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Old 09-12-2010, 09:43 PM
barry123400 barry123400 is offline
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Join Date: Nov 2004
Location: Nova Scotia, Canada.
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[QUOTE=qwerty;2543230]
Quote:
Originally Posted by barry123400 View Post

The links in post #7 should clear up any confusion.
Thanks. got it. The partially open lift pumps check or delivery valve if you wish was the way of less resistance for the fuel you were pumping with the lift pump. There has been a visual back and forth surging of the fuel effect observed before on several posts in the primary filter. Thats with the car running. The valve possibly was not quite as open as yours in those cases. Or perhaps more so. They exhibited some questionable running but all would start after sitting for periods I think I remember.

For your no fuel available after the car sits overnight there may still be someplace air is entering the system. This would have allowed the fuel to escape back towards the tank with the poorly fitting lift pump check valve. A truly sealed system cannot back drain even with a very poor check valve in general. My guess at these cars ages most those valves and seats are in less than stellar condition.

The air that displaces the fuel can come from even before the lift pump in my opinion rising through a leaky check valve. Over time moving upward and enabling the fuel to back down by gravity.

What happens then I suppose is instead of the lift pump building presssure instantly it has to compress air first. Either internally or somewhere ahead of it. Generally speaking at reasonable temperatures all my diesels catch almost instantly with the key after sitting for prolonged periods.

This indicates to me on those engines their fuel supply systems are tight and in reasonable condition. I know they are getting good sustained fuel at pressure as soon as the engine turns or very quickly if not. The level of fuel in the injection pump has not been depleted in some of the elements by back drainage over time. Even in one extreme example of sitting for four years.

Since any place past the lift pump is under positive pressure it would vsuially leak under loading. So the remaining sources if any might be gunk in the relief valve on the injection pump or a point of air ingress before the lift pump. This relief valve gunking possibility is based on your finding gunk in the area of the check valve increasing chances of the remote possibility.

Although your car will probably run and start okay after long periods of sitting. A slight problem may still remain. I have been wanting to establish how long a good system retains base fuel pressure in the injection pump for some time now. Or how quick the pressure rises on the first crank or two of the engine. This may be important for quick and clean starting.

Most lift pumps in service probably have a little valve leakage at their age on this series of cars. We just never have bothered to quantify where the acceptable level of retention is. Instead I personally have done the clamp off test to make sure the lift pump can supply at least 30 lbs presssure as a general indication of lift pump performance.

We are basically restoring functions on cars of this age as well as general repairs to get them back to what they were at one time. Or as close as economically practical. This whole area is a cheap one to recondition. The bottom line is get this system right and overall the car will thank you for it.

Your proof all is okay for air leakage is simple. After sitting for at least overnight. In reasonable ambient temperatures. How much does the engine crank before it catches. Any more than two turns of the engine is probably too much if compression and glow plugs are in reasonable shape.

Now you are just left with the unknown of how much sustained pressure is present when running. If this pressure is also very low starting may be delayed a little. Simple to check by closing off the return fuel line temporarily. If improvement in starting ability occurs under test. Chances are that return line valve on the injection pump is either gunked up or weak.

The fuel supply system is actually fairly simple on these cars. At the same time it needs to be in reasonable condition overall. This general area makes a difference
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