94 OMC 5.8 EFI "slow mode"

[jimbrodigan]

Boat is a 94 Four Winns Horizon 230 with a OMC 5.8 EFI/Cobra SX. The engine will not rev above 2500 to 2800 RPM with the drive engaged. Runs to full RPM in neutral. The engine acts like its overpropped but has been trouble free for years. Im somewhat familer with the "limp home" mode in this engine model and have checked engine cooling and found it to be ok. I pulled both computer temp sensor and temp guage wires off the sensors with no benefit. No water in fuel. Intake air not restricted. Drive turns with no binding. Thermostat ok. Anyone know more about the "limp home" mode in the 5.8 EFI system and how I may check it for codes, etc. No one in my area is familier enough with this system to be more helpful than I am on my own. I have seen several posts with the same symptoms and any help on this would be helpful to several boaters I have read about on various web sites.

 

[Ocean 22]

Re: 94 OMC 5.8 EFI "slow mode"

there are four of us on the forum that have this same issue with these engines. I have been trying to get a FIX for this problem, but it seems to be a mystery that nobody has been able to solve. It seems that it is some type of computer issue. I have not taken the boat to a dealer due to lack of funds. I am hoping that someone on the forum can lead us in the right direction.

 

[jimbrodigan]

Re: 94 OMC 5.8 EFI "slow mode"

Ok, I found a factory manual for this engine. After lots of reading and researching I am going to try a few things. 1) Check ignition advance 2) Check that the shorting bar associated with the SPOUT connector is intact. Like everyone else with this problem, I have checked sensors, etc with no bad findings. Im heading towards ignition rather than fuel. Im going to the lake today and if I come up empty handed, I have a couple recommendations from Craigslist for experienced OMC mechanics that are a couple hours away. If the mechanic(s) find the problem I will post it here.

 

[jimbrodigan]

Re: 94 OMC 5.8 EFI "slow mode"

OK, ran it at the lake today, checked timing and spout. Neither one changed the problem. Before I went to the lake, I checked the flapper valves in each exhaust side. Port side was missing and starboard side was broken but able to pivot. I removed the broken one, checked the crossover tube with a mirror and flashlight (didnt see the missing flapper valve), put the exhaust back together and hit the road. I had no change at all on the water. Checked codes and there were none. Tomorrow the boat is going to a shop in Phoenix that I have had some positive replys to my Craigslist inquiry. If I have to spend a thousand, thats whats its gonna take....the boat needs to be fixed. I will let you know what they find.

 

[fabrimacator21]

Re: 94 OMC 5.8 EFI "slow mode"

I know you don't want to hear it but to troublshoot the system you REALLY need to be able to read both the error codes and the stored codes with a diagnostic tool.

Yup... thats why they are there... otherwise you'll spend a lifetime and a fortune trying to figure out what the problem is. Just take the hit and buy a scanner. Don't know about boat motors but for cars they're only about 40 bucks.

 

[Ocean 22]

Re: 94 OMC 5.8 EFI "slow mode"

Jim, I have the same engine, and i was having the exact problem with my engine. I was finally able to fix it last weekend. The problem was in the wiring that goes to the distributor from the main engine harness. I checked the connector that connects the distributor to the main harness, and found that there was a purple wire with black stripe that had cracked insulation, and it was rubbing next to the ground wire that is next to it on the harness. I checked that ground wire, and it was not getting a proper ground. The ground wire does not have any insulation on it. on my engine it is just a bare wire. You can check that wire for a ground by using a test light connected to the battery positive. I removed the tape on part of the harness and spliced a new wire to that ground, and connected straight to an engine ground. I attached it to the bolt that holds the starter solenoid to the engine bracket. I took the boat out yesterday, and now it gets up on plane and revs up to 4500 rpm at WOT. Check this out before you spend thousands at a shop. Please keep us updated on your progress.

 

[fabrimacator21]

Re: 94 OMC 5.8 EFI "slow mode"

No need to spend thousands at a shop... just buy a scanner.

 

[jimbrodigan]

Problem Solved

Problem Solved

While waiting 2 weeks for my appt at the shop, I have continued to work on this problem. Used a Snap-On auto scanner to run the thing with no codes stored and all parameters normal. Fuel new, pressures good, compression ok, timing advance working properly.....So I checked for exhaust restrictions again. Im certain i have found the culprit. Previously, I checked the flapper valves and one was missing. In a previous post I wrote that I used a mirror and flashlight to look at the bottom of the crossover tube and couldnt see any obstruction. What I should of done was look further, as the transom bracket has a large area aft of the crossover tube entries that is not visable with a mirror from above. So I knuckled down and pulled the drive and there it was, completely blocking the entry to my exhaust bellows....the missing flapper valve lodged up tight against the transom bracket exhaust hole. I couldnt fit it up thru the crossover tube so I used a long handled needlenose pliers to twist it until it broke in half and pulled the pieces out of the hole.

Coincidently, http://www.marinemechanic.com/site/page18.html has a OMC service bulletin listed that pertained to my flapper valves making a metallic ticking noise that I had for over 2 years. I've removed both flapper valves for now pending arrival of the new updated parts per the SB.

Ocean22, I am glad you found your problem and thanks for the info.