1996 OMC 150 HP V6 shudder kicking above idle

Model: E150ELERA
History: New to me boat/outboard. Previous owner suggested it needs a prop shaft. Claimed he'd used it several times recently at local lake but I don't believe him. The below deck fuel tank had significant water mixed with and both batteries were dead. He claims new VRO pump put in last year

I am running on a portable 6 gallon tank with premix 50:1. I verified VRO is not pulling oil from the reservoir. I know this because I added a clear section of hose along the oil line and It's not pumping oil from the tank, however this is my first time with an oil pump system, I'm thinking maybe I needed to fill the line and get the air out of it before hooking it to outboard. May try that later

I checked compression on all cylinders and it was OK I think, 92,93,94, 100,100, 102.

I've only had this a couple days but thought I'd post my problem, seek your counsel and share the fix. I'm gonna check fuel pressure and take some time to familiarize myself with the VRO I've got the service manual ordered. my thesis is it has a fuel restriction and once the idle increases, fuel delivery is not meeting demand.. but I dont know who he had look at it before or if a bad prop shaft would cause the symptom.

Abused boat. Sell it.

Your dropping cylinder(s)

dingbat said:

Your dropping cylinder(s)

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Thank you for telling me what you hear. I just confirmed there is spark at all 6 cylinders (though as I type I'm realising I did not measure for 1/2" gap, I had my tool set to much narrower gap).

Next cylinder drop test. Unclear results. My ears maybe aren't good enough to do that on a V6, it barely sounded different with one plug wire off. Maybe I'll redo the test but take off one of the other plug wires also so I'm really running on 5 to start and dropping to 4.

Since my hearing wasn't great, I put a tiny tach on each of the plug wires and the bottom two cylinders appear to be running at significantly less RPM which tells me those two cylinders are misfiring.

I'm out of time for now but I'll try swapping the coils and share the results

Tonight I swapped coils. It did not change the results of my tachometer readings, bottom two cylinders still showed almost 1000 rpm less than the other cylinders

I printed off the CDI electronics troubleshooting guide (which is amazingly thorough by the way (CDI Electronics Ignition Troubleshooting) and after reading the pages pertaining to my engine (pages 72 to 77). At this point I was suspecting timer base or powerpack but don't want to replace parts needlessly. Can't find my DVA meter so need to order one again.

Once it got dark I measured the spark on each and got good spark across 1/2" while cranking. To my surprise spark was strongest (brightest flash) on bottom two cylinders where my tinytach was reading less RPMs. I'm beginning to think my tiny tach test was a 'red herring' and maybe not accurate. perhaps its getting interference. I could try reading RPMs with my timing light tomorrow.

Wondering if its possible to have sufficient spark while cranking but then intermittently lose it at higher rpms. I will continue to pursue the ignition circuit troubleshooting when the DVA arrives.

Feeling a little discouraged tonight but just going to test and eliminate possibilities one step at a time.

Ok it is fixed! I will record a video showing the steps I took following the troubleshooting instructions on the CDI website. But long story short it was the temp sensor on the port side. unplugged the temp sensor and it ran perfectly. I guess it was sending an overheat signal and putting it in S.L.O.W. mode. I checked the temperature with a temp gun and it is cooling fine. Running about 140 deg

Great post. Glad you stuck with it. If persons are unfamiliar with the warning and slow mode features this type of issue can be quite elusive to figure out. When you plug the sensor back in it should do the same thing . Try it . If you replace it with a new one and it does the same thing look into the in harness diode . If it is bad and your sensor is good I think you will again end up in slow mode. Chime in if I am wrong . I am dealing with a harness issue myself . New post for that issue.

w2much said:

Great post. Glad you stuck with it. If persons are unfamiliar with the warning and slow mode features this type of issue can be quite elusive to figure out. When you plug the sensor back in it should do the same thing . Try it . If you replace it with a new one and it does the same thing look into the in harness diode . If it is bad and your sensor is good I think you will again end up in slow mode. Chime in if I am wrong . I am dealing with a harness issue myself . New post for that issue.

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Thanks, I did plug in the sensor again to confirm that was the issue. Good to know that there's a diode in the harness that can cause the same issue. I'll tuck that in the back of my mind in case I need it!

Here's my follow up video. I could not affordably (quickly) get my hands on the correct part to replace but in the video I explain a work around solution.

Also to follow up on the weird tinytach results .. I pulled out my timing light instead and read the RPM at each plug wire and RPM was even on all wires (where tiny tach showed half RPM on bottom cylinder port and bottom cylinder starboard)... So I believe my tiny tach was getting interference and I would not recommend testing that way. Also to note: I was doing my readings at a lower idle RPM where the engine wasn't in 'slow' mode. I was not brave enough to take readings while it was kicking. Afraid to run the engine in that state

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