2002 200hp OX-66...Rodbolt, what is this sound

[big_b16]

When working on the engine, I occasionally hear a faint pulsing sound (about once every 15 seconds). It has happened since I had the motor (about a year). Tonight it got the best of me and I had to figure out where it was coming from. I usually hear it from the throttle plates. I narrowed it down to number 5. From there I started pulling the vacuum lines. I pulled the one on the starboard side of the number 5 throttle body and the sound stopped. I traced it back to a couple T fittings with the pressure regulator and the two vent lines on the top of the VST. What is causing this...and is it normal?

Could this be causing a low RPM rough idle/stall problem?

 

[big_b16]

Re: 2002 200hp OX-66...Rodbolt, what is this sound

Below is a link to a video showing my motor. The idle is kind of quiet, but it can be heard. There is what I would describe as sneezing, but the plugs are usually pretty wet with oil when I'm done running. If I get the engine over 1500rpms it'll run fine. Just below that it'll stumble. I can hold 1000rpm sometimes, but if I let off the gas and the rpms drop to idle, it'll start sneezing and sometimes stall. I checked the low and high speed charging circuit resistances and they're good. I don't have a DVA so I can't check the voltages under load. Any ideas would be helpful...I no longer have any idea what to check. All I haven't checked for proper operation is the fuel injectors (they do have clean screens). Not sure what to check in the ignition side with the limited equipment I have. I might punt and take it to a dealer...I'm selling this motor soon so I don't want to buy test equipment I will only use for one time.

 

[big_b16]

Re: 2002 200hp OX-66...Rodbolt, what is this sound

Anyone have any thoughts?

 

[rodbolt]

Re: 2002 200hp OX-66...Rodbolt, what is this sound

no sound on this computer at work and I still dont have my home box up yet.
does the engine run well?

 

[big_b16]

Re: 2002 200hp OX-66...Rodbolt, what is this sound

No it doesn't. I've got the top end problem fixed...new O2 sensor. But there has been a stumble problem at idle up through 1200rpm. It coughs and stumbles and may stall at times. If i give it gas to load it on the trailer it'll usually stall. The plugs are fouling up pretty bad. Once I get above 1500 rpm it will run up to WOT fine and run there all day. But once I come back down it sputters and coughs. I read a post you had a couple years ago and it ended up being a pressure sensor (on my motor, behind the fuse block). I don't believe any fuel related problems are left (since it'll run WOT). You may recall I tested both pressures and vacuum trying to find something wrong before replacing the O2 sensor (different thread). So my symptoms are low speed cough/stumble, occasional stall if I don't feather the gas to keep it running, and fouling plugs. Any insights would be greatly appreciated.

If you have a blackberry or the like, PM me your number and I can send you the video...I took it on my phone.

 

[rodbolt]

Re: 2002 200hp OX-66...Rodbolt, what is this sound

hit me with a PM, I dont know how.

 

[big_b16]

Re: 2002 200hp OX-66...Rodbolt, what is this sound

You should have one. Might be listed under your login name on the top of the page if you didn't get a pop-up.

 

[PBJohn]

Re: 2002 200hp OX-66...Rodbolt, what is this sound

Check the spark plug caps for proper resistance. One might be bad causing a misfire. Does it happen during all operating temperatures?

 

[big_b16]

Re: 2002 200hp OX-66...Rodbolt, what is this sound

Caps were all good. Ended up having to replace a coil since I was not able to believe the only connection on a plug wire was actually a screw into a braided wire. I ripped a wire out of the coil assy before realizing exactly how they were assembled.