Greenie727

1999 Mercruiser 5.0L EFI w/throttle body erratic operation after 20-30 min at cruise RPM

5 posts in this topic

Gentlemen,

New to this forum but lots of helpful info on this site. I just purchased a 1999 Chaparral 2130SS with 330 hours on  5.0L EFI MerCruiser engine and hull from original owner. Boat was always maintained with required maintenance as original owner was corporate aircraft pilot and kept good maintenance records which he provided to me at purchase. I have operated the boat without any problems and now have 360 hours on the meter. The engine has now developed erratic operation after about 20-30 minutes at 2500-3000 RPM while underway. The engine RPM will surge and drop back to 600rpm and then increase back to 2500-3000 and then drop back to idle and occasionally stall when shift lever is selected to neutral. Engine will restart after 30 seconds and will get boat up on plane but will again start to surge with wide RPM swings indicated on tachometer. Engine temp is around 145 and never above with good oil pressure and no warning horns for low fuel pressure. I have removed and replaced fuel/water separator filter. I cut the old filter body open and did not notice any water or excessive contamination. Other than an Idle air control actuator that the previous owner had replaced I do not think any additional engine work has been accomplished. The engine is equipped with the MEFI 3 throttle body fuel system. I would like to retrieve the stored codes from the ECM. I do not have a code reader but have seen on youtube a gentleman retrieve codes on the ECM with MEFI 3 fuel control using digital VOM counting continuity beeps with the A and B pins jumped out at diagnostic connector to place the ECM in service mode. Engine ran without any problems for my first 30 hours and now this has developed .I found info on this site that MerCruiser had a recall on ignition sensor which is applicable to my serial number 5.0L V8.  Any comments or suggestions on troubleshooting as well as has anyone read codes from the ECM with the digital VOM would be greatly appreciated. 

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3 hours ago, Greenie727 said:

Any comments or suggestions on troubleshooting as well as has anyone read codes from the ECM with the digital VOM would be greatly appreciated. 

 

For that era of engine, I think you might have the shift cut out switch messing with the engine timing. Had a very similar episode with a late '90's 4.3L EFI with an Alpha 1 Gen II.

Mercury part # 808009A1. Item # 17 in the link below. This is a rather easy DIY fix for the average layman.

14166.GIF

For the ignition sensor, I would recommend installing a new one. New version is Mercury part # 87-892150K02 or Quicksilver part # 87-892150Q02. Will also need a new rotor as they often get bent out of shape when prying up and off the rotor shaft. Might as well get a new distributor cap and rotor kit 805759T3 or Q3. If you want the rotor only, Mercury part # 13524T1

14151.GIF

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Thanks Shepherd1,

Just returned from checking and found no stored codes in ECM. With control in service mode got continuous 12 codes signaling no faults. Looking at shift plate and cutout switch it looks like switch actuator is centered in low point on cam plate. Shifting from neutral to forward does not move cam plate or actuate switch as far as I can tell. Shifting from neutral to reverse causes cam plate to rotate and looks like it actuates switch. Does this switch momentarily cut off the ignition to allow easier shifting out of neutral into fwd or rev? If I manually move cam plate with engine running it seems to cause the engine to run rough and then return to normal when released. I have Mercruiser service manual #24 but can't find any reference in regards to description and operation, or adjustment of the switch and linkage that actuates it. Is the cam plate that actuates this switch supposed to actuate switch when selecting fwd as well as rev out of neutral position? Looks like the cam only moves when moving shift lever from neutral to Rev. From wiring diagrams it looks like when switch actuates it puts a ground signal on Pin 9 on J2 ECM connector. Any additional detailed information about the purpose, operation, and adjustment of this switch would be greatly appreciated.

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7 hours ago, Greenie727 said:

Any additional detailed information about the purpose, operation, and adjustment of this switch would be greatly appreciated.

Top marks for your findings! Here is what I believe to be true about the shift cut-out switch.

- for sure works when coming out offorward or reverse gear. On carbureted models, it would cut out the ignition altogether for a brief moment to reduce engine load,

- on EFI Alpha equipped engines, the shift cut-out switch reduces timing instead of killing the ignition briefly. Many Bravo models have a similar switch, but all it does is tell the ECM if the drive is in gear or in neutral.

The 4.3L EFI Alpha 1 engines that was giving us fits would do it when the shift cut-out switch wasn't even engaged. Mercury had a bulletin apparently.

On a side note, what is the fuel pressure while operating the engine, specifically when the engine is running poorly?

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Thanks again Shepherd1,

I have done some additional research on various forums about the function and operation of the shift interrupt switch (item #17) in the above IPC parts breakdown.  I believe all symptoms are likely caused by intermittent switch malfunctioning as you stated. The switch is on order and as soon as I install it and checkout the operation I will post results.  Thanks again for all your advice as possible causes of the above malfunction.

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