3.0 OMC ignition problem

[Jessfly1]

Re: 3.0 OMC ignition problem

As others said. try running at night and see if you can see spark jumping somewhere. Does a timing light on the wires (all 4) show it not sparking? Any water in the oil? Try grounding the spark plug for 1 and 2 and compare it to 3 and 4, do they look different (ie weaker)? You said with the plugs out you were getting spark on 1 and 2. Try also disconnecting the shift interrupt switch from the coil (long shot but vibration may be tweaking it). Are you getting a good ground to the engine block? Check resistance with an ohmmeter and such, check your ground cable to the block, check for a good ground at the spark plug holes. Check resistance with the plug in from the spark plug at the nut part to the coil.

First off thank you all for the inputs. Unforuatally after all these tests i am still dead in the water. I ran it at night and didnt see spark jump. Did an ohm check from the base of the plugs to the block and recieved no resistance. Checked all four plugs with timing light and all are getting spark. Pulled all the plugs and tested the spark by grounding them to the block and all seem to have a strong/blue spark. Ohm checked all wires going from coil to dist. and main wiring harness and all checked good. The interrupt and overstroke switches have been disconnected this whole time. No water in the oil.

Sounds a lot like a vacuum leak.
Here is a quick test since there is no place to hook up a vacuum gage on the 3.0L engine.
Remove the flame arrestor, and when idling slowly close the choke butterfly and see if the engine smooths out as it gets closed off. If it does, start looking at the base of the carb for a vacuum leak.

I also ran the vacuum test and no help. I closed the butterfly valve slowely and it never smoothed out just slowley died. I also poured water around carb to manifold, manifold to head, and head to block just to see if it would close the leak and smooth out for a second. NO GO!

Going after the timing gears. Process of elimination says its the only thing left.

 

[Jessfly1]

Re: 3.0 OMC ignition problem

Ok, I have attached some pictures of a 3.0 I have found on google. When I first bought the boat it was running fairly well. When I changed out the rotor and cap this spring I noted the location of the rotor when #1 was at TDC. It's location is depictied in the image with the blue dot on the #4 plug wire. Of course #1 plug wire was in #4 spot and continued the firing order going clockwise. After doing research for this problem i have noticed all the videos or photographs of 3.0 OMC indicate that the #1 plug wire is in the configuration of the image with the red dot. I have relocated the distributor and reclocked the plug wires to corrispond with everthing i have seen. Is this the correct location for the rotor? I posed this question before and some one told me the rotor should be pointing at the #1 plug when its at TDC. I know what your thinking thats my problem, I must have it off a tooth or two. Well Of course i thought this as well and have tried moving the distributor almost every tooth and reclocking the plug wires to match and i still have the same problem.

 

[tschmidty]

Re: 3.0 OMC ignition problem

You are right on the plug location being where the red dot is. Thing is, it shouldn't make a difference if they are all in the right order and firing starts at #1 TDC. Even the electronic distributor doesn't have a crank sensor so it will fire regardless of where the crank is, so position is not important as long as the plug wire lines up with the rotor at the right time. It shouldn't but it might. You could try and rotate the cap and plug wires 180 degrees.

You are getting compression so I wouldn't suspect the timing gears. I would back up and just start with timing and make 100% sure you are right. And try to get someone else to take a look. Fresh eyes will see things and make different assumptions about things you may "know"I think you are missing something basic in your troubleshooting and thinking past the problem.

 

[Silvertip]

Re: 3.0 OMC ignition problem

When you replaced the head gasket did you properly adjust the lifters. Too tight means the valves don't close tightly. Too loose they don't open fully. Is the firing order correct?

 

[[OBC]Patch]

Re: 3.0 OMC ignition problem

A bent distruibutor shaft might deviate from true at speed enough to drop/reduce spark to those two cylinders..

 

[tschmidty]

Re: 3.0 OMC ignition problem

FYI, if it were a bent distributor shaft, you could put a timing light on #3 (Or is it #4?) which should line up with TDC on #1 and check for a differnce between timing there and on #1. Good luck, this has got to be frustrating.

 

[[OBC]Patch]

Re: 3.0 OMC ignition problem

Isee in an earlier poost that you replaced the distributor, so maybe its not the distributor shaft. Thinking a little deeper, maybe its the camshaft which turns the distributor shaft is bent, or worn; enough that it forces the distributor shaft out of alignment, possibly a harmonic forced distortion to the dizzy shaft and that creates the symptom of dropping cylinders? If you replaced the dizzy, you have to look deeper. maybe worn teeth on the cam, (that seems more likely), allows enough play at speed to cause this. Did you put a new gear in the distributor, or reuse the one that was in it?

Also, verify you dont have a rag in your intake manifold blocking those cylinders-

 

[[OBC]Patch]

Re: 3.0 OMC ignition problem

I posed this question before and some one told me the rotor should be pointing at the #1 plug when its at TDC. I know what your thinking thats my problem, I must have it off a tooth or two.

Point of order, are you aware in the four stroke cycle that TDC is passed 2 times in the four stroke firing cycle? Once begining at expansion and the moment of ignition, and then again during at the end of exhaust stroke and begining of intake stroke? Are you aware you have to look at the valves of number one insuring they are both CLOSED at TDC of the compression stroke for #1?

 

[tschmidty]

Re: 3.0 OMC ignition problem

In an earlier post he did mention taking the valve cover off and verifying the valves. I'll stick with occam's razor and say it has to be something more basic than what we are poking at. Use a compression tester again to verify you are at tdc #1, make sure the rotor is facing the #1 spark plug wire and go from there.

 

[Eric 3.7LX Alpha 1]

Re: 3.0 OMC ignition problem

When you replaced the head gasket did you properly adjust the lifters. Too tight means the valves don't close tightly. Too loose they don't open fully. Is the firing order correct?

I like this possiblity. Good spark at all plugs, if the timing is correct I would confirm the lash on those valves on those cylinders is correct.

 

[tschmidty]

Re: 3.0 OMC ignition problem

Keep us posted if you figure it out, very curious to hear what it ends up being.

 

[sqbtr]

Re: 3.0 OMC ignition problem

Look down the throat of the carb while it's ideling, there should be no fuel coming out of the emulsion tubes. the idle circuit feeds below the throttle plates. I'm suspecting a flooding carb.

 

[Jessfly1]

Re: 3.0 OMC ignition problem

Here is an update of what i found when i pulled the timing cover. I put the motor to TDC with a compression gauge and pulled the valve cover just to make sure both valves were closed. When I pulled the cover i noticed the timing marks were opposite of each other. I thought this was strange since every motor i have built in the past (primarily 350's) have the marks together. I consulted my manual and it indicated the marks should be together as well as a machinist I gave a call to. He was surprised the motor even ran. I went through the firing order by turning the motor over by hand just to make sure I was in fact at TDC compression stroke and all the valves were working properly (at #1 compression stroke # 3's intake is still open but on its way shut). I have attached a picture of what i have found. I am not familiar with this motor so I am not going to attempt to move the cam until I get some feed back on this one. Thanks in advance!

 

[Jessfly1]

Re: 3.0 OMC ignition problem

Here is where i got the replacement parts from and what i replaced.

http://www.michiganmotorz.com/delco-voyager-marine-electronic-distributor-p-120.html

As you can see the new distributor had a new gear on it and i inspected it before i put it in. I also looked into the distributor hole and looked at the cam gear and it looked OK.

Look down the throat of the carb while it's ideling, there should be no fuel coming out of the emulsion tubes. the idle circuit feeds below the throttle plates. I'm suspecting a flooding carb.

The boat has ran rich ever since i bought it. I have rebuilt the carb numerous times and still runs rich. I have been all the way out and in on air fuel screws and no help. I have looked down the carb when it was running and yes there is a little fuel coming out i of the emulsion tubes but it was this way when it was running on all four. One of my coworkers suggested leaning it out by lowering the float, but of course he told me this after i had the timing cover off. I don't understand how it is flooding 1 and 2 to the point they wont fire but 3 and 4 are running like a champ?

 

[sqbtr]

Re: 3.0 OMC ignition problem

May only be running on the cruise circuit. How many turns counter clockwise does it take to close the throttle plate completely?

 

[tschmidty]

Re: 3.0 OMC ignition problem

Sounds like you are on the overlap stroke and not TDC although I would have thought it would have been clear with the compression tester. An no, it is not rich enough that it is only firing on two cylinders.

 

[sqbtr]

Re: 3.0 OMC ignition problem

Really

He states it is getting spark on all four but 3&4 are carboned up and 1&2 are wet. he's even put a new dist. in it

Line the dots up and see where your rotor points

 

[6meter]

Re: 3.0 OMC ignition problem

Its been a while but I think on a sbc, timing marks both at 12'oclock and drop the dizzy in pointing to #1. I should be the same on the 3.0. I could be wrong, it's been 24 years. Me thinks your plug wires are going around the dizzy in the opposite direction.

 

[Jessfly1]

Re: 3.0 OMC ignition problem

Its been a while but I think on a sbc, timing marks both at 12'oclock and drop the dizzy in pointing to #1. I should be the same on the 3.0. I could be wrong, it's been 24 years. Me thinks your plug wires are going around the dizzy in the opposite direction.

I know my plug wires are right because i have had the dist. cap off and turned the motor just to watch the rotor turn clockwise. The plug wires are oriented clockwise around the cap (1,3,4,2)

 

[Jessfly1]

Re: 3.0 OMC ignition problem

Sounds like you are on the overlap stroke and not TDC although I would have thought it would have been clear with the compression tester. An no, it is not rich enough that it is only firing on two cylinders.

Your answer...

I went through the firing order by turning the motor over by hand just to make sure I was in fact at TDC compression stroke and all the valves were working properly (at #1 compression stroke # 3's intake is still open but on its way shut)

May only be running on the cruise circuit. How many turns counter clockwise does it take to close the throttle plate completely?

From a wide open throttle position it is about 1/2 turns counter clockwise to close it. I have it disconnected from the throttle linkage so its not a factor.