More Perkins 4108 woes!

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neil1967

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Having discovered my newly acquired Perkins 4108 was leaking oil last weekend (see other threads), I ran it today to try and ascertain where. On start up (about 2-3 seconds of cranking) it ran quite roughly until I increased the revs to around 800-1000 (as it did the last time I started it). I left it like this while I inspected the engine for leaks. After about 5 minutes the engine revs increased to around 1200-1300, died away to 800-1000 and then kept cycling like that. Increasing the revs with the throttle showed the same effect at higher rev ranges too. I suspect a faulty/worn injector - any other ideas?

Thanks

Neil
 
I think you may be sucking air into the fuel system or have a partial blockage.
It certainly sounds like fuel , mine did the same then eventually stopped and had to be bled. Turned out to be a bum joint at the filter.
 
I agree with the others,does not sound like an injector problem, hunting is normally caused by inconsistent fuel or air.

I'm curious having read your post about how you start your 4108. From memory, for cold engines, Perkins instructions are to set the throttle at 1/3 to 1/2 of its movement, hold the key at "heat" position for 20 seconds so thermostart can do its job then turn key to start position. Once warm (for me that's anytime upto about 6 hours after using engine) just go straight to start position. Starting from cold this way will put about 1500rpm on the tachometer and I just ease the revs down once its started to warm up. It would seem as though you are starting the engine in neutral at tickover speed. Have you been given different instructions about cold starting or do I have the wrong end of the stick? I don't think this is relevant to your "hunting" problem by the way.
 
Think on the bright side Neil - the 4108 is an incredibly robust engine and the fault you have might well completely stop a lesser one.

I had a similar symptom on mine a couple of years ago, but it would settle down once the engine had warmed up. That turned out to be due to an old and badly worn high pressure fuel pump, which had to be replaced ... no DIY fix possible. Otherwise, I agree with others that its most likely a partial fuel blockage or air leak somewhere. Unlike Pete735, I do think it is possible this might be at one of the injectors. If you haven't done so recently, it would do no harm to take off the injectors and get them serviced, as part of your investigation.
 
It's air!

Probably an infuriating tiny air leak in the fuel system. Check your banjos copper washers etc. If it persists bypass the system, gravity feed fuel from a can through another filter into the injection pump and see if it's cured.

This surging on attached video on Perkins Perama M20 was a result of an air leak going into the secondary filter which I only found by taking whole system off the boat and putting the pipes and joints under air pressure underwater!

http://www.youtube.com/watch?v=lre3iKfwSM4&feature=youtube_gdata_player


ps how do you highlight a url on here?
 
Embarrassed!

thanks for all your replies. your comments about fuel lead me to think about what could be the problem, and then it dawned on me - i'd not turned the fuel tap on! The engine must have been sucking the bare minimum through the tap, but effectively it was being starved. I've got the cooling system apart at the moment, so can't prove to myself that was the problem, but i know it is!

As for my starting technique, i hadn't realised different engines needed different techniques - the beta bd422 on my previous yacht and the yanmar on my Jeanneau were both started with tickover throttle. best i read the manual again! Apologies if i have wasted anyones time, but you have put me on the right track!

Neil
 
a little bit of drift ...

My 4-108 starts first time every time and runs like a sewing machine.

I disconnected the cold start mechanism about 4 seasons ago and forgot to reconnect it but in spite of this it just cranks up and goes.

How come?
 
neil1967 said:
thanks for all your replies. your comments about fuel lead me to think about what could be the problem, and then it dawned on me - i'd not turned the fuel tap on!
Click to expand...
Nice one Neil1967! What did I say about a 4108 running with a problem that would fell a lesser engine?

Good to hear it's sorted.
 
Check the lift pump diaphragm, and while you have the lift pump apart clean the gauze filters. Then pump it back together and check for leaks before repriming the system
 
take the injectors out and get them serviced, £35 each plus vat, have the injection pump done too, full strip down new seals etc; £400 +vat all done with a 3 day turn around from Colchester fuel injection.
Oh take off the air intake and clean out the filter. And if you really want it to run better change the exhaust from dry to wet from the manifold.
that'll be it sorted for another 30 odd years.
oh yea and turn on the fuel!
 
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