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

[Crosen1971]

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

Point A is for an 8 cylinder cap/motor. The rotar is pointed at B which is #1 pin on the rotar cap.

 

[Don S]

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

It's in right then, at that point the ECU should be able to set it where it wants.
In the manual, they want it set as in position A. Which is fine for a V8, not so much for a V6.

I was typing while you was posting.

 

[Crosen1971]

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

can you confirm the map sensor should read very close to 5 volts. mine is at 3.38 with ign. on. not running. something seems a little strange with that voltage.

 

[Crosen1971]

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

so besides timing and an obvious intake leak. what else can lead to low vac at idle (600 rpm) . I eliminated the worn valve guides by putting in new valve seals(may not correct the problem but will help) . also checked for valve leakage. all good.
technology is great. when it works.

 

[Don S]

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

Nothing wrong with the technology, as long as things are tested properly using the proper diagnostic tools operated by trained professionals and following the OEM diagnostic manuals.
Then it's usually easy to find the problem and correct it.

Without a scan tool on these engines. you're just spittin' into the wind.

Reading time. https://www.dropbox.com/s/yaxe65eh3h96n3o/#36 555 Dia SBC R1 00-08.pdf

 

[Tail_Gunner]

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

What timing method did you use.... ..Ohh gonna get into some trouble with this one as to vacum leaks..i once heard if you use starting fluid around a leaky manifold things become apparent actually explosive....it see's just a micro burst of spray does the trick..not recomended

Very good manual http://boatinfo.no/lib/mercruiser/manuals/mercruiser33.html#/0

 

[Don S]

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

Link doesn't open a manual TG, wouldn't help much, it's only for the Digital Throttle and Shift models.

 

[Tail_Gunner]

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

Well dam now boatinfo is not shown manual's..Is this a EST Dist or tbolt 5..Gotta be est.

Edited to info...:focus:

 

[Don S]

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

Well dam now boat fix is not showin manual's..Is this a EST Dist or tbolt 5..Gotta be est.

Neither, it has the Delco HVS (High Voltage Switch).

And it's not boat fix, it's boatinfo.

 

[Crosen1971]

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

I used propane as well as carb cleaner and then I took off the intake and searched the belly for cracks. Etc. then a fresh install with new plastic type intake gaskets. Same result. I just went over every harness and fuse. Thebonlybthing I noticed is the large ground wire is bolted to one of the bell housing bolts. Meter said its good though. The spark is from a DEI system
It looks like I'm going to have to hook it to a puter. I just wished someone could tell me about the map voltage at ign. On.

 

[Crosen1971]

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

Oh. My timing method was lining up crank to timing chain marks and then setting to TDC compression. And setting distributor on #1 pole or small #6 on base of distributor. I tried attaching a timing light but not much luck.

 

[Fun Times]

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. Is this normal or a little low.

Actually, anything over 43 PSI would be considered to much fuel pressure and could be a sign of a problem, so an accurate fuel pressure number at all RPM is important for diagnostic purposes. Have you tried removing the vacuum hose off of the fuel pressure regulator to see if the fuel pressure goes up almost 5 psi at idle?

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.

The MAP/T sensor measures both manifold air temperature and manifold air pressure. The two measures can be seen as two separate circuits.

MAT CIRCUIT
The MAT portion of the sensor is a thermistor that controls signal voltage to the ECM. It is located at the rear of the engine in the intake manifold plenum. When intake air is cold, the sensor resistance is high. As the air temperature rises, resistance lowers. At normal engine operating temperature. A malfunction in the MAT will set the fault of AIR TMP CKT Hi or AIR TMP CKT Lo.

MAP CIRCUIT
The MAP portion of the sensor measures the changes in the intake manifold pressure. It is located on the intake manifold on the top of the engine. At key ON, the MAP is equal to atmospheric pressure. This information is used by the ECM as an indication of altitude and is referred to as BARO. Comparison of this BARO reading with a known good MAP sensor is a good check of a suspect sensor. The pressure changes as a result of engine load and speed change. The ECM receives this information as a signal voltage that will vary from about 1.0-2.0 volts at idle to about 4.0-5.0 volts at WOT. A malfunction in the MAP sensor circuit could set the fault of MAP Sensor Input HI, or MAP Sensor Input Lo.

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??

May sound kind of dumb here, but just in case, what spark plugs did you install? Plug number ?

Hopefully Spark plug (AC 41-993) or NGK ITR4A15

 

[Crosen1971]

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

Ok. Just to confirm. The fuel pressure is about 43 psi. When I unplug the vac from the regulator it jumps up about 3 psi. I assume it not 5 due to the lack of vacuum. Yes, the plugs are the AC ones. I am going to do another leak down test in the port side head. After idle and unplugging the spark plug wires one at at a time. The idling which is very uneven right now did not faulter a who lot. Even know I have equal compression. Perhaps I have a bad valve. Or many.

 

[Tail_Gunner]

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

Whoa first time ive looked at merc's 555 no adjustment after the fact. So distributor install and the crank sensor's would be critical. It seems your need a diag comp to get a actual read on where the timing is. Merc has a tight lid on there system i cannot even find the reference signal to the maf sensor. It would be prudent to find a skilled merc tech at this point in the light there is no public info as to how it function's

 

[Crosen1971]

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

Yes, I am beginning to think that. I almost have my hands on another 4.3. It's a Volvo but paint is cheap. 160 hrs with low oil pressure. So a bad pump or cylinder. I have had the one I have in out many times so one more wont make a difference. Just swap the intake and away I go. I know a scan will most likely find the problem. I'm just a huge DIY guy and want to do everything possible until the last resort. It's a good thing I have a lot of patience. Besides the erratic idling and stalling after coming off throttle the motor runs very strong. My buddy said just put up with it for now and play with it in the winter which are very long here in sask.
thanks for all your help.

 

[Crosen1971]

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

Update with fantastic results. All this crap[ for a $39 part. I received the boat from an auction house being complete or what I thought was complete, with a froze motor. when I go the boat only one neutral safety switch was on the motor. even know there were two plugs I thought nothing of it. it ran so I assumed it only had one. apparently the one one the top of the linkage is pretty important. I went down to the boat shop today and they had the identical motor on display. I went in for a map/t sensor. the owner lent me one to try and that obviously did nothing. I then noticed to screw holes ( where the neutral switch) that were very shiny on my boat. So I went down to the boat shop again and borrowed it. The owner did not think it would do anything as it would just be an open/close switch. Not the case, apparently this little switch advances the timing for some reason. I think it tricks it into the boat is in gear. They said they scanned it and no codes came up, just came up with low vacuum and timing issue/late. So I guess after countless hours and the boat shop almist pulling the motor out to check/change timing, it runs perfect. A $39 part could have cost thousands in searching for the problem.
thanks again to all on here. I have learned a lot about the mercruiser and with people like you around , we keep a lot of boats out of shops for minor issues.