Yanmar 3GM hard starting after injector service

[Rappey]

Before starting try pumping the fuel pump by hand (might require lots of pumps) and then see if its easier to start.

Has this been tried? A friend rebuilt his yanmar. Great compression but really hard to cold start. He tried virtually everything but no joy.
Yesterday he told me he pumped the fuel primer before cold starting and it fired straight up.

 

[Slowboat35]

My 60 year old bmc measures within 10 psi on all 4 cylinders ! I'm down to 260. It should be 340 for me. Saving grace is that it has glow plugs so still starts.
30 years ago i could do 7.5knts, now only 6.5knts.

For a start I clearly said "is seldom lost equally" - the operative word being "seldom"...
Secondly regardless of your quoted numbers "all the advice I have had on compression is that absolute numbers are a completely unreliable guide to compression health as there are so many variables in the (uncalibrated) measuring process."

 

[vas]

Didn't even know you had glow plugs. If you have, that is a must check first item on relay, wiring and plugs.

no glow plugs on GM series

 

[vas]

Had all sorts of issues with my 2GMF on a 8kW generator onboard.
Turned out (after an almost needless full engine rebuilt) that it was a combo of things all related to fueling.
Scrapped the awful lift pump that was leaking air in the circuit (replaced with a 50euro el fuel pump that I fire a few secs before cranking), rebuilt/replaced various bits in the primary yanmar filter and now it starts (OK not on the button when below 10C) reasonably well at 1/2 accel

 

[IanCC]

Has this been tried? A friend rebuilt his yanmar. Great compression but really hard to cold start. He tried virtually everything but no joy.
Yesterday he told me he pumped the fuel primer before cold starting and it fired straight up.

Just decompress and spin engine for 5 seconds or so. That will bring fuel up to pressure. If it works you definitely have an air leak.

 

[Skunther]

@Tillana, did you find you had white smoke upon startup before you figured out the fuel was draining back toward the tank? I’ve also heard that the o-ring on the secondary filter can be a bit problematic, causing a similar issue to what you describe. Would your engine run well once started, or would it both start and run poorly? Mine runs fine once started…

Could dirty fuel be an issue? Again, my engine runs well once started, so I’m not sure if dirty fuel could be the culprit. I did see one user post a similar starting issue that was resolved with cleaning their fuel. I’m sure it wouldn’t hurt to clean it, but it is an expensive shot in the dark (unless someone has a good way to clean the fuel without breaking the bank having the fuel and tank scrubbed?).

 

[Skunther]

Just decompress and spin engine for 5 seconds or so. That will bring fuel up to pressure. If it works you definitely have an air leak.

Would doing so not also increase compression, muddying the water on what the issue actually is? Or would compression remain unaffected, and only priming the system be achieved?

 

[Tillana]

The engine ran faultlessly. I had no issues after replacing the filter. Even when not started for 18 months due to vivid, she fired straight up.

 

[IanCC]

Would doing so not also increase compression, muddying the water on what the issue actually is? Or would compression remain unaffected, and only priming the system be achieved?

.. I see your point. Your thinking compression leakage past injectors. I haven't reread entire thread, so this may have been said. If you bleed and it starts fine it's an air leak deffo.

Interested to know why you had work done when it started so well before. To have IP attended to is a major item must have been a major problem.

 

[Skunther]

.. I see your point. Your thinking compression leakage past injectors. I haven't reread entire thread, so this may have been said. If you bleed and it starts fine it's an air leak deffo.

Interested to know why you had work done when it started so well before. To have IP attended to is a major item must have been a major problem.

I was thinking if there is low compression in the cylinders, running it with the compression levers open would oil the rings, increasing compression once they’re closed. Is that not true? If I’m trying to isolate if the issue is an air leak in the fuel system would it not be better to just use the lift pump to prime it? I will do this today.

Also, if there is an air leak in the system and fuel is draining back from the cylinders, wouldn’t there be visible leak somewhere in the engine compartment?

I had the IP serviced as there was a very small leak from it. I also wanted to address a very light amount of whitish/light blue smoke that would persist while cruising at 2700rpm. The light amount of smoke does seem fairly well addressed (once running), though this may also have to do with the fact I also had the mixing elbow, which was fairly clogged, replaced.

 

[Skunther]

Had all sorts of issues with my 2GMF on a 8kW generator onboard.
Turned out (after an almost needless full engine rebuilt) that it was a combo of things all related to fueling.
Scrapped the awful lift pump that was leaking air in the circuit (replaced with a 50euro el fuel pump that I fire a few secs before cranking), rebuilt/replaced various bits in the primary yanmar filter and now it starts (OK not on the button when below 10C) reasonably well at 1/2 accel

How did you determine your lift pump was faulty?

 

[IanCC]

I was thinking if there is low compression in the cylinders, running it with the compression levers open would oil the rings, increasing compression once they’re closed. Is that not true? If I’m trying to isolate if the issue is an air leak in the fuel system would it not be better to just use the lift pump to prime it? I will do this today.

Also, if there is an air leak in the system and fuel is draining back from the cylinders, wouldn’t there be visible leak somewhere in the engine compartment?

I had the IP serviced as there was a very small leak from it. I also wanted to address a very light amount of whitish/light blue smoke that would persist while cruising at 2700rpm. The light amount of smoke does seem fairly well addressed (once running), though this may also have to do with the fact I also had the mixing elbow, which was fairly clogged, replaced.

The manual says that if engine has been stood a while, i think they say a month, itbis best to decompress and spin for 5 seconds to oil the bearings while not under load. Probs does same for rings.

You can use the lift pump but it's a faff depending on access. I used to give it a hundred pumos just to be sure before thinking hang it i will let the engine do it for me.

No you won't see diesel unless it is a huge leak. I have a small leak. I have replaced primary filter, secondary filter, lift pump and all copper washers but still there is a tiny leak somewhere. I will replace the non return valve from the fuel pump next. Not easy.

 

[Skunther]

The manual says that if engine has been stood a while, i think they say a month, itbis best to decompress and spin for 5 seconds to oil the bearings while not under load. Probs does same for rings.

You can use the lift pump but it's a faff depending on access. I used to give it a hundred pumos just to be sure before thinking hang it i will let the engine do it for me.

No you won't see diesel unless it is a huge leak. I have a small leak. I have replaced primary filter, secondary filter, lift pump and all copper washers but still there is a tiny leak somewhere. I will replace the non return valve from the fuel pump next. Not easy.

Ah, the wonders of machines. You’d figure diagnosis would be more precise/methodical. Or at least I used to. I’ll try 100 pumps (hopefully the cam is in the correct position. I never can seem to tell) and see how it starts, then report back.

 

[IanCC]

Ah, the wonders of machines. You’d figure diagnosis would be more precise/methodical. Or at least I used to. I’ll try 100 pumps (hopefully the cam is in the correct position. I never can seem to tell) and see how it starts, then report back.

The lift pump has two parts to the movement. At first the lever moves easily and then it's quite a firm movement. It's the latter movement which is pumping. The former is just the taking up of slack. If it's in the wrong position, i don't think you will move it.

 

[Skunther]

The lift pump has two parts to the movement. At first the lever moves easily and then it's quite a firm movement. It's the latter movement which is pumping. The former is just the taking up of slack. If it's in the wrong position, i don't think you will move it.

I will rotate the engine manually until the latter movement you mention seems most pronounced.

 

[Tillana]

My fuel just ran back into the tank so no visible leak. The holes in the filter were tiny so over a few weeks of sitting, the fuel was able to run back to the tank when air got in

 

[Skunther]

Had all sorts of issues with my 2GMF on a 8kW generator onboard.
Turned out (after an almost needless full engine rebuilt) that it was a combo of things all related to fueling.
Scrapped the awful lift pump that was leaking air in the circuit (replaced with a 50euro el fuel pump that I fire a few secs before cranking), rebuilt/replaced various bits in the primary yanmar filter and now it starts (OK not on the button when below 10C) reasonably well at 1/2 accel

Vas, I’d be curious to know how you determined your lift pump was leaking air.

 

[Skunther]

Just decompress and spin engine for 5 seconds or so. That will bring fuel up to pressure. If it works you definitely have an air leak.

I tried pumping the lift pump around 200x, and the engine wouldn’t start up after 20 seconds of cranking, so I started with ether. Next time I needed to start, I opened the compression levers and cranked for 5 seconds, then closed them and tried to start. No luck after 20 seconds of cranking. Used ether again. Does this pretty definitively rule out an air leak as the culprit? I was thinking of possibly replacing the secondary filter to see if that might be leaking air into the system next.

 

[Skunther]

There should be a figure for the cranking RPM in the manual?

If you can measure the voltage at the starter motor during cranking, and also the voltage at the battery, you can see whether a better battery might help or maybe you have voltage drop in the cables and isolators etc? Personally, I'd try using the house battery paralleled with the engine battery. Ensure all batteries are fully charged!
I might us e a clamp ammeter to check the current too.
It's possible to have a partly failed starter motor, one or two coils burned out maybe, this can draw a lot of current while not delivering much torque or speed.

When the engine starts after 30s of cranking, do you get signs that fuel has been injected all this time? You might notice the exhaust water looking distinctly oily just after starting? If not then the fuel system may be the issue.

Double check the 'throttle' and fuel stop controls are properly connected and adjusted.

The compression test figures sound very low to me, either they were taken while the engine was not turning fast enough, they're in strange units, or the engine is pretty tired, If the engine is that worn, I'd expect lots of blow-by when running, take the oil filler cap off and I'd expect to see lots of fumes.

To test for blow by I started the engine cold, ran it for a 5 minutes at idle, revved to 2500 and then cut it. No fumes under the oil fill cap nor the dip stick.

When I crank for a bit without getting the engine to start, I do notice some light whispey vapor coming from the air intake.

 

[Skunther]

If an engine runs and starts well, has some work done and then immediately afterwards doesn't start properly it must be almost 100% certain the problem lies with the work that was done or something closely connected with it, not some vanishingly unlikely coincidence of all cylinders mysteriously losing compression equally and simultaneously for instance.
For a start compression is seldom lost equally across cylinders, there is almost invariably a fairly wide sperad of pressures between the cylinders, unlike the closely grouped figures the OP has quoted. This is the reason Yanmar and most engine makers don't specify figures for this.
Additionally all the advice I have had on compression is that absolute numbers are a completely unreliable guide to compression health as there are so many variables in the (uncalibrated) measuring process. It can only ever be a comparative indication, either instantly between cylinders or long-term as a trend over several tests over months or years by the same mechanic with the same test kit. (When I rebuilt the top-end of my 3GM) my comp tester showed about 175psi with a 5psi spread and it started on the first compression.)

The only rider I'd add to that is to ensure that the battery, connections and wiring really are sound. That is easily addressed by starting it direct from a known good battery with a set of decent quality jump leads applied direct to the starter motor terminals.
You can easily check for poor wiring by cranking the engine for several seconds then feeling each starter wiring connection with a finger. A hot connection (and maybe a yell of "Ow!") easily identifies a problem
But I'd bet good money that compression is almost certainly not the culprit.