Yanmar 3GM hard starting after injector service

[Skunther]

My 3GM30F recently had the injector pump and 2 injectors rebuilt and installed by a local shop. Since then, it is incredibly hard to start. They checked the injectors and pump and seem stumped as to what the issue is. Valve lash is fine. Both fuel filters are recently replaced. Once started, the engine idles, runs and cruises fine.

What could be the issue?

 

[fredrussell]

You don’t say where you are but if you’re in the UK are you using the cold start procedure? (ie plenty of throttle, gearbox in neutral)
Engines taking ages to fire can be a symptom of low compression. Did you replace rather than re-use sealing washers and the like on injectors? (assuming these engines have them)

 

[michael_w]

My Yanmar takes a surprising amount of cranking before it deigns to start. It's an indirect injection engine with no glow plugs IRRC. It's probably the worst starting diesel I've owned.

 

[Slowboat35]

Possibly incomplete bleeding after refitting the injectors? Have you re-bled the system thoroughly?
That said poor compression is a is consideration as fredrussel mentioned. A compression test will only tell you comparative figures cylinder by cylinder and not an accurate compression figure though if it is very low that will be apparent.
I very much doubt valves have anything to do with it as they haven't been disturbed though I have never heard of 'valve lash' before so it can't be anything significant.

 

[Skunther]

You don’t say where you are but if you’re in the UK are you using the cold start procedure? (ie plenty of throttle, gearbox in neutral)
Engines taking ages to fire can be a symptom of low compression. Did you replace rather than re-use sealing washers and the like on injectors? (assuming these engines have them)

Plenty of throttle (3/4) and neutral, yes. If the engine has low compression now, it also did before work was performed when it would start up fine, so I don’t think that is the issue. The shop doing the work said they used new compression washers.

 

[peterf]

Maybe there is an air leak in the fuel system and the time to start is the time it takes for the fuel pump to recharge the lines.

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

 

[lexi]

Air or low compression yes. Did you time the IP after removal. Shims would be disturbed.

 

[Bilgediver]

What could be the issue?

Is there any chance you did not replace the same shim pack that was removed from under the injection pump. The shim thickness determines injection timing

 

[Skunther]

Maybe there is an air leak in the fuel system and the time to start is the time it takes for the fuel pump to recharge the lines.

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

Do you mean to use the lift pump? I also have a manual pump on the primary Racor filter. Would one and/or the other pump prime the fuel lines past the injector pump, all the way to the injectors? I suppose I would need to bleed at the injectors, no?

 

[Skunther]

Is there any chance you did not replace the same shim pack that was removed from under the injection pump. The shim thickness determines injection timing

They said they used the same shims that were there before.

 

[Skunther]

Air or low compression yes. Did you time the IP after removal. Shims would be disturbed.

The shop said they used the same shims that were there before. They did not adjust the timing. Do you think using the same shims could have negatively affected the timing, causing the issue?

 

[Skunther]

The service manager mentioned that the lift pump may have been previously modified by another shop to order to adapt it to the low compression in the cylinders and make the them perform better. He said the rebuild was to spec, and any modifications to the pump would have been lost, possibly explaining why it now starts hard.

Has anyone heard of such a scenario? Does it sound reasonable?

 

[RunAgroundHard]

... I suppose I would need to bleed at the injectors, no?

Yes, you need to prime up to the injectors. Each HP fuel line at the injector should be cracked open. When the engine is cranked by key, wait until clean fuel is squirting out then nip the union. Repeat for the next injector. However, if there is air in this part of the circuit, I would not expect it to start. Yours does start, eventually and runs good.

I had a similar slow starting issue and the battery was not fully charged and as such the engine turned over to slow. A fully charged battery and it started instantly. Worth checking the state of charge, or charging fully.

 

[Skunther]

Yes, you need to prime up to the injectors. Each HP fuel line at the injector should be cracked open. When the engine is cranked by key, wait until clean fuel is squirting out then nip the union. Repeat for the next injector. However, if there is air in this part of the circuit, I would not expect it to start. Yours does start, eventually and runs good.

I had a similar slow starting issue and the battery was not fully charged and as such the engine turned over to slow. A fully charged battery and it started instantly. Worth checking the state of charge, or charging fully.

It is a new battery with 550 CCA and 700 MCA. It is connected to shore power and constantly kept at full charge, so it is always fully charged at each attempt to start the engine.

 

[Skunther]

Yes, you need to prime up to the injectors. Each HP fuel line at the injector should be cracked open. When the engine is cranked by key, wait until clean fuel is squirting out then nip the union. Repeat for the next injector. However, if there is air in this part of the circuit, I would not expect it to start. Yours does start, eventually and runs good.

I had a similar slow starting issue and the battery was not fully charged and as such the engine turned over to slow. A fully charged battery and it started instantly. Worth checking the state of charge, or charging fully.

Wouldn’t bleeding the system end up injecting fuel into the other cylinders from the injectors that are not being bled while I’m bleeding each one, causing an over-fuel situation at start up?

 

[RunAgroundHard]

Wouldn’t bleeding the system end up injecting fuel into the other cylinders from the injectors that are not being bled while I’m bleeding each one, causing an over-fuel situation at start up?

It shouldn't because each injector has its own fuel line independent from the others.

 

[earlybird]

The service manager mentioned that the lift pump may have been previously modified by another shop to order to adapt it to the low compression in the cylinders and make the them perform better. He said the rebuild was to spec, and any modifications to the pump would have been lost, possibly explaining why it now starts hard.

Has anyone heard of such a scenario? Does it sound reasonable?

That doesn't sound very likely to me. The lift pump either works adequately or it doesn't. More likely to show up on heavy load I'd have thought. If you wish, you can eliminate it from the list of suspects by arranging a temporary gravity feed fuel tank and trying the starting procedure with that.

 

[Channel Sailor]

My Yanmar takes a surprising amount of cranking before it deigns to start. It's an indirect injection engine with no glow plugs IRRC. It's probably the worst starting diesel I've owned.

My old 2gm20 starts extremely easily. No throttle required in the summer (spring and autumn) and half throttle in the winter. It has good compression (tested with a gauge a couple of years ago), a 3 year old manifold, refurbished injectors last year, air filter cleaned every year, 100 ish hours use a year, properly serviced. Though unusually the fuel tank is above the level of the injector pump, so the lift pump does not need to work very hard.

 

[Skunther]

That doesn't sound very likely to me. The lift pump either works adequately or it doesn't. More likely to show up on heavy load I'd have thought. If you wish, you can eliminate it from the list of suspects by arranging a temporary gravity feed fuel tank and trying the starting procedure with that.

I meant the injector pump, not the lift pump. My mistake. I edited my earlier post to correct it.

 

[Tillana]

My old md11c was a pain to start with lots of turning her over. Ended up being small holes in filter housing letting air in and caused the fuel to drain back toward the tank. Found out by doing as suggesting with priming with lift pump and it started loads quicker. Replaced filter housing and all was well.