Trouble Starting Diesel

[davidpbo]

Re: One possible cause...

[ QUOTE ]
One possible cause might be that air is leaking in to the fuel line slowly.

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I had this problem on a diesel vehicle. I pumped fuel through using the hand pump, it would start, run for a while then stop.

Eventually the pump was having difficulty pulling the fuel through because of air in the system so I used a 12V tyre inflation compressor with a football inflator nossle attached to the return fuel pipe. This presurised the tank slightly and sent fuel through to the intake pipe on the fuel pump. I also ended up with fuel on top of the tank indicating where the air leak was.

Dropped the tank, but a polly bag over the filler hole, plugged one of the feed/return pipes and attached the above compressor to the over and slightly pressurised the tank whereupon air came out where the leak was. It was a tiny tiny hole impossible to see.

The attachments to the end of the pipes were flexible rubber hoses so the above was easy to do. May not be so easy on a boat. (not many tyres to be inflated for one thing).

 

[andy_wilson]

No

That guy's engine won't start when warm, but starts well when cold.

 

[andy_wilson]

It\'s clear from the answers below....

You haven't given enough info.
1. Is the starter turning over as quick as it ever did (and would you know anyway)?
2. It the diesel supply line free from leaks. It is possible a small air leak on the suction side could be introducing enough air to cause starting difficulties. Does bleeding reveal any bubbles? Does bleeding improve starting? Does it occasionally faulter then 'rally' under normal operation?
3. What is the general condition of the engine. Is it ancient and in general need of an overhaul, could compression be down due to worn cylinder / rings or poor valve condition. How is the output power in general compared to previously?
4. Have you tampered with anything recently? Are the throttle linkages correct, is the cold starting mechanism or device(s) like glow plugs working.
5. Highly unlikely as it does run, but as all a diesel engine really needs is fresh air and clean diesel, is the diesel supply clean and functional?
6. Once running, is the exhaust normal? Is there any sign of foul smelling (persistant) grey smoke which is hot atomised diesel vapour indicating a poor injector spray pattern? (Persistant as opposed to steam which dissipates fairly quickly.)
7. Is it burning oil - lots of blue smoke.
8. Is it struggling to breath - excessive black smoke.
9. Have you recently / do you occasionally give it a long hard drive at full or near full throttle to drive out excessive carbon deposits from upper cylinder.

 

[DaveS]

As others have said, there are a number of possibilities but it would be worth checking the more straightforward issues first.

I have just fixed a starting problem with mine that turned out to be an air leak on the suction side: as others have said, not at all obvious and nothing visible. To confirm / eliminate, I would suggest that next time, before attempting to start it, open the bleed valve at the fine filter and work the lift pump manually. You should immediately get diesel: if not then you've got an air leak. If so, complete bleeding and the engine should then start normally. If it does, that pretty well eliminates all the other possibilities (filters, compression, etc.)

If it is an air leak then you can either try to find it by pressurising the system and looking for diesel or, as I did, simply take apart all the suction side connections and remake them all properly. (I was glad I did it this way BTW, for I also discovered foreign matter half clogging the pipes that I otherwise wouldn't have known about!)