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)

Click to expand...

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