Merc 5.7 ignition probs

[str8down]

Try to keep it short. My coil was arching on itself, so I decided to replace all my ignition equip. I replaced the coil, plugs wires, plugs, distributor and cap. Now it runs and idles great, but at ~ 2800-3000 rpm it bogs and has no power till the boat finally gets on plane then it goes on up to about 3800 rpms. It used to run at 4k-4.2k rpms before changing all this stuff. I have double and tripple verified the plug wires aren't mixed up. What else could be going on here? Could I have a bad new plug, or bad new plug wire? Bad new coil?

 

[rbezdon]

Re: Merc 5.7 ignition probs

What kind of ignition, point or electroinic? Did you set timing and dwell (if needed)?? Did you change fuel filters and check fuel pump pressure?? It may not be ignition, it may be fuel. Seems the 4K-4.2K was a little low before the change and an indication of a problem before as well so it is definately possible you have a fuel problam also.

 

[str8down]

Re: Merc 5.7 ignition probs

It's a points ignition. I changed the distributor cap and rotor. I didn't mess with timing, so I would assume it would be the same as it was before. The manual says 4.2k-4.6k is optimal WOT. But the main thing is, it didn't do this before I did the swap on those components. I plan to change the fuel filter next, just as a precaution, but that would be some crazy bad luck for a fuel issue to arise, immediately after changing the ignition.

 

[rbezdon]

Re: Merc 5.7 ignition probs

I think you had a fuel issue before too. Unless you are over propped, the 400 to 4200 is below the WOT range. It just may be time is making the thing worse. If you have some crud in the talk clogging the pickup screen or antisiphon for example, this will get worse over time. I am just saying, chacking the fuel system will take an hour and well worth the time with the issue you are having. I saw a post about 2 weeks ago where a guy had the same issue as you. He would up cleaning or replacing the pickup tbe and antisiphon and he thought he put in a larger engine because the performance was so much better then before when he though the below WOT rpms was normal. Check this thread and look at the last few postings.<br /><br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=24;t=013116#000009

 

[str8down]

Re: Merc 5.7 ignition probs

Well, I am going to the store right now to get a fuel filter, as that had occured to me before. It obviously can't hurt to replace it. But I live on the water and litterally, came home with boat running fine, put it on he lift, replaced components that I listed, then put it back in the water (same day even) went out and got the results I listed. So, even though, I don't doubt (since I just bought this boat used) that the fuel filter prob needs replacing, I doubt it would manifest itself that quickly and at the exact time that I made modifications. Hopefully I am wrong, and the filter will fix it, but can anyone think of anything that might cause said behavior, if the fuel filter/pump isn't the issue?

 

[rbezdon]

Re: Merc 5.7 ignition probs

my point was check the pick up tube and anti siphon too. Ultimately, this was the issue in the thread I posted above.

 

[str8down]

Re: Merc 5.7 ignition probs

Ok, I replaced the fuel filter and took apart the antisiphon, and pulled the pickup tube. Everything is squeeky clean. The problem still exists. Any suggestions? Like I said, I am leaning towards something ignition related, since I replaced that stuff and it started happening. But the only fuel thing left really is the fuel pump. Do these sound like symptoms of a faulty fuel pump?

 

[rbezdon]

Re: Merc 5.7 ignition probs

I think they could fit a bad pump. If you have a vacuum guage it usually has a pressure sense good for checking the fuel pressure. It is not too hard. In my opinion your problems sound more fuel than ignition but dont forget I am here and you are there and that is a big difference. Tough to help troubleshoot through a computer screen. <br /><br />By the way, when you changed the ignition, id you change the points and set the dwell?? I didn't see it in the posts above.

 

[Fishermark]

Re: Merc 5.7 ignition probs

I didn't mess with timing, so I would assume it would be the same as it was before.

Your point gap will affect the timing. I don't know if that is your problem or not, but you always need to check your timing after changing points. And, as was mentioned already - it is more accurate to set your points with a dwell meter than with feeler gauges.<br /><br />Did you also replace the condensor? I had a similiar problem years ago with a vehicle that had points. It idled and started and ran great until it got much beyond 1500 rpms, then it ran like a dog. It turned out to be a bad condensor.

 

[str8down]

Re: Merc 5.7 ignition probs

I am pretty sure there is no condensor. As for the point gap, I'm not sure what you mean. The points are fixed to the rotor cap. Maybe I am missing something here. The engine is a 1997 Merc 5.7 with 2 barrel carb. I didn't think you could adjust the point gap.

 

[Fishermark]

Re: Merc 5.7 ignition probs

In the words of a famous man, "What we have here is a failure to communicate." <br /><br />It sounds like you have electronic ignition, not a points ignition as you mentioned. Here is a picture of a distributor with points:<br />

<br /><br />The item marked "B" is the points, the item marked "F" is the condensor.<br /><br />When you say "the points are fixed on the rotor cap," well.... no. The rotor cap is different from the points.<br /><br />By the way, I "borrowed" the above image from a page which may help you understand your ignition system a little better, here is the link: "How stuff works"

 

[str8down]

Re: Merc 5.7 ignition probs

Yeah, my distributor looks nothing like tha. It has a rotor that spins an archs to each plug terminal. I thought the underside of the plug terminals that the rotor archs to, were call points. I looked at your lin to How Stuff Works, and my ignition is like the one on top. Sorry for the miscommunication. So now where do we go?

 

[Fishermark]

Re: Merc 5.7 ignition probs

To check for a bad plug or wire, with the engine running remove one spark plug cable at a time and see if the engine begins to miss. If you remove one and there is no change, then you either have a bad wire or bad spark plug.

 

[str8down]

Re: Merc 5.7 ignition probs

Would it show more at like 600 rpms or like 1500 rpms? Because it is tough to tell with a V8.

 

[Fishermark]

Re: Merc 5.7 ignition probs

Do it at whatever your idle speed is. If it is already running so rough that you can't tell, then I'm not sure what to suggest next.

 

[str8down]

Re: Merc 5.7 ignition probs

No it runs fine until 2800-3000 rpms. Then it bogs and sounds like it's running on fewer cylinders. Until the load comes off by the boat getting on plane, then you can actually hear the cylinders kicking in.

 

[rbezdon]

Re: Merc 5.7 ignition probs

I dont know what drive you have but have you checked to see if the ESA (OMC drive interrupt switch) is getting activated. I did this by just disconnecting the switches by pulling out the connector in the wire harness going to the shift mounting bracket. While the ESA i disconnected you'll have to be careful as the boat will be hard to get out of gear but for one run it is not a big deal, use the middle of the lake. After the run slow to idle and shut off the engine in gear, then shift to neutral. Then plug the ESA back in. If the problem was gone when disconnected you know the issue is adjusting the shift cables so there is less drag and the ESA is not activated by moving the throttle.

 

[vipzach]

Re: Merc 5.7 ignition probs

vatter41, he has a merc 5.7, so he has no OMC crap on his boat. <br />srt8down, you have a cap and rotor, not points, you don't need to worry about setting dwell timing. You do need to make sure that your timing is set correctly though. I know you said you just put the new stuff on there, but you could have bumped the dist. and knocked the timing off just a little. If timing is correct, then maybe you got a bad part when you bought all the new stuff, maybe a weak coil.

 

[str8down]

Re: Merc 5.7 ignition probs

I don't know how to set timing, but I am very mechanical. Can anyone easily tell me how?

 

[str8down]

Re: Merc 5.7 ignition probs

Think it could be the accelerator pump?