Help! Engine popping! 4.3l merc i/o

[bluewaterboater]

I've been chasing a problem for 2 years or so now, see my past threads. It's been frustrating and costly. Thought it was fixed again recently at local marina but last night its back.

Here is the basics:

- i have a 1999 Sea Ray 190BR with a 4.3l engine EFI throttle body.
- at about 30-34mph it starts to pop but it is intermitant and doesn't happen all the time. Even out of the hole sometimes it pops or hesitates.
- Lately its starting to back fire or make a noise like a "fart" in the engine compartment too.
- just all around not performing the way it should.
- mechanic

I have had it looked at by 2 different marinas now. The one place has one mechanic and the other has three that have been in the business all their lives. When I had it in recently they replaced the ignition control module and they thought they got it but last night about 20 minutes into a cruise it started running badly again.
I have had the fuel system cleaned, fuel/water separator changed twice, plugs changed, wires changed, compression checked, cap and rotor changed, Ingition control module changed, fuel pump checked, tach checked.... and the list goes on.....
The last mechanics said with my 21p or 23p prop they can hit my rev limitor at high speeds but that my tach was working properly - this surprised me because last night again my tach goes wacky even when i'm not revving too high. I don't know if this has anything to do with the problem since they have run my boat without the tach as well. my computer shows no faults.

It seems the more diagnostics that are done and the more work i have done to it the worst it runs.

Can anyone help with suggestions or has anyone had this problem before?

Thanks!

 

[Bt Doctur]

I`ll take a guess and say to check the even numbered plugs 2,4,6 to see the color. Betting #6 will be white. a injector running lean
Only other reason I can think of is a weak/broken valve spring . A burned valve seat wont go away. This can easily be checked by tapping on the rocker arm.
A bad spring will have a softer thud and you may even be able to push the valve by hand.

 

[bluewaterboater]

Thanks Bt Doctur! You had mentioned that on my original post of this problem in June of 2012 and we had checked and all seemed fine.

 

[Volphin]

A lifter is failing, or your camshaft is worn. These are roller lifters with a high angle of attack... they don't fail often, but when they do, it drives people nuts.

 

[Volphin]

While at it, check for bent push rods.

 

[bluewaterboater]

While at it, check for bent push rods.

i'm not a mechanic so please excuse me if my questions sound ignorant. Can you test for this or do you have to rip the engine apart? we had done a compression check in the past and it was all good.

 

[bluewaterboater]

After 2 years of frustrations and a couple thousand dollars I found the problem!!! After searching the Iboats Forums I stumbled across a story that sounded the same as mine. After water testing my boat multiple times with and without the shift interrupter hooked up there was a significant difference in performance. I changed out the shift interrupter and wouldn't you know it, fixed!! My shift interrupter was working but apparently it was messing up and stopping the spark intermittently while driving. This would cause the popping sound, poor performance and make my tach jump all over the place. We had the boat out all day yesterday and it didn't miss a beat.

I had two places do work on the boat, 5 mechanics between them, over 2 seasons, and they were not able to find and fix what should have been a $40 problem! Thanks Iboats for all your valuable posts and information!!

 

[MikDee]

OMG! Who'd have known? A simple overlooked item, that should have no effect whatsoever? Giving such havoc! Now that appears to be another issue to check out? Don't know how you found it, but thanks for the feedback!