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|T O P I C R E V I E W
||Posted - May 14 2012 : 06:56:01
Runs all day at 2000RPM when trying to plane out Starboard engine acts like it's not getting gas Does not cough spit or backfire. Acts like it's in some kind of safe mode
I found some water in the stbd engine fuel/water seperator leading me to think water in tank that was not the problem
Boat - 1996 Chaparral twin 5.7EFI (2BL TBI) Bravo 3
Recent work (Both engines)
Replaced Plugs, dist cap & Rotor.
Surveyor had the engine analyzer on it prior to sea trial said no codes alarms and compression all checked great
Drives pulled for yearly maintenece
Engine Oil changed yearly and always looks good per Oil analysis
1-150gal gas tank cleaned by Clean Fuel nothing found. Replaced Fuel filters again
Port engine was pulled prior to sea trial to replace transom assembly, why couldn't the problem be with that engine, get them to fix it
Disconnected one at a time the Oil & Temp senders on stbd engine no luck there
Checked filter in Vapor Seperator Tank it was clean & electric fuel pump inside is working
Replaced Plugs on Stbd engine again just in case
No alarms all gauges working & reading normal
Not a lack of air intake, had the arrester off while out trying some of the above
Looking at replacing Mech type Fuel pump on Stbd engine next would this be a good move
Any other suggestions
|8 L A T E S T R E P L I E S (Newest First)
||Posted - May 16 2012 : 10:18:47
Last fill up was October
Gas is clear and clean
Port Eng no issue same tank
||Posted - May 16 2012 : 09:33:10
How fresh / old is the fuel?
||Posted - May 16 2012 : 04:18:35
I hadn't thought of codes not clearing.
I always wanted one of those scan tools looks like a good time to invest in one
||Posted - May 15 2012 : 17:50:57
In my MEFI diagnostic manual it indicates one of the knock sensor situations that will trigger a diagnostic trouble code DTC, besides out of normal range voltage cycles, is if the KS signal is not present at all. So I would think simply disconnecting or grounding the KS may likely still keep the engine in Safe Mode if that is already the case. It can also trigger a code if the KS is tightened to the wrong torque ti inhibit proper sensing.
The scan device or software (used in conjunction with the ignition diagnostic manual) could rule out a lot of things quickly & quite possibly show something that is clearly out of parameter range. But without the scan device , swapping items from the normal-performing engine certainly may reveal the culprit. Nice when you have identical twins to help provide swap parts.
Keep in mind however, running the engine with a sensor temporarily removed may set a code, and if it is a sensor associated with "latching code" , the code won't go off just by correcting the perceived issue by reinstalling a good sensor. It may take several run cycles or a scan device to clear. I don't know which have the potential latching codes. Also , this apparently is not related to your problem , but in the case of the Idle Ar Control IAC & possible some other parts, the ECM may take a while to "relearn" the optimum-setting voltage output commands for that part and the engine may run a bit erratically during that process.
If no joy there, it may pay in the long run to revisit an authorized Merc tech with specific experience and scan tool he knows how to quickly interperet.
FWIW- the MEFI-4 Diagnostic Manual says under Symptoms/ Lack of Power :#15 Check for engine going into RPM reduction mode. If yes , go to OBD ( onboard diagnostics system check,... i.e. check with scan device). I'm just a boater, but that is why I have the scan device (actually 2 different types by Rinda, Marine Diacom and TechMate.) Also because there are no authorized Crusader techs on the island here.
||Posted - May 15 2012 : 05:07:00
Sandy correct mine only monitors (3) sensors ECT, Low engine Oil & Low outdrive oil
Sorry I have no access to the scan tool
All recent work above is this year, opening boat up for season, last year no issues
I believe the water/sep filter did it's job and any water that got by probably burned up during the 30 min run to/from open water, filter was replaced out on the sea trial and was clean when replaced
However it is a sensor, do you know if the knock sensor can be disconnected or grounded out
I think I'll also try swapping one at a time the TPS & Fuel pump relay
||Posted - May 14 2012 : 11:40:58
You're right it does sound like it may well be in Safe Mode that limits injected fuel flow to 2000 RPM for some conditions. Your '96 TBI may have somewhat more limited monitoring, but my 2003 mpi's will set a code and limit speed (on bothe engine since they are connected with a twin engine harness) to 2000 if the ECM detects out of parameter feedback from :
-ECT Engine Coolant Temp Sensor
-TPS Throttle Position Sensor
-MAP Manifold Absloute Pressure Sensor
-KS Knock Sensor System
-CKP Crankshaft Positioning Sensor
-CMP Camshaft Positioning Sensor
-IAT Intake Air Temp Sensor
I think low oil & high oil or transmission temp would be more likely to shut down the engine.
I would put the MEFI ECM scanner back on the stbd engine and see if it threw a code when the engine was run up under load on the sea trial. Especially if you noticed water in the separator I am wondering if the knock sensor is "advising" the ECM to limit advance and fuel supply. That's only just a WAG though. (Not a mechanic , just like these puzzles. )
When was the fuel tank cleaned ? Last year? New stabilized fuel since then or just polisshed? Is the fill cap o-ring integrity very good & lubed?
If you use Marine Diacom scan software, you can record graphical dynamic output from the sensors. But as noted, the MEFI version in 1996 had limited data monitoring compared to more recent versions ( my 2003's are MEFI-4).
Your Owner's Manual, if you still have one, may explain which conditions can put your TBI engine in safe mode.
You might also just confirm your stbd throttle control can advance the engine throttle to 100% full. The scanner can show you that too.
And make sure if your engine requires being put in Timing Mode to set timing, that the mechanic put it back into Run Mode when finished with the distributor. I don't think that's the problem.
||Posted - May 14 2012 : 10:29:45
If it's EFI, running fine but slow, look at the Fuel Pressure Relay.
Make sure the fuel flow is good.
||Posted - May 14 2012 : 07:33:40
Check for loose plugs loose wire or firing order. Any could limit RPMs. I used to have one wire the would vibrate off and drive me crazy. Of coarse these are the easy things fuel is a little harder to check.
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