5.7 Digital Ignition EFI has high idle

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PaulGMT

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Hey guys,
I have a 1998 5.7L digital ignition EFI Serial # OL025515. At idle it is consistantly at 2000 RPM... Without a DDT, and another engine that is identical in my garage, what would you recomend I do first? I have swapped TPS, IAC, MAP... I know that the engine I am robbing parts off of works because it is my other boat and use it every weekend.. Could my tach be stuck in a "start up mode" at the ECM.?? Could it be the ECT is keeping it cool and making it rev high? Any suggestions would be great.
 
Bondo

Bondo

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Re: 5.7 Digital Ignition EFI has high idle

Without a DDT, and another engine that is identical in my garage, what would you recomend I do first?
Click to expand...

Ayuh,... The Quickest, Easiest answer is Pop the motor out, 'n Plant the other 1....
 
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PaulGMT

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Re: 5.7 Digital Ignition EFI has high idle

If you dont know anything dont bother answering. Thanks!
 
Bondo

Bondo

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Re: 5.7 Digital Ignition EFI has high idle

PaulGMT said:
If you dont know anything dont bother answering. Thanks!
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Ayuh,... Sorry...

I didn't get to 35, 'n 1/2 thousand posts, sayin' Nothin'....

With the Info provided, I gave you My Opinion...




It also keeps yer question at the Top of page 1....
 
Don S

Don S

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Re: 5.7 Digital Ignition EFI has high idle

Short of getting a scanner of some sort, and a service manual and actually troubleshooting the various parts of the ignition and fuel systems along with the wiring and sensors, there just is no way of telling you in an instant what your problem is.
You can replace parts all day long and never find the problem because it's a wiring problem or an ECM problem.
 
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PaulGMT

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Re: 5.7 Digital Ignition EFI has high idle

I do have the manual and I know the ECM is not bad because it was just replaced. Just wondering if someone did have another opinion or has ran into this problem before. I will keep plugging away, but if anyone has seen this problem before then any input is good. Three dealers now have looked at this engine and cannot figure it out.. Kind of depressing!
 
Don S

Don S

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Re: 5.7 Digital Ignition EFI has high idle

Have you disconnected the throttle cable from the throttle body to see if the engine slows down? Checked for vacuum leaks? Troubleshoot the IAC?

Three dealers now have looked at this engine and cannot figure it out.. Kind of depressing!
Click to expand...

Were any of these actually Mercruiser dealers? or just boat dealer in general?
A REAL Mercruiser dealer wouldn't be stuck, he has a hotline to Merc Tech to figure out odd problems. They wouldn't just give up, or should say they shouldn't.
 
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PaulGMT

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Re: 5.7 Digital Ignition EFI has high idle

Every single dealer was Mercury, Mercruiser, Sport Jet. I cannot figure out why it is being so difficult. Must be a wire that is back by the distributor (tach signal maybe?) Would the ECT cause this problem? Running high to compensate for cold temp?
 
Don S

Don S

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Re: 5.7 Digital Ignition EFI has high idle

Would the ECT cause this problem?
Click to expand...
I doubt it, but who knows. That is why you need a scan tool. Then you can read what the senders are saying and see what is wrong, and I don't mean just look for codes, The ECT is a perfect example, it may tell the ECM that the engine is 10?F and the engine is actually 180?, but that isn't a fault that would set a code of any kind.
You need the tools of the trade to troubleshoot and work on EFI.
http://www.rinda.com/marine/mtspec.htm#techmate
 
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