Starts perfectly but then loses revs, but okay after 30 ses

[wfillingham]

I have a recent problem with my 1961 Dexta.

Its been fine for the past ten years, but in the past few weeks when it starts (and it starts perfectly on the heater/pump), it will go to the correct revs (for about 10 seconds) and then start to die, ie run on two, then one cylinder... very similar to if you had air in the system.

This is not the case, as I have a new filter, and the lift pump is working fine. (ie crack off a bleed screw, and diesel immediately comes out under pressure)

basically, after losing revs it will slowly pick up again, and be fine and run perfectly.

It will then run perfectly all day, similarly, if it is stopped that day, then started again a couple of hours later it will be perfect.

ie, it exhibits all he symptoms of air in the system, but yet there is no air in it....

the injectors are about ten years old, and the pump as far as I know is original.

Please help... as it runs perfect apart from this problem, in fact when warm its smoother and quieter than the 2.0 TDCI engine in my 2005 Jaguar X-type !!!

[Brian]

My first thought is partially blocked filter in the fuel tap, my second thought would be the diesel itself, some of our older tractors can have problems with the new lower sulphur diesel. Your fuel pump rack may be sticking.

Try a litre of Automatic Transmission Fluid in the fuel tank and see how she runs after a bit of work.

[wfillingham]

Ok, thanks for that.

I will try that this weekend.

[wfillingham]

An update to this if anyone has the same problem.... I put in 1 litre of ATF to 1 tank of diesel, and the problem appears to have vanished...

note thtat prior to this I had been running on white diesel from the garage at the top of my road... as I had not been able to get to buy any red diesel from town... so had been running on white for about maybe two tankfuls..

hence, the complete lack of lubrication in the modern fuel was most likely the cause.

I am now back on red diesel (which appears more oily anyway, and also mixed with the ATF.

One other problem the "thin" modern diesel had caused was that the lift pump arm wore badle on the cam in the pump, but with the red diesel/ATF mix the remaining "oil" on the cam/pump arm actually seems oily now.... rather than before where it was about the same as white spririt....

I have researched that 2 stroke oil is also a betetr option than ATF as it is designed to burn, and is designed to be "low ash", and I happen to have about 5 litres of 2 stroke oil left over that will never get used from the past, then I might as well make use of that on my next fill up.

Note that since using this red diesel / ATF mix the exhaust smoke has virtually disappeared!!! it also starts easier, and is smoother when cold.

Since doing this my Dexta is now MUCH smoother than my 2005 X type diesel Jaguar.....

[Cvans]

Thanks for posting your results. You bring up an interesting option about the fuel. I have not heard of using ATF as an additive.

[rich098]

I am having a simular problem with my dexta. but it shuts down and will not run again for a while. have changed fuel and oil filters,drained fuel take and put new fuel in it also added some transmission fulid to the fuel. I have a miss in the #3 enjector and is smoking. it will run for about 30 minutes and then shut down like the fuel has been shut off or air shut off. some time if I work the throttle lever it will run a little longer but then shuts off. it will not start again for a while. do not know if it is getting to hot or what radiator had a leak last month had it repaired and flushed. I put a new exhast manifold on it last month also and it sets a little closer to the #3 injector line. I was wondering if the heat on that line may be my problem with that injector.I also wandered if the govenor diaphram may be the problem but if that is it would I not have the problem as soon as I started the tractor and not 30 minutes later. I cleaned the fuel bowl and lines but noticed a little more trach in the float bowl arfer it shut down but pulle the fuel line off and got good fuel flow.any sugestion on where to go from here.

[commander]

couple of things come to mind.

1) Did you check the strainer in the tank, attached to the petcock? if you're getting good flow at petcock it's probably ok.
possibly a large bit of trash floating around in the tank?

but it sounds more like..........
2) wrong fuel cap can cause problems.....fuel cap needs to be vented type....sometimes people wind up with an oil filler cap
on the fuel tank (yeah it will fit).... Try running it with the cap loose or no cap and just a shop towel stuffed in the opening and see if that solves your problem. leave the tank no more than half full so it doesn't slosh out all over the place while trying this. If it is a vented cap, vent could be plugged with rust, sludge....

If the tank isn't properly vented, you build up a vacuum in there and eventually the lift pump can't overcome it.
And some of the suppliers sell the non-vented caps as being suitable for the fuel tank ...they're not... at least on these old machines with external fuel pumps.

This has come up a few times on the board before......it happened to me a few years back also.

[rich098]

the fuel cap is the same one that has been on it for years and it ran fine befor but I might try cleaning it . there is a floatbowl under the tank and it is full when the tractor shuts down on me so i think it is still getting fuel. the puel pump went out years ago so my dad put an electrical fuel pump onit. I drained the tank but did not take it off and clean it out.I did not want to disconnect all the electrical wires to get the tank of but I may have to do that just to make sure there is no big pices of trash in it.

[ol'Blue]

I had this exact same issue and it ended up being like what was described earlier. The screen just above the fuel shutoff was clogged. When I had the issue I pulled off the tube going into the fuel pump that supplies fuel from the filter. Hardly any fuel would drip out of it. I used compressed air and blew back threw the filter and bubbled into the tank (fuel cap off) Then the fuel would gravity feed to the pump very nicely. The screen in the tank was plugged. If it happens again I will remove the pitcock and give it a good cleaning along with flushing the tank. dave

[commander]

Sure has all the markings of a fuel problem of some sort......My advice is to work through the system till you find it....starting with the easier (and cheaper) things first...tank,cap and petcock, filters, 'lift' pump (electric on yours) , fuel lines .... Make sure it's not starving the injection pump ..and that it's not sucking air into the line.

Other than the checking diaphram for holes , and checking the 'rack' and linkage for binding, not too much you can do to repair the injector pump and injectors except swap with rebuilt units.


Is there a filter / screen in that electric fuel pump? Might have one in the inlet.

Excessive smoking sounds like an injector - if it's black smoke ...High oil consumption (typically rings) tends to burn blue/greyish.

Fuel inlet on the injection pump is at the front, near number one pump element......if it's not getting enough fuel, that might show up in the number three element first (farthest from fuel inlet).

Got any way to install a fuel pressure gauge in the line between the electric pump and the injection pump? See if the pressure is holding there when the engines dies.

I have an electric pump on mine also (a Carter)......got tired of the low quality of the available mechanical units I was getting. So far, no problems ..but only have about 40 hrs on it so far. Too early to comment on how long it will last.