4.3 MPI late valve timing/late ignition timing or both(poor idle)

[Crosen1971]

Hello,
I have recently swapped out a 2007 4.3 mpi on a monterey 180 ( frozen block)
It starts fine and just does not seem to idle correct. It performs flawless from idle to wide open throttle. Then when I bring it back to idle again it stalls.
I replaced the iac. New plugs. Inspected all wires. Changed out distributor and cap. New fuel filter. I was stumped so I took it into a shop. There were no alarms or codes and they diagnosed it with late valve timing or Late ignition timing or both.
I am a journeyman mechanic so the timing marks are dead on. The distributor is right on the money at #6.
So after the shops diagnosis, I advanced the ignition by one clog. Ran ****ty. I then advance the timing by one chain link. Seemed not to change anything.
So now I am grasping at straws. They shop wanted to pull the engine to do the setting but I could do it with out.
What else should I check. Oh yes I sprayed around the intake looking for a vac leak as well. Nothing. Does the computer adjust timing by itself or does this need to be done via scanner?
Any help would be appreciated.
Thanks

 

[alldodge]

Re: 4.3 MPI late valve timing/late ignition timing or both(poor idle)

The computer controls to spark curve, the curve is set by an external computer, and once set does not need to be redone. The only reason it would need to be redone is if a different type engine was installed. What is the serial number of the engine removed and what is the serial number of the engine installed?

 

[NHGuy]

Re: 4.3 MPI late valve timing/late ignition timing or both(poor idle)

Did you reconnect all the wiring as before? Did you get all the grounds connected?
It's EFI...find a shop that can read it.
AllDodge has a point, does the replacement engine have the exact same setup as the old one?
Does it use a crank sensor? Does the replacement motor have a tone wheel for the sensor to read? Just a guess, no reason, it's just something I have seen on car motors.

 

[Crosen1971]

Re: 4.3 MPI late valve timing/late ignition timing or both(poor idle)

Ok the old serial # is 1A057141. I am not sure of the new one. All I know it is a 2006 reman. Yes , both engines had the crank sensor. The heads were identical. Even the markings on the crank and cam gear are identical. They have arrows instead of dots. I just did a vac test at idle and I got a fluctuating 5-10 psi. I assume this is because of the poor idle. I am going to advance the timing by one chain link and see if this helps. As to wires, yes all are hooked up and ground is connected to bell housing. I am going to measure resistance in spark plugs and see if all are good. I did take it to a qualified boat shop and they hooked it to a computer to get me the diagnosis of late valve timing, or late ignition timing or both.

 

[Crosen1971]

Re: 4.3 MPI late valve timing/late ignition timing or both(poor idle)

Ok.
I just advanced the cam shaft one and then two links with no change to idle. Still poor. Vacuum is still in the range of 6-8 psi. At idle. 600 rpm.
How long does it take the computer to correct the timing. Immediately or does it take minutes?

 

[alldodge]

Re: 4.3 MPI late valve timing/late ignition timing or both(poor idle)

Should be manual 32
http://boatinfo.no/lib/mercruiser/manuals/mercruiser32.html#/426

The above is the service manual for your engine starting on page 427 is the troubleshooting section for rough idle. I don't think you have a timming issue it is being caused from the engines low and rough vacuum. With you low and unstable vacuum reading I'm thinking worn valve guides.

Also the computer will regulate to a steady idle the best it can immediately

 

[Crosen1971]

Re: 4.3 MPI late valve timing/late ignition timing or both(poor idle)

I'm sorry. I did not mean psi I ment in hg. So 6-8 in hg

 

[Crosen1971]

Re: 4.3 MPI late valve timing/late ignition timing or both(poor idle)

Ok. Thanks for your help. I will look into it after pulling valve covers.

 

[alldodge]

Re: 4.3 MPI late valve timing/late ignition timing or both(poor idle)

Agree I said psi as well and ment in hg. The vacuum should reading steady around 15 in hg

 

[Crosen1971]

Re: 4.3 MPI late valve timing/late ignition timing or both(poor idle)

Ok so I ripped the intake / heads off. Valve guides all good and did a leak test on valves and all good.
The one thing I noticed is that when I got the gasket set they have me thicker (plastic) intake gaskets then where in the gasket kit. Do you think this may have a difference ?? I thought maybe I could be 180 deg out in timing but then the motor would not run at all. So at idle (600 rpm)the vac fluctuates from 7-9 in. And when I idle up to 1200 rpm it jumps to 15 in and steadies.
Any other ideas??

 

[alldodge]

Re: 4.3 MPI late valve timing/late ignition timing or both(poor idle)

I'm out of ideas, most always when its a low vacuum and it bangs around constant (7-9 or so) its worn valve guides. The valve rattles just a bit in the guide just prior to making full closer. You did the inspect and found nothing so I'm out of ideas. Hope someone else can help think of something. Sorry

 

[Crosen1971]

Re: 4.3 MPI late valve timing/late ignition timing or both(poor idle)

Ok so I put a fuel gauge on it and it reads 45 psi at first ignition on and while idle.
Compression is 150 psi straight across. Is this normal or a little low. I know it's not the value but the difference in cylinders.
Input a volt gauge on map sensor is 5 volts and a reading of 3.38 volts with key on. Drops about to 2.3 at idle.
I have some new info on the history of the motor. The fellow I got it from informs me that it came from a 2006 chev truck( the cam was changed over to the mercruiser cam and brass frost plugs were installed. Also marine head gaskets were installed. I thought maybe the heads were different but the casting numbers are identical. Would there be any difference in the blocks? They look identical. I put new valve seals and still no change. I'm stumped.

 

[alldodge]

Re: 4.3 MPI late valve timing/late ignition timing or both(poor idle)

I think we need to go back to the basics because to many things don't add up. In the first post you mention timing is right on the money at #6 not #1. Timing is set by putting the engine in base timing mode, 1800 RPM, all warmed up, timimg light on #1 and set at 8 BTDC

 

[Crosen1971]

Re: 4.3 MPI late valve timing/late ignition timing or both(poor idle)

I thought I could not set the timing with an mpi . The timing marks were aligned and then the distributo was dropped in at TDC compression stroke. So this puts the timing chain sprocket mark somewhere at about 1 o'clock. Just so we are clear . The timing marks DO NOT line up when on TDC on compression stroke. Otherwise if they did, I would be 180 degrees out . The motor would not even run if so.
So will the computer set the timing if I idle up to 1800 rpm for a specific amount of time?

 

[Don S]

Re: 4.3 MPI late valve timing/late ignition timing or both(poor idle)

You can't set the timing, but when you set the distributor, you have to have the engine at #1 TDC on the compression stroke and have the distributor rotor pointing in the correct location and the distributor aimed right.
Here is a picture out of the OEM service manual #32. Is this how you aimed your rotor in relation to the distributor body?

 

[Crosen1971]

Re: 4.3 MPI late valve timing/late ignition timing or both(poor idle)

Yes, it is exactly pointing on a small 6.

 

[Tail_Gunner]

Re: 4.3 MPI late valve timing/late ignition timing or both(poor idle)

Ok so I put a fuel gauge on it and it reads 45 psi at first ignition on and while idle.
Compression is 150 psi straight across. Is this normal or a little low. I know it's not the value but the difference in cylinders.
Input a volt gauge on map sensor is 5 volts and a reading of 3.38 volts with key on. Drops about to 2.3 at idle.
I have some new info on the history of the motor. The fellow I got it from informs me that it came from a 2006 chev truck( the cam was changed over to the mercruiser cam and brass frost plugs were installed. Also marine head gaskets were installed. I thought maybe the heads were different but the casting numbers are identical. Would there be any difference in the blocks? They look identical. I put new valve seals and still no change. I'm stumped.

You need to go a bit deeper here..what intake was used and what injection rail..Marine efi uses much different componet's

GM Performance :: View topic - Vortec L31 MARINE MANIFOLD project! Q&A

 

[Don S]

Re: 4.3 MPI late valve timing/late ignition timing or both(poor idle)

Where was the 6 located, position A or B? Make sure, this is very important.

 

[Crosen1971]

Re: 4.3 MPI late valve timing/late ignition timing or both(poor idle)

I used the rail and manifold that was on the froze motor. I took the intake plenum off and inspected the intake for cracks before installing. I talked to the mechanic at the boat shop I took it to and they just put a vac gauge on it and came up with the late timing, late ignition diagnosis. The iac checked out fine.

 

[Crosen1971]

Re: 4.3 MPI late valve timing/late ignition timing or both(poor idle)

I have it pointed at "B".