Question on lift pump TEST.

[jnhutch]

Ok, here is my question.

I changed out my electric lift pump on my 94 6.5td.

I dont think it was bad, I just did it because it has 200000 miles on it.

Now, I tested the pump while the truck was running and it is recieving 12v as it should, If I open the valve on top of the fule filter, while the truck is running, I can bleed the air and diesel will shoot out. But If I open the water drain valve with the truck running, nothing comes out and the truck dies. I read on some other fourm that you should see gas coming out of the water drain valve when it is running. If I manually turn on the pump with the truck off, I can bleed the fuel filter and when I turn on the water drain disel will come out at a pretty good rate. The master question is, should you see diesel at the water drain valve when the truck is running or not... If so, what should I look at to try to fix this.... Keep in mind, I have tested and verified that the lift pump is running while the truck is running...

Thanks, please help if you can.

Mike.

[Turbine Doc]

Yes you should see fluid with the filter bowl drain cock open and engine running, if not I suspect bad OPS common fail item, better test of lift pump is put 0-15 psi gage on filter drain, and drive while watching gage, make sure rubber tube does not get pinched in routing, or you will get false dead head reading of pressure, you should see pressure go up and down in response to throttle/engine load.

At idle good lift pump will supply 4-6 psi, running steady about 4 psi, on hard accel or heavy load going up hill may drop to as low as 1 depending on pump condition but eventually back to 4 psi or max seen at steady state speed.

Less than that possible weak lift pump, blocked fuel filter, or power to lift pump, something I'm close to installing is a 12V LED in parallel with hot leg of lift pump power, if LED is on power is going to the pump, which eliminates that element of doubt when running,

[ol9465er]

Bought my truck in 2000 from dealer - don't know if new pump or pmd installed.

Just starting stalling couple weeks ago. Has been increasing - seven today alone (worst day so far). Have DTC 35 code and suspect PMD of course but still testing. Local diesel mechanic (BD Diesel Power) says might be electro-magnetic valve in ip sticking causing DTC 35 - suggested filling filter bowl with concentrate Standyne fuel additive when filter changed - did that but still stalling.

When changed filter week ago (was dark) tried the water drain test and truck died and no fuel came out. Will try again after new pump install.

Did test lift pump by applying 12 volt at DTC connector terminal and ran, sounded clicky or undulating (is this normal?) However, have bought new lift pump and am just going to change it as would like a new one on as insurance - not going to do further tests on old one.

You advised that I should connect pressure gauge to drain hose and drive for while to test pressures - will try this after new pump on. Thanks for tip.

Question about LED - where are you connecting this - from the DTC connector or other?

Question - any good tests for Oil pressure switch.

ol9465er
1994 Chev 6.5 3/4 Ton - Stock
279500 Kms (174600 Miles +/-)
Just took cover off when stalling started.
PMD warm but can hold hand on even after engine hot.

[rameye]

I just went thru this PITA with my truck.

Short version:

When you are turning the truck over to start the lift pump gets it's power from a different place as opposed to when its running.

If the you get no pressure measured on the pet cock when it's running but you did have pressure when you were cranking it over its the oil pressure switch...99% (there is always the chance of a strange occurance)

Yes the lift pump goes click, click, click.

So you need to replace the OPS located in the rear drivers side of the engine...and to eliminate a future occurance you can search the forum and wire in an OPS relay.

have fun..let us know how you make out.