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Muffler delete cause high idle?


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To make a long story short i purchased a 1996 malibu sunsetter vlx at the end of season last year, took it out once and it was smooth as butter. Same for this year 2 more times. Third time out i blew the large diameter J-hose and the a hole in the back of the large fiberglass muffler. I replaced all of the hoses on the motor and fabbed up some some elbows out of aluminum pipe and tossed the muffler which appeared to be patched several times already. Now it seems i have a high idle around 1000rpms. I also notice a stronger smell of gas, and the back of my boat turns black and suit after running a day on the water. Ive looked for vacuum leaks and found none. Could the muffler delete and lack of back pressure cause my high idle and rich condition? Any help would be appreciated! thanks!

Thing ive replaced since- 

-spark plugs (which turn black dirty again after 10 min of running on hose)

-IAC sensor

-TPS sensor

-MAF sensor

-all of the water hoses

-water impeller

-New exhaust manifolds and elbows/hose/piping

- engine temp sensor

-thermostat

-changed all fluids including transmission

-transmission cooler hoses

-

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8 hours ago, Cable418 said:

To make a long story short i purchased a 1996 malibu sunsetter vlx at the end of season last year, took it out once and it was smooth as butter. Same for this year 2 more times. Third time out i blew the large diameter J-hose and the a hole in the back of the large fiberglass muffler. I replaced all of the hoses on the motor and fabbed up some some elbows out of aluminum pipe and tossed the muffler which appeared to be patched several times already. Now it seems i have a high idle around 1000rpms. I also notice a stronger smell of gas, and the back of my boat turns black and suit after running a day on the water. Ive looked for vacuum leaks and found none. Could the muffler delete and lack of back pressure cause my high idle and rich condition? Any help would be appreciated! thanks!

Thing ive replaced since- 

-spark plugs (which turn black dirty again after 10 min of running on hose)

-IAC sensor

-TPS sensor

-MAF sensor

-all of the water hoses

-water impeller

-New exhaust manifolds and elbows/hose/piping

- engine temp sensor

-thermostat

-changed all fluids including transmission

-transmission cooler hoses

-

Does your engine really have a MAF sensor?  Manifold vacuum maybe, but not mass air flow.  Anyway, from the parts list, you have an injected engine.

Have you cleaned the throttle body?  Grab a can of spray cleaner and have at it, especially the edge of the butterfly where it contacts the throat.  Open the throttle to make sure you can get everything clean.

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High idle would be possibly caused by an air leak like you said, but it'd also trigger a lean, not a rich condition.  How do the plugs look?

Are you sure you didn't ruin your throttle cable and somehow have the throttle body not quite returning to the idle set screw?

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10 hours ago, justgary said:

Does your engine really have a MAF sensor? 

No MAF sensor on that engine, just MAP.

I have the muffler delete on mine with none of these symptoms.

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Thanks for the replies, i  am new here and i cant figure out how to reply to individuals. Sorry the MAP sensor (manifold absolue pressure) was replaced. Not MAF 

I have cleaned the throttle body several times and the butterflies. I have adjusted the throttle cable to make sure its pulling tight on the linkage keeping the butterfly closed.

The plugs are very black and gummy. Event the new ones were black and gummy after a few minutes on the hose. i gapped them to spec. 

The muffler was deleted because it had a i giant hole in it and it was patched several times already. A new one is 400-500$. i just spent 850$ on exhaust manifolds and risers so i was trying to save some coin. Not to mention all of the sensors and hoses. 

I checked the fuel pressure which was 41psi at keyup. It was about 41psi at idle. And it held about 43psi after i shut it off and left the guage on it for about 20 min. Should the pressure regulator at the end of line release the fuel after shutoff? 

I should have mentioned the boat has the monsoon 320 5.7 throttle body fuel injection. I should also mention that it runs out perfectly fine out on the water aside from the high idle.

Thanks for the trouble shooting help everyone!

 

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2 hours ago, electricjohn said:

Why would anybody delete their mufflers?

Frees up a great deal of space in the engine bay, making impeller changes and other repairs a snap.

With the addition of the FAE, it made for a quieter ride and less exhaust at the back of the boat.

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4 hours ago, Cable418 said:

 I have adjusted the throttle cable to make sure its pulling tight on the linkage keeping the butterfly closed.

Are you sure that it isn't too tight?

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Yes it freed up a lot of room to work on the front of the engine. 
 
No I am not sure if the cable is too tight. It is definitely tighter than it was as the throttle lever isn’t as smooth. But if I let some slack out of the cable the butterfly opens a little bit and the idle goes from 1000 to 1100-1200. I could work on the linkage a little more I suppose and try to let some tension off of the cable to make it smoother But either way it’s idling high with the butterfly all the way shut now. When I got the boat the throttle lever was butter and the idle was low. 

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10 hours ago, electricjohn said:

Why would anybody delete their mufflers?

Have a FAE...muffler does nothing but take up space and rob power once you install one.  Some say the delete makes it quieter but I didn't notice a difference, though a buddy of mine thought it did.

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18 hours ago, Cable418 said:

Yes it freed up a lot of room to work on the front of the engine. 
 
No I am not sure if the cable is too tight. It is definitely tighter than it was as the throttle lever isn’t as smooth. But if I let some slack out of the cable the butterfly opens a little bit and the idle goes from 1000 to 1100-1200. I could work on the linkage a little more I suppose and try to let some tension off of the cable to make it smoother But either way it’s idling high with the butterfly all the way shut now. When I got the boat the throttle lever was butter and the idle was low. 

I have not seen a throttle body injected engine before, so I don't know where it is, but it will have an idle set screw on the housing near where the throttle cable attaches.  On the newer MPI engines, the set screw is a T25 that is almost flush to the casting.  Try turning it out just a touch to see if your idle will come down.  It might be a good idea to remember how much you turn it so that you can put it back if you need to....

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On 6/19/2020 at 10:35 AM, Cable418 said:

Thanks for the replies, i  am new here and i cant figure out how to reply to individuals. Sorry the MAP sensor (manifold absolue pressure) was replaced. Not MAF 

I have cleaned the throttle body several times and the butterflies. I have adjusted the throttle cable to make sure its pulling tight on the linkage keeping the butterfly closed.

The plugs are very black and gummy. Event the new ones were black and gummy after a few minutes on the hose. i gapped them to spec. 

The muffler was deleted because it had a i giant hole in it and it was patched several times already. A new one is 400-500$. i just spent 850$ on exhaust manifolds and risers so i was trying to save some coin. Not to mention all of the sensors and hoses. 

I checked the fuel pressure which was 41psi at keyup. It was about 41psi at idle. And it held about 43psi after i shut it off and left the guage on it for about 20 min. Should the pressure regulator at the end of line release the fuel after shutoff? 

I should have mentioned the boat has the monsoon 320 5.7 throttle body fuel injection. I should also mention that it runs out perfectly fine out on the water aside from the high idle.

Thanks for the trouble shooting help everyone!

 

If you disconnect the throttle cable from the engine and start the boat, will it idle lower (normal) ?

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The boat idles a little higher with the cable disconnected because it doesn’t pull the butterfly all the way shut tight. About 200rpms higher

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1 hour ago, Cable418 said:

The boat idles a little higher with the cable disconnected because it doesn’t pull the butterfly all the way shut tight. About 200rpms higher

Hmmmm.  What happens if you hold it against the idle stop? 

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What was the cause of the posted failure?  If that does not lead you to the reason, review each step of the changes you made to see if an answer lies there.  A simple muffler delete wont effect a 4 stroke engine idle.

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If the cable is disconnected and I pull the linkage back as if the cable were pulling back on it the idle goes back down From about 1200 to 1000. 
 

the failure happened when I blew a hole in on of the water hoses and the muffler at the same time. 
 

good new is I took the boat out this weekend. And I must have done something while adjusting the throttle cable in my yard because it was idling about 800rpms. The bad news is after a whole day on the water I have some vibration at higher speeds 😑. It’s always something... thanks for the replies. If I find a fix I’ll be sure to post about it

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After removing the partitions and climbing from one side to the other many times doing the exhaust and water hoses it would be a real Possibility I bumped the distributor. To be honest I’m decent mechanically but mainly on Newer dirt bikes, and ls engine cars. Haven’t messed with sbc engines and certainly not distributors. How hard would you have to bump one to get it off time? It has crossed my mind that the timing chain could have skipped and the engine jumped time but I’m trying to narrow down the smaller fixes before I just into the big stuff. I did get the idle down some to around 800-100 this weekend by messing with the cable and linkage some more. Planning to fiddle with it a little more and try this week 

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If you can disconnect the throttle cable from the engine, then press the throttle all the way closed with your finger and it doesn't idle at 650, something is wrong.  I'm assuming you didn't mess up the idle setting after I told you to try....

The distributor clamp should hold it in place, but if it is loose, it could turn.  Grab the cap and try to turn it.  It shouldn't budge.  If it does, check your timing.  Heck, check the timing anyway.  You may have to put the ECM into service mode to see the 10* BTDC value.

I really can't think of too many things that would dramatically increase idle RPM besides bad timing and a vacuum leak.  Check around the intake manifold and throttle body to make sure you didn't dislodge a vacuum hose or maybe crack one.  They are cheap, so if they are suspect, just change all of them.

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