3.0 OMC ignition problem

[Jessfly1]

I have a '91 3.0 OMC with an ignition problem. It wont fire on 1 and 2. Took the boat out last weekend (after replacing the head gasket) and it ran great. Replaced plugs and go to fire it up in preperation for this weekend and 1 & 2 not firing. I DIDNT DO ANYTHING BUT CHANGE PLUGS. What I have done... I would get the motor running (not well) and would pull 1 & 2 plug wires and no change to the motor, pull 3 or 4 and it will die! Compression test GOOD! Tried new and old plugs and wires, rotated distributor and moved teeth. Put #1 piston to TDC with a compression gauge to make sure i wasnt a 180 degrees out and made sure the rotor and #1 plug wire were in line. Made sure i had spark on 1,2 and 4 by putting a spark plug in the wire and holding it next to the block. Although the spark was orange in color and seemed week. This would point me to belive the coil is weak or bad but i dont understand why 3 and 4 would fire. And yes I have the plug wires in the correct firing order. Any help is appriciated, thanks in advance.

 

[Bondo]

Re: 3.0 OMC ignition problem

Ayuh,... How burnt up are the Points,..??

 

[[OBC]Patch]

Re: 3.0 OMC ignition problem

*Maybe*, you cracked one and two during the install and they are shorting to block. Number them with a marker and then swich them for 3 and 4. Or you damaged your plug wires during theswap out. try running it in the dark, look for escape voltage!

 

[bruceb58]

Re: 3.0 OMC ignition problem

What is your dwell at..that is if you have points? 90/91 is the year they changed over from point to electronic ignition. Did you check it with a meter?

If you have to readjust your dwell, make sure you recheck timing.

 

[Jessfly1]

Re: 3.0 OMC ignition problem

Yeah, this is not a points sys. Its the electronic ignition. As soon as I had a problem I put the old plugs back in and the problem was still there so i dont think the plugs are cracked although I will still check. As far as plug wires, I put on a set of brand new 8mm MSD Ignitor wires after the issue and still no help. WTF?

 

[Jessfly1]

Re: 3.0 OMC ignition problem

update...after going through everything AGAIN I am still stumped. I have checked everything mechanical i.e. distributor gear/shaft, rotor, and cap. I also pulled the valve cover just to make sure the valves were opening and closing properly. I put another set of plugs and wires on and the problem is still there. It seems the only thing left is to start throwing parts at it and hope for the best. Does anyone know where i can get a pertronix unit for my 3.0?

 

[Jessfly1]

Re: 3.0 OMC ignition problem

Ok guys, I just replaced the EST (ECU) module on the distributor and still no help. I guess the next thing is the distributor.

 

[bruceb58]

Re: 3.0 OMC ignition problem

Why not get the proper manual and go through the trouble shooting procedure rather than throwing parts at this?

 

[Don S]

Re: 3.0 OMC ignition problem

Make sure you didn't mix up #1 and 2 plug wires and have them backwards.

 

[Jessfly1]

Re: 3.0 OMC ignition problem

Why not get the proper manual and go through the trouble shooting procedure rather than throwing parts at this?

I have a clymers manual and from what I have read there are no other trouble shooting procedures other than voltage tests coming from the coil to the distributor and that checks good. Also, I have checked and rechecked the firing order to plug orientation and that is all good. I even swapped #1 and 2 plug wires because I am still scratching my head and nothing. Does anyone know where the rotor should be positioned when #1 is at TDC? My manual doesnt tell me where it should be but from previous motors I have built it is always pointing to the #1 cylinder.

 

[CobiaXL]

Re: 3.0 OMC ignition problem

I have a clymers manual and from what I have read there are no other trouble shooting procedures other than voltage tests coming from the coil to the distributor and that checks good. Also, I have checked and rechecked the firing order to plug orientation and that is all good. I even swapped #1 and 2 plug wires because I am still scratching my head and nothing. Does anyone know where the rotor should be positioned when #1 is at TDC? My manual doesnt tell me where it should be but from previous motors I have built it is always pointing to the #1 cylinder.

#1 piston should be up to top,crankshaft mark should point to 0 and rotor will point to #1 plug.Sounds if u have #1 marked wrong on cap or have firing order wrong,check all again and have a buddy check too,4 eyes are always better then 2.good luck

 

[bruceb58]

Re: 3.0 OMC ignition problem

I have a clymers manual.

You need the OMC manual.

 

[Jessfly1]

Re: 3.0 OMC ignition problem

Ok guys update... I just put a all new parts on including a new distributor, coil, plug wires, rotor and cap and the thing is still only running on 3 and 4. I went through the gamut of checks and balances again and im still having the same issue. It ran great for maybe 5-10 seconds then it went to $#!+. The crank to valve-train ratio seems correct. I put it to #1 TDC and checked intake and exhaust valves (with the valve cover off) and they are both shut. I did this through the firing order (1,3,4,2) and all seems fine. All the valves seem to be opening and closing like normal. Is there a problem with these motors having timing gears slip or sheering teeth?

 

[Borchik]

Re: 3.0 OMC ignition problem

Id like to see what the plugs look like after you run it for a minute. id be curious to see if they are wet or dry...

 

[Don S]

Re: 3.0 OMC ignition problem

Have you done a compression check?

 

[Jessfly1]

Re: 3.0 OMC ignition problem

Id like to see what the plugs look like after you run it for a minute. id be curious to see if they are wet or dry...

3 and 4 are carbon fouled because of the carb.1 and 2 are wet with fuel every time I pull them. I also know its not firing on those two because the plugs are a lot cooler temperature wise then 3 and 4. Yes I have done numerous compression checks and its about 150 across the board.

 

[Jessfly1]

Re: 3.0 OMC ignition problem

Ok from the top... I am still having the same issue of the motor only running on 3 and 4. this is a 1991 3.0 OMC cobra. This is not a point system it is electronic. I know its only running on 3 and 4 because 1. it runs like crap 2. I can pull 1 and 2 plug wires while it is running and there is no change to the way it runs 3. If i pull 3 or 4 plug wires it will die 4. When i pull 1 and 2 plugs they are fouled with fuel and cool to the touch while 3 and 4 plugs are carbon fould and much hotter to the touch. I have replaced plugs, wires, distributor, rotor, cap, and coil. I have done a half dozen compression tests and it is about 150 across the board. I have gone through the firing order numerous times (1,3,4,2) and it is all put together correctly. I have brought #1 to TDC with a compression gauge and made sure the rotor was pointing to the #1 plug. I am at a loss. Timing gears perhaps?

 

[tschmidty]

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.

 

[Don S]

Re: 3.0 OMC ignition problem

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.

 

[glennwolf]

Re: 3.0 OMC ignition problem

Get a spark tester and see if those are firing at all. Or use your timing light on each plug wire and see if you are getting spark.