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Tim Mohr
Tim Mohr, ASE MASTER TECH
Category: Nissan
Satisfied Customers: 560
Experience:  30 YRS EXPERIENCE, FOREIGN AND DOMESTIC, GAS AND DEISEL
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2003 Nissan Xterra, 3.3 litre SOHC, slight backfire and lost

Customer Question

2003 Nissan Xterra, 3.3 litre SOHC, slight backfire and lost of power with rich exhaust smell. Problem started without warning on way home from work during good weather. Got a few blocks from home when engine began to sputter at about 30-35 mph. Made it home and dad quickly checked out and confirmed problem. He called and I suggested a tow since shop is about 8 miles away. Towed to shop and able to start and drive in parking lot. Problem confirmed. DTCs retrieved P0506 & P0328 (to be expected with the way engine is running). Checked ignition, good. Check fuel pressure. KOEO fuel pressure at 95-100 psi. KOER same. Still checked with vacuum on and off at regulator although I did not expect a change because it is so high. Checked at fuel line connections to fuel rail, in and out. Have replaced fuel pump w/strainer and fuel pressure regulator (have not changed fuel filter but will do so because of fuel pump change). No change in fuel pressure. What is going on? Do I have an ECM failure as the cause. No TSBs for excess fuel pressure found.
Submitted: 1 month ago.
Category: Nissan
Expert:  Jay replied 1 month ago.

Hello my name is ***** ***** thank you for your question.

Fuel pressure for your truck should be around 36 psi. That is crazy fuel pressure. Are you sure the gauge is good?

Expert:  Jay replied 1 month ago.

The codes you have, did you use a code reader to get them? Also, the P0506, do you mean P0505?

Customer: replied 1 month ago.
Used my fuel pressure guage (tool truck multi-vehicle set) and that from another shop in our business park. Used a Snap-on Solus Ultra. All info correct.
Expert:  Jay replied 1 month ago.

Well, the fuel pressure is nuts. That is something you may want to stick another gauge on to verify. The fuel filter is a external filter so that should be change if not changed in a while.

As for the code, I am using the factory service manual and the code P0506 is not a good code. The closest code is the P0505 which is for the Idle Air Control Valve. Which could also make sense on what the truck is doing, but doesn't make sense on for the fuel pressure gauge. The other code is a Knock Sensor, that code does not turn on a Service Engine Light. Normally you find this code when something else turns on the light.

Are you a shop?

Customer: replied 1 month ago.
I am a shop owner. Have never had this issue. I expect higher fuel pressures on direct fuel injection but I also check with factory specs. on my Mitchel ProDemand. The code is P0506 described as Idle Speed Control System RPM less than expected by both Snap-on Troubleshooter and Mitchel.
Expert:  Jay replied 1 month ago.

Is this Super charged?

Customer: replied 1 month ago.
No SC. Just the basic model. Here is the VIN if useful: 5N1ED28T63C695443
Expert:  Jay replied 1 month ago.

I am using the Factory Service manual. The P0505 is a Idle Speed Control code. So it is more or less the same thing. Just was wondering why it's is reading the code wrong. No biggie.

So with this code, the Idle Air Control normally will need the IAC replaced and could have damaged the Ecm when it fails. This can certainly affect how the truck runs.

The fuel pressure, I can't see any way it can put out 100 Psi! That would blow up and damage injectors if that is true. I have never seen anything like that. I would borrow another gauge to verify that if I encountered that. Thinking my gauge has to be wrong. That is also why I have two volt meters. If I can't believe a particular voltage, I will double check it.

Customer: replied 1 month ago.
Jay, as I stated with the initial question, I did borrow another professional type pressure guage from another shop in this complex. I also thought that my guage could be wrong. I also keep multiple volt meters and other pieces of equipment. I understand what you also know is good shop procedures but this has thrown me for a loop. I don't see this as a fuel pump that has variable output controls since it is not ECM driven. Maybe I should try a 3rd fuel pressure guage? Can you run this up the Nissan tech support line?
Customer: replied 1 month ago.
Jay, I have to leave for awhile. Please respond with any info and I will contact later. Thank you
Expert:  Jay replied 1 month ago.

The only way that would happen is if you got the wrong fuel pump. It is a 12 volt circuit to power the pump.

Is the fuel pump you installed from the dealer or after market?

Also where are you checking the fuel pressure? What line are you tapping into? Are you tapping into the fuel system in line?

Customer: replied 1 month ago.
What was removed was a Denso (I could tell by markings it was a replacement pump before I removed from its plastic cover) and the replacement is a Delphi. These are as good as OEM. If there is no fuel injector rail service port, you hook up at the nearest fuel line connection to the fuel injector rail (stated in my initial comment). I will use a 3rd different fuel pressure guage. By the way, I have been repairing this vehicle for about 10 years. It went elsewhere for for about 2 years 6 years ago (probably when it got the Denso).
Expert:  Jay replied 1 month ago.

Is the gauge you are using a inline type of gauge or does it just go into the end?

Customer: replied 1 month ago.
My bad. I was not using a "t" connection. With it, fuel pressure goes up to 10 psi and drops, KOEO. I pinch the return hose and it goes up to 100 psi. Where is the fuel return check valve? With the gauge connection as it should be, the fuel issue is not excess fuel pressure but insufficient fuel pressure because the check valve must be stuck open.
Expert:  Jay replied 1 month ago.

What is the fuel pressure when you check it in line before you pinch the return?