LB7: Fuel Pressure specification
- Thread starter nh_duramax
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On a LB7 at full temp its about 4600-4800 PSI. While coming up to temp I see mine as much as 5200-5500 PSI.
Not sure for other DMAX's but I would bet its similar.
Not sure for other DMAX's but I would bet its similar.
Yes but I think he may be asking to diagnose a issue and he may not have the tools to able to see whats commanded/actual.
If he can't read desired and actual, he won't be able to diagnose anything. Unless he has one of those gauges that T in to the factory sensor.
From the stock tunes I have on hand, here are the pressures you should see for a HOT engine (it will be higher while warming up):
LB7 - 35 MPa (5,076 psi)
LLY - 32 MPa (4,641 psi)
LBZ - 30 MPa (4,351 psi)
LMM - 30 MPa (4,351 psi)
LML - Lol, wish I had a LML tune in EFILive...
True, but what I was thinking was along the lines of that he at least had a gauge to read actual.
thank you for the responses. I have looked high and low for this data. I was able to get to a friend who has a scanner that shows command and actual. the symptom is hard start warm or cold. my little scanner shows 5400-6100 psi while running. the more capable scanner (Snap-On) shows FRP 35MPa commanded and single digits while cranking for actual FRP until it starts then it is a solid 35MPa. I am thinking the Fuel Pressure Regulator should provide a higher actual so the engine will start quicker. the hard start is about 10-12 seconds. Does this sound right or could something else be open preventing the regulator from operating correctly. as costly as thie parts are, I am trying to diagnose this before buying lots of parts. I appreciate the advice.
Mine does lope a little. Didn't think much about it. What causes the loping ?
since i don't have a lift pump, I guess it points me to the fpr. do think the fpr would just drop the pressure and stall the motor?
The fact that the rail pressure holds steady once started would lead me to believe injectors are the problem. If the FPR was the problem, it would have to have a bad lope at idle before it got hard to start.
However, as you said, these parts are expensive, so you might want to replace the FPR and see. I personally don't think that is the real problem. Though it may also be bad.
Sent from my Galaxy Nexus using Tapatalk 2
However, as you said, these parts are expensive, so you might want to replace the FPR and see. I personally don't think that is the real problem. Though it may also be bad.
Sent from my Galaxy Nexus using Tapatalk 2
would injectors allow it to die while at an idle? the last time it died , I was at an intersection and had my scanner hooked up. I was watching th pressure and it from 4200 to 3800 then completely away. does that sound like injectors?
thank you. I will try that. would an after market gasoline fuel pump work or do i need a diesel fuel pump for the test?
For a quick test, it would be fine. However, diesel will destroy seals designed for gas, and it will start leaking quickly (within a week, most likely).
Parts are indeed very expensive... The cheapest thing to do first is to see if you do have air getting into the system. You can try to methods to test for this.... One is to hook up an air line to the fuel tank and regulate it down to about 12-15 PSI. It should hold the pressure but if it doesn't what you will be looking for is fuel being pushed out somewhere on the fuel system from the tank to the CP3. Common places for these leaks are the fuel filter mounting housing and the pressure port shrader valve located at the front of the engine on the passenger side.
If this method is not available to you then I would suggest installing a clear hose from the filter housing that feeds the CP3 and then you can litterly see the air flowing to the CP3 if any. Make sure your tank is full otherwise you could get air into the fuel lines from sloshing.
If you determine that no air is getting in then next would be to do a return test on the injectors. It's a major pita but it will prevent you from buying parts you don't need. Do a search on the forum and you can find plenty of good info on to do this.
If your injectors test good then next is your CP3. Try running some 2-stroke first to see if maybe its just sticking, after that I would replace the regulator.
The fact that your actual pressure is tracking right along with commanded rules out a bad CP3 almost 100%. I think personally its air getting in.
Hope you get it nailed down though.
If this method is not available to you then I would suggest installing a clear hose from the filter housing that feeds the CP3 and then you can litterly see the air flowing to the CP3 if any. Make sure your tank is full otherwise you could get air into the fuel lines from sloshing.
If you determine that no air is getting in then next would be to do a return test on the injectors. It's a major pita but it will prevent you from buying parts you don't need. Do a search on the forum and you can find plenty of good info on to do this.
If your injectors test good then next is your CP3. Try running some 2-stroke first to see if maybe its just sticking, after that I would replace the regulator.
The fact that your actual pressure is tracking right along with commanded rules out a bad CP3 almost 100%. I think personally its air getting in.
Hope you get it nailed down though.
