Technical Fuel pump/pump rod

[AndrewRL]

Season's greetings to all!

So Luigi has decided to be a Scrooge and not start. By process of elimination (sparks at the plugs, no fuel coming out of the pump, no blockages in fuel pipes, filter seems OK) I have deduced a problem with the pump (let me know if logic wrong ).

Having removed the pump I was hoping to dismantle it and check it over but it seems totally sealed with no obvious nuts/bolts on the cover unlike those in Haynes and the workshop manual. I know pumps aren't that expensive so may just replace it.

However, before I do that I was wondering if there was any way to check the pushrod. I assume that the engine turning should push this in/out. So I have held my finger on the end of the exposed pushrod and turned the engine via the bolts on the timing cover (or whatever it is called!) as I do to get the timing mark aligned) but can feel no movement. Is this a valid test or is there some other test? I am concerned that the starting issue is not the fuel pump itself but the rod disconnected somewhere.

As always suggestions (in idiots language) gratefully received.

Many thanks!

 

[Paolo66]

The rod should move about 1.5-2mm after 1 full revolution of the engine. It does this by a cam on the camshaft. A cam is basically an oval on a round shaft at an offset. So I think the only way it could not move is either your camshaft is fully worn or the pushrod has snapped. You should be able to pull the pushrod out and it should have a smooth end on it.
By the way I wouldn’t turn the engine over by the bolts on the timing cover. They are only M6 and will shear off if stressed too much. Trust me I speak from experience!
You could test the pump by putting the inlet tube into some water and then pumping the lever the pushrod pushes on. If you get water out the outlet there’s nothing wrong with the pump

 

[Franko500]

Its highly unlikely to be the rod unless it is bent.
As Damian said it only moved about 1.5mm.
You should be able to see it move slightly but you will have to keep your finger on it pushing it in. Otherwise it will always be on its maximum position.
The cam has a lobe on it which pushes it out. Its the spring loaded lever on the pump that pushes it back in. So without the pump in place, once the cam has turned to its highest point you wont see it move again.
Was the car running before?
Have you done anything to the pump or the push rod to change anything?
If not, buy a new pump, preferably a better quality one that you can change the diaphragm and clean the filter. You can always keep a spare diaphragm in your toolkit then.
You will still need to measure how much the rod sticks out of the engine though so that you can fit the correct amount of gaskets when fitting the new pump.

 

[AndrewRL]

Great. Thanks guys.

Will double check the rod again and see if it moves. I was holding it in but perhaps didn't turn the engine enough.

Will perhaps order a new pump but would love it quickly as I have a couple of days later this week to try and get this sorted.

No, I hadn't touched the pump or anything. The last time I was out in the car there was an odd noise from the rear (see my previous post) and I had the car up to check a few things but could see nothing wrong. I put the car down and wanted to drive to see if the noise was still there but it wouldn't start...turns well but won't fire...and that's where the story here starts.

As for the rod sticking out...do pumps come the required "protusion" measurement or is it trial and error? Should I order several spare gaskets in case?

 

[Pazzo500]

Does one revolution of the generator belt = 1 revolution of the camshaft? My 500 came with an electric pump in line with my mechanical pump, so a few months ago out of curiosity I inspected the mechanical pump just to see if it worked. I noticed the same thing as Andrew, that the pump rod did not move at all (while keeping a finger on the end of it) through one revolution of the generator belt. Did we just not turn the engine enough?

 

[Franko500]

If my memory serves me well it will take 2 full rotations of the crankshaft for one complete turn of the camshaft.
As you can see in the photo the crankshaft has a smaller sprocket than the cam shaft. This allows the pistons to go up and down twice through the full cycle of the camshaft.
Therefore as there is only 1 high point on the camshaft lobe driving the pump, chances are if you only turned the engine over once it would not have fully operated the push rod

 

[Franko500]

Here's a good animation of how the camshaft operates at half the speed of the crankshaft to operate the valves for the full cycle of the engine.
http://www.animatedengines.com/otto.html

 

[AndrewRL]

Thanks all. New pump and Luigi eventually coughed into life Had to check the timing again and adjust the carb settings to get the engine to fire and run. Not sure why the carb adjustments were needed...does a new pump upset the carb?

Anyway now need to get out and see if the odd noise from the rear is still there.

Thanks again

 

[F123C]

The rod should move about 1.5-2mm after 1 full revolution of the engine. It does this by a cam on the camshaft. A cam is basically an oval on a round shaft at an offset. So I think the only way it could not move is either your camshaft is fully worn or the pushrod has snapped. You should be able to pull the pushrod out and it should have a smooth end on it.
By the way I wouldn’t turn the engine over by the bolts on the timing cover. They are only M6 and will shear off if stressed too much. Trust me I speak from experience!
You could test the pump by putting the inlet tube into some water and then pumping the lever the pushrod pushes on. If you get water out the outlet there’s nothing wrong with the pump

Other than the pump is now full of water!
Followed by a subsequent thread entitled "How do I get all the water out of my fuel pump?"

AL.

 

[Paolo66]

Just keep pumping it out. If it doesnt come out the pump is knackered anyway. Or you could strip it down. Or instead of water use a small container of fuel [emoji12]

 

[Franko500]

Thanks all. New pump and Luigi eventually coughed into life Had to check the timing again and adjust the carb settings to get the engine to fire and run. Not sure why the carb adjustments were needed...does a new pump upset the carb?

Anyway now need to get out and see if the odd noise from the rear is still there.

Thanks again

Chances are the pump was on its way out and the fuel pump was either pumping a lower pressure of fuel that could upset the mixture, or worse still pulling air in and upsetting the mixture. You would probably have set the mixture based on the fuel coming from the pump.
Now you have fitted a new pump you should be getting a good supply of just fuel and it was running a bit rich.

 

[Chris Botton]

Hi, Not sure if I must open new thread (new to site). My son's '92 Fiat Uno Fire 1100cc had blown head gasket. I removed head to replace gasket, and did so successfully. However when trying to start the car it ran for about 6 seconds and died. Checked spark, fine. Checked fuel, and nothing coming out of fuel pump. Opened pump and when engine turns over diaphram does not move up and down. I found a small shaft/rod (40mm X about 4mm) on the work bench where we cleaned the head. I presume this shaft actuates the mechanical fuel pump, but cannot work out how to fit it back into side of block. If I stick my finger into hole in block where fuel pump sits, I think I can feel a cam. Any ideas how to put this rod in so that it actuates pump.