bypass valve will close momentarily. This verifies the bypass will close and is functioning. Actuator failure could lead to intercooler fires, poor performance and erratic idle. If the actuator fails, it could have an air leak which will result in poor idle qualities. A failed actuator will also allow the bypass to open it’s internal butterfly during boost, which will circulate air and reduce airflow to the engine, consequently lowering the boost level and power

see if you have something that looks like this, these hook to a diaphragm with 2 other hoses that control vacuum while in boost........... I know your blowers are different


https://cimg9.ibsrv.net/gimg/www.off...9031758d8.jpeg

I just went through this late last season with my TCM1200 efi's. Poor idle that had a "blower surge" loading up with any amount of idling, fouling plugs etc. Tested my bypass vlaves and sure enough the diaphragms were blown, easy $300 fix. I was pulling my hair out thinking it was a MAP sensor or IAC which both tested good.

Sorry to step in, but man…,,that valve sure looks like the GM 3800 motor’s bypass valve found in:

• 97-08 Pontiac Grand Prix
• 96-03 Pontiac Bonneville SSEi
• 96-04 Buick Park Avenue Ultra
• 97-04 Buick Regal GS
• 04-05 Chevrolet Impala & Monte Carlo SS
• 95-99 Buick Riviera

https://cimg3.ibsrv.net/gimg/www.off...924f250d4e.png

Maybe ?

Supercharger Bypass Valve Actuator - GM (89018120)

Found for under $140

https://cimg1.ibsrv.net/gimg/www.off...2dab73648d.jpg

I was told by Whipple that a backfire will usually blow the diaphragm...........

Snd then this. They state they get from same manufacturer that supplies gm snd eaton with them. ??? $80

https://zzperformance.com/collection...0-bypass-valve


https://cimg8.ibsrv.net/gimg/www.off...c097481779.png

Mine only had one vacuum fitting on it...from what I was told Whipple uses a specific spring pressure. Not sure how true it is but I didn't want to be the guy to find out the hard way..
https://cimg6.ibsrv.net/gimg/www.off...1b3d9230a8.jpg

with those TCM 1200's you're probably running 8L Whips ?

5.0's
https://cimg7.ibsrv.net/gimg/www.off...511ec75b27.jpg
https://cimg3.ibsrv.net/gimg/www.off...fd6cc322f1.jpg