2007 R-21 EC shuddering at start up

[r67boxer]

When starting our Yanmar 3YM30 it has a brief but noticeable shudder. The shuddering lasts only a split second and then the engine settles into a smooth idle. I've checked the engine mounts etc and everything seems snug. The rubber has not deteriorated, as far as I can see. No cracking. The mounts are OEM Yanmar mounts. I've spoken to a couple of mechanics and they're saying that it is probably the engine torque upon startup which is being transferred to the mounts which, in turn, is making the noise. Has anyone else experienced shuddering?

 

[Mastercraft]

I have not had that on my boat, yet I have had that on a diesel tractor. My guess it is fuel related. Of course everybody has a different opinion. So ask ChatGPT and it says fuel.
"Why would a diesel engine shutter briefly upon start up"

 

[r67boxer]

I have not had that on my boat, yet I have had that on a diesel tractor. My guess it is fuel related. Of course everybody has a different opinion. So ask ChatGPT and it says fuel.
"Why would a diesel engine shutter briefly upon start up"

I did before posting. It suggested engine mounts hence my fixation with the engine mounts.

 

[Mastercraft]

You must have a different ChatGPT. It did not mention engine mounts to me.

 

[r67boxer]

You must have a different ChatGPT. It did not mention engine mounts to me.

This is what it said - please see below. I don't think its fuel or glow plug related because it starts immediately.



A Yanmar 3YM30 shuddering at startup usually points to an issue with engine torque transmission, fuel delivery, or mounting, rather than something minor. Let’s break it down carefully:

---

1. Engine Mounts​

• Symptoms: Shuddering or vibration, especially during start-up or under load.
• Why: Worn, broken, or loose mounts allow the engine to rock as it fires.
• Check: Inspect all mounts for cracks, excessive movement, or broken bolts.

---

2. Fuel Delivery Issues​

• Symptoms: Hesitant start, shuddering, rough idle, or black smoke.
• Why: Air in fuel lines, clogged filters, or failing injectors can cause uneven combustion.
• Check:
  • Replace fuel filters (primary and secondary).
  • Bleed the system to remove air.
  • Inspect injectors for uneven spray or leaks.

---

3. Glow Plugs / Cold Start​

• Symptoms: Hard start, shuddering, or misfires, particularly in cold weather.
• Why: If glow plugs aren’t heating correctly, combustion may be uneven at startup.
• Check: Test each glow plug with a multimeter for proper resistance.

 

[Mastercraft]

Does startup mean shifting into gear and moving forward or starting the engine?

 

[venajeff]

Just an FYI about AI large language models, they collect all of their answers from sources just like this forum (and this forum in particular, I have tested it and found answers referencing this forum). That said, posting AI responses inside this forum reinforces incorrect outputs when they exist. This currently is not a problem but if you play out the feedback loop into the next decade AI responses and this forum will lose their effectiveness.

 

[r67boxer]

Does startup mean shifting into gear and moving forward or starting the engine?

Sorry, I mean starting the engine.

 

[r67boxer]

Just an FYI about AI large language models, they collect all of their answers from sources just like this forum (and this forum in particular, I have tested it and found answers referencing this forum). That said, posting AI responses inside this forum reinforces incorrect outputs when they exist. This currently is not a problem but if you play out the feedback loop into the next decade AI responses and this forum will lose their effectiveness.

Good to know. My typical searches end in -AI which removes any AI involvement to the best of my knowledge.

 

[NorthernFocus]

If this is new/different behavior then it sounds like a fuel issue. Likely a failing or partially plugged injector. Or possibly(less likely)the valve that regulates fuel pressure or the fuel pump. The shuddering is caused by misfiring cylinder(s). I'd start with the injectors.