Running out of ideas

[shaps1001]

I've made a few other posts about this, but it seemed like a good time to start over. I have a 1993 OMC Cobra 5.0 EFI that is not reaching WOT RPM. It tops out at about 3800 with the trim all the way down. With trim adjustment I can get 3900 and 40mph on a GPS. The only other symptom is a minor surge at idle (approx 150 rpm)

Recently I removed flappers lodged in the exhaust which significantly improved acceleration but only helped WOT RPM a little (change from 3500-3800). I checked the timing, and reset it to 5 deg BTDC. The TPS and MAP sensor both check out OK, and the throttle cable is adjusted per the instructions in the manual, but it does to seem to be restricted in the last tiny bit of travel.

The fuel pressure was checked a long time ago, but it might be worth another look. I'm planning on cleaning the flame arrestor which does have some belt dust on it. I also found a vaccum clamp missing on the VST so I'll be replacing that. I'm not particularly optimistic on either of these fixing it, so what else should I try?

edit: I should add that it throws a code 13 on the KOER test with a scan tool. I'm going to reset the idle using the correct procedure, but I don't think this has anything to do with my WOT RPM issue.

 

[mcleaves]

Re: Running out of ideas

I have not read any of your other posts so forgive me if I ask three simple questions

What size/weight boat
What size prop
Did it ever hit WOT with your present configuration?

 

[shaps1001]

Re: Running out of ideas

The boat is a Chris Craft Concept 217, I believe it weighs 3500lbs. I don't know the prop size. I've had it as high as 4200 RPM with the current configuration several years ago, it may go higher than that.

 

[mcleaves]

Re: Running out of ideas

Are you setting the timing in base timing mode with the SPOUT removed? Are you sure your timing marks are correct? The balancer on those spin and slip. I just had to have mine serviced. If you don't know how to check the timing marks we can walk you through it.

 

[mcleaves]

Re: Running out of ideas

Tell me how you obtained the code BTW.

 

[shaps1001]

Re: Running out of ideas

Thanks for your help mcleaves. I did have the spout out when setting the timing, but I did not verify if the timing marks were correct. I used a code reader to pull the codes using the KOER test. The first time I actually got a code 21 for the coolant temp sensor in addition to the code 13. After doing some reading I realized that the code reader was set for the wrong engine. After fixing that I reran the test and only got the code 21. I tested the sensor with an ohmmeter and got an open circuit so I replaced it. Now it doesn't throw any codes but I'm still not reaching WOT RPMs.

I'm inclined the think that the timing is not the problem, but rather something fuel related or maybe a vacuum leak. Thoughts?

 

[shaps1001]

Re: Running out of ideas

I believe I remembered the prop size, 14.5x19. I also remember that when I achieved 4200rpm in the past was before we installed the bimini top. Obviously I'm running with it closed. Could that knock 300rpm off the top? Could the boat just be over propped?

 

[Lou C]

Re: Running out of ideas

Boat could be over propped, my 88 4.3 had a 14.5x19 on it when I got it (9 years ago), and it never hit the max spec rpm of 4600-4800...I put a 15x17 on it and it easily hits peak rpm now. I did some reading on the Four Winns website and what I found was that the 200 Horizons with the V-6 were supposed to have the 15x17, who knows how long mine had the wrong prop on it....

 

[jerryjerry05]

Re: Running out of ideas

Things like saturated(water)foam,dirty bottom,too much junk and carrying too many people.
The wrong prop.
Do a compression test.Install a tiny tach to see if it's actually reading right.

 

[mcleaves]

Re: Running out of ideas

I believe I remembered the prop size, 14.5x19. I also remember that when I achieved 4200rpm in the past was before we installed the bimini top. Obviously I'm running with it closed. Could that knock 300rpm off the top? Could the boat just be over propped?

When I asked about running the same setup these are some of the things I meant. Any changes to the boat in terms of weight or resistance will add up. Is a bimini gonna cost you 300 RPM? Not typically, but it, with an extra person and a cooler might. Think hard about the boat, not just the engine. Saturation can certainly be an issue. Poor bottom paint is a big culprit. Growth on the bottom is often an issue. You shouldn't be over-propped if it's the same prop you were using before, UNLESS things like I just mentioned have changed. Then you'll need to run a prop appropriate for that conifg. I have two set's of props. One for running fast and light over long distances (offshore fishing on good days) and one for hosting a group of people. You shouldn't be overpropped if it's the same prop you were using before, UNLESS things like I just mentioned have changed. Then you'll need to run a prop appropriate for that conifg. I have two set's of props. One for running fast and light over long distances (offshore fishing on good days) and one for hosting a group of people.

 

[shaps1001]

Re: Running out of ideas

When I asked about running the same setup these are some of the things I meant. Any changes to the boat in terms of weight or resistance will add up. Is a bimini gonna cost you 300 RPM? Not typically, but it, with an extra person and a cooler might. Think hard about the boat, not just the engine. Saturation can certainly be an issue. Poor bottom paint is a big culprit. Growth on the bottom is often an issue. You shouldn't be over-propped if it's the same prop you were using before, UNLESS things like I just mentioned have changed. Then you'll need to run a prop appropriate for that conifg. I have two set's of props. One for running fast and light over long distances (offshore fishing on good days) and one for hosting a group of people. You shouldn't be overpropped if it's the same prop you were using before, UNLESS things like I just mentioned have changed. Then you'll need to run a prop appropriate for that conifg. I have two set's of props. One for running fast and light over long distances (offshore fishing on good days) and one for hosting a group of people.

I completely forgot about the bimini top until a relative suggested it as the cause. That was the only change. I have two identical model props so I may have been running the other one when I hit 4200rpm. Since they are both old its possible there are minor differences from dings and the extra rpm was just slip.

While doing my recent testing I have been the only person in the boat with about 1/3 of tank so it's pretty much a best case scenario in terms of load. The bottom is dirty, but it's a fresh water boat so there's nothing really growing on it.

I think the engine is probably OK at this point. All the little fixes I have done eliminated the idle surge and there are no more codes. I think I was probably on the edge of being under propped before, and now the bimini top just pushed me over the top. The 4200 I was getting before is still the lower limit of the WOT spec for the motor.

I've been reading prop section of the forum and I realized that even though the boat is a 5.0 it's only 200hp so it's not really that much motor for a 22' boat. I figure with a decent 15x17 prop I will get 42-43 mph with the correct RPM. Thanks for your help.

 

[dbaran]

Re: Running out of ideas

I am having this same issue with my 5.8L EFI on a 1994 21ft Fourwinns.

I'm still working on the coolant sensor being bad. If that's not the concern, then I am going to have to check the timing and balance. I'm suspecting something there, because it seemed like there was something out of balance and an unusual vibration coming from the engine on our last day on the lake.

The knock sensor would also be a suspect that would retard your WOT rpm's. It could also be defective. They are very sensitive.

I am at the same point you are at here with my 5.8L EFI. This is a good post, so keep us updated.


Thanks.

Dave