HELP Mercury 5.7 willnot idle

alldodge

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I have a 04 Tahoe Q5 5.7 It has been sitting for about 4 or 5 years with about 100 hours on it. I started digging into it replacing all sorts of things that were not working. starter, battery, trim motor, solenoids, impeller and trim switch. I got it to the point of firing it up but it will not idle. I rebuilt the carb and it still the same. the motor seem to run great when you give it some throttle. I can get it to run at about 1100 to 1200 RPM's but any less it dies. It seem to be dumping to much fuel into the carb and it floods itself out at low RPM's. I have had it idling at 600 to 800 a few times but only for about one minute and it will idle up and die after that. I took the fuel pump and fuel filter off and checked them seems to working fine. not sure what to do please help.

Need to try that rebuild again. Your carb at no time should be dumping or pouring gas into the engine. This is way you can only keep it running if you rev it up. Either your float is sinking, float level is set incorrectly, needle valve is not seating and shutting off the fuel into the bowl when bowl is full. Pull the carb back apart and recheck settings and if it is clean.

Also you did clean/check fuel lines going to carb and replace filters?

To get more input on your issue this should be posted in the Mercruiser I/O section (or other I/O section if it is something else), this is for outboards.
 
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JBlow

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I have a 04 Tahoe Q5 5.7 It has been sitting for about 4 or 5 years with about 100 hours on it. I started digging into it replacing all sorts of things that were not working. starter, battery, trim motor, solenoids, impeller and trim switch. I got it to the point of firing it up but it will not idle. I rebuilt the carb and it still the same. the motor seem to run great when you give it some throttle. I can get it to run at about 1100 to 1200 RPM's but any less it dies. It seem to be dumping to much fuel into the carb and it floods itself out at low RPM's. I have had it idling at 600 to 800 a few times but only for about one minute and it will idle up and die after that. I took the fuel pump and fuel filter off and checked them seems to working fine filter looked brand new. I have taken the carb off apart and checked everything so many times I could rebuild it in my sleep. not sure what to do please help.
 

funk6294

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I am assuming this has the Quadrajet carb on it, correct? As mentioned it should not be dumping fuel into the motor at idle. A fuel soaked float, mis adjusted float, dirty needle seat or valve, could all cause this to happen in addition to excess fuel pressure. If this is a quadrajet carb, when you did the rebuild did you hook the clip on the foat needle through the hole or did you rest the little bend on the hole. If you looped it through that will cause you the needle to not seat. You may want to pull the carb back apart and verify everything is correct and then trouble shoot from there.
 

JBlow

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I believe its a Rochester 2 barrel. I did it the same way it was. A little pin with rubbery pointed tip then spring then pin going threw the spring then the float flap just sits on that. measurement are perfect.
 

JBlow

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I rebuilt it Friday night had it all soaking and cleaned everything very good for 2 days. its doing the exact same thing it did before I rebuilt it. It's like I didn't even touch it. the fuel pump I am giving an educated guess at around 40psi. Not sure where is suppose to be but its working.
 

achris

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Back to basics.... Compression test, leakdown test, check timing... Check spark quality..
 

JBlow

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I have done pretty much everything except ghost ride it into a bridge. :lol: but im almost at that point. I had a mechanic come look at it along with 5 to 10 guys at the boat dock. everybody is clueless. Boat mechanic said I should get a shop to rebuild the carb. :mad-new:
 

alldodge

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I have done pretty much everything except ghost ride it into a bridge. :lol: but im almost at that point. I had a mechanic come look at it along with 5 to 10 guys at the boat dock. everybody is clueless. Boat mechanic said I should get a shop to rebuild the carb. :mad-new:

Yep, it's flooding the engine
 

midcarolina

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In your first post you said it would idle at around 600-800 for a minute then would idle up and die........ that sounds like a lean idle condition. When you cleaned the carb did you use compressed air to blow out every little nook cranny and passage? If not thats what I would do.........

You can easily verify if it is either too much or too little fuel during idle........ when it starts to stumble simply squirt a little fuel in the carb, if it stays running you know it's starving during idle.
 

midcarolina

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I rebuilt it Friday night had it all soaking and cleaned everything very good for 2 days. its doing the exact same thing it did before I rebuilt it. It's like I didn't even touch it. the fuel pump I am giving an educated guess at around 40psi. Not sure where is suppose to be but its working.

I hope not.......... should be 5-7 lbs
 

JBlow

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yes it has idled at 600-800 like it should only a few times but it never last and it is getting to much fuel I watched it dumping in. I did clean it with carb cleaner let it soak for about 2 days then I blew it all out I didn't cut any corners. I work in the hose industry and pressure is something I know all about I am 100% its over 5 to 7 psi and I want say its around 40psi. I put it in a bucket of water connected the wires and it shot out about 5 ft up in the air I put my finger over it and could stop the pressure.
 

JBlow

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Just called my buddy he said its a high pressure fuel pump. Does anybody know what psi is should be at? I am looking and finding nothing.
 

alldodge

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Just called my buddy he said its a high pressure fuel pump. Does anybody know what psi is should be at? I am looking and finding nothing.

Yep, 40psi is for fuel injection and yours should be as midcarolina stated 4-7 psi. Need to get a carb fuel pump

Edit: WAIT A MINUTE. Are you calling your throttle body a carb? What is your serial number
 
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JBlow

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864943 all the low pressure fuel pumps say there for the 4.3 and the 5.0. high pressure for 5.7?
 

Bondo

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864943 all the low pressure fuel pumps say there for the 4.3 and the 5.0. high pressure for 5.7?

Ayuh,..... Welcome Aboard,... If you have a carb, you need a low pressure fuel pump, at 'bout 6psi,....

Hi-pressure is for Efi,....
 
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