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Discussion Starter #1
We bought a 2008 Sentra SE-R Spec V with the 2.5 engine. When the engine is cool it will run perfectly. When it gets to full operating temperature it doesn't have the power it did when cold, especially going up a hill. I have replaced the catalytic converters, MAF sensor, changed the plugs, two 02 sensors on bank 1, new gas cap and I am sure I have left something out.

Just yesterday I replaced the downstream 02 sensor on bank 1 because one of the wires was cut in half. The fans are so close to that sensor it may have cut it again as I am getting a pending code for that sensor again. I will check that later this morning. Anyone have any suggestions where I should check next?

I am thinking the throttle body may need cleaning or maybe a new fuel filter. From what I have read the fuel filter is on the bottom of the fuel pump. Can that filter be replaced? Any help would sure be appreciated. I have posted on several forums and only one person has ever given me help and that was very much appreciated.
 

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NF Mod/Nissan Master Tech
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The fuel filter is part of the fuel pump module. Rather than replace it, I would suggest you test the fuel pressure. If the fuel pressure is good, the filter is not the problem, nor is the fuel pump.
 

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Discussion Starter #4
Still fighting the little Sentra. SMJ, you are right, it was not the fuel pump or filter. I have replaced the exhaust Manifold gasket but still no good. The live stream shows I have a slight leak of vacuum, somewhere. I tried to flush it out with starter fluid but no go. I will make one of the smoke machines and see if I can find it that way. I will also cut the tail pipe to see if the muffler is stopped up. If all else fails, then the engine is worn too bad.

It has 150 pounds compression so I thought it may be ok, but I am also having a very low oil pressure when it gets warm. When it is cold the oil pressure is 80 pounds but when at idle, when hot the pressure is 10 or 12 at idle and runs about 30 or so when driving, so that concerns me a lot.

If I have to jerk this engine out, can I go back with a standard 2.5 instead of the high performance Sepc V?

If and when that time comes I may tear this engine down and see if I can maybe just rebuild it. I don't think there will be much wear on the cylinders at 130,000. But I could be wrong since the cats were gutted and this being a straight stick, it would be easy to suck the stuff from a damaged cat back into the engine. I guess we will see. But for now I will keep trying to find why it bogs and jerks some when accelerating. If I don't crowd it when accelerating it doesn't do too bad. When I hit 5th and 6th gears, it does fine on a straight away, but hills are a different story.
 

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Sup Mod keeping the peace
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Still fighting the little Sentra. SMJ, you are right, it was not the fuel pump or filter. I have replaced the exhaust Manifold gasket but still no good. The live stream shows I have a slight leak of vacuum, somewhere. I tried to flush it out with starter fluid but no go. I will make one of the smoke machines and see if I can find it that way. I will also cut the tail pipe to see if the muffler is stopped up. If all else fails, then the engine is worn too bad.

It has 150 pounds compression so I thought it may be ok, but I am also having a very low oil pressure when it gets warm. When it is cold the oil pressure is 80 pounds but when at idle, when hot the pressure is 10 or 12 at idle and runs about 30 or so when driving, so that concerns me a lot.

If I have to jerk this engine out, can I go back with a standard 2.5 instead of the high performance Sepc V?

If and when that time comes I may tear this engine down and see if I can maybe just rebuild it. I don't think there will be much wear on the cylinders at 130,000. But I could be wrong since the cats were gutted and this being a straight stick, it would be easy to suck the stuff from a damaged cat back into the engine. I guess we will see. But for now I will keep trying to find why it bogs and jerks some when accelerating. If I don't crowd it when accelerating it doesn't do too bad. When I hit 5th and 6th gears, it does fine on a straight away, but hills are a different story.
The 150 psi reading during compression testing is the standard minimum which is OK. The oil pressure looks OK considering the miles that are on the engine. The minimum at idle is spec'd at 14 psi; at 2,000 rpm it's spec'd around 43 psi which is a little low but you should be OK.

Loss of power can be caused by the following:
  • The cam position sensor or the crankshaft position sensor may be marginal. If replacing them, us only Nissan OEM components; not aftermarket types - may cause new problems, don't last long, may be DOA.
  • Incorrect fuel pressure. Tee-in a temporary fuel pressure gauge at the input side of the fuel rail. The reading at idle should be 51 psi.
  • There may be a major intake system vacuum leak. To check the intake system for a vacuum leak, attach a vacuum gauge to a full vacuum source. With the engine fully warmed up, the reading at idle should be 18 - 20 InHg. At 3,000 RPM, it should be around 21 InHg. If readings are under 18 InHg, check the intake manifold nuts to make sure they are tight. The gasket may have failed; spray a water mist at the gasket to see if the gauge reading changes. Also check the intake plenum bellows at the throttle valve and at the MAF for cracks or loose clamps.
  • Dirty fuel injector(s). Run some good injection cleaner, like Techron, Redline SL-1 or BG products 44K, through the system; give the cleaner about a week or two to do it's job.
 

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Discussion Starter #6
Sir I really do appreciate your information and time. I will check these out and let you know. I hope I can post a couple of photos of the last datastream I did, on the long and short fuel trim. I also have a question about the voltage on my two 02 sensors. If I am not mistaken they are reading high. The photos are at idle, at 2500 rpm and of the 02 sensors bank 1.
@ Idle.jpg
@ Idle.jpg
02 sensors upstream both banks.jpg
 

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