Another Lift Pump Thread

[tanman_2006]

Well it must be their time of the month, my lift pump is getting flakey too. :nonod:

I noticed the other day my truck was making a weird knocking sound but it wasn't coming from the engine bay :???:

The next day I realize the LP isn't running after I shut the truck off... :mad2:

Later that day I figure out my LP is the knocking sound, no hummmm as usuall, it sounds like a wood pecker :???: I haven't checked the pressure yet but it used to sit ~7 at idle but i lost the line for my mech guage and have been too busy with classes to get it figured out.

On a brighter note my neighbor is swaping the 12psi FASS off of his 01 Cummins for an Airdog 150 (i think that is the model) and said it will be forsale for a reasonable price. I might offer the price of an OEM 93 pump.

On a very annoyed note I STILL have not recieved the Walbro I bought from someone a few months back. :WTF:

 

[bshull]

I would do a pressure/volume test on your lift pump. I have found when I can hear a lift pump "hammering" it is not getting fuel to pump. I suggest back blowing the fuel line from the lift pump to the tank (remove fuel cap first!), blowing from the lift pump to the ffm and do you have a lot of vacuum when you take the fuel cap off.

What is the temperature, you might have a diesel cloud point issue going on that is clogging socks (especially if you have a gas sock on your sender) or clogging fuel filter. I was shocked when I took a sample of "pump" diesel and set it in the freezer and it clouded up and thickened up. I also added additives to the sample to try to keep it from clouding up, the test scared me. Too many variable to be conclusive tho.

let us know what you find

Brian

 

[Matt Bachand]

Always a great time to have a fuel pressure gauge.

I had a walbro fail on me a few months in and would probably have never noticed if I didn't have the gauge.

 

[tanman_2006]

I would do a pressure/volume test on your lift pump. I have found when I can hear a lift pump "hammering" it is not getting fuel to pump. I suggest back blowing the fuel line from the lift pump to the tank (remove fuel cap first!), blowing from the lift pump to the ffm and do you have a lot of vacuum when you take the fuel cap off.

What is the temperature, you might have a diesel cloud point issue going on that is clogging socks (especially if you have a gas sock on your sender) or clogging fuel filter. I was shocked when I took a sample of "pump" diesel and set it in the freezer and it clouded up and thickened up. I also added additives to the sample to try to keep it from clouding up, the test scared me. Too many variable to be conclusive tho.

let us know what you find

Brian

I do have vacuum but my truck has always had some and it does have a diesel cap.

It has been abnormally cold lately here in Ok, all time record low of -31* 3 miles north of where i live, hasnt been over freezing for a couple weeks here either. But i do run a double dose of winter powerservice and nd30wt.

Always a great time to have a fuel pressure gauge.

I had a walbro fail on me a few months in and would probably have never noticed if I didn't have the gauge.

The Walbro I got is going on my 93.... AND IT SHOWED UP TODAY! The mail man heard my complaints!

The factory pump is what seems to be crapping out on my 95. My thoughts for replacement are either a 93 LP or my buddy's FASS if 12psi wont hurt the IP

 

[buddy]

Grab that FASS, it will actually help your IP. 12psi is a good pressure pre filter, because the filter will drop it at least 25%, so you should get 9psi to IP then. GM and Stanadyne wrote in the IP manual that it should have 9psi of inlet pressure, so there is actual tech data telling us all to get more powerful lift pumps. The problem is GM got a 9psi pump and put a 5micron filter and restrictive housing between it and the IP. So they messed up, and were only putting about 6psi to it, and dropping well below that under load. Then we further increased the fuel demand which made things even worse.

 

[tanman_2006]

Grab that FASS, it will actually help your IP. 12psi is a good pressure pre filter, because the filter will drop it at least 25%, so you should get 9psi to IP then. GM and Stanadyne wrote in the IP manual that it should have 9psi of inlet pressure, so there is actual tech data telling us all to get more powerful lift pumps. The problem is GM got a 9psi pump and put a 5micron filter and restrictive housing between it and the IP. So they messed up, and were only putting about 6psi to it, and dropping well below that under load. Then we further increased the fuel demand which made things even worse.

Good to hear, I will see what he will let go of it for.

He told me the electronic Cummins IP can't take much over 12-15psi before damaging the front seal and filling the crank case with diesel so I should make sure I don't have the same issue.

 

[JMJNet]

My suggestion is to do the relay mod for the LP!!! That 95, the OPS controls the LP when engine is running.

I am sure you know that.

 

[tanman_2006]

My suggestion is to do the relay mod for the LP!!! That 95, the OPS controls the LP when engine is running.

I am sure you know that.

I will do this on both truck when i put the new LP's in. The 95's still works so the OPS is still functional so the relay mod would do nothing to help this, but would be good preventative maintenance. However my 93's LP problem has yet to diagnosed so it could just be a bad OPS or w/e else controls them in 93.

 

[tanman_2006]

Ok so I did some diagnosing on both trucks today.

95: 3 psi in gear with key on truck not running. LP sounded terrible and unstable trying build 3psi and it took atleast a minute to build any pressure at all.

93: LP WORKS! I crawled under and it has a nice shiney LP under there, when jumpered off the battery i had a nice growl come out. Checked the fuze (pass side firewall) and it is good. How do i know if it is a bad relay or ops?

My plan at the moment is to put the Walbro on the 93 since it is my pulling truck and will need all of the fuel it can get and put the 93 LP on the 95 since it is mostly highway and light towing DD. I still plan to get the FASS but I doubt i put it on anytime real soon.

 

[buddy]

In both vehicles the relay only powers the LP when the igntion is in the start position. So in th 95 you were using the relay to test it.

In both vehicles the OPS powers the LP when the engine is running.

So if the LP is not running in the 93 with the engine running its because the OPS has failed. You can put a relay to run the LP, either trigerred by a new OPS or an ignition source. It runs off the OPS in case you wreck and fuel line is leaking, OPS will stop powering the pump if you couldnt turn off the key. Some people find the failed OPS will pass enough current to trigger the relay, but I'd get a new one if you want to do the OPS relay mod. On the 93, you can see how much voltage the OPS is allowing to pass to the LP by checking voltage at pin G of the DLC.

 

[tanman_2006]

Well crap, the 93 doesnt have pressure anytime so the relay and ops might both be bad. I have a new ops so i will put it in when I pull the intake to give the IP a 1/4-1/2 turn. Should be doing the ip turn up this week maybe even the walbro LP if time permits. Should make a big difference.

When i do the relay mod will both the start up relay and ops be going through the same relay? I have looked at pictures but my understanding of electrical components is very poor.

The 95 will most likely sit waiting until spring break to get torn down and get a whole list of upgrades. That will be in its own thread most likely.

 

[buddy]

There is likely a CRK fuse under the steering colum that allows the 93 to pump while cranking.
Unless you can crank for about 5 seconds without the truck starting you may not see any pressure as a result of the LP getting power from the relay. Supposedly its supposed to run your LP during WTS as well through the relay, but not heard anyone with a 93 say that works. There is supposed to be a purple/white wire between the Glow controller and the relay.

 

[JMJNet]

It is probably the OPS. You can put 12V source to the LP and open the t-valve to see if LP is good.

The OPS should be under the GP controller.

 

[tanman_2006]

It is probably the OPS. You can put 12V source to the LP and open the t-valve to see if LP is good.

The OPS should be under the GP controller.

Yeah, I am betting on the 93 being the OPS. I already jumped it and she purrs nicely.

I have to pull te intake already to turn up the pump so IMO while you have the intake off it is a good idead to throw in a new OPS if the current one is of unknow age/condition.

I am taking my 6.5's in to the Cummins performance shop (Outlaw Diesel) that my buddy works at and educating them on 6.5 how to and using their lift and tools in return There maybe an exchange of beverages too.

 

[buddy]

While youre at it the OPS relay mod will prevent future failure and better supply power to the Walbro. Also the OPS extension from PMDcable.com is pretty handy for getting the OPS from behind the engine for easy access to it and the harness.

 

[tanman_2006]

Got bored....

Well instead of just sittin on my butt after church today I decided to take a diesel bath... I swapped the LP's on my trucks. Result was 9psi @ idle 4psi WOT in Econ and 2.5psi WOT in performance :hihi: BIG DIFFERENCE

93 LP

95 LP

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