2nd daft 816 question

[martinsaunders06]

on my 816 the cold start fuel primer gauge shows pressure all the time the engine is running= is this correct or should it only show a reading when hand primer in cab is pumped?. ?should the the gauge side be isolated when primer is in locked/shut position.thanks

 

[jwaller]

does it drop down when you shut the eng off? If you are losing press after the eng has been sitting for a week then your primer pump has lost it's seals and the eng pump is sending press thru it into the eng and you prob need to reseal the primer pump.

If the press gauge stays pegged all the time even after a week then it's a bad gauge.

 

[jwaller]

in normal operation the gauge should show 0 when the engine is running and the primer pump is locked in the dash.

 

[martinsaunders06]

sounds like my seals are allowing pump pressure thru coz after a week gauge has dropped right down.i suppose there are o rings inside primer then.thanks for confirming that

 

[jwaller]

there are 2 orings in the back of the primer pump. I got mine at the hardware store. just use a wrench and unscrew the hand pump from the dash and pull it straight out. 2 new orings and your good to go.

also since you are having this problem you know your getting raw fuel thru the primer system while the eng is running. make sure you haven't diluted the oil with fuel.

 

[martinsaunders06]

do you mean excess fuel going into inlet manifold thru cold start injector?mine has a shut off tap in line just before injecter which is off?

 

[jwaller]

Re: RE: 2nd daft 816 question

do you mean excess fuel going into inlet manifold thru cold start injector?mine has a shut off tap in line just before injecter which is off?

what I mean is that with your seals gone the cold start injector is dumping fuel into the motor all the time. thats why your are seeing pressure on the gauge when your not supposed to. fix those 2 orings and fix them quickly. does your truck otherwise run good? I would imagine it could lead to some slight run on when you try and shut it down. it should shut off but not until it's sucked all the fuel out of the cold start system first.

report back when you have them replaced. I bet it will run lots better.

 

[rmgill]

RE: Re: RE: 2nd daft 816 question

Martin, that shut off tap just before the injector is not what you think it is. The fuel hand starting pump is also a priming pump for clearing air out of the fuel system. That tap is the high point in the system and you pump the handle to get fuel out of that point. If it's closed it does NOT shut off the fuel going to the flame heater nozzle.

And the more I think about it (and look at the -20 and -20P manuals), the more I think that that gauge should not show pressure unless you're pumping on it. I think the source of fuel for that pump is before the Injector pump's pressure side which should mean it's NOT going to see pressure from the engine running. Which makes me think you have a faulty gauge or something else going on.

First thing to check is to see if you have fuel spraying. Crack that valve with a bucket under it while the engine is running it should NOT spray with any pressure OR you can pull the spray nozzle and see if it sprays or dribbles fuel while the engine is running. If it does it either needs to be cleaned or likely replaced.

 

[martinsaunders06]

yeah mine actually has a inline rotary brass tap fitted before the injector which blocks fuel flow to that injector as well as the venting tap to bleed system

 

[martinsaunders06]

that last post wasnt meant to sound as it reads,perhaps mine has been retro fitted at some time,its been painted sand colour in past and maybe it was done for operating in warm climates?.cant run it as pt pump being checked as previous owner ran it with no fuel filter!!.but thru this site i read previous posts aboout fuel hoses sucking in air which ive found my do so ive replaced hoses and now waiting for pump(engine had no power and slow throttle response).

 

[martinsaunders06]

thanks rmgill, it turns out that my pump has some sort of damper unit fitted at bottom which im told is a retro fit to try to help with engine rpm surging? and the connection for this is next to cold start primer supply pipe and the two of them were connected back to front hence the cold start system was under full pump pressure all time engine was running and hence gauge on dash flat out all time.have now swapped over and ok now thanks boys for info