I have a 1999 truck that are well known to have weak pumps on them. This truck has 140,000 on it with the pump wire peirced and I drove over 3000 miles with out a lift pump on it. Alot of these miles are pulling heavy. I have good pressure on the fuel, but I still suspect the pump is weak so how can I hook up a flow meter to it so that I can monitor fuel amounts passing through it.

 

A wire tapped early pump that went 3k with no LP
Man that pump aint ever gonna die

 

I can't complain about anything on this truck, "to much". I have used and abused it and it's never left me stranded. I think I got one of the better trucks built that year.

 

I've looked around quite a bit and the only flow meters I've found for diesels are quite expensive. See them here http://www.floscan.com/html/index.asp

 

Looks like these are so expensive because they measure flow rate into the pump and then the flow rate back through the return lines to the tank and figure up the differance to give you what the engine is actually pumping through, what I was thinking of is just a straight how much fuel is the pump pushing. Something way simpler than these meters.

 

There is a simpler and cheaper way - a fuel pressure gauge. Pressure is the measured resistance to flow. If the pressure is within specs, there will be adequate flow to the VP.

 

I show pressure as being good, but in previous threads there was talk that this does not give an accurate measure for the injector pump. They were saying that you need to measure the amount of fuel the pump is pushing, so I was looking for a way to monitor that. My truck is running way short of power these days under load, and I think I'm down to the problem being in the fueling system somewhere. I am running about 18# of fuel and that never budges unless the filter is ready to be changed, so now it is injectors or IP. Also have a little bit of a stumble at idle.

 

Most dealers use a flow test when checking for LP warranty replacement.
Pretty crude though, basically a measuring cup and stopwatch.
Can't use it with the engine running.

 

$1500!!! Holy CRAP!!

 

If you're measuring post filter, the the restriction should remain more or less constant.
The only variable would be flow, which would showing as reduced 'normal' pressure.

Or am I out in left field again......

 

I think the injection pump works or it doesn't, weather it be mechanical or electrical. If the internals of the pump were so badly worn I would think starting or idle issues would be present before low power. Have you checked for codes?

After all, isn't the pumps job to meters and pressurizes the fuel before delivery to the injectors?

You already know that the IP will still do its job without a working lift pump. Volume is more important than pressure. The IP delivers very little of fuel it receives to the injectors. Most of the fuel is used to cool and lubricate the pump and then is returned to the tank.

 

Yes, that is what I was getting at.....since pressure is just the resistance to flow, when the flow drops, so too, will the pressure.....When you are running at WOT and notice a pressure drop below your minimum spec, the flow has not actually changed but the pump has failed to deliver the minimum flow required maintain the desired pressure. I DO NOT agree with the Cummins approved method of measuring fuel volume to indicate if a lift pump is bad or not.....this is the free flow measurement and does NOT take into account the effect that pressure has on that flow. I see no problem with using a fuel pressure gauge to determine if the IP is getting an acceptable volume of fuel.

 

It seems like you could use a fuel pressure gauge before the pump and then use one at the overflow valve, because what the fuel isn't injected is used for cooling and lubrication and circulated back through the overflow valve to the tank, so comparing the pre IP pressure and overflow pressure could give you an idea of how much fuel is actually injected, and if the over flow rate gets higher for a constant pre IP pressure it could show ''blow by'' with in the pump and result in low power since more fuel is being returned to the tank than being injected

 

If you have a electric gauge I would suspect the sender is shot. I've seen several that read the highest pressure they have ever seen and zero with nothing in-between when the sender fails. Gives a false sense of security.
Check your pressure with a mechanical gauge to be sure.

 

It is a mechanical guage I use. It's setup up so that it sits by the windsheild wiper coming out of the hood over the cowl. By doing this I can see it while I drive with out having fuel to the inside of the cab.