Bloody fuel pump.

[burgundyben]

I've just fitted a recon fuel pump to one of my engines, under no load its fine up to 1500 then above that is hunting up and down all over the place. It wont rev above 2000. Under load its not hunting but still wont go above 2000, reckon the pump company might have got the govenor wrong.

Just about to phone them.

They're a bastard to change.

:-(

<hr width=100% size=1>Sod the Healey - I think I'll buy an E-Type.

 

[TonyBrooks]

You might be correct, but you do not give the engine, pump type, or why you changed it, so I can not advise.

From what you say I would be considering fuel starvation - blocked filter(s), blocked lift pump strainer, blocked pick up strainer in the tank (if fitted) and on Nanni's I have heard about blocked banjos.

It could even be air being drawn into the system - how much care did you take with fiting the unions?

Tony Briooks

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[burgundyben]

Tony,

Thanks for your response, I had wondered about asking you as I saw the offer of help, best share it here as others might be interested.

Its a T6.354, 145 hp, its an ex race boat and the engines are 15% over fuelled to make them up to 165, a common mod on this engine, the pump is a CAV DPA.

Both engines have been rebuilt, new blocks and liners and pistons etc, the injectors were serviced but the pumps not. they have done about 100 hrs.

One of the pumps started leaking so I sent that and a spare I had off to be rebuilt (in july) and both set at 165. I fitted one back on the engine where the leak was and it ran fine.

The other one I have only just got round to fitting, there has been a problem of air being drawn into the pipe and so there is now a new 5/16 copper pick up pipe which is clear (checked it), I'm pretty sure its not lack of fuel as I have clear lines and I can see no air gaps in either the line or the return, this was a visible problem before I fitted the new pick up pipe.

The engine does not hunt, it misses, when they are suffering fuel starvation/running out the revs tend to rise then return back down in a cycle over say 2 or 3 seconds, this is different, they rev at say 1800 and then dip just for a spilt second, like a miss fire rather than hunting.

Suggestions? I think it might be the govenor in the pump.







<hr width=100% size=1>Sod the Healey - I think I'll buy an E-Type.

 

[burgundyben]

Forgot to say, changed it cos wanted to fit a pair of rebuilt ones, nothing wrong with the existing one but it was the only stone left unturned when the engines were rebuilt.

Ta.

<hr width=100% size=1>Sod the Healey - I think I'll buy an E-Type.

 

[Nick2]

Ah Tony you just slipped in with advice ahead of me on this one .

I'll leave this one to you as you have already started.......



Nick

<hr width=100% size=1><A target="_blank" HREF=http://arweb.co.uk/argallery/Nick2>http://arweb.co.uk/argallery/Nick2</A>

 

[TonyBrooks]

Please jump in - my practical experience can be a bit out of date when people start talking engine makes etc.

We all learn from each other

Tony Brooks

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[TonyBrooks]

Sort of running through the DPA pump, as we now know it was operating ok before, and you are sure there is no air getting in.

1.two type of DPA Mechanically governed - long and thinish.

2. Hydraulically governed - short with a sort of turret on it where the throttle & stop are.

First the transfer pump in the round end of the pump - a vane type pump, that is simple and robust - I can nopt see this being a problem.

Second the regulating valve - right in the swelling on the round end cover - if sticking (a bit of grit or something) this would cause the fuel pressure inside the pump to rise & fall as it stuck and freed itself. On a hydraulically governed pump this would caause the governor to jump up an ddown & you would get a rise and fall in speed. On both a mechanically governed pump the varying pressure so created would "bugger up" the amout of fuel flowing into the "pumping chamber" to push the high pressure pistons out, again you would get speed alterations.

The governor Could give thses symptoms, especially a hydraulic one if the governer piston was sticky.

The high pressure pump - two or four pistons (perhaps 6 pistons on a six cylinder) driven together by an internal cam ring - forced apart by fuel pressure via teh governer - I can not see this being the cause.

Advance retard mechanism - this is in the swelling at the bottom of the pump and moves the cam ring according to transfer pump pressure. If the regulator valve was sticking (as above) the varying fuel pressure would advance & retard injection, giving a varying speed.

Now I have taken a DPA pump apart (to remove water) withj a hammer, screwdriver and a pair of gland nut pliers, but I would not advise you to try - dirt is fatal to injection equipment - and I think you could have some inside the pump.

However much trouble it is, get it back to the overhauler for a report at least.

Hope this helps, but I can not see how.

Tony Brooks




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[burgundyben]

Thanks chap, I had come to the conclusion that it needed to go back to the pump shop.

Cheers.

Will give them a call now.

<hr width=100% size=1>Sod the Healey - I think I'll buy an E-Type.

 

[Nick2]

You are too kind and far too modest...

Nick

<hr width=100% size=1><A target="_blank" HREF=http://arweb.co.uk/argallery/Nick2>http://arweb.co.uk/argallery/Nick2</A>

 

[TonyBrooks]

More rumination

Don's suppose you managed to transpose the two pipes between the filter and teh DPA pump? Given a slightly faulty or missing NRV in the filter head, I think what you describe could be a result of incorrect pipe connection.

The pipe comming from the filter that has an outgoing arrow on teh filter head, by the union, should go to the round, injector pipe, end of the DPA pump.

Its a long shot, but worth a check.

Tony Brooks

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