Engine idling at 3000+rpm

[Lucrative]

7.4 mpi bravo gen VI

Just rebuilt top end, new head. All back together and trying to set timing and I'm showing that I'm running at 3k+ rpm idling in neutral. Any ideas?

 

[alldodge]

7.4 mpi bravo gen VI

Just rebuilt top end, new head. All back together and trying to set timing and I'm showing that I'm running at 3k+ rpm idling in neutral. Any ideas?

How about a ever so slight bit more info. Is it a carb, EFI, MPI etc, etc. Have a year and other stuff which could help us figure it out

 

[Paramedic927]

Following, I have a 2006 mercrusier 4.3L I just put a new carb in and it revving very high rpm in neutral.

 

[Bondo]

Ayuh,...... Seems to be a popular problem,...... BD explains it well,....

 

[Lucrative]

www.boats. net/parts/search/MercuryMarine/0L609594/2705/parts.html

That is my engine. If it will let me post the link...... It's MPI as stated. Gen VI were only made from 1998 to 2000 I believe. I'm not sure of the actual year of the engine.

It seems to be idling now at around 2800 rpm. I think I need to be idling at around 1200 rpm, right? To add on, it doesn't seem like the engine is actually running at almost 3k rpm. It seems to be idling smoothly, throttle doesn't seem to be opened, it seems like the engine is at rest. If I had to slow it down enough to get from where it is now to 1200, it seems like it'd stall out, it's not like it's 100-200 rpm I'm dealing with here.

Almost seems like there's something wrong with a sensor.

 

[Lucrative]

Also, to add some more information, I tried putting the engine in base timing by doing this as was explained to me in a previous post. It brought the idle speed up, I think it's supposed to be to 1800rpm, and the weird thing is that it sounds like it's at 1800 rpm when I do this, but my gauge is showing 3200-3400rpm. For a second or two, the gauge flipped out and went down to 1200 or 1400rpm, then shot back up with no difference in how the engine was running.

 

[Bondo]

I think I need to be idling at around 1200 rpm, right?

Ayuh,.... It oughta be 650/ 700 rpms,.....

Sounds like ya need a new tach 1st,.... or verify the one ya got,.....

 

[Lucrative]

Is it possible this is caused by a connection that could have been fouled during the rebuild? Im having trouble tracing the wire from the tach gauge to whereve er it ends up. Anyone know where it goes and where a bad connection might have occured? Any way to pull my tach and see if its good by an ohms reading?

 

[Lucrative]

Ok, so problem solved. Not sure exactly why or how, but I figured "screw it, I'll just try and time it anyways" because the rpms seemed like they were actually ok even though the gauge wasn't on the same page as me. So, I put in in base timing mode and adjusted the distributor to set it to 8 degrees. When I got back up out of the engine compartment, it was reading 800rpm, no jumping around or anything. Stopped and started and it's still looking right. I guess it must have had something to do with the distributor being off? I was maybe 1/12 of a rotation off from where I shoulda been. Hope it stays this way, lol.

Also, in reference to my above post about a loose or bad connection....it seems that this might be possible if the connection to the tachometer goes to the distributor. Does it??? If so, it seems that I might have to get in there and get a more solid connection.

 

[alldodge]

Yes, the tack wire goes to the Negative side of the coil. If your distributer does not have a good ground there can be issues. Moving it during timing set may have cleared that up. Could also be you moved other wires and caused them to make a better connection. There is a bolt on the back of the engine which is used for battery ground and others, needs to be clean and tight