RESOLVED! Tach Jumping & Boat Backfiring Under Load

H2Oski

New Member
Aug 5, 2017
6
Park City, Utah
Boat Info
1998 Sea Ray 210 Signature Bow Rider
Engines
8 cylinder Mercruiser fuel injected ~ I should know more, but I don't :(
Help! I have owned a 1998 Sea Ray 210 Signature Open Bow for about 10 years. Purchased it with 40 hours on it and it now has approximately 600 hours.

A couple of years ago it started backfiring periodically under load. The problem has become increasingly worse and is now a problem every time we take the boat out.

There is definately a connection between the tachometer and the backfiring. Under load, the tach begins jumping/bouncing around sporadically, jumping up to 5000 or 6000 rpms; however, the engine does not surge. Then the backfiring, sputtering and popping starts right after the tach begins jumping. It's extremely frustrating when trying to pull a skier up and the boat is jerking and losing power as it backfires. Once up to speed, the ride is usually normal and uneventful, until making a turn with a skier or something else that puts it under load.

We've had a lot of repairs made and tests performed that the mechanic thought would resolve the problem, but it's still as bad as ever.

The repairs made and tests performed include:
· Tach replaced
· New wires from tach to engine
· New distributor and distributor cap
· New spark plugs
· New fuel pump
· New coil
· New fuel filter
· Compression test (normal)
· Valve test (normal)

Here is a short video that shows the tach jumping. Although it's hard to hear on the video, there is backfiring and popping.


Any help/suggestions are very much appreciated!
 
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You've ruled out quite a few things. Not too sure I'd have replaced the tach though.

First places I'd look are timing and advance, and carburetor (assuming that vintage is carb and not injected). Does the problem manifest when you romp on the throttle? Possible area to look would be accelerator pump (although if it just does it when the load changes and no throttle movement I'd be less inclined to look there).
 
what do you call normal compression ? valve test....can I assume a leak down test ? plug wires replaced ?
 
You've ruled out quite a few things. Not too sure I'd have replaced the tach though.

First places I'd look are timing and advance, and carburetor (assuming that vintage is carb and not injected). Does the problem manifest when you romp on the throttle? Possible area to look would be accelerator pump (although if it just does it when the load changes and no throttle movement I'd be less inclined to look there).

Hi MJoplin,

Thank you for your reply. It is fuel injected and timing was checked. The problem does manifest the majority of the time when romping on throttle. It will occassionally do it other times, like while turning when pulling a skier, which puts the boat under load.

I'll have the accelerator pump checked into, unless you have other ideas based upon the additional information.

Thanks!
 
what do you call normal compression ? valve test....can I assume a leak down test ? plug wires replaced ?

Compression test was 140 and above and valve test was indeed a leak down test which came out normal.
 
H20,

I had the same problem as you about a year ago. I asked my SR dealer replace the plugs, wires, dist. cap and rotor - no change. Any time I tried to accelerate hard (from a stand still or going from a low speed cruise to higher cruise speeds) or go to wide open throttle, the engine backfired frequently and the tach was jumping all over the place. My SR dealer called Mercury and suggested bypassing the shift interrupt switch - the switch was the culprit. A new shift interrupt switch was installed which resolved the issue. Essentially, the old switch was interrupting the spark under power while in gear leading to the backfiring, poor performance and tach issues. FYI, I have '99 230 BR powered by a 5.7 EFI with an Alpha Drive. This may not be your issue, but its certainly worth having your mechanic check into it.
 
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Dear SeaRide,
Thank you SO MUCH! I think this may be the solution! My SR dealer was going to replace the computer as the next step, but I'm going to skip it and go straight to having the shift interrupt switch replaced, or at least bypassed and tested. I having a feeling you hit the nail on the head. Everything you described is identical to the issues I'm having.

I'll keep you posted. I see light at the end of the tunnel! ;)
 
You are welcome and good luck. Hopefully, this will be your issue as well. For what it's worth, this problem is a fairly rare occurrence according to my dealer.
 
Hi MJoplin,

Thank you for your reply. It is fuel injected and timing was checked. The problem does manifest the majority of the time when romping on throttle. It will occassionally do it other times, like while turning when pulling a skier, which puts the boat under load.

I'll have the accelerator pump checked into, unless you have other ideas based upon the additional information.

Thanks!

I looked up the engine, it is an EFI chevy 305. You don't have an accelerator pump. Those are on carbs only.

First I would re-verify the plug wires are on correctly. The firing order is 1-8-4-3-6-5-7-2 for a standard rotation small block GM. Make sure the wires are routed correctly.

Next look for vacuum leaks around the intake manifold and throttle body. Vacuum leaks cause a lean condition and would cause backfires under acceleration. It's a very common cause of what you are experiencing. One trick is to spray carb cleaner around the intake or throttle body junctions/gaskets while running. NOTE - Carb cleaner is highly flammable, be careful and have a fire extinguisher close by.

If there is a vacuum leak, you will hear the idle speed pick up from ingesting the cleaner through the leak. Look at any vacuum hoses for leaks. Check the throttle position sensor (bolted on the side of the throttle body), that could also cause it.

The fuel pumps, if too weak, could not be delivering enough fuel and creating a lean condition. Plugged fuel filters could also do that. Hope this helps and gives you some ideas where to look.
 
You are welcome and good luck. Hopefully, this will be your issue as well. For what it's worth, this problem is a fairly rare occurrence according to my dealer.
Hi SeaRide!
I don't know how I can ever thank you enough! Picked up my boat this morning from the SR dealer after having the shift interupt switch replaced (all because of your experience) and headed straight to the lake. Spent a couple hours on the lake and for the first time in 2 years there was no backfiring and no tach jumping! Even under load! We couldn't make it do it (and we tried just to confirm that it's really fixed!)! Everything worked perfect!

I hope I have the opportunity to "pay it forward" as you did and help another desperate boat owner with this same problem. I'm also happy to have educated the mechanic at the SR dealer so he now knows the fix should any one else come in with the same problem.

Again, thank you! Today was a very good day and the stress of this problem is finally over!:):):)
 
H20,

You are more than welcome. I'm glad it worked out for you. Your mechanic will be contacting you for advice from this point forward :)
 
houdini.jpg
 
Glad you fixed the problem. That sounded like a very frustrating situation. Once again one of Club Sea Rays fine members comes to the rescue!! It seems to me that they should put out some sort of technical bulletin regarding this (although rare) very frustrating situation to spare the owner all the expense of part swapping of perfectly good parts.
 
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I'm also happy to have educated the mechanic at the SR dealer so he now knows the fix should any one else come in with the same problem.

Seems like that should be the other way around. I bet the Sea Ray dealer was sad he didn't get to sell you that new computer!
 
All I can say is thank you, thank you, thank you! I have had the some problem on my 290 for a while now. I ordered the switch last week and installed this past weekend. No more problem! Cost about 40 bucks, saved me hundreds!
 
All I can say is thank you, thank you, thank you! I have had the some problem on my 290 for a while now. I ordered the switch last week and installed this past weekend. No more problem! Cost about 40 bucks, saved me hundreds!


Please post up a part number if you have it.
Thanks
 

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