I have had my Airdog 150 installed for a couple months now, and I just got around to asking this- When I first start the truck in the morning, it idles like it has a huge cam in it. The truck will run fine under load, but at an idle, it sounds (and feels) like a race car. After the truck warms up, it idles normally, but the engine still has much more diesel clatter than when the pump is switched off. I'm not really worried, but I guess I'm asking if I should be. I know that some pumps will cause this if they are not regulated to the proper pressure. Is this an issue?

my truck idled alot smoother and quieter after the lift pump , i would check the pressure of the supply line after the lift pump and make sure its under 10 psi .

OK i'm still learning so...

What's a lift pump? and what does it do???

my truck idled alot smoother and quieter after the lift pump , i would check the pressure of the supply line after the lift pump and make sure its under 10 psi .

Thanks for the reply- I suppose that I should check the pressure. I was just curious to see if anyone else has experienced this.

and for 148CMEUPHI:
A lift pump is an auxillary pump to feed your high pressure fuel pump (CP3). It helps eliminate fuel starvation problems associated with the higher power some of us are making with our trucks. There is tons of info on this site about lift pumps if you do a search.

Excessive lift psi inhibits the Pump regulator's ability to regulate rail psi. Excessive psi at idle causes the choppy, raspy idle.

From what I hear some people are actually writing tunes to duplicate this loping sound...

I get this sound in the morning when i start it up and if i go anywhere before i let it warm up it goes silent and starts blowing smoke....but i dont have a lift pump so that may be it. It does sound pretty cool though.

Most likely too much fuel pressure. It should be regulated. There is a spring in the pump that is responsible for this. Manually checking fuel pressure will point you to the problem.

mine does the same. mechanical lift pump. not sure on psi, but it has a nice tone to wake up too. sounds pretty good if you ask me

You are getting too much fuel at idle speed.

i have always noticed if you have above 9 psi at idle, it will make your motor idle choppy as if it had a cam.

Thanks for the replies guys! I had suspected too much pressure- I need to put a gauge on it and see where its at. I know that the pump is "supposed" to be internally regulated, but I do recall someone mentioning that some of the pumps were set up with the pressure too high. Is this hurting anything, or is it just a symptom of high fuel pressure? Like I said, I don't mind it, as the lope goes away after the truck is warm, but I don't want to cause any damage and/or accellerated wear and tear on my fuel system.

Someone mentioned 9psi at an idle but what do you want above idle? Cause some of the lift pumps are rated at 12psi, should a guy stay away from those pumps?

i thought the lb7s have the idle problem with higher pressures i think the air dog 150 comes preset at 12psi you can trim the spring to lower the pressure and it will still supplie enough fuel.how much to cut off i dont know im sure someone will chime in that has done it.

If you have a scantool all you need to do is look at the Desired rail pressure Vs the Actual rail pressure. If the Actual rail pressure is too high the lift pump has the pressure too high for your application. As a rule of thumb, anything over 8psi on a Duramax gets into a possible problem range. Some will take more and some will take less.

If you have a scantool all you need to do is look at the Desired rail pressure Vs the Actual rail pressure. If the Actual rail pressure is too high the lift pump has the pressure too high for your application. As a rule of thumb, anything over 8psi on a Duramax gets into a possible problem range. Some will take more and some will take less.

Its funny that you should mention that. I was just wondering if I could check it that way. Now I know. I'l post my findings tomorrow.
Steve, can you define "problem range"? By problem, do you mean a loping idle, or engine damage?

you should check for vacume leaks and fuel leaks as theese are comon symptons for the problems your haveing. is your pump loud or can you hear it easly if so check for va cume leaks as this is more then likely your problem

The problem range is when you cause the regulator to go out of control. In most cases it does not hurt but I did see one that cause fuel knock in the motor at low speeds and if you let that go it will cause damage. As far as a vacuum leak there is no throttle blade so there is no vacuum. Now it could be a fuel leak but most likely not. The lift pump pressure is the most common cause of the lope at idle if you've added a pump. LB7's seem to do it worse than the others for what it's worth.

I haven't had a chance to check the pressure yet, but I really appreciate the help. I definitely don't want to dmamge anything. Like I said, its not too bad- the lope is only present upon initial startup, and then goes away after running for about 5 minutes. That strikes me as odd- I would think that high pressure would be rather consistent, so my thinking is that the lope at idle should be consistent. However, I am far from an expert on a diesel fuel system. :o:

The problem range is when you cause the regulator to go out of control. In most cases it does not hurt but I did see one that cause fuel knock in the motor at low speeds and if you let that go it will cause damage. As far as a vacuum leak there is no throttle blade so there is no vacuum. Now it could be a fuel leak but most likely not. The lift pump pressure is the most common cause of the lope at idle if you've added a pump. LB7's seem to do it worse than the others for what it's worth.

theres no vacum ? yes there is on air dog 150 throught the air sperator

I haven't had a chance to check the pressure yet, but I really appreciate the help. I definitely don't want to dmamge anything. Like I said, its not too bad- the lope is only present upon initial startup, and then goes away after running for about 5 minutes. That strikes me as odd- I would think that high pressure would be rather consistent, so my thinking is that the lope at idle should be consistent. However, I am far from an expert on a diesel fuel system. :o:

is your pump kinda loud ? sound like its drawing air into me vacume

is your pump kinda loud ? sound like its drawing air into me vacume

Not loud at all. I can hear it, but its not loud enough that I can hear it with the truck running. I'll check to make sure the pump isn't pulling air as well as checking the pressure. You guys rock. :D

Ok, I finally checked rail pressure at idle. Desired is around 5800psi, and my actual is approximately 6800 psi. Obviously, I have too much pressure.
Here is where my curiosity comes into play- how does a small variance in pressure, lets say 12psi when it should be 9 as an example, cause the cp3 to produce an extra 1000psi? Is it because it overpowers the regulator?

The CP3 controls the high pressure side with low pressure. So for an example the CP3 uses a 500 to 1 control.
Low pressure side = 50 psi, high side pressure = 25,000.
Now low side = 11.6 psi, high side = 5800 psi.
Now force the low side up with a lift pump to 12 psi and you get 6000 psi high side

Does that answer your question?

The CP3 controls the high pressure side with low pressure. So for an example the CP3 uses a 500 to 1 control.
Low pressure side = 50 psi, high side pressure = 25,000.
Now low side = 11.6 psi, high side = 5800 psi.
Now force the low side up with a lift pump to 12 psi and you get 6000 psi high side

Does that answer your question?

Yes sir it does, and it makes perfect sense to me. I like being able to ask questions here and learn about the "new to me" diesel technology. Thank you for the explanation.

So now I have to ask, is the 1000psi difference in desired vs. actual fuel pressure a major cause for concern, and it it something that I should rectify asap?

The 1000 psi is because its more than the regulator can handle. I would fix it soon as I could, not guess what damage maybe done but that's just me. In the end it's all up to what you want to take a chance with.

I don't want to take a chance with anything these days-I'll be contacting Airdog on monday for a solution. Thank all of you for the help, and a big thanks to you, Steve!

Andy

I have an interesting update: I talked with a tech guy at Pureflow Technologies, and he explained that sometimes the regulator spring in the pump needs to be shortened to resolve this issue. He provided me with all the info on how to do it, and was very helpful.

Now the kicker: After obtaining all the info, my truck idles fine. I also verified proper fuel pressure on a few seperate occasions- approx 6000psi desired, and the actual is within 50 psi, plus or minus. All I can ask, is what happened? The only thing that has changed is the outside air temperature. Any thoughts?

It would be possible if the air temperature isn't as cool as it was before. If the temperature of the fuel is slightly warmer than before it's thinner and the pump may make slightly less pressure on thinner fluid. Keep an eye on it as you stated before it went away once the truck was warm before.

It would be possible if the air temperature isn't as cool as it was before. If the temperature of the fuel is slightly warmer than before it's thinner and the pump may make slightly less pressure on thinner fluid. Keep an eye on it as you stated before it went away once the truck was warm before.

Sorry, I was being dumb and didn't mention that it is colder outside than it has been over the past few months...that's why it doesn't make any sense to me. Oh well, maybe it fixed itself. Hahaha I'll just keep an eye on it and see what hapens. Thanks again, Mr. Cole. :o:

If you run too much lift pump pressure it can mess with the FICM and cause an erratic/rough idle. I would lean more towards that being your problem.

Standy i got your pm today then saw this thread. Sorry for the delay. But this happens often with the duramax. Just by lowering 1 psi fixes the problem. They are like a stubborn girlfriend when it comes to their desired pressure. Glad we can get you fixed. And by the way your pm was telling you to call me and I would tell you how to shorten you spring!!


Haha- I got it all fixed, as far as I can tell. Toby recommended that I remove one coil from the spring, and all is well at this point. Thanks again for everyone's input....it was very helpful.