Yanmar 3GMF brand new fuel injector question

[Capt Robbie]

so little history,
I’ve had an issue with my yanmar 1983 model 3GMF diesel not being able to get rpms above 2200.
I’ve been getting advice from both the marina technician and My friend a diesel Mechanic that works on large truck and heavy equipment like caterpillar as to what appears to be the issue. They both concur that the issue is a fuel delivery issue.
per there suggestions to solve my problem with out breaking the bank I have done the following.

1 confirmed fuel in tank is good by pulling samples from bottom, middle,
2 replaced primary and secondary fuel filters.
3 replaced all fuel lines and pick up tube in fuel tank.
( eliminate any clogged/ collapsing lines)
4 replaced fuel lift pump
( eliminate possible bad or stretched diaphragm not delivering enough fuel)
5 mixing elbow was replaced approximately four years ago and engine only has at best 20-40 hrs after installing it.
(Note old mixing elbow other than rusting looked in good shape for being 35 years old)
6 replaced throttle control cable and adjusted the linkage to max.
g( eliminate possible slacin cable)
7 bled fuel system completely from primary filter all the way to the last fuel injector.
( confirmed that fuel is flowing all the way back to the fuel tank)
8 bypassed the entire fuel tank and ran engine with a jug of diesel
( just to eliminate any fuel restrictions from tank or lines)

No change.
Note that other than the low rpms the engine runs perfectly, starts on the first crank, no smoking, and sounds great.

They both still believe it’s a fuel issue. So before I have a diesel technician look at it they suggested to replace the injectors.

Sorry for the long storyline.

here is my question?
I bought 3 brand new injectors genuine Yanmar part 728170-5300 and all the necessary parts to replace the old ones per Mac boring technician
I have never replaced them and it appears to be pretty straight forward job.
I opened one new box to be sure it looks correct before I start taking everything apart. The injector doesn’t appear to have a tiny hole in it like everything I have seen on YouTube. It has what appears to be a tiny pin protruding from it.

Is this normal?

I believe that inside the injector there is a spring that will allow this pin to operate and allow fuel to spray from it.

Is this correct?

I don’t want to open another box to check if the rest of the injectors are the same. After i open the package they are mine and they aren’t cheap. I’m hoping that they sent me the correct part. Again I’ve never pulled out an injector before and I don’t have the old one out yet to compare it to.

I’m trying to save about two thousand in labor by replacing them myself, this is most likely the next course of action that the marina technician is going to do without really getting into the engine. So far I’m into this for about $900 in parts and materials which is not to bad considering everything that I have replaced so far is 35 years old, original equipment, and needed to be replaced anyway. Unfortunately the other items on the list of possible causes are beyond my mechanical comfort level. If replacing these injectors resolves the issue, great, problem solved. If not I’m still ahead of the game as they really don’t owe me anything after thirty eight years.

 

[RitSim]

I think the pin you see is an internal part protruding. I'd go ahead and replace the injectors. Mske sure that you purge ALL air from the fuel system.

 

[Davidasailor26]

I don’t know about the injector, but just for completeness since I don’t see it on your list - did you confirm the engine speed with an optical tachometer?

 

[Ralph Johnstone]

Firstly, excellent write up and photo of the problem. This is a real pleasure to follow. Just sorry it's your problem .

I would definitely follow up with @Davidasailor26 's recommendation on the optical tach before tearing anything apart. $20.00 from Amazon. Maybe cheaper from HF.

Again I’ve never pulled out an injector before and I don’t have the old one out yet to compare it to.

Since you're eventually going to pull the old one(s), pull out an old one now to check for the presense of a pin. Please send pics for comparison.

 

[Benny17441]

Check the Tach is reading true. How about in Neutral, can it rev beyond 2,200? Make sure there is no obstruction in the air intake tube. Turn the prop shaft by hand to check for undue resistance. (transmission, cutless bearing, wrap around the prop, drag.) Is it burning oil, low compression? Lastly, probably not, but always a possibility, high pressure pump and governor.

 

[Capt Robbie]

unfortunately the boat is now on the hard for the winter and hopefully soon weather permitting early spring launch date. Can’t really do anything until boat is back in the water. I’m just trying to get some preparation done before having to call in the big guns to service it. I consider myself pretty mechanically inclined, however I have limited specialized mechanic tools and unfortunately from past experience leave things that are out of my comfort zone to the professionals. That being said thanks for any suggestions very much appreciated.

so under load and in gear only about 1000 rpm or less difference. No issues with prop or marine growth, boat hauled clean. The issue I truly believe is with the low rpms. My old log books show that hull speed was easy obtained at approximately 3800 rpms which is how I could gauge how fouled the bottom is. I don’t believe the tachometer is off either because my gps speed at 2200 rpms is what my hull speed should be at that low of rpm. Due to lower rpms I can’t achieve any higher hull speed under power. No other issues as I indicated, no smoking, oil pressure is good, no unusual noise, the engine runs perfectly fine at all throttle positions.

This is what I think is strange and have some issues with my diesel mechanic friend and the marina technician suggestions about injectors being bad. I would think that if a injector was bad then one cylinder would run rough or cause smoke as if a decompression lever was lifted? As I indicated, I’m not a diesel mechanic by any means and I’m relaying heavily on there expertise, however I do understand the basic operations of an engine and would think that the engine would smoke or run rough if an injector was bad. Unless all three were no good, which I think is unlikely, sort of like having all spark plugs in a gas engine bad at the same time. Again not impossible. The other things they thought of are much more involved such as the governor, fuel pump, cylinder issues, which are well beyond my comfort zone to mess with.

like I indicated before replacing the injectors after 38 years they don’t owe me anything and probably would have had to be done at some point anyway, so if this doesn’t resolved my issue not going to lose sleep over it. I’m just trying to go through some logical things that I can do myself and not be a parts changer. So far everything I’ve done was on my list of things that needed to be replaced anyway.

 

[kloudie1]

Does sound like fuel starvation since it is not smoking .. do check RPM with a known good optical tachometer .. my Yanmar tacho reads 800 RPM low .. check the valve clearance if that hasn't been done in a while.. The pin tip you are seeing is the injection valve, which retracts under the pressure of the injection pump to spritz in the fuel. It looks correct.
If the engine can rev to 3600 or so, it is probably not a governor issue.. but it may be a sticky fuel rack in the injection pump. (not a likely scenario) Hope you can fix this one!

 

[Mikem]

so little history,
I’ve had an issue with my yanmar 1983 model 3GMF diesel not being able to get rpms above 2200.
I’ve been getting advice from both the marina technician and My friend a diesel Mechanic that works on large truck and heavy equipment like caterpillar as to what appears to be the issue. They both concur that the issue is a fuel delivery issue.
per there suggestions to solve my problem with out breaking the bank I have done the following.

1 confirmed fuel in tank is good by pulling samples from bottom, middle,
2 replaced primary and secondary fuel filters.
3 replaced all fuel lines and pick up tube in fuel tank.
( eliminate any clogged/ collapsing lines)
4 replaced fuel lift pump
( eliminate possible bad or stretched diaphragm not delivering enough fuel)
5 mixing elbow was replaced approximately four years ago and engine only has at best 20-40 hrs after installing it.
(Note old mixing elbow other than rusting looked in good shape for being 35 years old)
6 replaced throttle control cable and adjusted the linkage to max.
g( eliminate possible slacin cable)
7 bled fuel system completely from primary filter all the way to the last fuel injector.
( confirmed that fuel is flowing all the way back to the fuel tank)
8 bypassed the entire fuel tank and ran engine with a jug of diesel
( just to eliminate any fuel restrictions from tank or lines)

No change.
Note that other than the low rpms the engine runs perfectly, starts on the first crank, no smoking, and sounds great.

They both still believe it’s a fuel issue. So before I have a diesel technician look at it they suggested to replace the injectors.

Sorry for the long storyline.

here is my question?
I bought 3 brand new injectors genuine Yanmar part 728170-5300 and all the necessary parts to replace the old ones per Mac boring technician
I have never replaced them and it appears to be pretty straight forward job.
I opened one new box to be sure it looks correct before I start taking everything apart. The injector doesn’t appear to have a tiny hole in it like everything I have seen on YouTube. It has what appears to be a tiny pin protruding from it.

Is this normal?

I believe that inside the injector there is a spring that will allow this pin to operate and allow fuel to spray from it.

Is this correct?

I don’t want to open another box to check if the rest of the injectors are the same. After i open the package they are mine and they aren’t cheap. I’m hoping that they sent me the correct part. Again I’ve never pulled out an injector before and I don’t have the old one out yet to compare it to.
View attachment 203066

I’m trying to save about two thousand in labor by replacing them myself, this is most likely the next course of action that the marina technician is going to do without really getting into the engine. So far I’m into this for about $900 in parts and materials which is not to bad considering everything that I have replaced so far is 35 years old, original equipment, and needed to be replaced anyway. Unfortunately the other items on the list of possible causes are beyond my mechanical comfort level. If replacing these injectors resolves the issue, great, problem solved. If not I’m still ahead of the game as they really don’t owe me anything after thirty eight years.

My daughter had the same issue in her 1984 37C. We did many of the things you did with no change. Turned out the pedestal/compass assembly had been rotated 90 degrees by the PO and that restricted full movement of the throttle. We modified the compass base (it is plastic) to allow full throw and problem solved.

 

[Whatfiero1]

I'd bet your boat is a little bit heavier than before and or you have less compression and she's getting a little tired . While on hard I'd pull prop and check pitch and diameter against other Boats same size weight hp.

 

[Ralph Johnstone]

My old log books show that hull speed was easy obtained at approximately 3800 rpms

Was that 3800 RPM perhaps a mistake with the specs stating a max. speed at 3600 ? This is from the shop manual:

Thinking about the performance of the engine:

Note that other than the low rpms the engine runs perfectly, starts on the first crank, no smoking, and sounds great.

No other issues as I indicated, no smoking, oil pressure is good, no unusual noise, the engine runs perfectly fine at all throttle positions.

It seems that when injector(s) are causing problems, there is also an issue with performance eg. smoking, rough running, rough idling, hard starting, etc, etc. Probability says that it's unlikely all three injectors crapped up at once. One crapped up injector would produce rough running which you don't have. And now I'm just repeating what you've said above. Your engine sounds like a well maintained piece of machinery in perfect running condition.

mixing elbow was replaced approximately four years ago and engine only has at best 20-40 hrs after installing it.

This is the one thing you haven't PROVED to be faultless. Logic says that 20-40 hours will not plug the elbow but it's not PROOF POSITIVE. My mantra in problem solving is always to start at the simplest ($cheapest$) and work up from there. It'll cost you about $20.00 for a new gasket for the riser section section but at least you'll have the proof you need before opening the other two boxes of injectors ($$$). And remember that CCW thread.

Go ahead and pull it and hope you don't see this:

This is five years old and about 500 operating hours.

Go ahead and pull it. You've got nothing better to do in this miserable weather right now and maybe (hope against hope) it might be your real problem.

so under load and in gear only about 1000 rpm or less difference.

Something not quite clear here, are you referring to max RPM conditions i.e. 2200 RPM under load and 3200 RPM in neutral. Please help me with a few examples of numbers.

I don’t believe the tachometer is off either because my gps speed at 2200 rpms is what my hull speed should be at that low of rpm.

Oops, not so much . GPS speed doesn't tell you anything you can hang your hat on when it comes to engine performance. Your GPS might tell you you're going like a bat out of hell (over ground) and yet your tach says 800 RPM, if you're going with a strong current. On the other hand, you could be crawling like a snail (says your GPS) at 3600 RPM if you're going against a strong current. The only thing that will tell you what's happening is an in hull speed transducer which is relative to the water around you. Again, I would encourage you to invest in a cheapo optical tach so you have proof positive info once you're back in the water.

Can you also supply a little more info as to what it was like as the max. RPM dropped to 2200. Did it drop over a period of time or suddenly ? How long you've had the boat ? Anything else in the operation ?

I'll look forward to your next posting.

 

[Capt Robbie]

Ralph,
Thanks for your input,
I do plan to pull the mixing elbow, just to eliminate any possibility of restriction however, as per my diesel mechanic and marina technician they both agree that it’s fine due to no smoke issue. Plus it for the most part is practically new with almost no hrs of use.

My rough gps speeds were based on true ground speed. Not influenced from current or wind. I totally get your point, however where I am boating theses factors don’t really apply during my testing.
Unfortunately this issue has been going on for the past three years, and as far as I can recall the low rpms didn’t happen suddenly more or less over time. However I can’t be 100% certain. I hate to say that when I really noticed this issue was approximately three years ago when I had run aground and had a hard time backing off the soft grounding because of the rpms being low.

I hate to admit that I normally don’t push the engine hard at all , partially due to its age and also I’m never really in that much of a rush to get anywhere. Normally motor at about 6 knots and I am ok with that, however I still like to know that I have the power available in reserve if needed.

I’m the original owner the boat, original engine now almost 38 year’s old. Fortunately until recently never had any issues with the engine Other than replacing normal ware and tear items and routine maintenance. Engine has been impeccably cared for over the years.

 

[Ralph Johnstone]

I’m the original owner the boat, original engine now almost 38 year’s old. Engine has been impeccably cared for over the years.

So THAT'S why it runs like a new engine. Just for my own curiosity, what are the engine operating hours ?

my diesel mechanic and marina technician they both agree that it’s fine due to no smoke issue.

Can't agree with the smoke issue due to clogging in the elbow. The sectioned elbow I show above never caused any smoke as it was slowly choking to death. The opening was about 1/4" in dia. when I chopped it up.

I hate to admit that I normally don’t push the engine hard at all

What is you normal cruising RPM ? And yes, I also doubt that would permanently slow the RPM. Just on the off chance, take a look up the exhaust system (after the elbow is off) with a mirror where it leaves the block to see if there's anything unusual in there. Remember, we're in the desperation stage so don't overlook anything, no matter how small .

so under load and in gear only about 1000 rpm or less difference.

Don't want to sound like a broken record, but could you please clarify this for me with a few operating examples as to what this means ? Tnx.

 

[Capt Robbie]

Ralph, thanks again for your input,

so I do plan to remove the mixing elbow and rule out any blockage, unfortunately I’m unable to physically do that myself right now, still recovering from shoulder and hand surgery. Still very limited as to things that I can physically do. Removing mixing elbow will have to be done by marina technician at their extortion rates.

So engine hours unfortunately are hard to say for certain, I don’t have a engine hours indicator and never installed one.
My best guess from my travel logs put engine hours 3800 -4800

normal rpms 3200 at three quarter throttle and average hull speed of 6.5 knots
Normal rpms 3800 -4000 at almost full throttle and average hull speed 7.5 knots with a little bit more reserve power available at approximately of 4000 - 4800 rpms if needed.

Maximum Rpms in neutral about 2200 and I can force the throttle body assembly to 2300
Maximum rpms In gear under load 2600.

Thanks again for everyone’s input, I really appreciate it

 

[Richard19068]

Maximum Rpms in neutral about 2200 and I can force the throttle body assembly to 2300
Maximum rpms In gear under load 2600.

Is that backwards? How could neutral be less than under load?

 

[Ralph Johnstone]

Maximum Rpms in neutral about 2200 and I can force the throttle body assembly to 2300
Maximum rpms In gear under load 2600.

So, I'm going to assume that, as @Richard19068 stated above, the loaded and unloaded RPM's are the result of your spellcheck reversing the order and they should be reversed back again.

Thinking out loud here, that says that you're suffering from either:

1. a lack of fuel.

2. or a lack of ability to dispose of the exhaust gasses.

I think we'd best wait until we find out what's happening in the exhaust department before any more wild guess work.

more reserve power available at approximately of 4000 - 4800 rpms if needed.

Now I've got a a question which I'm wrestling with. How can you get 4800 RPM out of your engine when the governor limits the maximum to 3600 RPM as shown in the spec page I show in post #10 ? I've got to call in that optical tach. just to be sure where we stand on RPM.

This looks like the one I bought a few years ago for about $10.00 CAN. Still ticking like a Timex and agrees with a friend's mechanical tach. within +/- 2 RPM at 2000 RPM. If you find a cheaper one, go for it.

I’m unable to physically do that myself right now, still recovering from shoulder and hand surgery

I can't think of too many more things that will really slow down a job like this. Once you do get back in harness again, I know one thing that always kills me in playing with the elbow is reinstalling it and holding the gasket in place. If I could ever find a guy with three arms, he'd be a shoe-in for the job. But until that guy comes wandering along your dock, try this next time you go to install it:

Install a couple of temporary studs (you really only need two) to hold the gasket in place and then to guide you into position with the other three pieces of the assembly. Temporary nut or two to keep things from falling apart and you're ready to install the real permanent bolts. I like to have everything swimming in parting compound so the gasket falls right off for inspection.

If you can just satisfy me with the question about the 4800 max. RPM, I'll sleep better at nights.

Take care of yourself until then.

 

[Capt Robbie]

sorry about the rpm number’s being wrong, I still have my hand and shoulder in a post surgical brace. Edited my previous post.

normal rpms 2600 at three quarter throttle and average hull speed of 6.5 knots
Normal rpms 2800-3000at almost full throttle and average hull speed 7.5 knots with a little bit more reserve power available at approximately of 3100- 3400 rpms if needed.

 

[Ralph Johnstone]

Edited my previous post.

Thanks. Now I can get to sleep at night .

 

[Ralph Johnstone]

I hate to admit that I normally don’t push the engine hard at all , partially due to its age and also I’m never really in that much of a rush to get anywhere.

Seemed to remember this comment from way back.

Normal rpms 2800-3000at almost full throttle and average hull speed 7.5 knots

Seems your normal operating RPM for the last 38 years has been right on the factory recommended mark. Should be good for another 38 years .