4.3GXI-E Excessive fuel consumption continued....

[stouchton]

Looking for some help with my thinking. I was chasing excess fuel consumption even though engine seems to run fine. Might be a squeak bit rougher idling, but starts fine and runs fine. Here is what I have so far:

Ended up using a Techmate to pull data from engines. Boat has twins, so easy to compare. Starboard engine is using more fuel, pulse injector width is wider. I replaced the MAP sensor on that engine since manifold pressure was higher (less vacuum???), but it was not causing the issue. Data below shows the Starboard with old MAP (cold), Starboard with new MAP (hot) and Port with 21 year old MAP (hot). Port engine is all Volvo Penta original (except fuel cell). Starboard has had the IAC changed plus new fuel cell and now MAP.

So - at the moment - I think I have a vacuum leak. I tried to educate myself on MEFI4 (mine is actually MEFI-4B). Because the manifold pressure is high, I think the engine thinks it is under load so it is enrichening the mixture. If it is a vacuum leak I think there can only be 4 sources?? - throttle body gasket, intake manifold gasket, pressure regulator vacuum line and PCV line. Am I missing something else? Also - could this be something besides a vacuum leak?

Hot data was after running for 15 minutes and gauge displayed 175. Spark advance at idle was hopping all around from 2 degrees to 10 degrees. This seemed to calm down a lot as RPM's went above 1000. This was the same for both engines.

Thanks in advance for your thoughts.

​	​	​	​	​	​	​
​	Starboard​	Cold​	Starboard​	175F​	Port​	175F​
​	Old MAP​	​	New MAP​	​	Original 2004 MAP​
​	Idle​	​	IDLE​	​	IDLE​	​
RPM​	650​	​	595​	​	595​	​
Desired RPM​	643​	​	600​	​	600​	​
IAC​	34​	​	60​	​	68​	​
IAC Follower​	0​	​	0​	​	0​	​
Barometric Pressure​	30​	​	30.3​	​	29.8​	​
MAP Volts​	2.68​	​	2.88​	​	2.31​	​
Manifold Pressure​	19.8​	​	21​	​	16.4​	​
TPS Volts​	0.62​	​	0.6​	​	0.58​	​
Throttle %​	0​	​	0​	​	0​	​
Coolant Temp​	90​	​	155​	​	154​	​
Manifold Air Temp​	81​	​	116​	​	109​	​
Inj A on pulse​	3.2​	​	3.4​	​	2.2​	​
Inj B on pulse​	3.2​	​	3.4​	​	2.2​	​
Fuel Flow GPH​	0.9​	​	0.94​	​	0.62​	​
Battery Voltage​	14​	​	13.7​	​	14.1​	​
Spark Advance​	2 to 10​	​	2 to 10​	​	2 to 10​	​
Cam Retard​	65​	​	66.7​	​	66​	​
Knock Retard​	0​	​	0​	​	0​	​
Octane​	100​	​	100​	​	100​	​
Knock​	0​	​	0​	​	0​	​

 

[alldodge]

Have you checked and compared compression numbers?

Compare color of plugs

 

[muc]

Have you checked and compared compression numbers?

Compare color of plugs

"could this be something besides a vacuum leak?" -- yes

Agree with @alldodge but that's a big job. So ---
First I would compare high AND low fuel pressures on both engine while doing four runs (in the lake) up to WOT and back to idle. Now compare what the needle did engine to engine and to the specs.
Next, I'm not real familiar with Techmate so I'm not sure what it's called but a 4B should have this function and I would guess Techmate will do this.
In the water, at operating temp and in gear at about 1500-1800 RPM. do a cylinder/power balance test on both engines, compare these reading for both engines. If you have questions on how to do this test just ask. Do not perform this test on engines under NO load, the results will be invalid.
You could also swap the MAPs from engine to engine and see if the numbers change.

It is important that while comparing tests and numbers from one engine to another that you try and make sure the conditions are the same for each set of tests.

 

[muc]

And just because I'm curious.
You bought a boat with twin 4.3s
What boat?
Why?
Just curious, I try not judge.

 

[stouchton]

Have you checked and compared compression numbers?

Compare color of plugs

I went down last week to do this, and my brand new tool set on the boat has a 5/8" spark plug socket too thick to fit under manifold! Will try again next week with thinner socket.

 

[stouchton]

"could this be something besides a vacuum leak?" -- yes

Agree with @alldodge but that's a big job. So ---
First I would compare high AND low fuel pressures on both engine while doing four runs (in the lake) up to WOT and back to idle. Now compare what the needle did engine to engine and to the specs.
Next, I'm not real familiar with Techmate so I'm not sure what it's called but a 4B should have this function and I would guess Techmate will do this.
In the water, at operating temp and in gear at about 1500-1800 RPM. do a cylinder/power balance test on both engines, compare these reading for both engines. If you have questions on how to do this test just ask. Do not perform this test on engines under NO load, the results will be invalid.
You could also swap the MAPs from engine to engine and see if the numbers change.

It is important that while comparing tests and numbers from one engine to another that you try and make sure the conditions are the same for each set of tests.

Thanks - I will research the ability to perform the balance test. I have not poked around with the Techmate too much yet. Fuel pressure test should be easy. I understand the need to be loaded and keeping the conditions same.

 

[stouchton]

And just because I'm curious.
You bought a boat with twin 4.3s
What boat?
Why?
Just curious, I try not judge.

2004 Monterey 282

Please judge - I value your opinion. I love and hate this boat. It is not my cup of tea, but fit the bill for all involved.

A couple reasons I picked this boat. I do over 100 mile runs (Chesapeake, Delaware, Atlantic) so twins are nice - so far in my 60 years on the water I was glad to have twins once - long before Towboat. I needed a separate berth for my son. Needed all the comforts of home for my late wife - she was disabled and needed many hand holds to get around the boat (rails everywhere). Fit and finish of boat are very nice. I bought it used in 2017, it was high and dry stored indoors, so gelcoat and vinyl were like new.

I did not want outdrives. I really wanted inboard. But the duoprops are sweet for docking. Handles like a dream, no crabbing.

The placement of engines absolutely sucks. Even changing spark plugs is a pain in the a$$. Engines are located under deck, not under the hatch! Can't even pull distributor without pulling engine. Fortunately I am 5'8" 160lbs so I can squish into pretty tight places. I called Monterey to find out how most people work on these. They told me: "remove rope locker at stern and cut access holes"

As for the 4.3's - they just seemed reliable thru the years. Nothing special, not fuel efficient and not bringing much performance. But good running motors. I might be wrong about this......